JP2000313170A - Optical information recording medium, method for regenerating it and method for recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve stability of an amorphous mark and to deal with a linear speed of a wide range by forming a phase change type recording layer of a specific composition in an optical information recording medium having at least the phase change type recording layer on a substrate such as a high density optical disk or the like utilizing a rewritable phase change medium. SOLUTION: A phase change type recording layer of a rewritable disk such as a high density optical disk or the like is formed of a composition represented by the formula ((SbxTe1-x)yGe1-y)zM1-z, wherein x is number of a range of 0.7<=x<=0.9, y is number of a range of 0.8<=y<1, z is number of a range of 0.88<=z<1, and M is In and/or Ga. In order to record a mark length-modulated information on such an optical information recording medium, a crystal state portion is processed in an unrecorded and erased state, an amorphous portion is processed in a recorded state, and an amorphous portion between recording marks is processed to be irradiated with a recording light of crystallizable erasing power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density optical disk using a rewritable phase change medium. In particular, it relates to a phase change medium that can be used at a wide linear velocity.

[0002]

2. Description of the Related Art As a rewritable optical disk, a phase change medium utilizing a change in optical characteristics such as a reflectance accompanying a reversible change between a crystalline state and an amorphous state is known. The phase change medium does not require an external magnetic field, and has the advantage that recording and erasing can be performed only by modulating the power of laser light, and the recording and reproducing apparatus can be downsized. A general phase change medium has a phase change type recording layer provided on a substrate, and has a protective layer made of a dielectric on both sides thereof. Further, it is usual that a reflection layer is further provided. The recording layer of the phase change type usually has an unrecorded / erased state in a crystalline state and amorphous bits as recording marks.

Conventionally, as such a phase change recording layer, S
A composition in which Sb is excessively added to the bTe eutectic point composition (Sb ₇₀ Te ₃₀ ) is known. For example, JP-A 1-3
No. 03643 discloses that (Sb _1-x Te _x ) _1-y M
_y (M is Ag, Al, As, Au, Bi, Cu, Ga,
At least one element selected from the group consisting of Ge, In, Pb, Pd, Pt, Se, Si, Sn and Zn)
It is described that an alloy film made of is used as a recording layer.

[0004]

Conventionally, an alloy material near the eutectic point has a high ability to form an amorphous phase, but is accompanied by phase separation during crystallization, so that it can be crystallized by heating for a short time of less than 100 nsec. However, it has been considered that this is not suitable as a recording layer of an overwritable optical recording medium. On the other hand, the present inventors have focused on such a binary alloy made of SbTe, and have described the crystallization / amorphization characteristics near the eutectic composition.
We studied using an optical disk evaluation machine suitable for higher density recording. As a result, Sb near the eutectic composition of Sb ₇₀ Te ₃₀
Although the initial crystallization of the recording layer containing a Te alloy as a main component is difficult, once the initial crystallization is performed, the subsequent amorphous
It has been found that recording and erasing by a change in crystal phase can be performed at an extremely high speed. Another advantage of using the composition near the eutectic point is that a coarse grain having a different reflectance from the initialized state is hardly generated in the peripheral portion of the amorphous mark or in the erased mark. This is a phenomenon peculiar to an alloy near the eutectic point where crystal growth is controlled by phase separation. Furthermore, especially when recording is performed with the gap between marks,
The above composition is suitable for high-density recording because a clearer reproduction signal can be obtained than a conventional recording layer having a composition near Ge ₂ Sb ₂ Te ₅ .

[0005] However, according to the study of the present inventors,
Such Sb₇₀Te₃₀Excess Sb in composition near eutectic point
SbTe alloy containing
It turned out to be difficult to function in minutes. The reason is recorded
The amorphous mark that has crystallized over time
This is because the marks are likely to disappear. What phase change
At room temperature, the crystalline state of the recording film is better than that of the amorphous mark.
Crystallizes soon after a sufficiently long time because it is stable
I think that the. However, as a recording medium, at least 10
It is necessary that the record mark be stable for more than
You. Sb_xTe _1-x(0.6 <x <0.9) recording layer
Means that the crystallization temperature of the amorphous state is as low as about 100 ° C.
The time for which a certain amorphous mark exists is too short,
It is not considered suitable for a practical phase change recording film.

[0006] In general, the current phase change medium has a problem that the usable linear velocity range is narrow. In the case of a disk-shaped recording medium, when the disk is rotated at a constant angular velocity which is preferable for the device, a difference in linear velocity between the inner peripheral portion and the outer peripheral portion of the disk is usually twice or more. In many cases, a new product that can record at an increased linear velocity is desired even if it is commercialized as a system with a constant linear velocity. In this case, recording under the old conditions (linear velocity, pulse Recording at a high linear velocity must be possible while maintaining the same strategy. Under these circumstances, a recording medium capable of supporting a wide linear velocity is required, but the current phase change recording medium is not sufficient.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, it has been found that a specific amount of a specific element is further present in a composition in which Sb is excessive in the vicinity of the SbTe eutectic point. The present invention has found that the stability of the amorphous mark can be improved, a wide range of linear velocities can be accommodated, and a phase-change recording medium utilizing the characteristics of the SbTe alloy can be obtained. Was completed. That is,
The gist of the present invention is an optical information recording medium having at least a phase change recording layer on a substrate, wherein the phase change recording layer has a composition represented by the following general formula (I). Optical information recording medium.

[0008]

Embedded image ((Sb _x Te _1-x ) _y Ge _1-y ) _z M _1-z (I)

(Where x is a number in the range of 0.7 ≦ x ≦ 0.9, y is a number in the range of 0.8 ≦ y <1, z
Is a number in the range of 0.88 ≦ z <1. M is In and / or
Or Ga. Another aspect of the present invention is that, when recording information having the mark length modulated on the optical information recording medium, a crystalline portion is set to an unrecorded state / erased state, and an amorphous portion is recorded. A recording light having an erasing power Pe capable of crystallizing an amorphous portion is irradiated between the recording marks, and the time length of the recording marks is set to nT.
(T is a reference clock cycle, n is a natural number of 2 or more), and the time (n−j) T is

[0010]

Embedded image α ₁ T, β ₁ T, α ₂ T, β ₂ T,..., Α _m T,
β _m T,

(Where Σαi + Σβi = n−j, j is an arbitrary number up to 0-2, m is a number that satisfies m = n−k, and k is an integer up to 0-2). , Α _i T (1
≦ i ≦ m), a recording light having a recording power Pw sufficient to melt the recording layer is irradiated, and β _i T (1
For a time of ≦ i ≦ m−1), there is a recording method of an optical information recording medium that irradiates a recording light with a bias power Pb that satisfies Pb <Pe.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the features of the present invention is that the composition of the recording layer is as follows.

[0013]

Embedded image ((Sb _x Te _1-x ) _y Ge _1-y ) _z M _1-z (I)

(Where x is a number in the range of 0.7 ≦ x ≦ 0.9, y is a number in the range of 0.8 ≦ y <1, z
Is a number in the range of 0.88 ≦ z <1. M is In and / or
Or Ga. ). The element M represents at least one of In and Ga. Preferably it is In. Here, x is 0.7-0.9, but the preferred lower limit is 0.71 and the preferred upper limit is 0.85, especially 0.8. If x is too large, the crystallization rate tends to be too high, and it tends to be difficult to form an amorphous phase. On the other hand, if it is too small, the crystallization rate tends to be too slow to make crystallization difficult.

As can be seen from the above description, in the present invention, the crystallization rate can be controlled by the Sb / Te ratio. That is, the amount of excess Sb with respect to the parent SbTe eutectic point composition is one factor that determines the crystallization rate. It is considered that when the amount of Sb increases, the number of Sb cluster sites precipitated in a quenched state increases, thereby promoting the formation of crystal nuclei.
This means that, assuming the same crystal growth rate from each crystal nucleus,
This means that the time required to fill the grown crystal grains is reduced, and consequently the time required to crystallize the amorphous mark is reduced. Therefore, it is advantageous when erasing by laser light irradiation at a high linear velocity for a short time. On the other hand, the cooling rate of the recording layer also depends on the linear velocity during recording.
That is, even with the same layer structure, the cooling rate decreases as the linear velocity decreases. Therefore, a composition having a lower critical cooling rate for forming an amorphous phase at a lower linear velocity, that is, a composition having a smaller excess Sb amount is desirable. In summary, it can be said that, based on the SbTe eutectic point composition, a composition having a larger excess Sb content is more suitable for a higher linear velocity.

Further, y is 0.8 or more and less than 1, and a preferable lower limit is 0.9. For the upper limit, y
Is preferably 0.97 or less. If y is too large, it is difficult to maintain high-density, low-jitter characteristics for a long period of time, and the effect of the present invention tends to be insufficient. On the other hand, if y is too small, noise at the time of recording increases, and it tends to be difficult to reduce the jitter particularly when performing mark length recording at high density. Further, z is 0.88 or more and less than 1, and a preferable upper limit is 0.999. A preferred lower limit is 0.94. If z is too large, it becomes difficult to cope with a linear velocity in a wide range. On the other hand, if z is too small, the noise of the recording signal tends to increase after recording many times.

In the present invention, reproduction is usually performed by utilizing the difference in optical characteristics between the crystalline state and the amorphous state of the recording layer. Normally, the crystal state is made to correspond to the recording state in accordance with the state. That is, in the recording medium of the present invention, recording / reproduction is usually performed using the amorphous portion as a mark. In the present invention, it is preferable that the recording layer is formed of a crystal phase having a face-centered cubic structure in the above-mentioned crystalline state. in this case,
The recording layer may be composed of a single crystal phase, or may be composed of a plurality of crystal phases. When the recording layer is composed of a plurality of crystal phases, it is preferable that the recording layer has no lattice mismatch. as a result,
Characteristics such as noise reduction, storage stability improvement, and easy crystallization at high speed can be improved.
This is because a crystal phase having a hexagonal structure such as Sb ₂ Te ₃ or S
When there is a crystal phase that is a cubic crystal such as b but has a significantly different lattice constant, and another crystal phase belonging to another space group such as Sb ₇ Te or Sb ₂ Te ₃ , crystal grains having a large lattice mismatch are present. As a result of the formation of the field, it is considered that the peripheral shape of the mark is disturbed or optical noise is generated, whereas in the case of the above crystal phase, such a crystal grain boundary does not occur. Conceivable.

The unit lattice constant of the preferred crystal phase is usually 5.5 ° or more, preferably 5.8 ° or more, and usually 6.8 ° or less, preferably 6.5 ° or less. When a plurality of crystal phases exist, lattice mismatch does not occur, and in order to be regarded as a substantially single phase, it is necessary to have the same crystal structure and a difference in unit cell constant of about ± 5% or less. preferable. The crystal phase may be a stable crystal phase obtained in a thermal equilibrium state, or may be a metastable crystal phase that appears depending on manufacturing conditions. The metastable phase crystal phase does not necessarily thermodynamically correspond to the lowest energy state, but is not completely unstable, and is substantially not present in the phase change type recording layer used in the optical information recording medium. It is a crystalline phase that can exist stably.

The preferred crystalline phase in the present invention is F
It is considered to belong to the m3m space group and / or the F43m space group. FIG. 5 shows In ₃ obtained by peeling a recording layer (thickness: about 20 nm) from a medium obtained by the same manufacturing method as a phase change type optical information recording medium manufactured in an example described later. Ge is an electron beam diffraction image by ₅ Sb ₇₀ Te ₂₂ film transmission electron microscopy (TEM). In the figure, A,
Points B, C, and D are respectively Miller indices (220),
(002), (222) and (111). The mirror index for each point of A, B, C, and D appearing in this diffraction image can be explained without contradiction, and the diffraction images of different patterns obtained similarly can be explained without contradiction. Which is a crystal structure belonging to the Fm3m or F43m space group. In addition, although the electron beam diffraction image has a rotation of the plane orientation, substantially only FIG. 5 is obtained.
It is presumed that it is formed from almost a single crystal phase. In addition, it was confirmed that a clear peak related to another crystal structure such as the Sb phase was not observed in the X-ray diffraction method.

From the electron beam diffraction image of FIG. 5, the recording layer belongs to either the F43m space group having a lattice constant of about 6.4 ° or the Fm3m space group having a lattice constant of about 6.1 °. You can see that. The former is a face-centered cubic Ge
₃ In ₁₃ Sb ₇ Te ₃ solid solution or F43 of AgInTe ₂
are those having the same structure as the crystal type belonging to m space group, the latter are those having crystal system belonging to Fm3m space group of AgInTe _2, or the same structure as the crystal type belonging to Fm3m space group of AgSbTe _2.

Note that there are crystal systems belonging to the same space group in GaSb and InSb, and the unit cell constants are also about 6.1 ° and about 6.5 °, respectively, which are obtained from the electron diffraction image of FIG. Very close to the value of the unit cell constant. This means that In and / or G in the recording layer composition of the present invention.
Considering that the presence of a is essential, it is suggested that these crystals promote the formation of a metastable structure in the parent Sb-Te-Ge solid solution.

In the case of a composition in which Sb is in excess of the eutectic composition of SbTe, the above-mentioned other crystal phases are particularly likely to be formed. It is necessary to have a face-centered cubic structure. The form of the crystal phase of the recording layer largely depends on the method of initializing the recording layer. That is, in order to form the above-mentioned crystalline phase which is preferable in the present invention, it is preferable to devise a method for initializing the recording layer as follows.

The recording layer is usually formed by a physical vapor deposition method in a vacuum such as a sputtering method.
In the ted state, since it is usually amorphous, it is usually crystallized to obtain an unrecorded and erased state. This operation is called initialization. The initialization operation includes, for example, oven annealing in a solid phase at a crystallization temperature (usually 150 to 300 ° C.) or higher and a melting point or lower, annealing with light energy irradiation such as laser light or flash lamp light, melting initialization, and the like. However, in order to obtain the above-mentioned recording layer in a preferable crystalline state, melting initialization is preferable. In the case of annealing in a solid phase, another crystal phase is likely to be formed because there is enough time to achieve thermal equilibrium.

In the melt initialization, the recording layer may be melted and directly recrystallized at the time of re-solidification. Alternatively, the recording layer may be made amorphous at the time of re-solidification and then solid-phase recrystallized near the melting point. You may. At this time, if the crystallization speed is too slow, another crystal phase may be formed because there is a margin for achieving thermal equilibrium. Therefore, it is preferable to increase the cooling rate to some extent.

For example, the time for maintaining the melting point or higher is preferably 2 μs or less, more preferably 1 μs or less. It is preferable to use a laser beam for the melting initialization. In particular, initialization is performed using an elliptical laser beam having a short axis substantially parallel to the scanning direction (hereinafter, this initialization method is referred to as “bulk erase”). Is sometimes referred to as "). In this case, the length of the long axis is usually 10 to 1000 μm
And the length of the minor axis is usually 0.1 to 10 μm.
Here, the lengths of the major axis and the minor axis of the beam are defined from the half-value width when the light energy intensity distribution in the beam is measured. The scanning speed is usually about 1 to 10 m / s. Various laser light sources such as a semiconductor laser and a gas laser can be used. The power of the laser beam is usually 1
It is from about 00 mW to about 2 W.

At the time of initialization by bulk erasing, for example, when a disk-shaped recording medium is used, the short axis direction of the elliptical beam is made substantially coincident with the circumferential direction, and the disk is rotated to scan in the short axis direction. The entire surface can be initialized by moving in the long axis (radius) direction for each rotation (one rotation). The moving distance in the radial direction per rotation is preferably shorter than the major axis of the beam so as to overlap, so that the same radius is irradiated a plurality of times with the laser light beam.
As a result, the initialization can be reliably performed, and the nonuniform initialization state due to the energy distribution in the beam radial direction (typically, 10 to 20%) can be avoided. on the other hand,
If the amount of movement is too small, the other undesirable crystal phase is likely to be formed, so that the amount of movement in the radial direction is usually set to １ ／ or more of the major axis of the beam.

At the time of melt initialization, the melt initialization may be performed by using two laser beams, once melting the recording layer with the preceding beam, and performing recrystallization with the subsequent second beam. it can. Here, if the distance between each beam is long, the region melted by the preceding beam is once solidified and then recrystallized by the second beam. Whether or not melt recrystallization has been performed depends on the reflectance R1 in the erased state after overwriting the amorphous mark with the actual recording light of about 1 μm and the reflectance R1 in the unrecorded state after initialization.
It can be determined whether or not 2 is substantially equal. Where R1
Is measured after overwriting a plurality of times, usually about 5 to 100 times, when a signal pattern in which an amorphous mark is recorded intermittently is used. By doing so, the influence of the reflectance between marks that can remain in an unrecorded state by only one recording is removed.

The above-mentioned erased state can also be obtained by irradiating the recording power in a DC manner to melt the recording layer and resolidify it without necessarily modulating the recording laser beam for recording in accordance with the actual recording pulse generation method. Can be In the case of the recording medium of the present invention, the difference between R1 and R2 is preferably small. Specifically, the following value defined by R1 and R2 is 1
It is preferably set to 0 (%) or less, particularly 5 (%) or less.

[0029]

2 | R1−R2 | / (R1 + R2) × 100 (%)

For example, in the case of a phase change medium in which R1 is about 17%, R2 should be approximately in the range of 16 to 18%. In order to achieve such an initialized state, it is preferable to give a thermal history substantially equal to the actual recording condition by the initialization.
The recording layer used in the present invention may further contain other elements as long as the effects of the present invention are not impaired. However, the recording layer usually has the quaternary composition described above.

The thickness of the recording layer is usually 5 nm or more, preferably 10 nm or more, particularly preferably 15 nm or more, and more preferably 30 nm or less, particularly preferably 25 nm or less. If the thickness is too thin, it is difficult to obtain a sufficient contrast between the reflectance in the crystalline state and the reflectance in the amorphous state, and the crystallization speed tends to be slow, so that recording and erasing in a short time tends to be difficult. Also,
The reflectivity tends to be too low. On the other hand, if it is too thick, it is still difficult to obtain optical contrast,
In addition, cracks are likely to occur. In addition, the heat capacity tends to increase and the recording sensitivity tends to deteriorate. Furthermore, since the volume change due to the phase change becomes remarkable, when the overwriting is repeated, microscopic and irreversible deformation is accumulated in the recording layer itself and the protective layer which can be provided above and below the recording layer, so that noise easily occurs. As a result, repeated overwrite durability tends to decrease. Rewrite type D
In a high-density medium such as VD, since the demand for noise is more severe, a more preferable recording layer thickness is 25n.
m or less.

In the recording layer, a predetermined alloy target can be obtained by DC or RF sputtering in an inert gas, particularly Ar gas. The density of the recording layer is usually at least 80%, preferably at least 90% of the bulk density. Here, the bulk density ρ is usually an approximate value according to the following equation (II), but it can also be measured by preparing an alloy lump.

[0033]

Ρ = Σm _i ρ _i (II)

(Here, _mi is the molar concentration of each element i, and ρ _i is the atomic weight of the element i.) In the sputtering film forming method, a sputtering gas (generally a rare gas such as Ar) is used at the time of film formation. : The case of Ar will be described below as an example.) By increasing the amount of high-energy Ar applied to the recording layer by lowering the pressure of the recording layer or arranging the substrate close to the front of the target, for example, Density can be increased. The high-energy Ar is one in which Ar ions applied to a target for normal sputtering are partially repelled and reach the substrate side, or Ar ions in plasma are accelerated by a sheath voltage on the entire surface of the substrate and reach the substrate. Either of The irradiation effect of such a high energy rare gas
Although it is called an omic peening effect, in the case of sputtering using a generally used Ar gas, an atomic peening effect is obtained.
Ar is mixed into the sputtered film by the ning effect.
The atomic peening effect can be estimated from the amount of Ar in the film. That is, if the amount of Ar is small, it means that the high-energy Ar irradiation effect is small, and a film having a low density is easily formed. On the other hand, when the amount of Ar is large, the irradiation of high-energy Ar is intense and the density is increased, but Ar taken in the film is repeatedly deposited as a void during overwriting, and the durability of repetition is easily deteriorated (J .Appl.Phys., Vol.78 (1995), pp69
80-6988). Therefore, an appropriate amount of Ar in the recording layer is 0.1.
1 at% or more and less than 1.5 at%. Further, it is preferable to use high-frequency sputtering rather than DC sputtering because the amount of Ar in the film is reduced and a high-density film can be obtained.

Other components of the structure of the optical information recording medium of the present invention will be described. As the substrate used in the present invention, a transparent resin such as polycarbonate, acrylic, or polyolefin, or a metal such as glass or aluminum can be used. Usually 20-80nm for substrate
Since the guide groove is provided to a degree, a resin substrate that can form the guide groove by molding is preferable. In order to prevent evaporation and deformation accompanying the phase change of the recording layer and to control heat diffusion at that time, a protective layer is usually formed on one or both sides, preferably both sides, of the recording layer. The material of the protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, and the like. Generally, oxides, sulfides, nitrides, Ca, and M of metals and semiconductors having high transparency and high melting point are used.
A dielectric such as a fluoride such as g or Li can be used. In this case, these oxides, sulfides, nitrides, and fluorides do not always need to have a stoichiometric composition, and it is effective to control the composition for controlling the refractive index and the like, or to use a mixture thereof. It is. Considering the repetitive recording characteristics, a mixture of dielectrics is preferred. More specifically, a mixture of a chalcogen compound such as ZnS or a rare-earth sulfide and a heat-resistant compound such as an oxide, a nitride, a carbide, or a fluoride may be used. For example, a mixture of ZnS and SiO ₂ is an example of a preferable protective layer composition.

In consideration of the repetitive recording characteristics, it is desirable that the film density of the protective layer be 80% or more of the bulk state from the viewpoint of mechanical strength (Thin Solid Film).
s, Vol. 278 (1996), pp. 74-81).
When a dielectric mixture is used, the theoretical density of the following formula (III) is used as the bulk density.

[0037]

Ρ = Σmiρi (III)

(Here, mi is the molar concentration of each component i, and ρi is the bulk density of the component i alone.) The thickness of the protective layer is generally from 10 nm to 500 nm. If it is too thin, the effect of preventing deformation of the substrate or the recording film is insufficient, and may not serve as a protective layer. On the other hand, if the thickness is too large, the internal stress of the protective layer itself and the difference in elastic properties between the protective layer and the substrate become conspicuous, and cracks are likely to occur. In particular, when a protective layer (sometimes referred to as a lower protective layer) is provided between the substrate and the recording layer, the thickness of the lower protective layer is preferably 50 nm or more because it is necessary to suppress substrate deformation due to heat. . If it is too thin, microscopic substrate deformation is accumulated during repeated overwriting, and the reproduction light tends to be scattered, resulting in a significant increase in noise. On the other hand, the thickness of the lower protective layer is usually about 200 nm or less, preferably about 150 nm or less, due to the time required for film formation. If it is too thick, the groove shape of the substrate viewed from the recording layer surface may change. That is, a phenomenon that the depth and width of the groove become smaller than the intended shape on the substrate surface is likely to occur.

On the other hand, when a protective layer (sometimes referred to as an upper protective layer) is provided on the side of the recording layer opposite to the substrate, the upper protective layer usually has a thickness of 10 nm in order to suppress deformation of the recording layer. That is all. On the other hand, if the thickness is too large, microscopic plastic deformation is accumulated inside the upper protective layer due to repeated overwriting, and the reproduction light tends to be scattered and noise rises remarkably. Is 30 nm or less. In addition, the thickness of the recording layer and the protective layer are good in terms of mechanical strength and reliability, as well as taking into account the interference effect associated with the multilayer structure, the laser beam absorption efficiency is good, and the amplitude of the recording signal, that is, It is selected so that the contrast between the recorded state and the unrecorded state is increased.

The phase change type information recording medium of the present invention may further include a reflection layer. The position where the reflective layer is provided usually depends on the incident direction of the reproduction light, and is provided on the side opposite to the recording layer with respect to the incident side. That is, when reproducing light is incident from the substrate side, it is normal to provide a reflective layer on the opposite side of the recording layer with respect to the substrate, and when reproducing light is incident from the recording layer side, the reflection layer is formed between the recording layer and the substrate. It is usual to provide a reflective layer between them.

The material used for the reflective layer is preferably a substance having a high reflectivity, and in particular, Au, Ag, which can be expected to have a heat radiation effect.
Alternatively, a metal such as Al is preferable. To control the thermal conductivity of the reflective layer itself and to improve the corrosion resistance, the above metals are made of Ta, Ti,
A small amount of Cr, Mo, Mg, V, Nb, Zr or the like may be added. The addition amount is usually about 0.01 to 20 atomic%. T
An aluminum alloy containing 15 atomic% or less of a and / or Ti, particularly an alloy of Al _x Ta _1-x (0 <x <0.15) is excellent in corrosion resistance and has excellent optical information recording medium. It is a particularly preferable reflective layer material for improving the reliability of the reflective layer. The thickness of the reflective layer is preferably 50 nm or more in order to completely reflect incident light without transmitted light. Also,
If the thickness is too large, the heat radiation effect is not changed and the productivity is unnecessarily deteriorated, and cracks are easily generated. Therefore, the thickness is usually 500 nm or less. In particular, when the thickness of the upper protective layer is 40 nm or more and 50 nm or less, the amount of impurities contained is set to 2 atomic% in order to increase the thermal conductivity of the reflective layer.
It is preferred to be less than.

A preferred layer configuration of the information recording medium of the present invention is a configuration in which a first protective layer, a recording layer, a second protective layer, and a reflective layer are provided in this order along the incident direction of the reproduction light.
That is, when reproducing light is incident from the substrate side, the substrate,
The lower protective layer, the recording layer, the upper protective layer, and the reflective layer has a layer configuration, and when reproducing light is incident from the recording film side, the substrate,
It is preferable that the reflective layer, the lower protective layer, the recording layer, and the upper protective layer have a layer structure. Of course, each of these layers may be formed of two or more layers, and an intermediate layer may be provided between them. For example, a semi-transparent extremely thin metal, semiconductor, dielectric layer having absorption, etc. are provided on the substrate / protective layer in the case of substrate-side incidence or on the protective layer in the case of incidence from the side opposite to the substrate, It is also possible to control the amount of light energy incident on the recording layer.

The recording layer, protective layer and reflection layer are usually formed by a sputtering method or the like. Target for recording film,
It is desirable to form a film using an in-line apparatus in which a target for a protective film and, if necessary, a target for a reflective layer material are installed in the same vacuum chamber, in order to prevent oxidation and contamination between layers. It is also excellent in productivity. On the outermost surface side of the recording medium of the present invention, it is preferable to provide a protective coat made of an ultraviolet curable resin or a thermosetting resin in order to prevent direct contact with air and prevent damage due to contact with foreign matter. The protective coat is usually 1 μm to several hundred μm thick. Alternatively, a dielectric protection layer having high hardness may be further provided, and a resin layer may be further provided thereon.

The recording / reproducing light which can be used for the recording medium of the present invention is usually a laser light such as a semiconductor laser or a gas laser, and its wavelength is usually about 300 to 800 nm, preferably about 350 to 800 nm. Especially 1Gbi
In order to achieve a high areal recording density of t / inch ² or more, it is necessary to reduce the diameter of the focused light beam.
It is desirable to obtain a focused light beam using a blue to red laser beam of 0 to 680 nm and an objective lens having a numerical aperture NA of 0.5 or more.

In the present invention, the amorphous state is usually used as a recording mark as described above. In the present invention, it is effective to record information by a mark length modulation method. This is especially true when the shortest mark length is 4 μm or less, especially 1 μm.
This is particularly noticeable when recording with a mark length of less than m. In the case where the mark length is too long or in the case of mark position recording, it is possible to obtain a certain degree of sufficient characteristics in the first place, so that the effect of the present invention is unlikely to appear. When forming a recording mark, recording can be performed by a conventional binary modulation method, but in the present invention, a ternary or more multi-level modulation method that provides an off-pulse period when forming a recording mark as described below is used. It is particularly preferable to employ a recording method.

FIG. 1 is a schematic diagram showing a power pattern of a recording light in the recording method of the present invention. When forming an amorphous mark having a mark length modulated to a length nT (T is a reference clock cycle, n is a mark length that can be taken in mark length modulation recording and is an integer value), (n−j) T (Where j is a real number of 0-2), m = nk (where k is 0 ≦ k)
The recording pulse is divided into ≤2 integer recording pulses, each recording pulse width is α _i T (1 ≦ i ≦ m), and each recording pulse is an off-pulse with a time β _i T (1 ≦ i ≦ m). Attach a section. Here, it is preferable that α _i ≦ β _i . Note Σα _i + Σβ _i is usually n, is _{Σα i + Σβ i = n-} j (j To obtain accurate nT mark greater than 0 2
The following number) can also be used.

At the time of recording, a recording light having an erasing power Pe capable of crystallizing an amorphous is irradiated between the marks. Further, at α _i T (i = 1 to m), a recording light having a recording power Pw sufficient to melt the recording layer is irradiated, and β _i T
In the time T (1 ≦ i ≦ m−1), Pb <P
e, preferably a recording light with a bias power Pb that satisfies Pb ≦ (１ ／) Pe. Note that the power Pb of the recording light applied during the period β _m T is β _i T (1
As in the period of ≦ i ≦ m−1), normally Pb <Pe, preferably Pb ≦ 1 / 2Pe, but Pb ≦ Pe may be satisfied.

By adopting the above recording method,
Power margin and linear velocity margin during recording can be expanded
Wear. This effect is especially effective in such a way that Pb ≦ 1 / 2Pe.
This is remarkable when the ease power Pb is set sufficiently low. FIG.
To α_i= Β_i= Pb = Pe when = 0.5
(A) and Pb ≒ 0 (extreme case) (b)
Schematically shows the temperature change of the recording layer. Here, three
The first pulse of the divided pulse divided into
Position is assumed. (A) shows the subsequent recording pulse
The first recording pulse
The cooling rate after irradiation is slow and P
e is emitted, and the temperature drops during the off-pulse section.
The lowest temperature TL reached is around the melting point. on the other hand,
In (b), Pb in the off-pulse section is almost zero.
Therefore, TL falls to a point well below the melting point, and
The cooling rate on the way is also large. The amorphous mark is the first pal
Melts during irradiation and then rapidly cooled during off-pulse.
Formed. The recording layer of the present invention is large only near the melting point.
Since it is considered to indicate the crystallization rate, the temperature shown in (b)
Taking a profile suppresses recrystallization and provides good
This is important for obtaining an amorphous mark. Conversely, cooling
Speed and T _LControl almost completely suppresses recrystallization.
And has a clear contour that almost matches the melting area.
Low jitter at mark edge due to crystalline mark
can get. GeTe-Sb conventionally used_TwoT
e_ThreeIn the case of a pseudo binary alloy, FIGS.
Amorphous mark formation process even with misaligned temperature profile
There is no big difference. Because the speed is a bit slow but the wide temperature
This is because recrystallization is exhibited in the temperature range. In this case, the pulse
Recrystallization occurs to some extent regardless of the division method.
Coarse grains around the crystalline mark
Tends to worsen the data. With such a recording layer composition
Does not require off-pulse, but rather conventional binary modulation
Overwriting is simple and desirable. That is, the book
The above recording method is extremely effective for the recording layer of the invention.
There is a conventional GeTe-Sb_TwoTe_ThreeUsing the system recording layer
This applies to cases where the
There is no necessity to adopt such a recording method. In addition,
Recording marks must be provided in either the groove or the groove.
Can be provided on both sides, but preferably the groove
To be provided.

[0049]

EXAMPLES Examples 1 to 3 and Comparative Examples 1 and 2 A GeInSbTe film was obtained by simultaneously sputtering a GeSbTe target and an InSbTe target. At the time of sputtering, the Ar gas pressure was set to 0.4 Pa, and RF power of 300 W was applied to the GeSbTe target. DC controlled by current control for InSbTe target
The composition was changed by applying power and changing the current value. As a result of the composition analysis, their compositions were as follows.

[0050]

Embedded image Comparative Example 1: Ge ₅ Sb ₇₁ Te ₂₄ (= (Sb _0.75 T
e _0.25 ) _0.95 Ge _0.05 ) Example 1: Ge ₅ In ₁ Sb ₇₀ Te ₂₄ (= ((Sb _0.74
Te _0.26 ) _0.95 Ge _0.05 ) _0.99 In _0.01 ) Example 2: Ge ₅ In ₃ Sb ₆₈ Te ₂₄ (= ((Sb _0.74
Te _0.26 ) _0.95 Ge _0.05 ) _0.97 In _0.03 ) Example 3: Ge ₅ In ₇ Sb ₆₃ Te ₂₅ (= ((Sb _0.72
Te _0.28 ) _0.95 Ge _0.05 ) _0.93 In _0.07 ) Comparative Example 2: Ge ₄ In ₁₂ Sb ₅₈ Te ₂₆ (= ((Sb _0.69
Te _0.31 ) _0.95 Ge _0.05 ) _0.88 In _0.12 )

Next, a phase change type optical disk having a recording layer manufactured by the same method as the above recording layer was manufactured by the following method. To 1.2mm thick disk-shaped polycarbonate substrate ZnS-SiO ₂ lower protective layer (95 nm),
GeInSbTe recording layer (18 nm), ZnS-SiO
₂ Upper protective layer (40 nm), Al alloy reflective layer (200 n
The structure of m) was formed by a sputtering method, and a protective coat made of an ultraviolet curable resin was further applied thereon. The recording layer was sputtered under the same conditions as above to obtain a recording layer having the same composition as described above. These disks were melt crystallized. That is, an elliptical laser beam having a major axis of about 100 μm and a minor axis of about 1.5 μm is applied to the recording layer, which has been in an amorphous state after film formation, in the minor axis direction in the circumferential direction of the disk and in the major axis direction. Was irradiated in the radial direction. The entire surface of the disk was initialized by rotating the disk at 4 m / s and moving the disk in the radial direction by about 40 μm per round. The irradiation power was about 400 mW. Then, at 780 nm, NA
The following recording and measurement were performed using an optical system of 0.55.

That is, in the portion where overwriting was performed five times using the recording pulse for a single recording pattern shown in FIG. 3A, the recording pulse for a single recording pattern shown in FIG. After one overwrite recording, the mark jitter was measured. Here, FIG.
FIG. 3B shows a pattern in which 8T marks and 8T spaces (between marks) are alternately repeated with respect to the reference clock cycle T.
Is a pattern in which 11T marks and 11T spaces (between marks) are alternately repeated. In each case, the recording pattern conforms to the recording method of the present invention.
And i is uniformly α _i = β _i = 0.
It was set to 5. Recording power P at α _i T (i = 1 to m)
w is constant regardless of i, and β _i T (i = 1 to m)
The bias power Pb at is constant regardless of i.
At this time, Pb was set to 0.8 mW, and the ratio Pe / Pw between the erasing power Pe and the recording power Pw between the marks was kept constant at 0.5.

The recording power Pw is 1 m between 8 and 17 mW.
Change every W (total 10 points), linear velocity is 1.2 ~
Twelve points between 8.1 m / s (1.2, 1.4, 1.7,
2.0, 2.4, 2.9, 3.4, 4.0, 4.8,
The mark length jitter was measured at 5.7, 6.8, and 8.1 m / s).

The reference clock period T at each linear velocity v is (115.7 * 2.4) / v nanosecond, and the mark length is made constant in inverse proportion to the linear velocity.
That is, the 8T mark and the space are about 2.2 μm, 1
The 1T mark and space correspond to a length of about 3.1 μm. This is the normal compact disc 8T and 11T
The length is equal to the mark length. The measurement of mark jitter (mark length jitter) after recording was performed at 2.4 m / s regardless of the recording linear velocity.

FIG. 4 shows the above results. FIG. 4 is a diagram showing the relationship among mark jitter, recording power, and linear velocity in the above embodiment. The vertical axis and the horizontal axis are the linear velocity and the recording power, respectively, and the mark jitter is shown by contour lines.
The unit of the mark jitter is ns. FIG. 4 shows that the usable linear velocity range is widened by adding In.
Next, using the same measurement system as used for the above measurement,
The linear velocity was 2.4 m / s, the recording power was 11 mW, the erasing power was 5.5 mW, and the other conditions were based on the Orange Book Part 3. Repeated overwrite recording of the EFM random signal was performed, and the jitter between 3T marks was measured. here,
The recording pulse conforming to Orange Book Part 3 is shown in FIG.
, M = n-1, α ₁ = 1, α _i = 0.5 (i =
2 to m), βi = 0.5 (i = 1 to m), and j = 0.5, and n was an integer of 3 to 11. The results are shown in Table 1. The disc of Comparative Example 2 does not deteriorate after repeated recording for several hundred times, but deteriorates after recording for 1,000 times or less, which is the standard of Orange Book Part 3, 17.5n.
The jitter is s or more. 1 for other disks
Even after recording 000 times, it is 17.5 ns or less. 100
Regarding the repetitive recording deterioration of zero or more times, it can be seen that the tendency is that the larger the In amount, the faster the deterioration.

[0056]

[Table 1]

In each of Examples 1 to 3, the recording layer in the crystalline state was composed of a single crystal phase having a face-centered cubic structure.

According to the present invention, it is possible to obtain a phase change recording medium which has a wide usable linear velocity range, has stable recording marks, and is excellent overall. Further, a reproducing method and a recording method suitable for this can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a power pattern of recording light in a recording method of the present invention.

FIG. 2 is a schematic view showing a change in temperature of a recording layer, showing an effect of the recording method of the present invention.

FIG. 3 is a schematic diagram showing a power pattern of a recording light in an embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between mark jitter, recording power, and linear velocity in an example of the present invention.

FIG. 5 is an example of an electron beam diffraction image by TEM of the recording layer of the medium of the present invention.

Claims (13)

[Claims] An optical information recording medium having at least a phase change type recording layer on a substrate, wherein the phase change type recording layer has a composition represented by the following general formula (I). Optical information recording medium. Embedded image ((Sb _x Te _1-x ) _y Ge _1-y ) _z M _1-z (I) (where x is a number in the range of 0.7 ≦ x ≦ 0.9,
y is a number in the range of 0.8 ≦ y <1, and z is 0.88 ≦
It is a number in the range of z <1. M represents In and / or Ga. ) 2. The optical information recording medium according to claim 1, wherein 0.7 ≦ x ≦ 0.85. 3. The optical information recording medium according to claim 1, wherein 0.7 ≦ x ≦ 0.8. 4. The optical information recording medium according to claim 1, wherein 0.9 ≦ y <1. 5. The method according to claim 1, wherein 0.94 ≦ z <1.
The optical information recording medium according to any one of the above. 6. The optical information recording medium according to claim 1, wherein the phase-change recording layer comprises a crystal phase having a face-centered cubic structure in a crystalline state. 7. The optical information recording medium according to claim 1, wherein a protective layer is provided on one or both sides of the phase change recording layer. 8. The method according to claim 1, further comprising a reflection layer.
8. The optical information recording medium according to any one of items 1 to 7. 9. On a substrate, at least a first protective layer, a phase-change recording layer,
9. The method according to claim 1, wherein the second protective layer and the reflective layer are provided in this order.
The optical information recording medium according to any one of the above. 10. The phase change type recording layer having a thickness of 5-30 nm
The optical information recording medium according to any one of claims 1 to 9, wherein 11. The optical information recording medium according to claim 1, wherein information according to a mark length modulation method is recorded. 12. The optical information recording medium according to claim 1, wherein the wavelength is 350 nm.
A laser beam of not less than 800 nm and a numerical aperture NA of 0.
A method for reproducing an optical information recording medium, comprising irradiating focused light condensed by five or more objective lenses to reproduce the information. 13. Recording of mark-length modulated information on the optical information recording medium according to any one of claims 1 to 11, wherein a portion in a crystalline state is set to an unrecorded state / erased state, and The crystalline portion is set in a recording state, and a recording light having an erasing power Pe capable of crystallizing an amorphous portion is irradiated between recording marks. N
Assuming that T (T is a reference clock cycle and n is a natural number of 2 or more), the time (n−j) T is expressed as follows: α ₁ T, β ₁ T, α ₂ T, β ₂ T,.・, Α _m T,
β _m T, where Σαi + Σβi = n-j, where j is 0-2
Any number up to. m is a number satisfying m = nk. k is 0-
Integer up to 2. ), And at a time of α _i T (1 ≦ i ≦ m), a recording light having a recording power Pw sufficient to melt the recording layer is irradiated, and β _i T (1 ≦ i ≦ m−1). )
A recording method for an optical information recording medium, comprising irradiating recording light with a bias power Pb satisfying Pb <Pe for a certain time.