JP3433641B2 - Optical information recording medium and optical recording method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recordable and erasable optical information recording medium utilizing a reflectance difference or a reflected light phase difference caused by a phase change caused by laser light irradiation.

[0002]

2. Description of the Related Art Optical discs include a read-only type, an optical recordable type, and a rewritable type. The read-only type is a video disc,
It has already been put to practical use as an audio disc and a disc memory for large-capacity computers. Typical examples of the optical recordable type are a drilling / deformable type, a magneto-optical type, and a phase change type. A recording layer made of a low melting point metal such as Te or a dye is used as the perforation / deformation type and is locally heated by laser light irradiation to form a hole or a recess. The magneto-optical type performs recording and erasing depending on the magnetization direction of the recording layer, and reproduces by the magneto-optical effect. As a disc for recording a CD format signal, an optical disc having a recording layer made of a dye or a polymer containing the dye on a substrate, and an optical information recording method using the optical disc have been proposed.

On the other hand, the phase change type utilizes the fact that the reflectance or the phase of the reflected light changes before and after the phase change.
Playback is performed by detecting the difference in the amount of reflected light without the need for an external magnetic field. Compared to the magneto-optical type, the phase-change type is easy to manufacture a drive because it does not require a magnet and has a simple optical system, and is advantageous in downsizing and cost reduction. Further, there is an advantage that recording / erasing can be performed only by modulating the power of laser light, and one-beam overwriting in which erasing and re-recording are simultaneously performed with a single beam is also possible.

As a recording layer material used in the phase change recording method, a chalcogen alloy thin film is often used. For example, Ge-Te system, Ge-Te-Sb system, In-Sb
-Te system, Ge-Sn-Te system, Ag-In-Sb-T
Attempts have been made to use e-based alloy thin films and the like.

In the one-beam overwritable phase change recording method, it is general that the recording film is made amorphous to form a recording bit and is crystallized to erase the recording bit. In this case, since the as-depo state is generally amorphous, it is necessary to crystallize the entire surface of the disk in a short time in order to make the initial state crystalline. This process is called initial crystallization. Usually, this initial crystallization is performed by irradiating a rotating disk with a laser beam focused to about several tens to hundreds of microns.

[0006]

Conventionally, alloy materials near the eutectic composition have a high amorphous forming ability, but since they are accompanied by phase separation during crystallization, they can be crystallized by heating for a short time of less than 100 nsec. Therefore, it has been considered unsuitable as a recording layer of an overwritable optical recording medium (Ref. Ap.
pl. Phys. Lett. , Vol. 49 (1986), p. 502, etc.). Especially when focusing on GeSbTe and ternary alloys,
A practical crystallization rate has not been obtained in the vicinity of the Te ₈₅ Ge ₁₅ eutectic composition. On the other hand, in the vicinity of the Sb ₇₀ Te ₃₀ eutectic composition,
This is a very rudimentary method in which only changes in reflectance are monitored, but Sb _x Te _1-x , 0.58 <x <0.75, 2
It is also disclosed in US Pat. No. 5,015,548 that the original alloy can be repeatedly recorded and erased between the crystalline and amorphous states.

As prior applications in which a third element is added to Sb ₇₀ Te ₃₀ , Japanese Patent Laid-Open Nos. 1-115685, 1-115686, 1-251342, and 1-303643 are cited. Since then, there has been no progress toward practical use of phase change media near the SbTe eutectic composition. In particular,
Since the initialization operation for crystallizing the recording layer after the film formation is difficult, there is a serious problem that the productivity is low and the recording layer cannot be put to practical use.

Therefore, it has been considered that only a material near the composition of the intermetallic compound, which is easy to initialize, or a pseudo binary alloy thereof has practical properties (Japanese Patent Laid-Open No. 2-2433).
88, flat 2-243389, flat 2-243390, flat 2
-255378, JP-A-63-228433, 61-
89889 Publications, References Jpn.J.Appl.Phys., Vol.69 (1
991), page 2849). For example, regarding GeSbTe ternary alloys, in recent years, only the composition near the GeTe-Sb ₂ Te ₃ pseudo binary alloy has been noticed and put to practical use. Such a trend is conspicuously shown in the paper (published in the proceedings) of the "Phase Change Optical Memory Symposium", which has been held every year since 1991, for example.

The present inventors have focused their attention on binary alloys made of SbTe for simplification, and are not restricted to the conventional theory, and have a crystallization / amorphization characteristic in the vicinity of the eutectic composition composition, and are required for higher density recording. Using a suitable optical disk evaluation machine, we reexamined from the viewpoint of suitability for mark length recording. As a result, Sb ₇₀ Te
_{Although the} initial crystallization is difficult for the recording layer mainly composed of SbTe alloy in the vicinity of the eutectic composition, once the initial crystallization is performed, the subsequent recording / erasing due to the amorphous-crystalline phase change should be performed at an extremely high speed. I found that I can do it. further,
When the ternary material with In added near the eutectic composition was evaluated, InSbTe ternary alloy near the SbTe eutectic was widely known for repetitive overwriting when a specific recording pulse pattern was used. InGe
It has been found that there is an advantage that the deterioration is less than that of the material near the Te-Sb ₂ Te ₃ pseudo binary alloy or that the jitter of the mark edge when recording the mark length is small. Further, the crystallization temperature is higher than that of the Sb ₇₀ Te ₃₀ binary eutectic alloy,
It was also found to have excellent stability over time. However, since it is extremely difficult to once completely crystallize and initialize the amorphous film formed by film formation as compared with the SbTe eutectic alloy, it was practically unsuitable for mass production.

In recent years, Sb₇₀Te₃₀Ag near the eutectic composition,
By adding In at the same time, the stability of In with time can be improved.
Improvement and easy initialization by Ag are achieved at the same time
It has been reported (Japanese Patent Application Laid-Open No. 4-232779, 5)
-185732). This is a specific combination
By adding an appropriate amount of binary or three elements of ₇₀
Te₃₀Practical use of eutectic composition binary material with dramatically improved characteristics
It shows that the target level can be reached. Record like this
Useful materials of the layers are combinations of quaternary or quaternary alloys
And very limited because of the need to optimize the composition of each
Only in specific cases (Japanese Patent Laid-Open No. 8-267)
926 publication). Further unknown limited combinations and
There is a composition and it is expected that further improvement will be obtained.

[0011]

According to the present invention, at least a lower protective layer, a phase change type optical recording layer, an upper protective layer, and
The phase-change optical recording layer has a multilayer structure including a reflective layer, and the phase-change optical recording layer is ZnαInβSbχTeδ, 0.01 ≦ α <0.1,
0.03 ≦ β ≦ 0.08, 0.5 <χ <0.7, 0.2
5 <δ <0.4, α + β + χ + δ = 1,
The present invention relates to an optical information recording medium, characterized in that a crystalline state is an unrecorded state, an amorphous state is a recorded state, and amorphous bits are overwritten by modulation of at least binary light intensity.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The composition range of the ZnInSbTe quaternary alloy thin film of the present invention is such that Zn and In are added based on the vicinity of the Sb70Te30 eutectic composition. The greatest advantage of using the recording layer material of the present invention is that coarse grains having a reflectance different from that in the initialized state are unlikely to occur in the periphery of an amorphous mark or in an erased mark. This is a phenomenon peculiar to alloys near the eutectic point where crystal growth is rate-controlled by phase separation. The recording layer material of the present invention is
If the crystallization rate in the solid phase is increased, the recrystallization rate at the time of re-solidification at the time of amorphous mark formation will be extremely fast, and the outer peripheral portion of the molten region will be recrystallized to form amorphous marks. It has the characteristic that it tends to be insufficient. That is, since the recording layer of the present invention has a composition near the eutectic point, the crystallization rate is dominated by the diffusion rate of atoms for phase separation. It is considered that high-speed erasing cannot be performed. Compared with the recording layer near the composition of GeTe-Sb2Te3 pseudo binary alloy which is widely used at present, the temperature range in which a high crystallization rate can be obtained is narrow and the temperature is biased to a high temperature. Therefore, in order to achieve both the high crystallization rate and the formation of a sufficiently large amorphous mark, it is necessary to particularly increase the cooling rate near the melting point during resolidification. In the recording medium of the present invention, Sb
On the line showing the constant 70Te30 ratio, the fact that the Sb phase and the Sb2Te3 phase are separated is basically used in reverse. When thermally annealed at equilibrium, phase separation can be confirmed by X-ray diffraction. However, in a non-equilibrium supercooled state where an amorphous mark is formed in the optical recording medium, if excessive Sb is contained, fine Sb clusters are first precipitated during resolidification. Since the Sb clusters remain in the amorphous mark as crystal nuclei, it is considered that the subsequent erasing (recrystallization) of the amorphous film is completed in a short time without spending time for phase separation. .

The present invention was made based on a consideration of these characteristics of the present recording layer composition. The recording medium of the present invention is based on the Sb ₇₀ Te ₃₀ binary eutectic composition as described above, to which Zn and In are added. The recording characteristics of the recording medium of the present invention, that is, the reversible process of amorphous and crystallization, is almost the Sb / Te ratio, that is, the parent S.
b ₇₀ Te ₃₀ Determined by the amount of excess Sb contained in the eutectic composition. S
It is considered that as the amount of b increases, the number of Sb cluster sites precipitated in the rapidly cooled state increases and crystal nucleation is promoted. This means that even if the same crystal growth rate is assumed from each crystal nucleus, the time required to fill up with grown crystal grains is shortened,
As a result, it means that the time required to crystallize the amorphous mark is shortened. 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, it is desirable that the lower the linear velocity, the smaller the critical cooling rate for amorphous formation, that is, the composition in which the amount of excess Sb is small. In summary, based on the Sb ₇₀ Te ₃₀ eutectic composition, a composition having a large amount of excess Sb is more suitable for high linear velocity.

The composition of each element contained in the recording layer of the present invention is preferably in the range of the following formula. That is, ZnαIn
βSbχTeδ, 0.01 ≦ α <0.1, 0.03 ≦ β
≦ 0.08, 0.5 <χ <0.7, 0.25 <δ <0.
4, the composition range is α + β + χ + δ = 1. According to the studies by the present inventors, by limiting the composition as described above, overwriting can be performed at least at a linear velocity of 1 to 10 m / s, and particularly as a CD-E, it is 6 times the CD linear velocity at most. It was found that the composition can be selectively used as a composition having excellent repetitive overwrite durability and stability over time when overwriting is performed at a level (7.2 to 8.4 m / s). The optimum compositional range of this combination and of the individual elements is hitherto unknown.

In has the effect of increasing the crystallization temperature and increasing the stability of the amorphous marks over time. If it exceeds 8 atomic%, phase separation is likely to occur in exchange for improvement in stability over time, and segregation occurs due to repeated overwriting, which is not preferable. On the other hand, if it is less than 3 atomic%, the stability of the amorphous mark with time is insufficient.

Zn is used in an amount of 1 atomic% or more for facilitating the initialization of the amorphous film immediately after the film formation. Although it depends on the initialization method, addition of less than 10 atomic% is sufficient, and too much is not preferable because it deteriorates stability over time. The mechanism by which the addition of Zn facilitates initialization is not clear, but it is considered that fine ZnSb phase precipitates together with Sb clusters and acts as crystal nuclei. SbTe
By adding In and Zn to the eutectic, the crystallization time in the initialization operation described later can be shortened while maintaining the stability of the amorphous mark with time. By adding In and Zn,
It seems that the base SbTe becomes a eutectic crystal from Sb ₆₀ Te ₄₀ to Sb ₆₅ Te ₃₅ . Therefore, the linear velocity dependence of the ZnInSbTe alloy of the present invention as a whole depends on how much excess Sb is contained based on this composition as described above. In order to correspond to a high linear velocity, it is sufficient to increase the excessive Sb amount as described above, but if it is excessively increased, the stability of the amorphous bit is impaired, so 0.50 <χ <
It is preferably 0.7. More preferably 0.5
5 <χ <0.65. Further, the Te content is 0.25 <δ <0.4.

The layer structure of the disk of the present invention is, as schematically shown in FIG. 1, provided with at least a lower protective layer 2, a phase change type recording layer 3, an upper protective layer 4 and a reflective layer 5 on a substrate 1. . The protective layers 2, 4, the recording layer 3, and the reflective layer 5 are formed by a sputtering method or the like. It is desirable to form a film by an in-line apparatus in which the target for the recording film, the target for the protective film, and if necessary, the target for the reflective layer material are installed in the same vacuum chamber in order to prevent oxidation and contamination between the layers. It is also excellent in terms of productivity.
A protective coat layer 6 may be provided on the reflective layer 5,
UV curable resin or the like is used.

The substrate 1 of the recording medium in the present invention may be any of glass, plastic, glass provided with a photo-curable resin, and the like. In terms of productivity including cost, polycarbonate resin is used. preferable. The recording layer 3 of the present invention is a phase change type recording layer as described above,
The thickness is preferably in the range of 15 nm to 30 nm. When the thickness of the recording layer is less than 15 nm, it is difficult to obtain a sufficient contrast, and the crystallization speed tends to be slow, which makes it difficult to erase the recording in a short time. On the other hand, if it is thicker than 30 nm, the heat capacity tends to be large and the recording sensitivity tends to be poor.

The materials for the upper and lower protective layers 2 and 4 are determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion and the like. Generally M, which has high transparency and high melting point
g, Ca, Sr, Y, La, Ce, Ho, Er, Yb,
Ti, Zr, Hf, V, Nb, Ta, Zn, Al, S
Oxides such as i, Ge and Pb, sulfides, nitrides, carbides and fluorides such as Ca, Mg and Li can be used.
These oxides, sulfides, nitrides, carbides, and fluorides do not necessarily have to have a stoichiometric composition, and it is effective to control the composition or mix them for controlling the refractive index and the like. is there. Considering the repetitive recording characteristics, the dielectric mixture is preferable. More specifically, a mixture of ZnS or a rare earth sulfide and a heat resistant compound such as an oxide, a nitride, or a carbide can be used.

Since the lower protective layer 2 is also required to have a function of suppressing the thermal deformation of the plastic substrate, it is preferable that the film thickness is at least 50 nm. However, if it is 500 nm or more, cracks are likely to occur due to internal stress, which is preferable. Absent. Therefore, the film thickness range is 50 nm or more, 500
Although it is as wide as nm or less, it is usually selected from this range so that the reflectance, the reflectance difference before and after recording, and the phase difference have appropriate values in consideration of the optical interference effect.

The same material is used for the upper protective layer 4, but the film thickness range is preferably 10 nm or more and 50 nm or less. The biggest reason is that heat radiation to the reflection layer 5 is effectively applied. By adopting a layer structure that promotes heat dissipation and increases the cooling rate at the time of resolidification of the recording layer, the problem of recrystallization is avoided and a high erasing ratio by high-speed crystallization is realized. If the thickness of the upper protective layer is more than 50 nm, the heat of the recording layer takes a long time to reach the reflective layer, and the heat dissipation effect of the reflective layer may not work effectively. Although it depends on the thermal conductivity of the upper protective layer, the thermal conductivity of a thin film having a thickness of less than 100 nm is generally 2-3 orders of magnitude smaller than the thermal conductivity of the bulk, and there is no great difference, so the thickness is an important factor.

On the other hand, if the upper protective layer is thinner than 10 nm,
It is not preferable because it is easily destroyed by deformation during melting of the recording layer. In addition, the heat dissipation effect is too large and the power required for recording becomes unnecessarily large, which is also not preferable. The layer structure proposed here is called a "quenched structure" in the phase change medium,
As such, it is publicly known (Japanese Patent Laid-Open No. 2-56746,
Reference Jpn.J.Appl.Phys., Vol.28 (1989), suppl.28-3, 12
page 3).

The reflective layer 5 is preferably made of a material having a high reflectance, and in the present invention, 90% Au, Ag or Al, which has a particularly high thermal conductivity and is expected to have a heat dissipation effect even through the upper dielectric layer.
A metal layer containing at least atomic% is preferably used. In general, the thermal conductivity of a thin film differs greatly from the thermal conductivity in the bulk state and is usually small. Especially 40 nm
A thin film of less than 1 is not preferable because the thermal conductivity may decrease by one digit or more due to the influence of the island structure at the initial stage of growth. further,
The crystallinity and the amount of impurities differ depending on the film forming conditions, and this causes a difference in thermal conductivity even with the same composition. In the present invention, the thermal conductivity of the reflective film can be directly measured in order to define the reflective film having a high thermal conductivity which exhibits good characteristics, but the quality of the thermal conductivity is estimated by using the electrical resistance. be able to. This is because in a material such as a metal film in which electrons mainly control heat or electric conduction, the thermal conductivity and the electric conductivity have a good proportional relationship.

The electric resistance of the thin film is represented by a resistivity value standardized by the area of the thin film and the measurement region. Volume resistivity or area resistivity can be measured by the ordinary 4 deep needle method, and JIS K7
194. Data that is much simpler and has better reproducibility can be obtained than when actually measuring the thermal conductivity of the thin film itself. In terms of volume resistivity, the preferable reflective layer in the present invention is 20 or more and 300 nΩ · m or less.

The low volume resistivity as described above can be obtained with almost pure Al, Au and Ag films having an impurity content of less than 10 atomic%. More specifically, the Al alloy material suitable for the present invention will be described in JIS6061, 6101, 6151, 626.
The Al alloy No. 2 is preferable because it has a track record of being used as a sputtered film as a reflective film for a conventional CD or a wiring material for an IC. In addition, Al, Ta, Ti, Co, Cr, Si, S
c, Hf, Pd, Pt, Mg, Zr, Mo, or M
It is known that an Al alloy containing n in an amount of 0.2 atomic% or more and less than 2 atomic% has an increased volume resistivity in proportion to the concentration of the additional element and improved hillock resistance (Iwamura et al., Journal of Japan Institute of Metals, Younger Brother, Volume 59 (1995), pp 673-6
78) (Onishi et al., J. vac. Sci. Tech., A.
14 (1996), pp2728-2735), it can be used in consideration of durability, volume resistivity, film forming rate and the like. Regarding Al alloys, if the amount of added impurities is less than 0.2 atom%, the hillock resistance is often insufficient depending on the film forming conditions. Ta is preferred when more importance is attached to stability over time.

On the other hand, when the reflection film is an Ag alloy thin film, Ti, V, Ta, Nb, W, Co, Cr, Si,
Ge, Sn, Sc, Hf, Pd, Rh, Au, Pt, M
It is desirable to contain g, Zr, Mo, or Mn in an amount of 0.2 atomic% or more. T when the stability over time is more important
i and Mg are preferable. The present inventors have confirmed that the additive element to Al and the additive element to Ag increase the volume resistivity in proportion to the concentration of the additive element. It is considered that addition of impurities generally reduces the crystal grain size, increases electron scattering at grain boundaries, and lowers thermal conductivity. Limiting the amount of impurities is necessary in order to obtain the original high thermal conductivity of the material by increasing the crystal grain size.

The reflective layer is usually formed by a sputtering method or a vacuum evaporation method. However, the total amount of impurities including not only the amount of impurities in the target and the evaporation material itself but also the amount of water and oxygen mixed in during film formation is determined. It should be less than 2 atomic%. For this reason, the ultimate vacuum of the process chamber is 1 × 1.
It is desirable that the pressure is less than 0 ⁻³ Pa. Also, 10 ^-4 Pa
If film formation is performed with a lower ultimate vacuum, the film formation rate should be 1n
It is desirable to prevent the incorporation of impurities at m / sec or more, preferably 10 nm / sec or more. Alternatively, when the intentional additive element is contained in an amount of more than 1 atom%, it is desirable to prevent the addition of impurities as much as possible by setting the film formation rate to 10 nm / sec or more.

The film forming conditions may affect the crystal grain size regardless of the amount of impurities. For example, in an alloy film in which Al is mixed with Ta at most 2 atomic%, an amorphous phase is mixed between crystal grains, but the ratio of the crystalline phase and the amorphous phase depends on the film forming conditions. For example, as the sputtering is performed at a lower pressure, the proportion of crystal parts increases and the volume resistivity decreases (the thermal conductivity increases). The impurity composition or crystallinity in the film depends on the manufacturing method of the alloy target used for sputtering and the sputtering gas (Ar, Ne, Xe).
Etc.). As described above, the volume resistivity in a thin film state is not determined only by the metal material and composition, so that the prior application (for example, Japanese Patent Laid-Open No. 3-1) that defines the Al alloy reflective layer material is used.
338, flat 1-169571, flat 1-208744, etc.)
Obviously, does not directly imply the present application.

The thickness of the reflective layer is preferably 50 nm or more in order to completely reflect incident light without transmitting light.
When the film thickness is larger than 500 nm, there is no change in the heat radiation effect, which unnecessarily reduces productivity, and cracks are likely to occur. Therefore, the film thickness is preferably 500 nm or less. In particular, when the film thickness of the upper protective layer is 30 to 50 nm, the amount of impurities contained is set to less than 2 atomic% in order to make the reflective layer have high thermal conductivity.

In the present invention, the quenching structure is further used in combination with the following recording method to accurately control the cooling rate at the time of resolidification of the recording layer, whereby the recording layer material of the present invention suitable for mark length recording is obtained. It is possible to fully demonstrate the characteristics. FIG. 2 is a diagram showing an example of a laser power irradiation pattern during optical recording. An amorphous mark whose mark length is modulated to a length nT (T is a reference clock period, n is a mark length that can be taken in mark length modulation recording and takes an integer value of 2 or more) is formed. For the recording medium of the present invention, when recording on a mark of length nT, m = n−k (0 ≦ k ≦
2 integers, where n _min −k, where n _min is the minimum value of n
≧ 1) divided into recording pulses, each recording pulse width is α _i T, and each recording pulse is β _i T (2 ≦ i
In the case of ≦ m−1, an off-pulse section of time α _i ≦ β _i ) is attached. Here, k is a parameter for making m take a value smaller than n. For example, when n = 3, m =
It can take the values 1, 2, and 3. 0 <P in the off pulse section
Bias power of b ≦ 0.5 Pe is applied. Here, Σα _i + Σβ _i can be adjusted as n−j (j is a real number satisfying 0 ≦ j ≦ 2) so that an accurate nT mark can be obtained when the mark length is detected. j is a parameter for irradiating with a small heating amount in order to prevent the influence of heating by the last pulse.

The medium of the present invention has hitherto been used for GeTe-Sb ₂ T.
It is possible to perform recording and erasing by ternary modulation in which the off pulse section is provided and bias power Pb is radiated, rather than binary modulation of the recording power Pw and the erasing power Pe as used in the e ₃ pseudo binary alloy system. desirable. Although binary modulation overwriting is possible, the power margin and recording linear velocity margin can be widened by using the ternary modulation method. In particular, in the recording layer of the present invention, it is necessary to make the bias Pb at the time of off pulse sufficiently low so that 0 <Pb ≦ 0.5Pe. However, in β _m T, 0 <
It may be that Pb ≦ Pe.

FIG. 3 is a schematic diagram showing the temperature change of the recording layer when optical recording is performed on the medium of the present invention. α _i = β _i = 0.5
And when Pb = Pe (a), Pb≈0
In the case of (extreme case), it is (b). The position where the first pulse of the divided pulse divided into three is irradiated is assumed. In (a), since the influence of heating by the subsequent recording pulse extends forward, the cooling rate after the first recording pulse irradiation is slow, and since Pe is irradiated even in the off pulse section, there is a temperature drop in the off pulse section. The lowest temperature T _{La to} reach remains near the melting point. In (b), since Pb in the off-pulse section is almost 0, T _Lb drops to a point where the melting point is sufficiently lowered, and the cooling rate in the middle is also high. The amorphous mark is melted during the first pulse irradiation and is formed by the subsequent rapid cooling during the off pulse.
As described above, the recording layer in the phase change medium of the present invention is considered to show a large crystallization rate only near the melting point. Therefore, taking the temperature profile shown in FIG.
This is important for suppressing recrystallization and obtaining a good amorphous mark.

On the contrary, by controlling the cooling rate and T _L , the recrystallization is almost completely suppressed, and an amorphous mark having a clear contour which almost coincides with the melting region can be obtained. Is obtained.

On the other hand, in the GeTe-Sb ₂ Te ₃ pseudo binary alloy, there is no great difference in the amorphous mark formation process in any of the temperature profiles of FIGS. 3 (a) and 3 (b). This is because it is considered that recrystallization occurs although the velocity is slightly slow in a wide temperature range. In this case, recrystallization to some extent occurs regardless of the pulse division method, and this tends to cause coarse grains around the amorphous mark to worsen the jitter at the mark edge. With this composition of the recording layer, conventional overwriting by binary modulation, rather than performing off-pulse, is simple and desirable. That is, the off-pulse is suitable for the recording layer of the present invention, but the conventional GeTe-Sb ₂
A Te ₃ recording layer or a main recording layer is disclosed in JP-A-1-3036.
It is not an essential requirement when applied to pit position recording as shown in the 43rd embodiment.

As described above, the medium of the present invention is slow in crystallization and poor in productivity in the initial crystallization in which the recording layer is crystallized in the solid phase at a crystallization temperature or higher. This is considered to be because the composition of this recording layer needs to be once phase-separated from the amorphous state immediately after film formation to form a stable crystalline state, and this phase separation is usually a solid phase (below the melting point). Then, heating for 1 μs or more is required.

For example, when Ge ₂ Sb ₂ Te ₅ is used as the recording layer, the Ge ₁₀ Sb ₆₆ Te ₂₄ film can be crystallized at a sufficiently high speed after the film formation (as-deposited or as-depo. State). When the initial crystallization of a disk having a recording layer such as the above is attempted, many parts remain in an amorphous state without being crystallized. By repeating this operation several tens of times, phase separation may be completed and initialization may be possible, but this is not practical and is not practical. However, once initialized, crystallization (erasing) can be performed at high speed thereafter. as-depo. As-depo is one of the reasons why the film in the as-deposited state is difficult to crystallize.
It is considered that the amorphous state of is unlikely to crystallize unlike the amorphous state of the recording mark. It is also considered that the fact that the crystal nuclei are scarcely present in the recording layer in the as-depo state may cause the crystallization to be difficult. In fact, when observing the part where initial crystallization was attempted with an optical microscope, the part where crystallization was advanced is observed as islands with high reflectance. This can be understood if the crystallization progresses only in the part where the crystal nucleus is formed.

When the initial crystallization is difficult as described above, the productivity is significantly deteriorated. In the present invention, the difficulty of initialization is solved by adding Zn in an appropriate amount. The amount of Zn to be added is 1 atom% or more and is 1 or more in total.
It is preferably less than 0 atomic%. If it is less than 1 atomic%, the addition effect is insufficient, and if it is 10 atomic% or more, the amorphous bit stabilizing effect due to the addition of In is lost. Further, it is considered that a new alloy phase is precipitated, but this is not preferable because jitter at the recording mark edge is deteriorated.

Furthermore, as one method for shortening the time required for the initialization and for surely performing the initialization with one light beam irradiation, it was found that the melt initialization is effective for the recording layer of the present invention. . As long as it has the above-mentioned layer structure, the recording medium is not immediately destroyed by being melted. For example, a light beam (gas or semiconductor laser light) focused to a diameter of 10 to several hundreds μm or a long axis 50 to several hundreds μm
The recording medium will not be destroyed if it is locally heated by using an elliptical light beam with a minor axis of about 1 to 10 μm and melted only in the central portion of the beam. In addition, the peripheral portion of the beam is heated, so that the melted portion is preheated, so that the cooling rate becomes slower, and good recrystallization is performed.

Although melt initialization itself is a known method, it has been found that it is very suitable for the recording medium of the present invention. By using this method, for example, the initialization time can be shortened to 1/10 of the conventional solid-phase crystallization, the productivity can be significantly reduced, and the change in crystallinity during erasing after overwriting can be suppressed. It can be prevented. Conventionally, GeSbT
Although there is an example in which a ternary alloy is used as a phase change medium, it is basically based on a Sb ₂ Te ₃ -GeTe pseudo binary alloy (Japanese Patent Laid-Open Nos. 61-89889 and 62-53886,
No. 62-152786, etc.) is very different from the composition range of the present invention, and the composition range of the present invention has been practically abandoned from the practical application study to the disk.

As mentioned above in some patents, an alloy having a composition near the SbTe eutectic is disclosed (US Pat. No. 46703).
45, JP-A-1-115685, 1-251342,
Nos. 1-303643 and 4-28587).
It is not mentioned that the recording method suitable for the mark length recording disclosed in the present invention is required. Therefore, the limitation of the composition, layer structure and recording method of the present invention is indispensable for making an alloy near the eutectic composition of Sb ₇₀ Te _{30 a} practical phase change medium. It is also surprising to find that even a composition which has been rarely omitted in the past can be initialized once and used in combination with the recording method of the present invention for rather high density recording. Furthermore, it is also industrially important to combine an initialization method suitable for the recording medium of the present invention for initialization in a short time.

[0041]

The present invention will be described in detail with reference to the following examples. In the following examples, evaluation was made on the basis of a rewritable CD, but the recording medium of the present invention is not necessarily limited to a medium of a specific format. In studying the alloy recording layer of the present invention shown below, Zn ₅ In ₅ Sb ₆₀
Te ₃₀ , Zn ₅ In ₃ Sb ₆₀ Te ₃₀ , or Zn ₇ I
n ₅ Sb ₅₃ Te ₃₀ alloy target and Sb, Zn, In
Co-sputtering was used with at least two types of targets such as metal or alloy targets such as Sb and ZnSb.
The composition was adjusted by adjusting the discharge power of each target. The composition of the obtained alloy thin film was measured by fluorescent X-ray intensity calibrated by chemical analysis.

Example 1 On a polycarbonate substrate
(ZnS)₈₀(SiO₂)₂₀The layer is 85 nm, and the recording layer
Zn_FiveIn_FiveSb₆₀Te₃₀Layer 20 nm, (ZnS)₈₀
(SiO₂)₂₀Layer 20 nm, Al_98.5Ta_1.5Alloy layer
170 nm, product sequentially by magnetron sputtering method
Layer and then UV-curing resin 4 μm to make a disk
Made This disk is used for the long axis of the elliptical irradiation beam.
The length of the optical axis is 80 μm and the length of the minor axis is about 1.4 μm.
Using a disc initialization device, linear velocity 3.5 m / s, beam
Feed rate (disk radial direction) 50 μm / revolution, laser
-Attempted melt recrystallization initial crystallization with power of 550 mW
However, the initial crystallization was possible with one scan. Light day
Disk evaluation device (laser wavelength 780 nm, NA 0.5
5), EFM random with a linear velocity of 2.4 m / s
Recording of signals (clock cycle 115nse, the same applies below)
I did. When recording, α in Fig. 2₁= 1, α_i= 0.
5 (i ≧ 2), β _i= 0.5, Pw = 13 mW, P
e = 6.5 mW and Pb = 0.8 mW. That is,
m = n−1 and j = 0.5 (the same applies hereinafter). Real faith
The jitter value indicating the signal characteristic is the shortest mark length and the clock period.
Was less than 10%, and a good value was obtained. Also, 100
This property was maintained even after overwriting 0 times. Furthermore
The recorded signal shows that the temperature is 80 ° C and the humidity is 80% RH.
Doesn't it show deterioration even after left in the environment for 1000 hours?
It was.

Example 2 A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 80 nm and a Zn ₇ In ₅ Sb ₅₈ Te ₃₀ layer having a thickness of 20 nm and a (ZnS) ₈₀ layer as a recording layer were formed on a polycarbonate substrate.
A (SiO ₂ ) ₂₀ layer of 20 nm and an Al _98.5 Ta _1.5 alloy layer of 170 nm were sequentially laminated by a magnetron sputtering method, and an ultraviolet curable resin was further provided to 4 μm to prepare a disk. This disc was used with an optical disc initialization device in which the major axis length of the elliptical irradiation beam was 80 μm and the minor axis length was about 1.4 μm, and the linear velocity was 4 m / s and the beam feed velocity (disc radial direction). When initial crystallization was attempted at 50 μm / rotation and a laser power of 550 mW, the initial crystallization was possible with one scan. 1. Using an optical disk evaluation device (laser wavelength 780 nm, NA 0.55)
EFM random signal recording was performed at a linear velocity of 4 m / s. At the time of recording, in FIG. 2, α ₁ = 1 and α _{i =} 0.5 (i
≧ 2), β _i = 0.5, Pw = 13 mW, Pe =
It was 6.5 mW and Pb = 0.8 mW. The jitter value, which shows the actual signal characteristics, is the shortest mark length and is 10 clock cycles.
It was less than%, and a good value was obtained. Further, this characteristic was maintained even after overwriting 1000 times. Further, the recorded signal was not deteriorated even after being left for 1000 hours in an environment of temperature 80 ° C. and humidity 80% RH.

Comparative Example 1 A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 80 nm and a Ge ₁₂ Sb ₆₆ Te ₂₂ layer having a thickness of 20 nm and a (ZnS) ₈₀ (S
iO ₂ ) ₂₀ layer 20 nm, Al _98.5 Ta _1.5 alloy layer 20
0 nm was sequentially laminated by magnetron sputtering, and an ultraviolet curable resin was further provided at 4 μm to prepare a disk. This disc is used with an optical disc initialization device in which the major axis of the elliptical irradiation beam is 80 μm and the minor axis is about 1.4 μm, and the linear velocity is 2.0 to 5.0 m / s and the beam feed velocity is 10 to 10. 50 μm / rotation, laser power 500
The initial crystallization was tried by irradiating several times with ˜900 mW, but only the initial crystallization with incomplete unevenness was possible. 800 m
Above W, defects were generated due to deterioration due to heat.

(Comparative Example 2) A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 80 nm and a Zn ₅ In ₁₀ Sb ₆₀ Te ₂₅ layer having a thickness of 20 nm as a recording layer were formed on a polycarbonate substrate (ZnS).
_{A 80} (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al _98.0 Ta _2.0 alloy layer having a thickness of 200 nm were sequentially laminated by a magnetron sputtering method, and an ultraviolet curable resin was further provided to a thickness of 4 μm to prepare a disk. Using an optical disk initialization device in which the major axis length of the elliptical irradiation beam is about 80 μm and the minor axis length is about 1.4 μm, a linear velocity of 3 m / s, a beam feed rate of 50 μm / rotation, and a laser beam When the initial crystallization was tried with a power of 600 mW, the initial crystallization was possible with one scanning. Optical disk evaluation device (laser wavelength 780n
m, NA 0.55) was used to record an EFM random signal at a linear velocity of 2.4 m / s. Figure 2 when recording
, Α ₁ = 1, α _i = 0.5 (i ≧ 2), β _i = 0.
5, Pw = 13 mW, Pe = 6.5 mw, Pb =
0.8 mW. The value of the jitter showing the actual signal characteristics was less than 10% of the clock cycle at the shortest mark length, and the initial characteristics were good. However, after overwriting 100 times, the jitter sharply increased. In particular, long marks such as 11T were found to disappear and remain. It is considered that since a large amount of In was contained, segregation occurred and recrystallization (erasing) was hindered.

Comparative Example 3 A (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 80 nm and a Zn ₅ In ₂ Sb ₆₂ Te ₃₁ layer having a thickness of 20 nm and a (ZnS) ₈₀ layer were used as a recording layer on a polycarbonate substrate.
A (SiO ₂ ) ₂₀ layer of 20 nm and an Al _98.0 Ta _2.0 alloy layer of 200 nm were sequentially laminated by a magnetron sputtering method, and an ultraviolet curable resin was further provided to 4 μm to prepare a disk. Using an optical disk initialization device in which the major axis length of the elliptical irradiation beam is 80 μm and the minor axis length is about 1.4 μm, this disk is used with a linear velocity of 4.5 m / s and a beam feed rate of 50 μm / rotation. When the initial crystallization was tried with a laser power of 500 mW, the initial crystallization was possible with one scanning. Optical disc evaluation device (laser wavelength 780
nm, NA 0.55) was used to record an EFM random signal at a linear velocity of 2.4 m / s. At the time of recording, in FIG. 2, α ₁ = 1, α _i = 0.5 (i ≧ 2), β _i =
0.5, Pw = 13 mW, Pe = 6.5 mw, Pb
= 0.8 mW. The jitter value, which shows the actual signal characteristics, is less than 10% of the clock cycle at the shortest mark length,
The initial characteristics were good. Further, the jitter after overwriting 1000 times was also good at less than 10% of the clock cycle. However, the recorded signal shows that the temperature is 80 ° C,
After being left for 500 hours in an environment with a humidity of 80% RH, it deteriorated and the jitter reached 20% of the clock cycle. It was found that the amorphous bits were partially recrystallized and disappeared. It is considered that this is because the amount of In was too small and the crystallization temperature was as low as about 140 ° C., resulting in insufficient thermal stability of the amorphous mark.

(Comparative Example 4) In Example 1, the recording layer was made of Z.
It was n ₁₃ In ₅ Ge ₃ Sb ₅₂ Te ₂₇ . Initialization was performed in the same manner as in Example 1, and an optical disk evaluation device (laser wavelength 78
0 nm, NA 0.55) was used to record an EFM random signal at a linear velocity of 2.4 m / s. At the time of recording, in FIG. 2, α ₁ = 1, α _i = 0.5 (i ≧ 2), β _i =
0.5, Pw = 13 mW, Pe = 6.5 mW, Pb
= 0.8 mW. At the time of the first recording, the jitter value was slightly higher at about 15% of the clock cycle at the shortest mark length. In addition, the jitter increased remarkably after 1000 times of overwriting, which was 20% or more of the clock cycle.

[0048]

By using the recording medium of the present invention, a phase change type optical information recording medium having low jitter, high durability in repeated overwriting, and excellent stability over time in high density mark length recording can be obtained. realizable. Further, by using the optical recording method of the present invention together, more accurate mark length recording can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a layer structure in an optical information recording medium of the present invention.

FIG. 2 is an explanatory diagram showing an example of a laser power irradiation pattern during optical recording on the optical information recording medium of the present invention.

FIG. 3 is a schematic diagram of temperature change when optical recording is performed on the optical information recording medium of the present invention.

[Explanation of symbols]

1 ... substrate 2 ... Lower protective layer 3 ... Recording layer 4 ... Upper protective layer 5 ... Reflective layer 6 ... Protective coat layer

Continuation of the front page (56) Reference JP-A-3-6108 (JP, A) JP-A-1-303643 (JP, A) JP-A-1-251342 (JP, A) JP-A-4-28587 (JP , A) JP 1-115685 (JP, A) JP 8-267926 (JP, A) JP 9-7176 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) B41M 5/26

Claims (4)

(57) [Claims] 1. A multilayer structure comprising at least a lower protective layer, a phase-change optical recording layer, an upper protective layer and a reflective layer on a substrate, wherein the phase-change optical recording layer is ZnαInβSbχTeδ,
0.01 ≦ α <0.1, 0.03 ≦ β ≦ 0.08, 0.
5 <χ <0.7, 0.25 <δ <0.4, α + β + χ +
An optical system having a composition of δ = 1, a crystalline state as an unrecorded state, an amorphous state as a recorded state, and an amorphous bit is overwritten by modulating at least binary light intensity. Information recording medium. 2. The thickness of the phase-change optical recording layer is 15 nm or more 3
0 nm or less, the thickness of the upper protective layer is 10 nm or more and 50 nm
The optical information according to claim 1, wherein the reflective layer is a metal having a thickness of 50 nm or more and less than 500 nm and a volume resistivity of 20 or more and less than 300 nΩ · m and containing 90 atomic% or more of Au, Ag, or Al. Recording medium. 3. When the phase-change optical recording layer and the multi-layer structure are formed, and the recording layer is subjected to an initialization operation of irradiating with an energy beam to crystallize, the recording layer is locally melted and re-formed. claim is crystallized upon solidification 1 or 2
The optical information recording medium described. 4. When recording a mark length modulated information by irradiating a focused light beam on the recording medium according to any one of claims 1 to 3 , a length nT (T is a reference clock period, (n is a natural number of 2 or more) When forming amorphous marks having a natural number of 2 or more, an erasing power Pe for erasing the already recorded amorphous marks is applied between the marks, and a period for applying the recording power Pw is set. α1T, α2T, ..., αm
And the period for which the bias power Pb is applied is β1
As Tβ2T, ... βmT, application periods for laser power are sequentially α1T, β1T, α2T, β2T,
, .Alpha.mT, .beta.mT are used to divide the laser power into m pulses, .alpha.i.ltoreq..beta.i in 2.ltoreq.i.ltoreq.m-1, k is an integer parameter from 0 to 2, and j is 0 to Nmin-, where n is the minimum value of n and is a parameter consisting of real numbers up to 2.
k ≧ 1, m = n−k, α1 + β1 + ... αm + βm =
When n-j, Pw> Pe, 0 <Pb ≦ 0.5Pe
(However, in βmT, 0 <Pb ≦ Pe can be satisfied.) The optical recording method.