JP4724127B2 - Optical recording medium - Google Patents

Description

  The present invention relates to an optical recording medium, and more particularly to an optical recording medium having a recording layer containing a dye.

  In recent years, blue lasers capable of ultra-high density recording have been rapidly developed, and write-once type optical recording media corresponding thereto have been developed. In particular, development of a dye-coated write-once medium that enables efficient production at a relatively low cost is strongly desired. In a conventional dye-coated write-once optical recording medium, a recording layer made of an organic compound containing dye as a main component is irradiated with laser light, and optical (refractive index / absorption) changes due to decomposition and alteration of the organic compound. Recording pits are formed mainly by generating them. The recording pit portion is not only optically changed, but is usually accompanied by deformation due to the recording layer volume change, formation of a mixed portion of the substrate and the dye due to heat generation, substrate deformation (primarily rising due to substrate expansion), etc. (Patent Document 1, Patent) (Refer to Literature 2, Patent Literature 3, and Patent Literature 4).

  The optical behavior of the organic compound used in the recording layer with respect to the laser wavelength used for recording / reproducing, and the thermal behavior such as decomposition / sublimation and the heat generated thereby become important factors for forming good recording pits. Yes. Therefore, as the organic compound used for the recording layer, a material having an appropriate optical property and decomposition behavior is selected.

  In the first place, in a conventional write-once medium, particularly a CD-R or DVD-R, a read-only recording medium (ROM) in which a reflective layer made of Al, Ag, Au or the like is coated on a concave pit formed in advance on a substrate. The purpose is to maintain reproduction compatibility with the medium), and to achieve a reflectivity of approximately 60% or higher and, similarly, a high degree of modulation exceeding approximately 60%. First, in order to obtain a high reflectance in an unrecorded state, the optical properties of the recording layer are defined. Usually, a refractive index n of about 2 or more and an extinction coefficient of about 0.01 to 0.3 are required in an unrecorded state (see Patent Documents 5 and 6).

  In a recording layer containing a dye as a main component, it is difficult to obtain a high degree of modulation of 60% or more only by such a change in optical properties due to recording. That is, since the amount of change in the refractive index n and the absorptance k is limited with a dye that is an organic substance, the change in reflectance in a planar state is limited.

  Therefore, a method of apparently increasing the change in reflectivity (decrease in reflectivity) at the recorded pit portion using the interference effect of the reflected light from both portions due to the phase difference between the reflected light at the recorded pit portion and the unrecorded portion is used. Has been. That is, the same principle as that of a phase difference pit such as a ROM medium is used, and in the case of an organic recording layer whose refractive index change is smaller than that of an inorganic substance, it is rather advantageous to mainly use a change in reflectance due to the phase difference. Has been reported (see Patent Document 7). Further, a study that comprehensively considers the above-described recording principle has been performed (see Non-Patent Document 1).

  In the following description, a portion where recording is performed as described above (sometimes referred to as a recording mark portion) is referred to as a recording pit, a recording pit portion, or a recording pit portion regardless of its physical shape. Call it.

  FIG. 1 is a diagram for explaining a write-once medium (optical recording medium 10) having a recording layer mainly composed of a dye having a conventional configuration. As shown in FIG. 1, an optical recording medium 10 is formed by forming at least a recording layer 12, a reflective layer 13, and a protective coating layer 14 in this order on a substrate 11 in which grooves are formed. A recording / reproducing light beam 17 is incident through 11 and irradiates the recording layer 12. The thickness of the substrate 11 is usually 1.2 mm (CD) or 0.6 mm (DVD). Further, the recording pit is formed in a portion of the substrate groove portion 16 called a normal groove on the side close to the surface 19 on which the recording / reproducing light beam 17 is incident, and is not formed in the substrate groove portion 15 on the far side.

  In the above-mentioned prior art documents, the change in phase difference increases the refractive index change before and after recording of the recording layer 12 containing the dye as much as possible, while the shape change of the recording pit portion, that is, the recording pit formed in the groove The groove shape locally changes (the substrate 11 swells or sinks and the groove depth changes equivalently), and the film thickness changes (the film thickness due to expansion and contraction of the recording layer 12). It has also been reported that the effect of (transparent change of) contributes to the change of phase difference.

  In the recording principle as described above, in order to increase the reflectance at the time of non-recording and to decompose the organic compound by laser irradiation and cause a large refractive index change (this can obtain a large degree of modulation), Normally, the recording / reproducing light wavelength is selected so as to be located at the bottom of the long wavelength side of the large absorption band. This is because the bottom of the large absorption band on the long wavelength side is a wavelength region having an appropriate extinction coefficient and a large refractive index.

  However, no material has been found that has a conventional optical property with respect to the blue laser wavelength. In particular, in the vicinity of 405 nm, which is the center of the oscillation wavelength of a blue semiconductor laser currently in practical use, an organic compound having an optical constant comparable to the optical constant required for the recording layer of a conventional write-once optical recording medium is present. There are few, and it is still in the search stage. Furthermore, in a write-once optical recording medium having a conventional dye recording layer, since the main absorption band of the dye exists near the recording / reproducing light wavelength, the wavelength dependence of the optical constant increases (the optical constant varies greatly depending on the wavelength). Recording characteristics such as recording sensitivity, modulation degree, jitter and error rate, and reflectivity greatly change with respect to fluctuations in the recording / reproducing light wavelength due to individual differences of lasers, environmental temperature changes, etc. There is a problem of doing.

  For example, the idea of recording using a dye recording layer having absorption in the vicinity of 405 nm has been reported. However, the dyes used therein are required to have the same optical characteristics and functions as in the past. (See Patent Document 8 and Patent Document 9). Further, in the write-once type optical recording medium 10 using the conventional recording layer 12 mainly composed of a dye as shown in FIG. 1, the groove shape and the thickness of the substrate groove portion 16 and the substrate groove portion 15 of the recording layer 12 are shown. It has been reported that the distribution of the above must be properly controlled (see Patent Document 10, Patent Document 11, and Patent Document 12).

That is, as described above, only a dye having a relatively small extinction coefficient (about 0.01 to 0.3) with respect to the recording / reproducing light wavelength can be used from the viewpoint of securing a high reflectance. For this reason, it is impossible to reduce the thickness of the recording layer 12 in order to obtain light absorption necessary for recording in the recording layer 12 and to increase a change in phase difference before and after recording. As a result, the film thickness of the recording layer 12 is usually about λ / (2n _s ) (where n _s represents the refractive index of the substrate 11), and the dye used for the recording layer 12 is grooved. In order to reduce the crosstalk, it is desirable to use the substrate 11 having a deep groove. Since the recording layer 12 containing a dye is usually formed by a spin coat method (coating method), it is more convenient to fill the dye in a deep groove to increase the thickness of the recording layer 12 in the groove. On the other hand, in the coating method, a difference occurs in the recording layer film thickness between the substrate groove portion 16 and the substrate groove portion 15. This difference in the recording layer film thickness results in a stable tracking servo signal even when a deep groove is used. It is effective in that it is obtained.

That is, the groove shape defined by the surface of the substrate 11 in FIG. 1 and the groove shape defined by the interface between the recording layer 12 and the reflective layer 13 are not recorded at the proper values unless both are maintained at appropriate values. Both the signal characteristics and the tracking signal characteristics cannot be maintained well. The depth of the groove is usually desirably close to λ / (2n _s ) (where λ represents the wavelength of the recording / reproducing light beam 17 and n _s represents the refractive index of the substrate 11). The range is about 200 nm for -R and about 150 nm for DVD-R. The formation of the substrate 11 having such a deep groove becomes very difficult, which is a factor of deteriorating the quality of the optical recording medium 10.

  In particular, in an optical recording medium using blue laser light, if λ = 405 nm, a deep groove close to 100 nm is required, while the track pitch is often set to 0.2 μm to 0.4 μm for high density. . It is even more difficult to form such a deep groove with such a narrow track pitch, and in practice, mass production is almost impossible with conventional polycarbonate resins. That is, in the case of a medium using blue laser light, it is highly likely that mass production will be difficult with the conventional configuration.

  Furthermore, many of the embodiments described in the above-mentioned prior art publications are examples using a conventional configuration (substrate incident configuration) represented by the optical recording medium 10 shown in FIG. However, in order to realize high-density recording using a blue laser, a so-called film-surface incident configuration has attracted attention, and a configuration using an inorganic material recording layer such as a phase change recording layer has been reported ( Non-Patent Document 3). In a configuration called film surface incidence, contrary to the conventional case, at least a reflective layer, a recording layer, and a cover layer are formed in this order on a substrate having grooves formed therein, and recording and reproduction are performed via the cover layer. Is incident on the recording layer. The thickness of the cover layer is usually about 100 μm in a so-called Blu-ray disc (see Non-Patent Document 9). The recording / reproducing light is incident from such a thin cover layer side to the objective lens for focusing thereof, which has a higher numerical aperture (NA (numerical aperture), usually 0.7 to 0.9, Blu-ray). This is because 0.85) is used for the disc. When an objective lens having a high NA (numerical aperture) is used, the cover layer is required to be as thin as about 100 μm in order to reduce the influence of aberration due to the thickness of the cover layer. Many examples of such blue wavelength recording and film surface incident layer configurations have been reported (see Non-Patent Document 4, Patent Document 13 to Patent Document 24). In addition, there are many reports on related technologies (see Non-Patent Document 5 to Non-Patent Document 8 and Patent Document 25 to Patent Document 43).

“Proceedings of International Symposium on Optical Memory” (USA), Vol. 4, 1991, p. 99-108 “Japanese Journal of Applied Physics”, (Japan) vol. 42, 2003, p. 834-840 “Proceedings of SPIE” (USA), Volume 4342, 2002, p. 168-177 “Japanese Journal of Applied Physics” (Japan), Vol. 42, 2003, p. 1056-1058 Heitaro Nakajima and Hiroshi Ogawa, “Compact Disc Reader”, 3rd edition, Ohm, 1996, p. 168 “Japanese Journal of Applied Physics” (Japan), Vol. 42, 2003, p. 914-918 “Japanese Journal of Applied Physics” (Japan), Vol. 39, 2000, p. 775-778 “Japanese Journal of Applied Physics” (Japan), Vol. 42, 2003, p. 912-914 "Optical Disc Dismantling New Book", Nikkei Electronics, Nikkei BP, 2003, Chapter 3 Hiroyuki Fujiwara, “Spectroscopic Ellipsometry”, Maruzen Publishing Co., 2003, Chapter 5 Alphonsus V. Pocius, Hiromi Mizumachi, Hirokuni Ono "Introduction to Adhesives and Adhesive Technology", Nikkan Kogyo Shimbun, 1999 Japanese Patent Laid-Open No. 2-168446 JP-A-2-187939 JP-A-3-52142 Japanese Patent Laid-Open No. 3-6943 Japanese Patent Laid-Open No. 2-87339 JP-A-2-132656 JP-A-57-501980 International publication 01/74600 pamphlet JP 2002-301870 A JP-A-3-54744 Japanese Patent Laid-Open No. 3-22224 JP-A-4-182944 JP 2003-331465 A JP 2001-273672 A JP 2004-1375 A JP 59-19253 A JP-A-8-138245 JP 2004-30864 A JP 2001-273672 A JP 2002-245678 A JP 2001-155383 A JP 2003-303442 A JP 2002-367219 A JP 2003-16689 A Japanese Patent Laid-Open No. 5-128589 JP-A-5-174380 JP-A-6-4901 JP 2000-43423 A JP 2001-287466 A JP 2003-266554 A JP-A-9-277703 Japanese Patent Laid-Open No. 10-26692 JP 2000-20772 A JP 2001-155383 A Japanese Patent Laid-Open No. 11-273147 Japanese Patent Laid-Open No. 11-25523 JP 2003-217173 A JP 2004-86932 A JP 2004-98542 A JP 2004-160742 A JP 2003-217177 A WO03 / 003361 pamphlet JP 2005-504649 A

  By the way, in a film surface incident type phase change medium that has been developed in advance, a recording mark is formed in the groove of the cover layer as viewed from the incident light side. This is the same as recording on a substrate groove on a conventional substrate when viewed from the incident light side, and means that it can be realized with almost the same layer configuration as CD-RW and DVD-RW. Has been obtained. On the other hand, in the case of a recording layer containing a dye as a main component, particularly a coating type, recording in the cover layer groove is not easy. This is because, usually, in spin coating on a substrate, the dye tends to accumulate in the groove portion of the substrate. Even if a pigment is applied to the substrate groove portion with an appropriate film thickness, a considerable amount of pigment is usually accumulated in the substrate groove portion, so that the recording pits (record marks) formed in the cover layer groove portion are the cover layer groove portion. Therefore, the track pitch that increases crosstalk cannot be reduced, and there is a limit to increasing the density.

  However, most of the prior art documents mentioned above mainly focus on the fact that the reflected light intensity is reduced by recording in the cover layer groove on the side closer to the incident light side as usual. Alternatively, attention is paid to a decrease in reflectance that occurs only in a flat state without considering a change in phase of reflected light due to a step of the groove. Alternatively, it is assumed that a change in reflectance in a planar state in which a phase difference is not used as much as possible is used. Under such preconditions, the problem of crosstalk in cover layer groove recording cannot be solved, and the recording layer forming process by solution coating does not suit. It cannot be said that the phase change is effectively utilized to achieve good recording characteristics in the cover layer groove portion. In particular, in mark length modulation recording, there is no example that has a practical recording power margin with respect to all mark lengths from the shortest mark length to the longest mark length and realizes good jitter characteristics.

  As described above, a film-surface incident type write-once optical recording medium compatible with a blue laser having a recording layer mainly composed of a high-performance and low-cost dye comparable to conventional CD-R and DVD-R is still known. The current situation is not.

The inventors of the present invention diligently studied a film surface incident type medium corresponding to a blue laser having a recording layer mainly composed of a dye. As a result, the guide groove portion on the side farther from the surface on which the recording / reproducing light beam is incident on the cover layer is used as the recording groove portion, and the reflected light intensity of the recording pit portion formed in this recording groove portion is determined when the recording groove portion is unrecorded. It has been found that a film surface incident type medium having good recording characteristics can be obtained by making the intensity higher than the reflected light intensity (for a detailed description of such a film surface incident type optical recording medium, see International Publication WO 2006/009107 pamphlet (see International Patent Application PCT / JP2005 / 013145).
As a result of further investigation based on the above knowledge, it has been found that further improvement is necessary in order to obtain better jitter characteristics.

The present invention has been made to solve such problems.
That is, an object of the present invention is to provide an extremely high density optical recording medium having excellent jitter characteristics and good recording / reproducing characteristics.

  As a result of intensive studies in view of the above problems, the present inventors have a light reflection function mainly composed of Ag in a blue laser compatible film surface incident type optical recording medium having a recording layer mainly composed of a dye. It has been found that better jitter characteristics can be obtained by providing an intermediate layer between the recording layer and the recording layer.

That is, the gist of the present invention is that a substrate having guide grooves formed thereon, a layer having a light reflection function mainly composed of Ag on the substrate, and a light absorption function with respect to the recording / reproducing light wavelength in an unrecorded state. A recording layer containing as a main component a dye and a cover layer capable of transmitting recording / reproducing light incident on the recording layer in this order, between the layer having the light reflection function and the recording layer, An intermediate layer is provided, and the intermediate layer contains any one element of Ta and Nb (claim 1).

  Moreover, it is preferable that the film thickness of the said intermediate | middle layer is 1 nm or more and 15 nm or less.

  Moreover, it is preferable that the film thickness of the layer which has the light reflection function which has Ag as a main component is 30 nm or more and 90 nm or less.

  In addition, when the recording groove portion is a guide groove portion on the side far from the surface on which the recording / reproducing light beam obtained by focusing the recording / reproducing light is incident on the cover layer, the reflected light of the recording pit portion formed in the recording groove portion It is preferable that the intensity is higher than the intensity of reflected light in the recording groove when not recorded.

  Here, it is preferable that the recording layer thickness when the recording groove portion is not recorded is 5 nm or more and 70 nm or less.

  Here, it is preferable that the recording layer thickness when the recording groove portion is not recorded is 10 nm or less.

  Moreover, it is preferable that the wavelength λ of the recording / reproducing light is 350 nm or more and 450 nm or less.

  In addition, it is preferable to provide an interface layer between the recording layer and the cover layer to prevent mixing of the recording layer material and the cover layer material.

  Here, it is preferable that the thickness of the interface layer is 1 nm or more and 50 nm or less.

  Thus, according to the present invention, an extremely high density optical recording medium having good jitter characteristics can be obtained.

  Hereinafter, the present invention will be specifically described with reference to embodiments. However, the present invention is not limited to the embodiments described below, and various modifications can be made within the scope of the invention.

FIG. 2 is a diagram for explaining a write-once medium (optical recording medium 20) having a film surface incidence configuration having a recording layer mainly composed of a dye to which the present embodiment is applied.
In the present embodiment, recording is performed in a non-recorded (before recording) state on the substrate 21 on which the guide groove is formed, a layer having a reflecting function (reflection layer 23) having at least Ag as a main component, and the intermediate layer 30. It has a structure in which a recording layer 22 having a light absorption function mainly composed of a dye having absorption with respect to reproduction light, and a cover layer 24 are sequentially laminated, and recording / reproduction is performed by using the objective lens 28 from the cover layer 24 side. Then, the recording / reproducing light beam 27 condensed through the light is incident. That is, a “film surface incidence configuration” (also referred to as a reverse stack) is adopted.

In the following, a layer having a reflection function mainly composed of Ag is simply referred to as “reflection layer 23”, and a recording layer having a light absorption function mainly including a dye is simply referred to as “recording layer 22”. As described above, the conventional configuration described with reference to FIG. 1 is referred to as a “substrate incident configuration”.
When the recording / reproducing light beam 27 is incident on the cover layer 24 side of the film surface incident configuration, a high NA (numerical aperture) of about NA (numerical aperture) = 0.6 to 0.9 is usually used for high-density recording. These objective lenses are used.
As the recording / reproducing light wavelength λ, a red to blue-violet wavelength (about 350 nm to 600 nm) is often used. Further, for high-density recording, it is preferable to use a wavelength range of 350 nm to 450 nm, but the present invention is not necessarily limited thereto.

  In this embodiment, in FIG. 2, the guide groove portion (recording / reproducing light beam is incident on the side far from the incident surface (surface 29 on which the recording / reproducing light beam is incident) of the recording / reproducing light beam 27 on the cover layer 24 is incident. (Guide groove portion on the side far from the surface to be recorded) is used as a recording groove portion, and recording is performed such that the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity when the recording groove portion is not recorded (“Low to High” recording Hereinafter, it may be referred to as LtoH recording). The main mechanism is that the increase in reflected light intensity is due to the phase change of reflected light at the recording pit portion. That is, the change before and after recording of the reciprocal optical path length of the reflected light in the recording groove is used.

Here, in the film surface incident type optical recording medium 20, the guide groove portion (coincidence with the groove portion of the substrate 21) far from the incident surface (surface 29 on which the recording / reproducing light beam is incident) of the recording / reproducing light beam 27 on the cover layer 24. The cover layer groove portion (in-groove) 25, the guide groove portion near the surface 29 on which the recording / reproducing light beam 27 is incident (matching the groove portion of the substrate 21), and the cover layer groove portion (on-groove) 26. (The names of on-groove and in-groove are based on Non-Patent Document 3.)
More specifically, a preferred embodiment of the present invention can be realized by devising the following.

(1) A groove having a depth such that the phase difference Φ between the reflected light from the cover layer groove portion in an unrecorded state and the reflected light from the cover layer groove portion is approximately π / 2 to π is formed. The recording layer film thickness in the inter-groove portion (in-groove) is a thin film that is thinner than the groove depth, while the film thickness in the cover layer groove portion (on-groove) is very thin. Is provided as a main component. A recording / reproducing light beam is irradiated from the cover layer side to the gap between the cover layers to cause alteration of the recording layer, and recording pits are mainly formed due to an increase in reflected light intensity due to a phase change. In the film surface incidence structure, the performance of the coating type dye medium is greatly improved as compared with the conventional on-groove and HtoL recording. In addition, recording at a high track pitch density (for example, 0.2 μm to 0.4 μm) with small crosstalk becomes possible. Further, it becomes easy to form a groove with such a high track pitch.

(2) The recording layer 22 has a relatively low refractive index (for example, a refractive index of 1.3 to 1.9) and a relatively high extinction coefficient (for example, an extinction coefficient of 0.3 to 1) in an unrecorded state. The recording pit portion where the refractive index is lowered is formed on the recording / reproducing light incidence side of the reflecting surface by recording using the main component dye. As a result, a phase change occurs in which the optical path length of the recording / reproducing light that has passed through the recording pit portion becomes shorter than before recording. That is, a change occurs such that the recording groove depth becomes optically shallow, and the reflected light intensity increases.
The refractive index may be lower than that of a recording medium using a conventional dye recording layer, and the degree of freedom increases in the relative relationship between the main absorption band and the recording / reproducing light wavelength, particularly for recording in the vicinity of the recording / reproducing light wavelength of 400 nm. The range of suitable dye selection increases.

(3) For lowering the refractive index at the recording pit portion, the formation of a cavity in the recording layer 22 or at the interface portion may be used. In addition, it is preferable to use a deformation that the recording layer 22 swells in the direction of the cover layer 24, and at least the recording layer 22 side of the cover layer 24 is provided with a soft deformation promoting layer made of an adhesive having a glass transition point of room temperature or less. To facilitate the deformation. As a result, the direction of phase change in which the reflected light intensity increases due to recording is aligned (the distortion of the recording signal waveform is eliminated). In addition, the phase change amount (recording signal amplitude) can be increased even with a relatively small change in refractive index. Furthermore, a decrease in the extinction coefficient of the recording layer and an increase in reflected light intensity due to a change in reflectance that occurs in the planar state can also be used.

  As described above, the substrate on which the guide groove is formed, at least a layer having a light reflection function, an intermediate layer, and a dye having a light absorption function with respect to the recording / reproducing light wavelength in an unrecorded state on the substrate. A recording layer containing as a component and a cover layer on which recording / reproducing light is incident on the recording layer are arranged in this order, and a recording / reproducing light beam obtained by focusing the recording / reproducing light is incident on the cover layer When the guide groove portion on the side far from the surface is used as the recording groove portion, an optical recording medium in which the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity of the unrecorded portion in the recording groove portion. realizable. That is, there is a feature that the polarity of the LtoH recording signal having a high degree of modulation and no distortion can be obtained from the recording pit portion.

  The optical recording medium using such a recording method has already been described in the specification of the pamphlet of International Publication No. WO2006 / 009107, and here, the essential points are extracted and described below. To do.

In the following, the optical characteristic of the recording layer in an unrecorded state (before recording) at the recording / reproducing light wavelength λ is represented by a complex refractive index n _d ^* = n _d −i · k _d . Here, the refractive index real part n _d, the imaginary part k _d is referred to as the extinction coefficient. In the recording pit part after recording, n _d is 'a = n _d -δn _d, k _d is k _d' n _d in = k _d -δk _d, shall be changed, respectively.

  Furthermore, the distinction between the two terms “reflectance” and “reflected light intensity” used below will be described. The reflectance is the ratio of the reflected energy light intensity to the incident energy light intensity in the reflection of light generated between two substances having different optical characteristics in a planar state. Even if the recording layer is planar, the reflectance changes if the optical characteristics change. On the other hand, the reflected light intensity is the intensity of light that returns to the detector when the recording medium surface is read through the focused recording / reproducing light beam and the objective lens.

  In the ROM medium, since the pit portion and the unrecorded portion (pit peripheral portion) are covered with the same reflective layer, the reflectance of the reflective layer is the same in the pit portion and the unrecorded portion. On the other hand, due to the phase difference between the reflected light generated at the pit portion and the reflected light from the unrecorded portion, the reflected light intensity appears to change (usually appears to decrease) due to the interference effect. . Such an interference effect is caused when the recording pit is locally formed and the recording / reproducing light beam diameter includes the recording pit portion and the surrounding unrecorded portion. The reflected light is caused by interference due to the phase difference. On the other hand, in a recordable medium that causes some optical change in the recording pit portion, a change in reflectance occurs due to a change in the refractive index of the recording layer itself even in a flat state without irregularities. This is referred to as “reflectance change occurring in a planar state” in the present embodiment. In other words, "reflectance change that occurs in a planar state" is a change in reflectance that occurs in the recording layer depending on whether the refractive index of the entire recording layer plane is the refractive index before recording or the refractive index after recording. This is a reflected light intensity change that occurs without taking into consideration interference between the recording pits and the reflected light at the periphery thereof. On the other hand, when the optical change of the recording layer is a local pit part, two-dimensional interference of reflected light occurs when the phase of the reflected light of the recording pit part and the phase of the reflected light of the peripheral part are different. The reflected light intensity appears to change locally around the recording pit.

  Thus, in this embodiment, the reflected light intensity change that does not take into account two-dimensional interference of reflected light with different phases is referred to as “reflected light intensity change that occurs in a planar state” or “reflected light intensity change in a planar state”. The reflected light intensity change in consideration of the two-dimensional interference of reflected light having different phases between the recording pit and its peripheral part is “(local) reflected light intensity change caused by phase difference” or “reflected light intensity caused by phase difference” “Change” is considered separately.

In general, when a sufficient reflected light intensity change, that is, an amplitude (or optical contrast) of a recording signal is obtained by the “reflected light intensity change due to phase difference”, the refractive index change of the recording layer 22 itself is changed. Must be very big. For example, in CD-R and DVD-R, it is required that the real part of the refractive index of the dye recording layer is 2.5 to 3.0 before recording and about 1 to 1.5 after recording. It is done. It imaginary part k _d of the complex refractive index before recording of the dye recording layer is less than about 0.1, has been considered preferable for obtaining a high reflectance ROM compatibility in the unrecorded state. In addition, it is desirable that the recording layer 22 is as thick as 50 nm to 100 nm. Without such a thickness, most of the light passes through the recording layer 22 and sufficient reflected light intensity change and light absorption necessary for pit formation cannot occur. In such a thick dye recording layer, the local phase change due to deformation at the pit portion is merely used as an auxiliary. On the other hand, in the above-mentioned ROM medium, it is considered that there is no local refractive index change at the recording pit portion and only “reflected light intensity change due to phase difference” is detected. In order to obtain good recording quality, when the reflected light intensity change in the recording pit is caused by mixing the above two kinds of reflected light intensity changes, it is desirable to strengthen both of them. The fact that the two types of reflected light intensity changes are intensified means that the direction of the reflected light intensity change that occurs in each case, that is, whether the reflected light intensity increases or decreases, is aligned.

  The decrease in the refractive index of the recording layer as described above results in a decrease in reflectivity and, in turn, a decrease in reflected light intensity in “a change in reflected light intensity in a planar state”. In the conventional CD-R and DVD-R, as described above, this refractive index change can be 1 or more, so that the reflectivity decrease due to the “planar reflected light intensity change” causes a considerable portion of the amplitude of the recording signal. Occupy. Therefore, the reflectance is basically reduced by recording. Further, it can be said that various studies have been made so that the direction of “reflected light intensity change due to phase difference” in the recording pit portion used as an auxiliary contributes to a decrease in reflectance. On the other hand, a decrease in the extinction coefficient due to the decomposition of the recording layer dye leads to an increase in reflectivity, which rather lowers the signal amplitude. Therefore, it is desirable to reduce the change in the extinction coefficient. Furthermore, in order to make the reflectance before recording as high as the ROM medium, it is desirable to reduce the extinction coefficient of the recording layer before recording. Therefore, it is intended to reduce the extinction coefficient to generally 0.3 or less, preferably 0.2 or less.

  Next, a reflection reference plane is first defined. As the reflection reference surface, the recording layer side interface (surface) of the intermediate layer serving as the main reflection surface is taken. The main reflecting surface refers to a reflecting interface that contributes the most to the reflected reflected light. In FIG. 2 showing the optical recording medium 20 to which the present embodiment is applied, the main reflection surface is at the interface between the recording layer 22 and the intermediate layer 30. This is because the target recording layer 22 in the optical recording medium 20 to which the present embodiment is applied is relatively thin and has a low absorption rate, so that most of the light energy simply passes through the recording layer 22. This is because the boundary between the recording layer 22 and the intermediate layer 30 can be reached. There are other interfaces that can cause reflection, and the reflected light intensity of the reproduction light is determined by the contribution of the reflected light intensity from each interface and the entire phase. In the optical recording medium 20 to which the present embodiment is applied, since the contribution of reflection on the main reflection surface is large, only the intensity and phase of light reflected on the main reflection surface need be considered. For this reason, the main reflection surface is used as a reflection reference surface.

  In the present embodiment, first, in FIG. 2, it is preferable to form pits (marks) in the cover layer inter-groove portions 25. This is because the recording layer 22 formed mainly by a spin coating method (coating method) that is easy to manufacture is used. That is, by using the coating method, the recording layer thickness of the cover layer groove portion (substrate groove portion) 25 is naturally larger than the recording layer thickness of the cover layer groove portion (substrate groove portion) 26. Its thickness is “planar reflected light intensity change” and is not so thick that sufficient reflected light intensity change can be obtained. Mainly with “reflected light intensity change considering interference”, the film thickness is relatively thin. In addition, even if the refractive index change of the recording itself is small, a large reflected light intensity change (high degree of modulation) can be realized in the pit portion formed in the cover layer groove portion 25.

  In the present embodiment, due to the change in the phase of the reflected light in the recording pit portion, the step between the cover layer groove portion 25 and the cover layer groove portion 26 constituted by the reflection reference surface in FIG. It is preferable to produce a change that looks optically shallow. At that time, in order to stabilize the tracking servo, first, a phase change that does not cause the inversion of the push-pull signal and increases the reflected light intensity after recording compared to the reflected light intensity before recording is performed. It occurs in the recording pit.

  In order to explain the layer configuration of the optical recording medium 20 having the film surface incidence configuration to which the present embodiment shown in FIG. 2 is applied by paying attention to the phase of the light reflected by the reflection reference surface, the cover shown in FIG. As an example of the case of recording in the inter-slot portion 25, FIG. 3A and FIG. 3B are used.

  FIGS. 3A and 3B are diagrams for explaining the layer structure of the film surface incident type medium (optical recording medium 20) and the phase difference of the reflected light when recording is performed on the cover layer groove portion 25 part. is there. 3A and 3B show the reflection of the recording / reproducing light beam 27 incident from the incident surface 28 side of the cover layer 24 having the film surface incident structure in the optical recording medium 20 having the film surface incident structure shown in FIG. It is a figure for demonstrating the phase difference of light. 3 (a) and 3 (b), elements common to FIG. 2 are denoted by the same reference numerals. 2 are omitted in FIGS. 3A and 3B.

  Specifically, FIG. 3A is a cross-sectional view including recording pits before recording and FIG. 3B is a recording pit after recording. Hereinafter, a groove or an inter-groove portion that forms a recording pit is referred to as a “recording groove portion”, and a portion therebetween is referred to as a “recording groove inter-portion”. That is, in FIGS. 3A and 3B showing a preferred embodiment of the present invention, the cover layer groove portion 25 is a “recording groove portion” and the cover layer groove portion 26 is a “recording groove portion”.

  First, in obtaining the phase difference between the reflected light of the recording groove and the reflected light of the recording groove, a phase reference plane is defined by A-A ′. In FIG. 3A showing an unrecorded state, A-A ′ corresponds to the interface between the recording layer 22 and the cover layer 24 in the recording groove portion. On the other hand, in FIG. 3B showing the post-recording state, A-A ′ corresponds to the interface between the recording layer 22 and the cover layer 24 in the recording groove portion. There is no optical difference depending on the optical path in front of the A-A ′ plane (incident side). Further, as shown in FIG. 3A, the reflection reference surface in the recording groove portion before recording is BB ′, and the bottom surface of the recording groove portion of the cover layer 24 before recording (recording layer 22 / cover layer 24 interface) is C−. Define with C '.

The recording layer thickness at the recording groove part before recording is d _G , the thickness between the recording groove parts is d _L , the step between the recording groove part and the recording groove part on the reflection reference surface is d _GL , and the recording on the surface of the substrate 21 is performed. The level difference between the grooves is defined as d _GLS . Usually, the reflective layer 23 and the intermediate layer 30 have substantially the same film thickness at the recording groove portion and the recording groove portion, depending on how the recording layer and the recording groove portion of the reflective layer 23 and the intermediate layer 30 are covered. Since the step on the surface is reflected as it is, d _GL = d _GLS .

The refractive index of the substrate 21 to n _s, a refractive index of the cover layer 24 and n _c. Generally, the following changes occur due to the formation of recording pits. In the recording pit part 25p, the refractive index of the recording layer 22 changes from n _d to _{n d '= n d -δn d} . Further, in the recording pit portion 25p, mixing occurs between the material of the recording layer 22 and the material of the cover layer 24 at the incident side interface of the recording layer 22 to form a mixed layer. Further, the recording layer 22 undergoes a volume change, and the position of the reflection reference plane (the recording layer 22 / intermediate layer 30 interface) moves. Normally, the formation of a mixed layer between the material of the substrate 21 that is an organic material and the material of the reflective layer 23 that is a metal is negligible.
In the following description, the relationship between two layers may be indicated by separating the names of the two layers by separating them with “/”. For example, the “recording layer / intermediate layer interface” represents the interface between the recording layer and the intermediate layer.

Accordingly, it is assumed that the material of the recording layer 22 and the material of the cover layer 24 are mixed between the recording layer 22 / cover layer 24 (FIG. 2) to form a mixed layer 25m having a thickness d _mix . In addition, the refractive index of the mixed layer 25m is set to n _c ′ = n _c −δn _c (FIG. 3B).

At this time, the interface of the recording layer 22 / cover layer 24 moves by d _bmp after recording with reference to CC ′. Note that d _bmp is positive in the direction of movement into the recording layer 22 as shown in FIG. Conversely, if d _bmp is negative, it means that the recording layer 22 expands beyond the CC ′ plane. Also, if an interface layer that prevents the mixing of both is provided between the recording layer 22 and the cover layer 24, d _mix = 0. However, the deformation of d _bmp may occur due to the volume change of the recording layer 22. It is considered that the influence of the refractive index change accompanying the _dbmp deformation of the substrate 21 or the cover layer 24 when the dye mixture does not occur is negligibly small.

On the other hand, let d _pit be the amount of movement of the reflection reference surface in the recording groove portion with reference to the position BB ′ of the reflection reference surface before recording. As shown in FIG. 3B, d _pit is positive in the direction in which the recording layer 22 contracts (the direction in which the reflection reference surface moves into the recording layer 22). Conversely, if d _pit is negative, it means that the recording layer 22 expands beyond the BB ′ plane. The film thickness d _Ga of the recording layer 22 after recording is represented by the following formula (1).
d _Ga = d _G −d _pit −d _bmp equation (1)
Note that d _GL , d _G , d _L , d _mix , n _d , n _c , n _s, and d _Ga do not take negative values due to their definitions and physical characteristics.

  As a method for modeling such a recording pit and estimating a phase described below, a known method was used (Non-Patent Document 1).

  Now, the phase difference of the reproduction light (reflected light) between the recording groove portion and the recording groove portion on the phase reference plane A-A ′ is obtained before and after recording. The phase difference of the reflected light between the recording groove portion and the recording groove portion before recording is Φb, and after recording, the phase difference of the reflected light between the recording pit portion 25p and the recording groove portion is Φa, and is collectively referred to as Φ. These Φa and Φb are both defined by the following formulas (2) and (3).

Φ = Φb or Φa
= (Reflected light phase between recording grooves)-(Phase of recording groove (including pit after recording))
Formula (2)

Φ = Φb or Φa
= (2π / λ) · 2 ·
{(Optical path length between recording grooves) − (optical path length of recording groove (including pit after recording))}
Formula (3)

  Here, the reason why the coefficient 2 is multiplied in the equation (3) is to consider the round-trip optical path length.

In FIGS. 3A and 3B, the following formulas (4) and (5) are established.
Φb = (2π / λ) · 2 · {n d · d L - _{[n d · d G + n c} · (d L + d GL -d G) ]}
= (4π / λ) · {(n _c −n _d ) · (d _G −d _L ) −n _c · d _GL } Equation (4)
Φa = (2π / λ) · 2 · {(n d · d L - _{[n c · (d L + d} GL -d G + d bmp -d mix)
+ (N _d −δn _d ) · (d _G −d _pit −d _bmp ) + (n _c −δn _c ) · d _mix ]}
= Φb + ΔΦ Equation (5)

However, ΔΦ is expressed by the following formula (6).
ΔΦ = (4π / λ) {(n _d −n _c ) · d _bmp + n _d · d _pit + δn _c · d _mix +
_{δn d · (d G -d pit} -d bmp)} Equation (6)

In addition, since the recording groove portion is behind the recording groove portion when viewed from the incident side, Φb <0.
ΔΦ is a phase change in the pit portion caused by recording.

The degree of modulation m of the signal produced by ΔΦ is
m∝1−cos (ΔΦ) = sin ² (ΔΦ / 2) Equation (7)
≒ (ΔΦ / 2) ² (8)
It becomes. The rightmost side (8) is an approximation when ΔΦ is small.

  If | ΔΦ | is large, the degree of modulation increases, but usually the phase change due to recording | ΔΦ | is between 0 and π, and is generally considered to be about π / 2 or less. In fact, such a large phase change has not been reported in conventional dye-based recording layers such as conventional CD-R and DVD-R. Further, as described above, in the blue wavelength region, the phase change tends to be smaller due to the general characteristics of the dye. On the other hand, a change in which | ΔΦ | exceeds π may reverse the push-pull polarity before and after recording, and the push-pull signal may become too large, which is undesirable from the standpoint of maintaining the stability of the tracking servo. There is a case.

  Here, FIG. 4 is a diagram for explaining the relationship between the phase difference between the recording groove portion and the recording groove portion and the reflected light intensity. FIG. 4 shows the relationship between | Φ | and the reflected light intensity at the recording groove before and after recording. Here, for the sake of simplicity, the influence of absorption of the recording layer 22 is ignored. In the configurations of FIGS. 3A and 3B, Φb <0 is usually satisfied. Therefore, the case where ΔΦ <0 is the direction in which | Φ | in FIG. 4 increases. That is, it corresponds to a value obtained by multiplying the horizontal axis in FIG. 4 by (−1). Therefore, | Φb | increases to | Φa |.

Assuming that the reflectance of the recording groove in the planar state (d _GL = 0) is R0, as | Φ | increases, an interference effect is generated from the phase difference Φb of the reflected light between the recording groove and the recording groove, and the reflected light The strength decreases. When the phase difference | Φ | becomes equal to π (half wavelength), the reflected light intensity becomes a minimum value. Further, when | Φ | increases beyond π, the reflected light intensity starts to increase, and reaches a maximum value when | Φ | = 2π.

Here, the push-pull signal intensity becomes maximum when the phase difference | Φ | is π / 2, becomes minimum when the phase difference is π / 2, and the polarity is inverted. Thereafter, it increases / decreases again, reaches a minimum at 2π, and reverses the polarity again. Above relationship, in the ROM medium due to the phase pits is exactly the same as the depth of the pit part (equivalent to d _GL) and the relationship between the reflectance (Non-Patent Document 5).

The push-pull signal will be described below.
FIG. 5 is a diagram for explaining the configuration of a quadrant detector that detects a recording signal (sum signal) and a push-pull signal (difference signal). The quadrant detector is composed of four independent photodetectors, and outputs are Ia, Ib, Ic, and Id, respectively. The zeroth-order diffracted light and the first-order diffracted light from the recording groove portion and the recording groove portion in FIG. An arithmetic output represented by the following equations (9) and (10) is obtained from the signal from the quadrant detector.

Isum = (Ia + Ib + Ic + Id) Formula (9)
IPP = (Ia + Ib) − (Ic + Id) Formula (10)

  6 (a) and 6 (b) detect an output signal obtained while actually passing through a plurality of grooves and inter-groove parts after passing through a low-frequency pass filter (cutoff frequency of about 30 kHz). It is a figure which shows a signal.

In FIGS. 6A and 6B, Isum _pp is the signal amplitude of the peak of the Isum signal, and IPP _pp is the signal amplitude of the peak-to-peak of the push-pull signal. Push-pull signal strength refers to IPP _pp and is distinguished from push-pull signal itself (IPP).

  The tracking servo performs feedback servo using the push-pull signal (IPP) in FIG. 6B as an error signal. In FIG. 6B, for example, the zero cross point where the polarity of the IPP signal changes from + to − corresponds to the center of the recording groove, and the zero cross point where the polarity changes from − to + corresponds to the portion between the recording grooves. When the push-pull polarity is reversed, the sign change is reversed. When the sign is reversed, the servo is applied to the recording groove (that is, the focused beam spot is irradiated to the recording groove), but conversely, the servo is applied to the recording groove.

  The Isum signal when the servo is applied to the recording groove is a recording signal, and in this embodiment, the change increases after recording.

Here, the calculation output represented by the following equation (11) is referred to as normalized push-pull signal strength (IPP _actual ).

IPP _actual = [{(Ia + Ib) (t)-(Ic + Id) (t)} /
{(Ia + Ib) (t) + (Ic + Id) (t)}] _pp
= {IPP (tb) / Isum (tb)}-
{IPP (ta) / Isum (ta)} Equation (11)
(Here, ta is the time when the IPP becomes the minimum value, and tb is the time when the IPP becomes the maximum value.)

  In many cases, the push-pull signal used by the optical recording / reproducing apparatus for tracking servo is a standardized push-pull signal calculated from the values of Isum and IPP.

  The relationship between the phase difference and reflected light intensity as shown in FIG. 4 is periodic as can be seen from the above equation (7). The change of | Φ | before and after recording, that is, | ΔΦ | is usually smaller than about (π / 2) in an optical recording medium having a dye as a main component of the recording layer. Conversely, in this embodiment, it is assumed that the change in | Φ | due to recording is π or less at the maximum. Therefore, if necessary, the recording layer thickness may be reduced appropriately.

Here, when viewed from the phase reference plane AA ′, when the phase (or optical path length) of the reflected light of the recording groove portion becomes smaller than before recording due to the formation of the recording pit portion 25p (when the phase is delayed from before recording). That is, when ΔΦ> 0, the optical distance (optical path length) of the reflection reference surface is reduced as viewed from the incident side, and the light source (or the phase reference surface AA ′) is approached. . Therefore, in FIGS. 3A and 3B, there is an effect equivalent to that the reflection reference surface of the recording groove portion moves upward (d _GL decreases), and as a result, the reflected light of the recording pit portion 25p. Strength increases.

On the other hand, when viewed from the phase reference plane AA ′, when the phase (or optical path length) of the reflected light of the recording pit portion 25p is larger than before recording (when the phase is delayed from before recording), that is, ΔΦ <0. In this case, the optical distance (optical path length) of the reflection reference surface is increased as viewed from the incident side, and the distance from the light source (or phase reference surface AA ′) is increased. 3A and 3B, there is an effect equivalent to that when the reflection reference surface of the recording groove portion moves downward (d _GL increases), and as a result, the reflected light intensity of the recording pit portion 25p is as follows. Decrease. Here, the direction of change in reflected light intensity, which is whether the reflected light intensity at the recording pit portion decreases or increases after recording, is called the recording (signal) polarity.

  Therefore, if a phase change that satisfies ΔΦ> 0 occurs in the recording pit portion 25p, the polarity of “Low to High” in which the reflected light intensity increases by recording in the recording groove portion of FIGS. 3 (a) and 3 (b). Is preferably used. On the other hand, if a phase change that satisfies ΔΦ <0 occurs, it is preferable to use the polarity of HtoL in the recording groove portion of FIGS. 3 (a) and 3 (b).

(Preferred embodiment of sign of phase change ΔΦ and recording polarity)
Now, in the recording pit portion 25p, a phase change due to optical index change or deformation of the recording layer 22 (that is, it contributes to a change in reflected light intensity considering the phase difference) and a planar state due to the refractive index change. Although the change in reflected light intensity at (that is, the change in reflected light intensity not considering the phase difference) can occur simultaneously, it is preferable that the directions of these changes are aligned. In other words, in order for the polarity of the recording signal to be constant regardless of the recording power and the length and size of the recording pits, it is preferable that the individual reflected light intensity changes are uniform.

Here, considering the case where cavities are likely to be formed in the recording layer or the adjacent interface, considering that the inside of the cavities is considered as n _d ′ = 1 and the refractive index is lowered, etc. In the recording media shown in FIGS. 3A and 3B, a phase change that satisfies ΔΦ> 0, that is, a polarity that satisfies LtoH is preferable.
Further, in order to match the direction of each phase change, it is preferable to easily control each phase change.

For example, it is preferable to set d _mix = 0 by providing an interface layer on the recording layer incident side interface. This is because the change in phase difference due to d _mix cannot be made so large that it is difficult to use it actively, and its thickness is difficult to control. Accordingly, it is preferable to set d _mix = 0 by providing an interface layer at the recording layer incident side interface.

  It is preferable that the deformation is concentrated in one place and limited to one direction. This is because better signal quality can be obtained more easily by controlling one deformation part more accurately than a plurality of deformation parts.

Here, the relationship between the phase change of ΔΦ> 0 and the push-pull signal will be considered.
When performing HtoL recording on the cover layer groove 26 by analogy with the conventional CD-R or DVD-R, in order to prevent the push-pull signal polarity from being reversed, a deep groove whose reciprocal optical path length is longer than one wavelength is used. It is limited to a step (referred to as a “deep groove”) or a groove step (referred to as a “shallow groove”) that barely generates a push-pull signal. In the case of a deep groove, the phase change in the direction of the arrow α in FIG. 4 is used to optically deepen the groove. In this case, the groove depth that is the starting point of the arrow is preferably about 100 nm at a blue wavelength of around 400 nm. As described above, when a narrow track pitch is used, defective transfer is likely to occur during molding, resulting in difficulty in mass production. Further, even if a desired groove shape is obtained, noise due to the minute surface roughness of the groove wall is likely to be mixed into the signal. Furthermore, it is difficult to uniformly form the reflective layer 23 on the bottom and side walls of the groove. The adhesion of the reflective layer 23 itself to the groove wall is also poor, and deterioration such as peeling tends to occur. As described above, when HtoL recording is performed using the phase change of ΔΦ> 0 in the conventional method using the “deep groove”, it is difficult to reduce the track pitch.

  On the other hand, in the case of shallow grooves, the phase change in the direction of arrow β is used on the slope between | Φ | = 0 to π in FIG. Become. If a certain push-pull signal intensity is obtained in the unrecorded state, the groove depth is about 20 nm to 30 nm at the blue wavelength. When the recording layer 22 is formed in such a state, the recording layer thickness is easily formed equally in the recording groove portion (in this case, the cover layer groove portion 26) and the groove portion as in the planar state, and the recording pits are formed. It is easy to protrude from the recording groove, and the diffracted light from the recording pit leaks into the adjacent recording groove, resulting in very large crosstalk. Similarly, when attempting to perform HtoL recording using a phase change of ΔΦ> 0 in the conventional method, it is difficult to reduce the track pitch.

  In order to overcome these problems, the present inventors have studied a film surface incident type dye medium, particularly a medium having a coating type recording layer. As a result, the preferred configuration for the film surface incident type dye medium is not the conventional HtoL recording using the “deep groove”, but the phase change in the direction of the arrow γ in FIG. It was found that a signal having a recording polarity of LtoH was obtained. That is, the optical recording medium 20 performs recording / reproduction by making recording / reproduction light incident from the cover layer 24 side, and the surface on which the recording / reproduction light beam 27 is incident on the cover layer 24 (surface 29 on which the recording / reproduction light beam 27 is incident). When the guide groove portion far from the recording groove portion is used as the recording groove portion, the reflected light intensity of the recording pit portion formed in the recording groove portion is higher than the reflected light intensity of the recording groove portion when not recorded. Conventionally, a write-once medium using a dye as a recording layer is characterized in that a recording signal equivalent to that of a ROM medium can be obtained after recording. For this purpose, it is only necessary to ensure reproduction compatibility after recording. It is not necessary to maintain the same high reflected light intensity as that of the ROM medium before recording, and the reflected light intensity at the H level after recording is reflected light intensity defined by the ROM medium (sometimes referred to simply as reflectance in the ROM medium). It may be within the range of many). LtoH recording is never inconsistent with maintaining playback compatibility with ROM media.

  It is to be noted that the important thing in the present embodiment is that the above-described decrease in the refractive index of the recording layer, the decrease in the refractive index at the pit portion due to the formation of cavities, and the deformation inside the recording layer 22 or at the interface thereof That is, the incident occurs on the recording / reproducing light incident side of the reflecting layer 23 which is the main reflecting surface. In the recording pit portion, the fact that no deformation or mixing occurs in any of the intermediate layer / recording layer and the reflective layer / substrate interface can simplify the elements that control the recording signal polarity, and distort the recording signal waveform. Is preferable.

  In the film surface incidence configuration as shown in FIG. 2 and FIGS. 3A and 3B, when the guide groove portion on the side far from the surface 29 on which the recording / reproducing light beam 27 is incident is used as the recording groove portion, the phase is the same as in the conventional configuration. If the recording principle based on change is applied, LtoH recording can be performed using a phase change such that ΔΦ> 0.

At first, a phase change in the recording pit part 25p is desirably one due to the formation of low refractive index portion than n _d on the incident light side of the reflective layer 23. In order to maintain the stability of various servos before recording, it is preferable to maintain a reflectance of at least 3% to 30%.

Here, the recording groove portion reflectance (R _g ) in an unrecorded state is formed by forming a reflective layer having a known reflectance (R _ref ) with the same configuration as that of the optical recording medium 20 shown in FIG. I _ref is the reflected light intensity obtained by irradiating the recording groove so that the recording groove is in focus, and similarly the reflected light intensity obtained by irradiating the recording groove with the focused light beam in the optical recording medium 20 shown in FIG. when to the I _s, is obtained as _{R g = R ref · (I} s / I ref). Similarly, after the recording, the recording signal amplitude, recording groove part reflectivity corresponding to low reflected light intensity I _L R _L between recording pits (space part), high reflected light intensity I _H of the recording pit (mark part) The recording groove portion reflectance corresponding to is called R _H.

In the following, when the change in reflected light intensity of the recording groove portion is quantified according to common usage, the recording groove portion reflectance is used for the quantification.
In the present embodiment, since the phase change caused by recording is used, it is preferable to increase the transparency of the recording layer 22 itself. When the recording layer 22 is formed alone on a transparent polycarbonate resin substrate, the transmittance is preferably 40% or more, more preferably 50% or more, and further preferably 60% or more. If the transmittance is too high, the recording light energy cannot be absorbed sufficiently, so it is preferably 95% or less, more preferably 90% or less.

  On the other hand, such a high transmittance is maintained because the reflectivity R0 in the planar state is measured at the flat portion (mirror surface portion) in the disc having the configuration shown in FIG. The relative value based on the reflectivity in the planar state of the disk having the same structure except that the recording layer thickness is zero is usually 40% or more, preferably 50% or more, more preferably 70% or more. It can be generally confirmed.

(Regarding the preferred embodiments of the recording groove depth d _GL and the recording layer thickness d _G of the recording groove and the recording layer thickness d _L between the recording grooves)
When the phase change of ΔΦ> 0 is used and LtoH recording is performed on the cover layer groove portion 25, the groove depth is optically changed at the pit portion. It becomes easy to change. Of particular concern is the phase change that reverses the polarity of the push-pull signal.

  In order to perform LtoH recording and not cause a change in the polarity of the push-pull signal, in FIG. 4, the optical phase is changed by the phase change in the direction of the arrow γ on the slope of 0 <| Φb |, | Φa | <π. It is preferable to use the phenomenon that a groove becomes shallow. That is, in FIGS. 3A and 3B, a change occurs in the recording pit portion 25p so that the optical path length to the reflection reference surface of the recording groove portion becomes small when viewed from the phase difference reference surface AA ′. .

Further, considering the value before and after the recording of the push-pull signal intensity and considering the optimum depth of the groove, when the recording / reproducing light wavelength λ is set to a blue wavelength of 350 to 450 nm, the groove depth d _GL is usually 30 nm or more, preferably 35 nm or more. On the other hand, the groove depth d _GL is normally 70nm or less, preferably 65nm or less, more preferably 60nm or less. A groove having such a depth is referred to as an “intermediate groove”. Compared with the case of using the “deep groove” described above, there is an advantage that the formation of the groove and the covering of the cover layer groove portion 25 with the reflective layer become much easier.

  That is, in the optical recording medium 20 to which the present embodiment is applied, the recording layer 22 is formed by coating, and (groove depth)> (recording groove recording layer thickness)> (recording layer film between the recording grooves) (Thickness) is preferable.

When the groove depth is 30 to 70 nm, the recording layer thickness of the recording groove is preferably 5 nm or more, and more preferably 10 nm or more. This is because the phase change can be increased and the light energy necessary for forming the recording pits can be absorbed by setting the recording layer thickness of the recording groove to 5 nm or more. On the other hand, the recording layer thickness of the recording groove is preferably less than 50 nm, more preferably 45 nm or less, and still more preferably 40 nm or less. It is desirable that the recording layer 22 be thin as described above in order to mainly use the phase change and reduce the influence of the “reflectance change in the planar state” due to the refractive index change. As in the conventional CD-R and DVD-R, the recording layer of high refractive index of the dye main component is the refractive index at unrecorded 2.5-3, if n _d is reduced by recording, "plane It may cause a decrease in the “state reflectance”. When LtoH recording is performed by a phase difference change, the polarity is likely to be reversed.

  Further, the thinner the recording layer 22, it is possible to suppress the deformation at the recording pit portion from becoming too large or protruding from the recording groove portion.

  In the present invention in which the recording pits are formed in the cover layer groove portion, the above-mentioned “intermediate groove” depth is used, and the recording layer thickness in the substrate groove portion is close to 0, so that the recording layer 22 It is even more preferable to confine it in a recording groove having a depth of “intermediate groove” when actively using the formation of a cavity in the recording pit portion and the bulging deformation toward the cover layer as described later. It becomes. Also in this respect, the present invention is more effective in suppressing crosstalk than the case where recording is performed in the cover layer groove and a cavity is formed to perform HtoL recording.

  Thus, the recording pit is almost completely confined in the recording groove, and the diffracted light of the recording pit portion 25p in FIGS. 3A and 3B also leaks into the adjacent recording groove (crosstalk). The advantage that it can be reduced is obtained. That is, the LtoH recording intended for the recording in the cover layer groove portion 25 is not only an advantageous combination of the phase change of ΔΦ> 0 and the recording in the cover layer groove portion 25 but also a narrow track pitch. Therefore, it becomes easy to obtain a configuration suitable for high-density recording by the process.

(Regarding preferred modes of recording layer refractive index, n _d , n _c , δn _d , and deformation d _bmp )
It is possible to maintain a specific relationship between the refractive index of the recording layer before and after recording, the magnitude relationship of the refractive index of the cover layer, and the direction of deformation in the vicinity of the recording layer 22 and the cover layer 24. This is effective in preventing the phenomenon that (HtoL or LtoH) is reversed or mixed (a differential waveform is obtained).

For example, in order to promote deformation with the phase difference adjusted to LtoH, it is desirable that a volume expansion pressure due to thermal expansion, decomposition, and sublimation is generated in the thermal alteration of the recording layer 22. Further, it is preferable to provide an interface layer at the interface between the recording layer 22 and the cover layer 24 so as to confine the pressure and prevent leakage to other layers. It is desirable that the interface layer has a high gas barrier property and is more easily deformed than the cover layer 24. In particular, when a dye having a strong sublimation property is used as a main component, a volume expansion pressure is likely to be locally generated in the recording layer 22 portion. Also, at this time, it is easy to form a cavity at the same time, and even if the change in the refractive index of the recording layer of the dye main component is small, the effect of the cavity formation (internal n _d ′ can be regarded as 1) is added to the recording. This is preferable because the amount of change in the refractive index of the layer 22 can be increased. That is, it is preferable that a cavity is formed in the recording layer 22 or at the interface with the adjacent layer in order to increase the phased refractive index, and the recording layer 22 is covered by the pressure in the cavity. The swelling toward the layer 24 side is most preferable because it is considered that the change of ΔΦ> 0 can be generated most efficiently.

(Concerning preferred embodiments of specific layer structure and materials)
In the following, regarding the specific materials and aspects of the layer structure shown in FIG. 2 and FIGS. 3A and 3B, in consideration of the development of the blue wavelength laser, in particular, the recording / reproducing light beam 27 Description will be made assuming that the wavelength λ is in the vicinity of 405 nm.

(substrate)
The substrate 21 may be made of plastic, metal, glass or the like having an appropriate workability and rigidity in a film surface incident configuration. Unlike conventional substrate incidence configurations, there are no restrictions on transparency or birefringence. A guide groove is formed on the surface. When metal or glass is used, a light or thermosetting thin resin layer is provided on the surface, and the groove is formed there. In this respect, it is preferable from the viewpoint of manufacturing that a plastic material is used and the shape of the substrate 21 (in particular, a disk shape) and the guide groove on the surface are formed all at once by injection molding.

  As the plastic material that can be injection-molded, polycarbonate resin, polyolefin resin, acrylic resin, epoxy resin, and the like conventionally used in CDs and DVDs can be used. The thickness of the substrate 21 is preferably about 0.5 mm to 1.2 mm. The total thickness of the substrate and the cover layer is preferably 1.2 mm, which is the same as that of a conventional CD or DVD. This is because the cases used in conventional CDs and DVDs can be used as they are. In the Blu-ray disc, the substrate thickness is 1.1 mm and the cover layer thickness is 0.1 mm (Non-Patent Document 9).

A tracking guide groove is formed in the substrate 21. In the present embodiment, the track pitch at which the cover layer groove portion 25 becomes the recording groove portion is usually 0.1 μm or more, preferably 0.2 μm, in order to achieve higher density than CD-R and DVD-R. In addition, it is usually 0.6 μm or less, preferably 0.4 μm or less. As described above, the groove depth depends on the recording / reproducing light wavelengths λ, d _GL , d _G , d _{L and the} like, but is preferably in the range of approximately 30 nm to 70 nm. Within the above range, the groove depth is appropriately optimized in consideration of the recording groove portion reflectance R _g in an unrecorded state, the signal characteristics of the recording signal, the push-pull signal characteristics, the optical characteristics of the recording layer, and the like. For example, in order to obtain an equivalent R _g with respect to changes in the optical characteristics of the recording layer, when n _d and k _d are large, the groove depth is relatively shallow, and n _d and k _d are small. In such a case, it is preferable to make it relatively deep. Even if the groove depth is the same, if n _d is about 1.5 or more, k _{d is set} to about 0.5 or less. Conversely, if k _d is about 0.5 or more, n R _g can be kept at 10% or more if a recording layer having a value of _d of about 1.5 or less is selected.

  In the present embodiment, since interference due to the phase difference of the reflected light in the recording groove portion and the recording groove portion is used, both are required to be present in the focused light spot. For this reason, the recording groove width (width of the cover layer groove portion 25) is preferably smaller than the spot diameter (diameter in the groove transverse direction) of the recording / reproducing light beam 27 on the recording layer 22 surface. In an optical system having a recording / reproducing light wavelength λ = 405 nm and NA (numerical aperture) = 0.85, when the track pitch is 0.32 μm, it is preferably in the range of 0.1 μm to 0.2 μm. Outside these ranges, it is often difficult to form grooves or inter-groove portions.

  The shape of the guide groove is usually rectangular. In particular, when forming a recording layer by coating described later, it is desirable that the dye is selectively accumulated on the substrate groove in several tens of seconds until the solvent of the solution containing the dye is almost evaporated. For this reason, it is also preferable that the shoulder between the substrate grooves of the rectangular groove is rounded so that the dye solution easily falls and accumulates in the substrate groove portion. Such a groove shape having a round shoulder can be obtained by etching the surface of a plastic substrate or stamper by exposing it to plasma or UV ozone for several seconds to several minutes. Etching with plasma is suitable for obtaining the shape of the shoulder of the rounded groove portion because the sharp portion such as the shoulder of the groove portion of the substrate (edge of the groove portion) is selectively cut away.

  The guide groove is usually added by groove modulation, groove modulation such as groove meandering, groove depth modulation, and irregular pits due to intermittent or intermittent recording grooves, in order to give additional information such as addresses and synchronization signals. Have a signal. For example, in a Blu-ray disc, a wobble address method using two modulation methods, MSK (minimum-shift-keying) and STW (saw-tooth-wobbles), is used (Non-patent Document 9).

(Layer having a light reflection function mainly composed of Ag)
The layer (reflection layer 23) having a light reflection function mainly composed of Ag preferably has a high reflectance with respect to the recording / reproducing light wavelength and a reflectance of 70% or more with respect to the recording / reproducing light wavelength. In general, Au, Ag, Al, and alloys containing these as the main components are those that exhibit high reflectivity in visible light used as recording and reproducing wavelengths. In the present invention, among these, an alloy mainly composed of Ag having a high reflectance at λ = 350 to 450 nm and a small absorption is employed. Here, “having Ag as a main component” means that the Ag content in the reflective layer is 50 atomic% or more, preferably 80 atomic% or more, more preferably 90 atomic% or more, particularly preferably. Is 95 atomic% or more. Mainly composed of Ag, Au, Cu, rare earth elements (particularly Nd), Nb, Ta, V, Mo, Mn, Mg, Cr, Bi, Al, Si, Ge, etc. 0.01 atomic% to 10 atomic% By adding, the corrosion resistance against moisture, oxygen, sulfur and the like can be improved, which is preferable. In addition, a dielectric mirror in which a plurality of dielectric layers are stacked can be used.

The film thickness of the reflective layer 23 is preferably about the same as or thinner than _dGL in order to maintain the groove step on the surface of the substrate 21. Similarly, when the recording / reproducing light wavelength λ = 405 nm, as described above, d _GL is preferably 70 nm or less. Therefore, the thickness of the reflective layer is preferably 90 nm or less, and more preferably 70 nm or less. . Except when forming a two-layer medium, the lower limit of the reflective layer thickness is preferably 30 nm or more, more preferably 40 nm or more. The surface roughness Ra of the reflective layer 23 is preferably 5 nm or less, and more preferably 1 nm or less. Ag has a property that flatness is increased by the use of an additive. In this sense as well, it is desirable that the amount of the additive element used is usually 0.1 atomic% or more, preferably 0.5 atomic% or more. The reflective layer 23 can be formed by a sputtering method, an ion plating method, an electron beam evaporation method, or the like.

(Middle layer)
An intermediate layer 30 is provided between the reflective layer 23 and the recording layer 22. By providing the intermediate layer 30, it is possible to improve the jitter characteristics.
The intermediate layer 30 usually contains an element selected from the group consisting of Ta, Nb, V, W, Mo, Cr, and Ti from the viewpoint of improving jitter characteristics. Especially, it is preferable to contain either Ta, Nb, Mo, and V, and it is preferable to contain either Ta or Nb. The intermediate layer 30 may contain any one of these elements alone, or may contain two or more kinds in any combination and composition. Since the above elements are low in reactivity and solid solubility with silver or silver alloy widely used as a reflective layer, if these elements are used as the intermediate layer 30, an optical recording medium having excellent storage stability can be obtained. Can be obtained.

  The intermediate layer 30 preferably contains the above element as a main component. In the present specification, the “main component” means that 50% by atom or more of the elements constituting the intermediate layer 30 is contained. Among them, the element is preferably contained in an amount of 70 atomic% or more, more preferably 90 atomic% or more, further preferably 95 atomic% or more, and 99 atomic% or more. Particularly preferred. Ideally, the element is contained at 100 atomic%. In addition, when the intermediate | middle layer 30 contains 2 or more types of the said element, it is preferable that the total ratio satisfy | fills the said range.

The mechanism by which the effect of improving the jitter is obtained by providing the intermediate layer 30 is not clear. However, according to the study by the present inventors, the intermediate layer 30 is composed of an element having a higher hardness than the alloy mainly composed of Ag used as the material of the reflective layer 23, and / or recording. It was found that the jitter tends to be improved by using as the intermediate layer 30 an element that has a large light absorption at the reproduction wavelength. On the other hand, when a layer made of the intermediate layer material was provided between the reflective layer 23 and the substrate 21, a remarkable jitter reduction effect was not obtained. From this, the effect of the intermediate layer 30 of the present invention is not only the function of suppressing the deformation on the substrate side by the hardness, but also the undesirable incidental deformation due to the function of suppressing the deformation / reaction between the reflective layer and the recording layer. It is presumed to have an effect of suppressing the above. In addition, since the intermediate layer 30 of the present invention has an appropriate light absorption function, heat generation on the reflective layer side of the recording layer is promoted, and the effect of accelerating the decomposition of the recording layer is combined, thereby obtaining good jitter. It is assumed that If only the hardness and the light absorption effect are available, there is room for selecting other metals. In particular, the material of the intermediate layer 30 used in the present invention is not only high in light absorption but high in hardness, but also an Ag alloy. Even when formed in contact with the Ag alloy, it was selected in consideration of the characteristics that it is difficult to diffuse mutually with the Ag alloy and is stable (low solubility in the solid phase with the main component Ag and difficult to form a solid solution). .
For this reason, it is presumed that the above condition can be easily satisfied by forming the intermediate layer 30 using the above elements.

  The intermediate layer 30 may contain elements other than the above elements as additive elements or impurity elements in order to impart desired characteristics. Examples of such additive elements or impurity elements include Mg, Si, Ca, Mn, Fe, Co, Ni, Cu, Y, Zr, Pd, Hf, and Pt. One of these additive elements or impurity elements may be used alone, or two or more thereof may be used in any combination and ratio. The upper limit of the concentration of these additive elements or impurity elements in the intermediate layer 30 is usually about 5 atomic% or less.

  The film thickness of the intermediate layer 30 can exert its effect as long as it is formed as a film, but the lower limit of the film thickness is usually 1 nm or more. On the other hand, if the film thickness of the intermediate layer 30 is too large, the light absorption of the intermediate layer increases and causes a decrease in recording sensitivity and a decrease in reflectivity. Therefore, it is usually 15 nm or less, preferably 10 nm or less, more preferably 5 nm or less. . When the film thickness is within the above range, a jitter improvement effect and appropriate reflectance and recording sensitivity can be obtained at the same time.

  The intermediate layer 30 can be formed by a sputtering method, an ion plating method, an electron beam evaporation method, or the like.

(Recording layer mainly composed of dye)
The recording layer 22 contains, as a main component, a dye having a light absorption function with respect to the recording / reproducing light wavelength in an unrecorded (before recording) state. The dye contained as the main component in the recording layer 22 is specifically an organic compound having a remarkable absorption band due to its structure in the visible light (and its vicinity) wavelength region of 300 nm to 800 nm. preferable. In an unrecorded state (before recording) in which such a dye is formed as the recording layer 22, it has absorption at the wavelength λ of the recording / reproducing light beam 27, is altered by recording, and the recording layer 22 has a reflected light intensity of reflected light. A dye that causes an optical change that can be detected as a change is called a “principal dye”. The main component dye may exhibit the above function as a mixture of a plurality of dyes.

  The main component dye content is preferably 50% or more, more preferably 80% or more, and still more preferably 90% or more in terms of% by weight. As the main component dye, a single dye absorbs the wavelength λ of the recording / reproducing light beam 27 and is preferably altered by recording to cause the optical change described above. The function may be shared so that the other pigment is indirectly modified to cause an optical change by having and generating heat. In addition to this, a dye as a so-called quencher for improving the temporal stability (temperature, humidity, light stability) of a dye having a light absorption function may be mixed with the main component dye. Examples of the inclusion other than the main component dye include a binder (binder) made of a low-polymer material and a dielectric.

The main component dye is not particularly limited by the structure. In the present embodiment, recording causes a change of δn _d > 0 in the recording layer 22, and in principle, as long as the extinction coefficient k _d > 0 in an unrecorded (before recording) state is optical. There are no strong constraints on the physical characteristics. Main component dye has an absorption for the wavelength λ of the recording and reproducing light beam 27, and, their absorbance, by heating, to cause a deterioration, reduction of the refractive index, .DELTA.n _d> 0, Shojire a. Here, the alteration refers specifically to phenomena such as expansion, decomposition, sublimation, and melting due to absorption and heat generation of the main component dye. The coloring matter itself as the main component may be altered, accompanied by some structural change, and the refractive index may be lowered. Further, .DELTA.n _d> 0 becomes changes may be cavities formed in the recording layer 22 and / or interface may be a depressed refractive index due to thermal expansion of the recording layer 22.

The temperature exhibiting such alteration is more preferably 100 ° C. or higher, usually 500 ° C. or lower, preferably 350 ° C. or lower. From the viewpoint of storage stability and reproduction light resistance, it is more preferably 150 ° C. or higher. Moreover, if the decomposition temperature is 300 ° C. or lower, the jitter characteristics particularly at a high linear velocity of 10 m / s or higher tend to be good, which is preferable. It is preferable that the decomposition temperature is 280 ° C. or lower because there is a possibility of further improving the characteristics in high-speed recording. Usually, the alteration behavior described above is measured as a thermal characteristic of the main component dye, and a rough behavior can be measured as a weight decrease start temperature by a thermogravimetric analysis-differential thermal analysis (TG-DTA) method. As described above, it is more preferable that d _bmp <0, that is, the deformation that causes the recording layer 22 to bulge toward the cover layer 24 occurs at the same time in order to use the phase change of ΔΦ> 0. Accordingly, it is preferable to have a sublimation property or a decomposition product having high volatility and capable of generating a pressure for expansion inside the recording layer 22.

  The film thickness of the recording layer 22 is usually 70 nm or less, preferably 50 nm or less, more preferably less than 50 nm, and still more preferably 40 nm or less. On the other hand, the lower limit of the recording layer thickness is 5 nm or more, preferably 10 nm or more.

Examples of the main component dye in the recording layer include methine-based, (metal-containing) azo-based, pyrone-based, porphyrin-based compounds, and mixtures thereof. More specifically, metal-containing azo dyes (JP-A-9-277703, JP-A-10-026692 etc.) and pyrone dyes (JP-A 2003-266954) are inherently excellent in light resistance. And the weight reduction start temperature _Td in TG-DTA is 150 to 400 degreeC, and it is preferable at the point which has a sharp weight loss characteristic (The volatility of a decomposition product is high and it is easy to form a cavity.). Particularly preferred are dyes having n _d = 1.2 to 1.9, k _d = 0.3 to 1, and T _d = 150 ° C. to 300 ° C. Among these, metal-containing azo dyes that satisfy these characteristics are preferable.

  More specifically, the azo dye includes a compound having a coupler component having a 6-hydroxy-2-pyridone structure and any one diazo component selected from isoxazole triazole and pyrazole, and the organic compound. Examples thereof include metal complex compounds composed of metal ions coordinated with a dye compound. In particular, a metal-containing pyridone azo compound having a structure represented by the following general formulas [I] to [III] is preferable.

（式中、Ｒ₁〜Ｒ₁₀は、それぞれ独立に、水素原子又は１価の官能基を表わす。）

(In the formula, R _{1 to} R ₁₀ each independently represents a hydrogen atom or a monovalent functional group.)

  Further, a metal-containing cyclic β-diketone azo compound comprising a cyclic β-diketone azo compound represented by the following general formula [IV] or [V] and a metal ion is preferable.

（式中、
環Ａは、炭素原子及び窒素原子とともに形成される含窒素複素芳香環を表わし、
Ｘ、Ｘ’、Ｙ、Ｙ’、Ｚは、各々独立に、水素原子以外に置換基（スピロ含む）を有していてもよい炭素原子、酸素原子、硫黄原子、Ｎ−Ｒ₁₁で表わされる窒素原子、Ｃ＝Ｏ、Ｃ＝Ｓ、又は、Ｃ＝ＮＲ₁₂を表わし、βジケトン構造と共に５員環又は６員環構造を形成する。
Ｒ₁₁は、水素原子、直鎖又は分岐のアルキル基、環状アルキル基、アラルキル基、アリール基、複素環基、−ＣＯＲ₁₃で表わされるアシル基、又は、−ＮＲ₁₄Ｒ₁₅で表わされるアミノ基を表わし、
Ｒ₁₂は、水素原子、直鎖又は分岐のアルキル基、又は、アリール基を表わす。
Ｒ₁₃は、炭化水基、又は、複素環基を表わし、
Ｒ₁₄、Ｒ₁₅は、各々独立に、水素原子、炭化水素基又は複素環基を表わす。
なお、上述の各基は、必要に応じて置換されてもよい。
また、Ｘ、Ｘ’、Ｙ、Ｙ’、Ｚが、各々独立に、炭素原子又はＮ−Ｒ₁₁で表される窒素原子の場合、隣接する両者の結合は、単結合であっても二重結合であってもよい。
更に、Ｘ、Ｘ’、Ｙ、Ｙ’、Ｚが、各々独立に、炭素原子、Ｎ−Ｒ₁₁で表される窒素原子、又は、Ｃ＝ＮＲ₁₂の場合、隣接するもの同士で互いに縮合して、飽和又は不飽和の炭化水素環或いは複素環を形成してもよい。）

(Where
Ring A represents a nitrogen-containing heteroaromatic ring formed together with a carbon atom and a nitrogen atom,
X, X ′, Y, Y ′, and Z are each independently represented by a carbon atom, oxygen atom, sulfur atom, or N—R ₁₁ that may have a substituent (including spiro) in addition to a hydrogen atom. It represents a nitrogen atom, C═O, C═S, or C═NR ₁₂ , and forms a 5-membered ring or 6-membered ring structure together with a β-diketone structure.
R ₁₁ represents a hydrogen atom, a linear or branched alkyl group, a cyclic alkyl group, an aralkyl group, an aryl group, a heterocyclic group, an acyl group represented by —COR ₁₃ , or an amino group represented by —NR ₁₄ R _15. Represents
R ₁₂ represents a hydrogen atom, a linear or branched alkyl group, or an aryl group.
R ₁₃ represents a hydrocarbon group or a heterocyclic group,
R ₁₄ and R ₁₅ each independently represents a hydrogen atom, a hydrocarbon group or a heterocyclic group.
Each group described above may be substituted as necessary.
In addition, when X, X ′, Y, Y ′, and Z are each independently a carbon atom or a nitrogen atom represented by N—R ₁₁ , the adjacent bonds may be a single bond or a double bond. It may be a bond.
Furthermore, when X, X ′, Y, Y ′, and Z are each independently a carbon atom, a nitrogen atom represented by N—R ₁₁ , or C═NR ₁₂ , adjacent ones are condensed with each other. A saturated or unsaturated hydrocarbon ring or a heterocyclic ring. )

  A metal-containing azo dye comprising a compound represented by the following general formula [VI] and a metal is also preferred.

（式中、
Ａは、これが結合している炭素原子及び窒素原子とともに複素芳香環を形成する残基を表わし、
Ｘは、活性水素を有する基を表わし、
Ｒ₁₆及びＲ₁₇は、各々独立に、水素原子、又は、任意の置換基を表わす。）

(Where
A represents a residue that forms a heteroaromatic ring with the carbon and nitrogen atoms to which it is attached;
X represents a group having active hydrogen,
R ₁₆ and R ₁₇ each independently represents a hydrogen atom or an arbitrary substituent. )

  Furthermore, metal-containing azo dyes represented by the following general formula [VII] are also included.

（式［VII］中、
環Ａは、炭素原子及び窒素原子とともに形成される含窒素複素芳香環を表わし、
ＸＬは、Ｌが脱離することによりＸが陰イオンとなり金属が配位可能となる置換基を表わし、
Ｒ₁₈、Ｒ₁₉は、それぞれ独立に、水素原子、直鎖又は分岐のアルキル基、環状アルキル基、アラルキル基又はアルケニル基を表わし、これらは各々隣接する置換基同士又は互いに縮合環を形成してもよい。
Ｒ₂₀、Ｒ₂₁、Ｒ₂₂は、各々独立に、水素原子、又は、任意の置換基を表わす。）

(In the formula [VII],
Ring A represents a nitrogen-containing heteroaromatic ring formed together with a carbon atom and a nitrogen atom,
XL represents a substituent in which X becomes an anion and metal can be coordinated by elimination of L;
R ₁₈ and R ₁₉ each independently represents a hydrogen atom, a linear or branched alkyl group, a cyclic alkyl group, an aralkyl group or an alkenyl group, each of which forms a condensed ring with each other adjacent substituents. Also good.
R ₂₀ , R ₂₁ and R ₂₂ each independently represents a hydrogen atom or an arbitrary substituent. )

These azo dyes have a main absorption band from a shorter wavelength than the azo dyes conventionally used in CD-R and DVD-R, and the extinction coefficient k _d near 400 nm is A large value of about 0.3 to 1 is preferable. Examples of metal ions include divalent metal ions such as Ni, Co, Cu, Zn, Fe, and Mn. Particularly, when Ni and Co are contained, they are excellent in light resistance, high temperature and high humidity environment resistance. It is preferable. In addition, the metal-containing azo dye represented by the formula [VII] can be used as the compound Y described later after having a longer wavelength.

  More specifically, the pyrone dye is preferably a compound having the following general formula [VIII] or [IX].

（式［VIII］中、
Ｒ₂₃〜Ｒ₂₆は、各々独立に、水素原子又は任意の置換基を表わす。また、Ｒ₂₃とＲ₂₄、Ｒ₂₅とＲ₂₆とが各々縮合して、炭化水素環又は複素環構造を形成していてもよい。その場合、該炭化水素環及び該複素環は、置換基を有していてもよい。
Ｘ₁は、電子吸引性基を表わし、
Ｘ₂は、水素原子、又は、−Ｑ−Ｙ（ここで、Ｑは、直接結合、炭素数１又は２のアルキレン基、アリーレン基、又は、ヘテロアリーレン基を表わし、Ｙは、電子吸引性基を表わす。）を表す。該アルキレン基、該アリーレン基、該ヘテロアリーレン基は、Ｙ以外に任意の置換基を有していてもよい。
Ｚは、−Ｏ−、−Ｓ−、−ＳＯ₂−、−ＮＲ₂₇−（ここで、Ｒ₂₇は、水素原子、置換されてもよい炭化水素基、置換されてもよい複素環基、シアノ基、ヒドロキシ基、−ＮＲ₂₈Ｒ₂₉（ここで、Ｒ₂₈、Ｒ₂₉は、各々独立して、水素原子、置換されてもよい炭化水素基、置換されてもよい複素環基、−ＣＯＲ₃₀（ここで、Ｒ₃₀は置換されてもよい炭化水素基又は置換されてもよい複素環基を表わす。）を表す。）、又は、−ＣＯＲ₃₁（ここで、Ｒ₃₁は、置換されてもよい炭化水素基、又は、置換されてもよい複素環基を表わす。）を表わす。）を表す。）

(In the formula [VIII],
R _{23 to} R ₂₆ each independently represents a hydrogen atom or an arbitrary substituent. R ₂₃ and R ₂₄ , and R ₂₅ and R ₂₆ may be condensed to form a hydrocarbon ring or a heterocyclic structure. In that case, the hydrocarbon ring and the heterocyclic ring may have a substituent.
X ₁ represents an electron-withdrawing group,
X ₂ is a hydrogen atom, or, -Q-Y (wherein, Q is a direct bond, an alkylene group having 1 or 2 carbon atoms, an arylene group, or represents a heteroarylene group, Y is an electron withdrawing group Represents). The alkylene group, the arylene group, and the heteroarylene group may have any substituent other than Y.
Z represents —O—, —S—, —SO ₂ —, —NR ₂₇ — (wherein R ₂₇ represents a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted heterocyclic group, cyano, Group, hydroxy group, —NR ₂₈ R ₂₉ (wherein R ₂₈ and R ₂₉ are each independently a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted heterocyclic group, —COR _30; (Wherein R ₃₀ represents an optionally substituted hydrocarbon group or an optionally substituted heterocyclic group), or —COR ₃₁ (where R ₃₁ is optionally substituted). Represents a good hydrocarbon group or a heterocyclic group which may be substituted. )

（式［IX］中、
Ｒ₃₂〜Ｒ₃₅は、水素原子又は任意の置換基を表わす。又は、Ｒ₃₂とＲ₃₃、Ｒ₃₄とＲ₃₅とが各々縮合して、炭化水素環又は複素環構造を形成していてもよい。この場合、該炭化水素環及び該複素環は、置換基を有していてもよい。
環Ａは、Ｃ＝Ｏと共に置換基を有していてもよい炭素環式ケトン環又は複素環式ケトン環を表わし、
Ｚは、−Ｏ−、−Ｓ−、−ＳＯ₂−、又は、−ＮＲ₃₆−（ここで、Ｒ₃₆は、水素原子、置換されてもよい炭化水素基、置換されてもよい複素環基、シアノ基、ヒドロキシ基、−ＮＲ₃₇Ｒ₃₈（Ｒ₃₇、Ｒ₃₈は各々独立して水素原子、置換されてもよい炭化水素基又は置換されてもよい複素環基、−ＣＯＲ₃₉（ここで、Ｒ₃₉は、置換されてもよい炭化水素基、又は、置換されてもよい複素環基を表わす。）を表す。）、又は、−ＣＯＲ₄₀（ここで、Ｒ₄₀は、置換されてもよい炭化水素基、又は、置換されてもよい複素環基を表わす。）を表わす。）を表わす。）

(In the formula [IX]
R _{32 to} R ₃₅ represent a hydrogen atom or an arbitrary substituent. Alternatively, R ₃₂ and R ₃₃ , R ₃₄ and R ₃₅ may be condensed to form a hydrocarbon ring or a heterocyclic structure. In this case, the hydrocarbon ring and the heterocyclic ring may have a substituent.
Ring A represents a carbocyclic ketone ring or heterocyclic ketone ring which may have a substituent together with C═O,
Z is —O—, —S—, —SO ₂ —, or —NR ₃₆ — (wherein R ₃₆ is a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted heterocyclic group; , A cyano group, a hydroxy group, —NR ₃₇ R ₃₈ (wherein R ₃₇ and R ₃₈ are each independently a hydrogen atom, an optionally substituted hydrocarbon group or an optionally substituted heterocyclic group, —COR ₃₉ (wherein , R ₃₉ represents an optionally substituted hydrocarbon group or an optionally substituted heterocyclic group.) Or —COR ₄₀ (where R ₄₀ is optionally substituted) Represents a good hydrocarbon group or a heterocyclic group which may be substituted. )

In the optical recording medium 20 to which this embodiment is applied, n _d is the larger dye X than about 2, n _d <n _c becomes dyes or other organic, and mixed inorganic material (mixture Y), lowering the average n _d of the recording layer 22, it is possible to equivalent to n _c or less.

The dye X is usually a dye having a high refractive index, where n _d > n _c , particularly n _d > 2, and the main absorption band is on the long wavelength side of the recording / reproducing light wavelength. Such a dye preferably has a main absorption band peak in the range of 300 nm to 400 nm and a refractive index n _d in the range of 2 to 3.

  Specific examples of the dye X include porphyrin, stilbene, (carbo) styryl, coumarin, pyrone, chalcone, triazole, methine (cyanine, oxonol), sulfonylimine, azlactone compound, or a mixture thereof. Etc. In particular, coumarin dyes (Japanese Patent Laid-Open No. 2000-043423), carbostyryl dyes (Japanese Patent Laid-Open No. 2001-287466), the above-mentioned pyrone dyes (Japanese Patent Laid-Open No. 2003-266554), etc. are appropriately decomposed or sublimated. Since it has temperature, it is preferable. Moreover, although it is not a main absorption band, the phthalocyanine which has the strong absorption band according to it in the vicinity of 350 nm-400 nm, a naphthalocyanine compound or its derivative, Furthermore, these mixtures are also preferable.

Examples of the mixture Y include metal-containing azo dyes having a main absorption band in the wavelength band of 600 nm to 800 nm. It is a dye suitable for use in CD-R and DVD-R, and has an extinction coefficient k _d of generally 0.2 or less, preferably 0.1 or less near 405 nm. Although the refractive index n _{d of the} dye is very high at 2.5 or more at the long wavelength end λ _L , it is about 1.5 because it is sufficiently far from the absorption peak at the short wavelength end. .

  More specifically, metal-containing azo dyes represented by the general formula [X] disclosed in JP-A-6-65514 can be mentioned.

（式［Ｘ］中、
Ｒ₄₁、Ｒ₄₂は、各々独立に、水素原子、ハロゲン原子、炭素数１〜６のアルキル基、フッ素化アルキル基、分岐アルキル基、ニトロ基、シアノ基、−ＣＯＯＲ₄₅、−ＣＯＲ₄₆、−ＯＲ₄₇、又は、−ＳＲ₄₈（ここで、Ｒ₄₅〜Ｒ₄₈は、炭素数１〜６のアルキル基、フッ素化アルキル基、分岐アルキル基、又は、環状アルキル基を表わす。）を表わし、
Ｘは、各々独立に、水素原子、炭素数１〜３のアルキル基、分岐アルキル基、−ＯＲ₄₉、又は、−ＳＲ₅₀（ここで、Ｒ₄₉、Ｒ₅₀は、各々独立に、炭素数１〜３のアルキル基を表わす。）を表わし、
Ｒ₄₃、Ｒ₄₄は、各々独立に、水素原子、炭素数１から１０のアルキル基、分岐アルキル基、又は、環状アルキル基を表わし、Ｒ₄₃、Ｒ₄₄が各々、隣接するベンゼン環と結合していてもよく、また、窒素原子とＲ₄₃とＲ₄₄とが一つの環を形成していてもよい。）

(In the formula [X],
R ₄₁ and R ₄₂ each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group, a nitro group, a cyano group, —COOR ₄₅ , —COR ₄₆ , — OR ₄₇ or —SR ₄₈ (wherein R _{45 to} R ₄₈ represent an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group, or a cyclic alkyl group),
X is each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a branched alkyl group, —OR ₄₉ , or —SR ₅₀ (where R ₄₉ and R ₅₀ are each independently 1 Represents an alkyl group of ~ 3),
R ₄₃ and R ₄₄ each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a branched alkyl group, or a cyclic alkyl group, and R ₄₃ and R ₄₄ are each bonded to an adjacent benzene ring. In addition, the nitrogen atom and R ₄₃ and R ₄₄ may form one ring. )

  Alternatively, a metal-containing azo dye represented by the general formula [XI] disclosed in JP-A No. 2002-114922 is also preferable.

（式［XI］中、
Ｒ₅₁、Ｒ₅₂は、各々独立に、水素原子、ハロゲン原子、炭素数１〜６のアルキル基、フッ素化アルキル基、分岐アルキル基、ニトロ基、シアノ基、−ＣＯＯＲ₅₅、−ＣＯＲ₅₆、−ＯＲ₅₇、又は、−ＳＲ₅₈（ここで、Ｒ₅₅〜Ｒ₅₈は、各々独立に、炭素数１〜６のアルキル基、フッ素化アルキル基、分岐アルキル基、又は、環状アルキル基を表わす。）を表わし、
Ｘは、水素原子、炭素数１〜３のアルキル基、分岐アルキル基、−ＯＲ₅₉、又は、−ＳＲ₆₀（ここで、Ｒ₅₉、Ｒ₆₀は、各々独立に、炭素数１から３のアルキル基を表わす。）を表わし、
Ｒ⁵³、Ｒ⁵⁴は各々独立に、水素原子、又は、炭素数１から３のアルキル基を表わす。）

(In the formula [XI]
R ₅₁ and R ₅₂ each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group, a nitro group, a cyano group, —COOR ₅₅ , —COR ₅₆ , — OR ₅₇ or —SR ₅₈ (wherein R _{55 to} R ₅₈ each independently represents an alkyl group having 1 to 6 carbon atoms, a fluorinated alkyl group, a branched alkyl group, or a cyclic alkyl group). Represents
X is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a branched alkyl group, —OR ₅₉ , or —SR ₆₀ (wherein R ₅₉ and R ₆₀ are each independently an alkyl having 1 to 3 carbon atoms) Represents a group)
R ⁵³ and R ⁵⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. )

  In the present embodiment, the recording layer 22 is formed by a coating method, a vacuum vapor deposition method, or the like, but is particularly preferably formed by a coating method. That is, the recording layer 22 coating solution is prepared by dissolving the dye as a main component together with a binder, a quencher, and the like in a suitable solvent, and is coated on the reflective layer 23 described above. The concentration of the main component pigment in the solution is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and usually 10% by weight or less, preferably 5% by weight. % Or less, more preferably 2% by weight or less. Thereby, the recording layer 22 is usually formed to a thickness of about 1 nm to 100 nm. In order to make the thickness less than 50 nm, the dye concentration is preferably less than 1% by weight, and more preferably less than 0.8% by weight. It is also preferable to further adjust the number of rotations of coating.

  Solvents for dissolving the main dye material and the like include alcohols such as ethanol, n-propanol, isopropanol and n-butanol diacetone alcohol; fluorinated hydrocarbons such as tetrafluoropropanol (TFP) and octafluoropentanol (OFP) Solvents; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether; esters such as butyl acetate, ethyl lactate, and cellosolve acetate; chlorinated hydrocarbons such as dichloromethane and chloroform; Hydrocarbons; ethers such as tetrahydrofuran, ethyl ether, dioxane; ketones such as methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone It can be. These solvents are appropriately selected in consideration of the solubility of the main component dye material or the like to be dissolved, and two or more kinds can be mixed and used.

  As the binder, organic polymers such as cellulose derivatives, natural polymer substances, hydrocarbon resins, vinyl resins, acrylic resins, polyvinyl alcohol, and epoxy resins can be used. Further, the recording layer 22 can contain various dyes or anti-fading agents other than the dyes in order to improve light resistance. As the antifading agent, a singlet oxygen quencher is generally used. The amount of the anti-fading agent such as singlet quencher is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 50% by weight with respect to the recording layer material. % Or less, preferably 30% by weight or less, more preferably 25% by weight or less.

  Examples of the coating method include a spray method, a spin coating method, a dip method, and a roll coating method. In particular, in a recording medium on a disk, the spin coating method ensures the uniformity of the film thickness and the defect density. Is preferable.

(Interface layer)
In the present embodiment, in particular, by providing an interface layer between the recording layer 22 and the cover layer 24, the swelling of the recording layer 22 toward the cover layer 24 can be used effectively.
Since the effect of the interface layer when it is formed as a film is effective, it is usually 1 nm or more, preferably 3 nm or more, more preferably 5 nm or more, and usually 50 nm or less, preferably 40 nm or less, more preferably 30 nm or less. Range. If the film thickness of the interface layer is controlled within this range, the bulge deformation toward the cover layer 24 can be controlled well.

  It is desirable that the reflection at the interface layer be as small as possible. This is because the phase change of the reflected light from the reflection layer 23 which is the main reflection surface is selectively used. It is not preferable in the present embodiment that the interface layer has a main reflection surface. For this reason, it is desirable that the difference in refractive index between the interface layer and the recording layer 22 or between the interface layer and the cover layer 24 is small. The difference is preferably 1 or less, more preferably 0.7 or less, and still more preferably 0.5 or less.

  Incidentally, the formation of the mixed layer 25m as shown in FIG. 3 is suppressed by using the interface layer, the corrosion prevention by the adhesive when the cover layer 24 is stuck on the recording layer 22 in the reverse configuration, the cover layer The effect of preventing the elution of the recording layer 22 by the solvent when applying the coating 24 is known, and in the present embodiment, such an effect can be used as appropriate. The material used for the interface layer is preferably a material that is transparent to the recording / reproducing light wavelength and that is chemically, mechanically, and thermally stable. Here, “transparent” means that the transmittance with respect to the recording / reproducing light beam 27 is 80% or more, and more preferably 90% or more. The upper limit of the transmittance is 100%.

The interface layer is preferably a dielectric compound such as oxides such as metals and semiconductors, nitrides, carbides, sulfides, fluorides such as magnesium (Mg) and calcium (Ca), and mixtures thereof. As described above, the refractive index of the interface layer preferably has a difference from the refractive index of the recording layer or the cover layer of 1 or less, and the value is preferably in the range of 1 to 2.5. Depending on the hardness and thickness of the interface layer, the deformation of the recording layer 22, particularly the bulge deformation toward the cover layer 24, can be promoted or suppressed. In order to effectively utilize the bulging deformation, a dielectric material having a relatively low hardness is preferable, and in particular, ZnO, In ₂ O ₃ , Ga ₂ O ₃ , ZnS, sulfides of rare earth metals, other metals, A material in which a semiconductor oxide, nitride, or carbide is mixed is preferable. A sputtered plastic film or a plasma polymerized film of hydrocarbon molecules can also be used.

(Cover layer)
The cover layer 24 is made of a material that is transparent to the recording / reproducing light beam 27 and has little birefringence. Usually, a plastic plate (referred to as a sheet) is bonded with an adhesive, or light, radiation, or heat is applied after application. It is formed by curing with, for example. The cover layer 24 preferably has a transmittance of 70% or more and more preferably 80% or more with respect to the wavelength λ of the recording / reproducing light beam 27. The upper limit of the transmittance is 100%.

  The plastic used as the sheet material is polycarbonate, polyolefin, acrylic, cellulose triacetate, polyethylene terephthalate, or the like. For adhesion, light, radiation curing, thermosetting resin, or pressure sensitive adhesive is used. As the pressure-sensitive adhesive, pressure sensitive adhesives made of acrylic, methacrylate, rubber, silicon, and urethane polymers can be used.

  For example, after the photocurable resin constituting the adhesive layer is dissolved in an appropriate solvent to prepare a coating solution, this coating solution is applied onto the recording layer 22 or the interface layer to form a coating film, Overlay the polycarbonate sheet. Thereafter, the coating liquid is further stretched and developed by rotating the medium, for example, in a superposed state as necessary, and then cured by irradiating with an ultraviolet ray with a UV lamp. Alternatively, a pressure sensitive adhesive is applied to the sheet in advance, the sheet is overlaid on the recording layer 22 or the interface layer, and then pressed and pressed with an appropriate pressure.

  The pressure-sensitive adhesive is preferably an acrylic or methacrylate polymer pressure-sensitive adhesive from the viewpoint of transparency and durability. More specifically, 2-ethylhexyl acrylate, n-butyl acrylate, iso-octyl acrylate and the like are used as main component monomers, and these main component monomers include acrylic acid, methacrylic acid, acrylamide derivatives, maleic acid, hydroxyl ethyl acrylate, A pressure-sensitive adhesive obtained by copolymerizing a polar monomer such as glycidyl acrylate is preferred. Glass transition temperature Tg, tack performance (adhesive force immediately formed when contacted at low pressure), peel strength by adjusting the molecular weight of the main monomer, mixing its short chain components, and adjusting the crosslink point density with acrylic acid Further, physical properties such as shear holding force can be controlled (Non-patent Document 11, Chapter 9). As the solvent for the acrylic polymer, ethyl acetate, butyl acetate, toluene, methyl ethyl ketone, cyclohexane and the like are used. The pressure-sensitive adhesive preferably further contains a polyisocyanate-based crosslinking agent.

  The pressure-sensitive adhesive is made of the above-mentioned material. A predetermined amount is uniformly applied to the surface of the cover layer sheet material in contact with the recording layer side, and the solvent is dried. If it has, it is cured by applying pressure to the surface) with a laminating roller or the like. When the cover layer sheet material coated with the pressure-sensitive adhesive is bonded to the surface of the recording medium on which the recording layer is formed, it is preferably bonded in a vacuum so as not to entrain air and form bubbles.

  Also, after applying the above-mentioned pressure-sensitive adhesive on the release film and drying the solvent, the cover layer sheet is bonded, and the release film is further peeled off to integrate the cover layer sheet and the pressure-sensitive adhesive layer, and then the recording medium You may paste together.

  When the cover layer 24 is formed by a coating method, a spin coating method, a dip method, or the like is used. In particular, the spin coating method is often used for a medium on a disk. Similarly, as the cover layer 24 material by application, urethane, epoxy, acrylic resin, or the like is used, and after application, it is cured by irradiating with ultraviolet rays, electron beams, or radiation to accelerate radical polymerization or cationic polymerization.

Here, in order to utilize the deformation to the cover layer 24 side, it is desirable that at least the recording layer 22 of the cover layer 24 or the layer on the side in contact with the interface layer can easily follow the bulging deformation. The cover layer 24 preferably has an appropriate softness (hardness). For example, when the cover layer 24 is made of a resin sheet material having a thickness of 50 μm to 100 μm and is bonded with a pressure-sensitive adhesive, the adhesive Since the glass transition temperature of the layer is as low as −50 ° C. to 50 ° C. and relatively soft, deformation toward the cover layer 24 side is relatively large. Particularly preferred is that the glass transition temperature is not more than room temperature. The thickness of the adhesive layer made of an adhesive is usually 1 μm or more, preferably 5 μm or more, and usually 50 μm or less, preferably 30 μm or less. It is preferable to provide a deformation promoting layer that controls the thickness of the adhesive layer material, the glass transition temperature, and the crosslinking density to positively control the amount of swelling deformation. Alternatively, in the cover layer 24 formed by a coating method, a relatively low hardness deformation promoting layer having a thickness of usually 1 μm or more, preferably 5 μm or more, and usually 50 μm or less, preferably 30 μm or less, and the remaining layers In order to control the deformation amount d _bmp , it is also preferable to divide the coating into multiple layers.

  As described above, when a deformation promoting layer made of an adhesive, an adhesive, a protective coating agent, or the like is formed on the recording layer (interface layer) side of the cover layer, a glass transition temperature Tg of 25 is given to give a certain flexibility. It is preferably at most 0 ° C, more preferably at most 0 ° C, still more preferably at most -10 ° C. The glass transition temperature Tg here is a value measured after curing of the pressure-sensitive adhesive, adhesive, protective coating agent, and the like. A simple method for measuring Tg is differential scanning calorimetry (DSC). It can also be obtained by measuring the temperature dependence of the storage elastic modulus with a dynamic viscoelasticity measuring device (Non-Patent Document 11, Chapter 5).

  Promoting such deformation has the advantage that not only the signal amplitude of LtoH can be increased, but also the recording power required for recording can be reduced. On the other hand, if the deformation is too large, the crosstalk becomes large or the push-pull signal becomes too small. Therefore, it is preferable that the deformation promoting layer retains an appropriate viscoelasticity even at the glass transition temperature or higher.

  The cover layer 24 may be further provided with a layer having a thickness of about 0.1 μm to 50 μm on the surface in order to provide functions such as scratch resistance and fingerprint resistance to the incident light side surface. The thickness of the cover layer 24 depends on the wavelength λ of the recording / reproducing light beam 27 and the NA (numerical aperture) of the objective lens 28, but is usually 0.01 mm or more, preferably 0.05 mm or more, and usually 0.3 mm or less. The thickness is preferably in the range of 0.15 mm or less. It is preferable that the entire thickness including the thickness of the adhesive layer, the hard coat layer, and the like be in an optically acceptable thickness range. For example, in a so-called Blu-ray disc, it is preferable to control to about 100 μm ± 3 μm or less.

Incidentally, as in the case of providing the deformation facilitating layer, if provided layers having different refractive index in the recording layer side of the cover layer, as a cover layer refractive index n _c of the present invention, refers to the value of the recording layer side of the layer To do.

(Other configurations)
Note that the optical recording medium of the present embodiment may have an arbitrary layer in addition to the above-mentioned layers or a part of the above-mentioned layers may be omitted without departing from the spirit of the present invention. Also good.
For example, in addition to the interface between the recording layer and the cover layer described above, an interface layer may be provided between the substrate and the reflective layer, for example, in order to prevent mutual contact and diffusion, and to adjust the phase difference and reflectance. Can be inserted.

  The present invention can also be applied to a multilayer optical recording medium in which a plurality of recording layers are provided on a substrate. In this case, an intermediate layer may be provided between all the recording layers and the reflective layer, or in some cases, an intermediate layer may be provided only between the specific recording layer and the reflective layer.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Example 1)
An alloy target having a composition of Ag _98.1 Nd _1.0 Cu _0.9 on a polycarbonate resin substrate on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm, and a groove depth of about 55 nm is formed (the composition is expressed in atomic%). The reflective layer having a thickness of about 65 nm was formed by sputtering. By sputtering Ta on the reflective layer, an intermediate layer having a thickness of about 3 nm was formed. Further, a dye represented by the following structural formula was dissolved in octafluoropentanol (OFP), and the resulting solution was formed on the intermediate layer by a spin coating method.

  The conditions of the spin coating method are as follows. That is, a solution in which the above dye is dissolved in OFP at a concentration of 0.6% by weight is applied in the form of a ring of 1.5 g in the vicinity of the center of the disk (the reflection layer and the intermediate layer formed on the substrate). Was rotated at 1200 rpm for 7 seconds to stretch the dye solution, and then rotated at 9200 rpm for 3 seconds to shake off the dye solution. After the application, the disc was kept in an environment of 100 ° C. for 1 hour, and the recording layer was formed by evaporating and removing the OFP as the solvent. The film thickness of the recording layer in the recording groove is about 30 nm, and the film thickness in the area between the recording grooves is almost 0 nm (in the observation with a cross-sectional TEM (Transmission Electron Microscope)), the existence of the recording layer is confirmed. It was difficult.)

Thereafter, an interface layer made of ZnS—SiO ₂ (molar ratio 80:20) was formed on the recording layer to a thickness of about 20 nm by sputtering. A transparent cover layer having a total thickness of 100 μm composed of a polycarbonate resin sheet having a thickness of 75 μm and a pressure-sensitive adhesive layer having a thickness of 25 μm is bonded to the optical recording medium (the optical recording medium of Example 1). Recording medium).

(Comparative Example 1)
Of the layers of the optical recording medium of Example 1, an optical recording medium was produced under the same conditions as in Example 1 except that the intermediate layer was omitted.

(Example 2)
Among the conditions of Example 1, the following points were changed. That is, the groove depth of the guide groove formed on the substrate was about 48 nm, the thickness of the reflective layer was about 70 nm, the material of the intermediate layer was Nb, and the thickness of the intermediate layer was about 3 nm. In addition, for spin coating of the dye at the time of forming the recording layer, a solution in which the dye was dissolved in OFP at a concentration of 1.2% by weight was used as a disk (a reflection layer and an intermediate layer formed on the substrate). In the vicinity of the center, 1.5 g was applied in a ring shape, and the disk was rotated at 120 rpm for 4 seconds and 1200 rpm for 3 seconds to stretch the dye solution, and then rotated at 9200 rpm for 3 seconds to shake off the dye solution. In addition, ZnS—SiO ₂ (molar ratio 60:40) was used as the material for the interface layer, and the thickness of the interface layer was about 16 nm. Otherwise, the optical recording medium was manufactured under the same conditions as in Example 1.

(Example 3)
An optical recording medium was manufactured under the same conditions as in Example 2 except that the thickness of Nb in the intermediate layer was changed to about 5 nm under the conditions of Example 2.

(Comparative Example 2)
Of the layers of the optical recording medium of Example 2, an optical recording medium was produced under the same conditions as in Example 2 except that the intermediate layer was omitted.

Example 4
An alloy target having a composition of Ag _99.45 Bi _0.35 Nd _0.20 on a polycarbonate resin substrate on which a guide groove having a track pitch of 0.32 μm, a groove width of about 0.18 μm, and a groove depth of about 48 nm is formed (the composition is expressed in atomic%). The reflective layer having a thickness of about 70 nm was formed by sputtering. An intermediate layer having a thickness of about 3 nm was formed by sputtering Nb on the reflective layer. Further, the same dye material as in Example 1 was dissolved in octafluoropentanol (OFP), and the resulting solution was formed on the intermediate layer by spin coating.

  The conditions of the spin coating method are as follows. That is, 1.5 g of a solution in which the dye is dissolved in OFP at a concentration of 0.7% by weight is applied in the form of a ring in the vicinity of the center of the disk (the reflection layer and the intermediate layer are formed on the substrate). Was applied at 120 rpm for 4 seconds, and further the disk was rotated at 1200 rpm for 3 seconds to stretch the dye solution, and then rotated at 9200 rpm for 3 seconds to shake off the dye solution. After the application, the disc was kept in an environment of 100 ° C. for 1 hour, and the recording layer was formed by evaporating and removing the OFP as the solvent.

Thereafter, an interface layer made of ZnS—SiO ₂ (molar ratio 80:20) was formed on the recording layer to a thickness of about 16 nm by sputtering. On top of this, a transparent cover layer having a total thickness of 100 μm consisting of a polycarbonate resin sheet having a thickness of 75 μm and a pressure-sensitive adhesive layer having a thickness of 25 μm was bonded to produce an optical recording medium.

(Comparative Example 3)
Of the layers of the optical recording medium of Example 4, an optical recording medium was produced under the same conditions as in Example 4 except that the intermediate layer was omitted.

(Comparative Example 4)
Among the layers of the optical recording medium of Example 4, the order of stacking the reflective layer and the intermediate layer was reversed. That is, an Nb layer is first formed on a substrate by sputtering to a thickness of about 3 nm, and then an alloy target having a composition of Ag _99.45 Bi _0.35 Nd _0.20 (the composition is expressed in atomic%) is sputtered. A reflective layer having a thickness of about 70 nm was formed. Otherwise, an optical recording medium was produced under the same conditions as in Example 4.

(Evaluation conditions)
For the evaluation, a measurement system based on the standard of Blu-ray Disc recordable disc (System Description Blu-ray Disc Recordable Format Version 1.1) was used. Specifically, it is as follows.
In the recording / reproduction evaluation for the optical recording media of Example 1 and Comparative Example 1, the recording / reproducing light wavelength λ is about 405 nm, NA (numerical aperture) = 0.85, and the diameter of the focused beam spot is about 0.42 μm (1 / e ² The measurement was carried out using an ODU1000 tester manufactured by Pulstec Corp. having an optical system of point of strength. Recording / reproduction was performed on the substrate groove (in-groove).

  The recording was performed by setting the linear velocity to 4.92 m / s to 1 × speed and rotating to 1 × speed or 2 × speed to record a (1, 7) RLL-NRZI modulated mark length modulation signal (17PP). The reference clock period T is 15.15 nsec. (Channel clock frequency 66 MHz) and 7.58 nsec. (Channel clock frequency 132 MHz). Recording conditions such as recording power and recording pulse were adjusted so that the following jitter was minimized. Reproduction was performed at 1 × speed, and jitter and reflectance were measured.

  Jitter measurement was performed according to the following procedure. In other words, the recording signal was waveform-equalized by a limit equalizer (manufactured by Pulse Tech) and binarized. The gain of the limit equalizer was 5 dB. Thereafter, the distribution σ of the time difference between the rising edge and falling edge of the binarized signal and the rising edge of the channel clock signal was measured with a time interval analyzer (manufactured by Yokogawa Electric Corporation). Then, with the channel clock period as T, jitter (%) was measured by σ / T (data to clock jitter).

Since the reflectance is proportional to the voltage output value of the reproduction detector, the value was obtained by normalizing this voltage output value with a known reflectance R _ref . As a result of confirming the change in reflectance before and after recording for each of Examples 1 to 4 and Comparative Examples 1 to 4, the reflectance after recording is higher than the reflectance of the unrecorded portion, and LtoH recording can be realized. It was confirmed that it was. Regarding the actual reflectance value, the recorded mark portion (recorded pit portion) and the space portion between the marks which are unrecorded portions were measured at 9T mark and 9T space portions, respectively. The reflectivities of the 9T mark portion having the highest reflectivity in the signal of the mark portion and the 9T space portion having the lowest reflectivity among the space portions are RH and RL, respectively. Was calculated.
m = (R _H −R _L ) / R _H

(Evaluation results)
The jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Example 1 are σ = 5.6%, R _H = 29.0%, and R _L = 12.3 in the 1 × speed recording. %, M = 0.58, and in double speed recording, σ = 6.4%, R _H = 28.7%, R _L = 12.1%, m = 0.58. Here, even when an alloy having a composition such as AgCuAuNd or AgBi is used as the reflective layer material, equivalent characteristics can be obtained.

On the other hand, the jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Comparative Example 1 are σ = 6.7%, R _H = 37.1%, and R _L = 15 in 1 × speed recording. 0.4%, m = 0.58, and in double speed recording, σ = 7.7%, R _H = 37.4%, R _L = 15.5%, m = 0.58.

The jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Example 2 are as follows: σ = 5.4%, R _H = 32.6%, R _L = 19.2 in 1 × speed recording. %, M = 0.41, and in double speed recording, σ = 6.1%, R _H = 32.3%, R _L = 18.8%, and m = 0.42.

The jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Example 3 are σ = 5.7%, R _H = 25.8%, and R _L = 14.3 in the 1 × speed recording. %, M = 0.45, and in the double speed recording, σ = 6.4%, R _H = 25.5%, R _L = 13.5%, m = 0.47.

On the other hand, the jitter σ, reflectivity R _H , R _L , and modulation degree m in the optical recording medium of Comparative Example 2 are σ = 6.2%, R _H = 39.1%, and R _L = 23 in 1 × speed recording. 0.5%, m = 0.40, and in double speed recording, σ = 7.0%, R _H = 39.3%, R _L = 23.6%, m = 0.40.
The jitter σ in the optical recording medium of Example 4 was σ = 6.1% in 1 × speed recording, and σ = 6.2% in 2 × speed recording.
On the other hand, the jitter σ in the optical recording medium of Comparative Example 3 was σ = 8.3% in 1 × speed recording.
Further, the jitter σ in the optical recording medium of Comparative Example 4 was σ = 7.5% in the 1 × speed recording.

  Also in the optical recording medium of Comparative Example 1, good jitter of 6.7% at 1 × speed recording and 7.7% at 2 × speed recording was obtained. However, it was not possible to satisfy the jitter (6.5% or less) that is the standard of Blu-ray Disc. On the other hand, in the optical recording medium of Example 1, the jitter was improved in both 1 × speed recording and 2 × speed recording compared to the optical recording medium in Comparative Example 1, and the effect of improving the recording signal characteristics by installing the intermediate layer was improved. It became clear.

  Further, even in the optical recording medium of Comparative Example 2, good jitter was obtained, but it was not possible to satisfy the jitter (6.5% or less) which is the standard of the Blu-ray Disc. On the other hand, in the optical recording media of Example 2 and Example 3, jitter was improved in both 1 × speed recording and 2 × speed recording with respect to the optical recording medium of Comparative Example 2, and the recording signal characteristics due to the installation of the intermediate layer The effect of improvement became clear.

  Furthermore, in the optical recording media of Comparative Examples 3 and 4, good jitter could not be obtained even at 1 × speed recording. On the other hand, in the optical recording medium of Example 4, the jitter was improved as compared with the optical recording media of Comparative Example 3 and Comparative Example 4, and the effect of improving the recording signal characteristics by installing the intermediate layer became clear.

  From the above results, it can be seen that by providing the intermediate layer defined in the present invention, an excellent optical recording medium satisfying the Blu-ray Disc standard for both 1 × speed recording and 2 × speed recording can be obtained.

  The present invention can be applied to various types of optical recording media. Among them, the present invention can be particularly preferably used for a film incidence type optical recording medium compatible with a blue laser having a recording layer mainly composed of a dye.

It is a figure explaining the write-once type medium (optical recording medium) which has a recording layer which has the pigment of the conventional composition as a main component. It is a figure explaining the write-once type medium (optical recording medium) of the film surface incidence composition which has the recording layer which has the pigment as a main component to which this embodiment is applied. (A), (b) is a figure explaining the phase difference at the time of recording on the layer structure of a film surface incident type medium to which this Embodiment is applied, and a cover layer groove part. It is a figure explaining the relationship between the phase difference of a recording groove part and a recording groove part, and reflected light intensity. It is a figure explaining the structure of the 4 division | segmentation detector which detects a recording signal (sum signal) and a push pull signal (difference signal). (A) and (b) both schematically illustrate signals detected after passing an output signal obtained while traversing a plurality of recording grooves and between the grooves through a low-frequency pass filter (cutoff frequency of about 30 kHz). FIG.

Explanation of symbols

10, 20 Optical recording medium 11, 21 Substrate 12, 22 Recording layer 13, 23 Reflective layer 14 Protective coating layer 15 Substrate groove portion 16 Substrate groove portion 17, 27 Recording / reproducing light beam 18, 28 Objective lens 19, 29 Recording / reproducing light Beam incident surface 24 Cover layer 25 Cover layer groove part 26 Cover layer groove part 30 Intermediate layer

Claims (9)

A substrate on which guide grooves are formed;
On the substrate, a layer having a light reflecting function mainly composed of Ag, a recording layer containing as a main component a dye having a light absorbing function with respect to a recording / reproducing light wavelength in an unrecorded state, and the recording layer A cover layer capable of transmitting incident recording / reproducing light in this order,
An intermediate layer is provided between the layer having the light reflection function and the recording layer,
The optical recording medium, wherein the intermediate layer contains any one element of Ta and Nb. 2. The optical recording medium according to claim 1, wherein the thickness of the intermediate layer is 1 nm or more and 15 nm or less. 2. The optical recording medium according to claim 1, wherein a film thickness of the layer having a light reflection function containing Ag as a main component is 30 nm or more and 90 nm or less. When the recording groove portion is a guide groove portion far from the surface on which the recording / reproducing light beam obtained by focusing the recording / reproducing light is incident on the cover layer, the reflected light intensity of the recording pit portion formed in the recording groove portion is The optical recording medium according to any one of claims 1 to 3, wherein the optical recording medium is higher than the reflected light intensity in the recording groove portion when not recorded. The optical recording medium according to claim 4, wherein the recording layer has a film thickness of 5 nm or more and 70 nm or less when the recording groove is not recorded. 6. The optical recording medium according to claim 4, wherein the recording layer has a thickness of 10 nm or less when unrecorded between the recording groove portions. The optical recording medium according to claim 1, wherein a wavelength λ of the recording / reproducing light is 350 nm or more and 450 nm or less. 8. The interface layer according to claim 1, further comprising an interface layer that prevents mixing of the material of the recording layer and the material of the cover layer between the recording layer and the cover layer. 9. The optical recording medium described. 9. The optical recording medium according to claim 8, wherein the thickness of the interface layer is 1 nm or more and 50 nm or less.

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