JPH10235997A - Phase-changing optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high-density recording by forming a crystal part of a phase change-type optical recording layer of a phase change-type optical recording medium to have a columnar structure perpendicular to a film face and a smaller heat conductivity at a crystal grain boundary than in a crystal grain. SOLUTION: A phase change-type optical recording medium has a dielectric protecting layer 12, a phase change-type optical recording layer 13, a dielectric protecting layer 14 and a reflecting layer 15 sequentially formed on a polycarbonate substrate 11. The phase change-type optical recording layer 13 contains a phase-changing, optical recording material showing different optical characteristics between a crystal state and an amorphous state consequent to the projection of light. Crystals of the phase-changing, optical recording material in the phase change-type optical recording layer 13 are in a columnar structure growing in a thicknesswise direction. A heat conductivity at a crystal grain boundary is smaller than in crystal grains. That is, the phase change-type optical recording layer 13 has a structure wherein an organic compound precipitates at the crystal grain boundary of the phase-changing, optical recording material, so that heat conduction in a direction of a film face can be restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a phase change optical recording medium for recording and reproducing information by irradiating a laser beam.

[0002]

2. Description of the Related Art Optical recording media have supported the rise of personal computers these days as large-capacity storage media having high capacity, high-speed access, and medium portability. Above all, the phase change optical recording medium has been rapidly put into practical use due to its simple recording principle. The principle of the phase change optical recording medium is as follows. During recording, the phase-change optical recording layer is irradiated with a relatively high-power, short-pulse laser beam to heat the recording portion to a temperature equal to or higher than the melting point, and then rapidly cooled to form an amorphous recording mark. At the time of reproduction, the recorded information is read by detecting a change in the reflectance of the recorded portion. At the time of erasing, the phase-change recording layer is irradiated with a long-pulse laser beam with a lower output than at the time of recording, and then gradually cooled to be maintained at a temperature higher than the crystallization temperature and lower than the melting point. As described above, in the phase change optical recording medium, since the change in the reflectance between the amorphous and the crystalline is read, the structure of the optical system is simple. Also, unlike a magneto-optical recording medium, it does not require a magnetic field, is easily overwritten by light intensity modulation, and has a high data transfer speed. Further, C
It is also excellent in compatibility with read-only disks such as D-ROM.

In order to improve the recording density of a phase change optical disk, it is conceivable to shorten the interval between recording marks or to reduce the size of recording marks. Among them, land groove (L / G) recording, mark length recording, and the like have been proposed to shorten the recording mark interval. The L / G record is
The crosstalk is reduced by setting the depth of the group to about 1/6 of the laser wavelength to enable recording on lands and grooves. Compared to the conventional method of recording only on lands or grooves About twice the density can be expected. The mark length recording detects a change in reflectivity (differential component of the reflectivity) at the edge of the recording mark, and can be expected to have approximately 1.5 times higher density than the conventional mark position recording. In addition to such a high-density recording technique, if a super-resolution technique proposed for a ROM medium or the like is used, at present, about 650 Mbps (bit / in)
It is anticipated that it is possible to ch ²⁾ recording density is improved 10-20 times.

However, when the track pitch is further increased in L / G recording, cross-erasure in which recording marks on adjacent tracks are erased during recording becomes a serious problem. Cross-erase occurs not only when the irradiation beam diameter is larger than the track width but also when the irradiation beam diameter is smaller than the track width due to heat conduction to adjacent tracks. That is, when the adjacent recording mark portion is heated to a temperature higher than the crystallization temperature by the irradiation beam, part or all of the recording mark is recrystallized and erased. The cross erase becomes more remarkable as the track pitch increases and the track density increases. To solve this problem, it is conceivable to make the irradiation beam diameter extremely smaller than the track width. Future short wavelength laser (eg 400nm wavelength)
If is commercialized, the irradiation beam diameter can be reduced, but the time of practical use is unknown. Therefore, there is a demand for achieving a higher density by solving the problem of cross-erase without waiting for the development of a short wavelength laser.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-change optical recording medium capable of preventing cross-erasing even if the track pitch is increased in density and enabling high-density recording.

[0006]

A phase-change optical recording medium according to the present invention comprises a phase-change optical recording medium having a phase-change optical recording layer which changes between a crystalline state and an amorphous state by light irradiation. Wherein the crystal part of the phase-change optical recording layer has a columnar structure perpendicular to the film surface, and the thermal conductivity of a crystal grain boundary is smaller than the thermal conductivity of the crystal grain.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The phase change optical recording medium of the present invention has a structure in which various layers including a phase change optical recording layer are laminated on a substrate. For example, a four-layer structure in which a first dielectric protection layer, a phase change optical recording layer, a second dielectric protection layer, and a reflection layer are formed on a substrate can be adopted. In addition, between the substrate and the first dielectric protection layer,
Alternatively, a layer for adjusting thermal conductivity or light absorption may be inserted between the second dielectric protection layer and the reflection layer to form a five-layer structure.

The phase-change optical recording layer constituting the phase-change optical recording medium according to the present invention reversibly transitions between two states, a crystalline state and an amorphous state, by irradiation with light, and has a different optical state between the two states. Phase-change optical recording material exhibiting dynamic characteristics.
Examples of such phase change optical recording materials include GeSbTe,
InSbTe, SnSeTe, GeTeSn, InSe
Semiconductors such as TlCo are mentioned. In this phase-change optical recording layer, the crystal of the phase-change optical recording material has a columnar structure grown in the thickness direction, and the thermal conductivity at the crystal grain boundaries is smaller than the thermal conductivity within the crystal grains. . Specifically, the phase change optical recording layer has a structure in which an organic compound is precipitated at the crystal grain boundary of the phase change optical recording material. Examples of the organic compound include polyimide, polytetrafluoroethylene (PTFE), a hydrocarbon-based polymer (for example, polyethylene), and an epoxy resin.

In general, these organic compounds have a lower thermal conductivity than the phase-change optical recording material. Therefore, in the phase-change optical recording layer having a structure in which the organic compound is aggregated and segregated at the crystal grain boundaries of the phase-change optical recording material. In addition, heat conduction in the film surface direction can be suppressed. Therefore, even when the pitch of the land groove is reduced, the heat conduction to the adjacent track can be suppressed to prevent the cross erase, so that the high density recording can be performed.

In the present invention, the content of the organic compound in the phase-change optical recording layer is preferably 10 vol% or less. This is because when the content of the organic compound exceeds 10 vol%, the organic compound is mixed into the crystal grains, and the recording mark itself becomes unstable. Further, in order to suppress the heat conduction in the film surface direction in the recording layer, it is effective to reduce the crystal grain size of the phase-change optical recording material. From this viewpoint, the average crystal grain size of the phase change optical recording material is 0.1 μm
The following is preferred.

The phase-change optical recording layer of the present invention comprises a method of simultaneously or alternately sputtering a target comprising a semiconductor phase-change optical recording material and a target comprising an organic compound; using a target comprising a plurality of metal materials and an organic compound. It can be formed by sputtering simultaneously or alternately in an inert gas atmosphere of Ar, Ne, Kr or the like containing oxygen, nitrogen or carbon. In either method, a separate target may be used, or a composite target may be used.

In these methods, by adjusting process parameters such as input power, ultimate pressure, sputtering pressure, reactive gas type, substrate bias, and additives,
The crystal grain size, grain spacing, thermal conductivity, and optical characteristics of the recording layer can be controlled. The other layers can be formed in the same manner, and the thermal conductivity and the optical characteristics can be controlled.

Next, other materials constituting the phase change optical recording medium of the present invention will be described. Substrate materials include polycarbonate (PC), polymethyl methacrylate (PMMA), and amorphous polyolefin (AP).
O), glass and the like can be used. Grooves for tracking guide are provided on the surface of the substrate.

The dielectric protective layer is made of SiO ₂ , SiO, Z
nO, Al ₂ O ₃ , CeO, Ta ₂ O ₅ , V ₂ O ₅ , C
oxide ceramics such as aO; AlN, Si ₃ N
₄ , BN, TiN, VN, NbN, TaN, HfN, Z
nitride ceramics such as rN; TiC, ZrC, H
carbide ceramics such as fC, VC, TaC, NbC, WC, B ₄ C, SiC; or ZnS, SIALO
It is preferable to use at least one or more dielectric materials selected from N and the like.

The reflection layer may be a translucent reflection layer or a total reflection layer. Examples of the translucent reflective layer include those using Al, Au, Cu, Si or an alloy containing these and adjusting the film thickness so as to exhibit optical transparency. As a total reflection layer,
Examples thereof include those in which Al, Au, Ti, Cr, Mo, Cu, or an alloy containing them is used and whose film thickness is adjusted so as not to have a light-transmitting property.

These dielectric protective layers, reflective layers, and the like can also be formed by physical vapor deposition or chemical vapor deposition in a vacuum. As described above, in the phase change optical recording medium of the present invention, the dielectric protection layer is provided adjacent to the phase change optical recording layer. The dielectric protective layer protects the recording layer from the atmosphere and prevents mechanical deterioration, and also plays a role in adjusting the temperature rise / fall process of the recording layer. Since the phase change optical recording layer of the present invention has low heat conduction in the film surface direction, it is preferable to increase heat conduction in the film thickness direction to reduce heat accumulation in the recording layer. As a means for achieving this object, adjustment of the film thickness of each layer can be mentioned. For example, the first dielectric protection layer on the substrate is 50 to 200 nm, and the phase change optical recording layer is 10 to 25 n.
m, the second dielectric protection layer on the recording layer is 30 to 200 nm,
It is preferable that the reflective layer has a thickness of 50 to 200 nm.

In the phase-change optical recording medium of the present invention, a counter substrate made of the same material as the above substrate may be bonded on the uppermost layer in order to prevent the substrate from warping and stabilize the recording / reproducing operation. . For the adhesive layer, for example, an ultraviolet curable resin can be used.

[0018]

Embodiments of the present invention will be described below. Embodiment 1 FIG. 1 is a cross-sectional view of a phase change optical recording medium according to an embodiment. ZnS-S on polycarbonate (PC) substrate 11
a first dielectric protection layer 12 made of iO _2, a phase change optical recording layer 13 made of GeSbTe and polyimide, a ZnS—
A second dielectric protection layer 14 made of SiO ₂ and a reflection layer 15 made of Al are sequentially formed.

This phase change optical recording medium was manufactured as follows. The grooved PC substrate 11 was mounted on a substrate holder in a multi-source sputtering apparatus, and after evacuating the inside of the apparatus, Ar gas was introduced. Sputtering was performed while revolving the substrate holder to form each layer sequentially. First,
RF power is applied to the ZnS-SiO ₂ target to perform sputtering, and a first 100 nm-thick
The dielectric protection layer 12 was formed. Next, RF power was applied to the GeSbTe target and the polyimide target, respectively, and sputtering was performed to form a phase change optical recording layer 13 having a thickness of 15 nm on the first dielectric protection layer 12. At this time, the mixing ratio of polyimide in the phase-change optical recording layer was changed by adjusting the throwing power to both targets, and the thermal conductivity, the crystal grain size, and the particle interval were controlled. Note that the thermal conductivity, the crystal grain size, and the particle interval can also be controlled by adjusting the bias power to the substrate, the substrate temperature, and the like. Next, RF power is applied to the ZnS—SiO ₂ target to perform sputtering, and a 200 nm-thick second dielectric protection layer 14 is formed on the phase-change optical recording layer 13.
Was formed. Finally, a DC power was applied to the Al target to perform sputtering, and a reflective layer 15 having a thickness of 100 nm was formed on the second dielectric protection layer 14. For each phase change optical recording medium having recording layers having different polyimide concentrations, recording / reproducing was performed under the conditions shown in Table 1, and the cross erase characteristics were evaluated.

[0020]

[Table 1]

Here, the cross erase characteristic is defined as follows. That is, after recording is performed on the land with the optimum recording power Pw so that the CNR is maximized, the erasing power Pe at which the CNR of the land starts to decrease when both adjacent grooves are DC-erased 200 times is determined. This is used as an index of erase characteristics. Therefore, Pe /
The larger the Pw, the better the cross erase resistance.

FIG. 2 shows the dependency of Pe / Pw on the polyimide concentration. FIG. 2 shows that the cross erase characteristic is most improved when the polyimide concentration is around 5 vol%. It is considered that the reason why the cross erase characteristic does not improve when the polyimide concentration exceeds 10 vol% is that the recording mark itself becomes unstable due to an increase in the polyimide concentration in the crystal grains.

Next, in order to examine the thermal conductivity of the recording layer for each medium, the sample was processed and the thermal conductivity was measured. FIG. 3 shows the dependence of the thermal conductivity of the recording layer on the polyimide concentration. Since the thermal conductivity in this figure is an average value without considering the direction, it decreases monotonically with an increase in the polyimide concentration.

Further, the composition distribution was examined by performing EDX analysis on a minute area of the recording layer. FIG. 4 shows that the polyimide concentration is 7 vol.
5 shows a line profile analyzed in a radial direction from an L / G boundary (measurement position 0) for a recording layer of%. FIG.
In the figure, the polyimide concentration is periodically increased, indicating that the polyimide is preferentially precipitated at the grain boundary of the GeSbTe crystal having a columnar structure. Since polyimide is present at the crystal grain boundaries, it can be expected that heat conduction in the film surface direction is low.

From the above results, if the amount of polyimide added to the recording layer is 10 vol% or less, the polyimide is preferentially precipitated at the grain boundaries of the GeSbTe crystal having a columnar structure, and the direction of the film surface of the recording layer is reduced. It was clarified that the thermal conductivity of the sample could be lowered, and the cross erase characteristic could be improved.

Embodiment 2 The phase-change optical recording medium of this embodiment has a structure similar to that of FIG. 1, but uses a different material and a different film thickness. That is, P
ZnS-SIA on C (polycarbonate) substrate 11
A first dielectric protection layer 12 made of LON, a phase change optical recording layer 13 made of InSbTe and polytetrafluoroethylene (PTFE), a second dielectric protection layer 14 made of ZnS-SIALON, and a reflection layer 15 made of AlMo are formed. It was done.

The phase change optical recording medium of this embodiment was manufactured in the same procedure as in the first embodiment. First, after mounting a PC board with a groove, evacuating and introducing a sputtering gas, Zn
RF power was applied to the S-SIALON target to perform sputtering, and a 200 nm-thick first dielectric protection layer 12 was formed on the substrate. Next, RF power was applied to the InSbTe target and the PTFE target, respectively, and sputtering was performed to form a phase change optical recording layer 13 having a thickness of 15 nm on the first dielectric protection layer 12. At this time, by adjusting the input power to both targets, the mixing ratio of PTFE in the phase-change optical recording layer was changed, and the thermal conductivity, crystal grain size, and grain spacing were controlled. Note that the thermal conductivity, the crystal grain size, and the particle interval can also be controlled by adjusting the bias power to the substrate, the substrate temperature, and the like. Next, R was added to the ZnS-SIALON target.
A second dielectric protection layer 14 having a thickness of 180 nm was formed on the phase-change optical recording layer 13 by applying a power of F and performing sputtering. Finally, a DC power was applied to the AlMo target to perform sputtering, and a reflective layer 15 having a thickness of 50 nm was formed on the second dielectric protection layer 14.

Recording / reproduction was performed for each phase change optical recording medium having recording layers having different PTFE concentrations under the same conditions as in Example 1, and the cross erase characteristics were evaluated. FIG. 5 shows the dependency of Pe / Pw on the PTFE concentration. From this figure, it is recognized that the cross-erasing characteristics are significantly improved when the PTFE concentration is in the range of 0.5 to 6 vol%. Also in this embodiment, by adding PTFE to the recording layer, PTFE is preferentially precipitated at the grain boundary of the InSbTe crystal having a columnar structure, so that the thermal conductivity in the film surface direction of the recording layer can be reduced. It was found that the erase characteristics could be improved.

Embodiment 3 The phase change optical recording medium of this embodiment has a structure similar to that of FIG. 1, but uses a different material and a different film thickness. That is, P
On C (polycarbonate) substrate 11, ZnS-A1 ₂
A first dielectric protection layer 12 made of O _3, a phase change optical recording layer 13 made of GeSbTe and PTFE, ZnS-Al
_{A second} dielectric protection layer 14 made of ₂ O ₃ and a reflection layer 15 made of AlTi are formed.

The phase change optical recording medium of this embodiment was manufactured in the same procedure as in the first embodiment. First, after mounting a PC board with a groove, evacuating and introducing a sputtering gas, Zn
RF power was applied to the S-Al ₂ O ₃ target to perform sputtering, thereby forming a first dielectric protection layer 12 having a thickness of 120 nm on the substrate. Next, RF power was applied to the GeSbTe target and the PTFE target, respectively, and sputtering was performed to form a phase change optical recording layer 13 having a thickness of 10 nm on the first dielectric protection layer 12. At this time, by adjusting the input power to both targets, the mixing ratio of PTFE in the phase-change optical recording layer was changed, and the thermal conductivity, the crystal grain size, and the particle interval were controlled. Note that the thermal conductivity, the crystal grain size, and the particle interval can also be controlled by adjusting the bias power to the substrate, the substrate temperature, and the like. Then, RF to ZnS-A1 ₂ O ₃ target
Power was applied to perform sputtering, and a 200 nm-thick second dielectric protection layer 14 was formed on the phase-change optical recording layer 13. Finally, a DC power was applied to the AlTi target to perform sputtering, and a reflective layer 15 having a thickness of 50 nm was formed on the second dielectric protection layer 14.

For each phase change optical recording medium having recording layers having different PTFE densities, recording / reproduction was performed under the same conditions as in Example 1, and the cross erase characteristics were evaluated. FIG. 6 shows the dependency of Pe / Pw on the PTFE concentration. From this figure, it can be seen that the cross erase characteristics are significantly improved when the PTFE concentration is in the range of 0.5 to 5 vol%. Also in the present embodiment, by adding PTFE to the recording layer, PTFE can be preferentially precipitated at the grain boundary of the GeSbTe crystal having a columnar structure, so that the thermal conductivity in the film surface direction of the recording layer can be reduced. It was found that the erase characteristics could be improved.

Embodiment 4 FIG. 7 shows a sectional view of a phase change optical recording medium in this embodiment. On a polycarbonate (PC) substrate 11, an absorptivity correction layer 16 made of Si and a first layer made of ZnS-SiO ₂
Dielectric protective layer 12, GeSbTe and second dielectric protective layer 14, reflective layer 15 made of Al formed of phase-change optical recording layer 13, ZnS-SiO ₂ made of polyethylene are sequentially formed.

The phase change optical recording medium of this embodiment was manufactured in the same procedure as in the first embodiment. First, after mounting a PC board with a groove, evacuating and introducing a sputtering gas,
DC power was applied to the couget to perform sputtering, and a 10 nm-thickness absorptivity correction layer 16 was formed on the substrate 11. Next, RF power was applied to the ZnS—SiO ₂ target to perform sputtering, thereby forming the first dielectric protection layer 12 having a thickness of 180 nm on the absorptance correction layer 16.
Next, RF power was applied to the GeSbTe target and the polyethylene target, respectively, and sputtering was performed to form a phase change optical recording layer 13 having a thickness of 12 nm on the first dielectric protection layer 12. At this time, by adjusting the input power to both targets, the mixing ratio of polyethylene in the phase-change optical recording layer was changed, and the thermal conductivity, crystal grain size, and particle spacing were controlled. Note that the thermal conductivity, the crystal grain size, and the particle interval can also be controlled by adjusting the bias power to the substrate, the substrate temperature, and the like. Then, Z
RF power is applied to the nS—SiO ₂ target to perform sputtering, and a film thickness of 60 nm is formed on the phase-change optical recording layer 13.
Of the second dielectric protection layer 14 was formed. Finally, a DC power was applied to the Al target to perform sputtering, and a reflective layer 15 having a thickness of 100 nm was formed on the second dielectric protection layer 14.

Recording / reproduction was performed on each phase change optical recording medium having recording layers having different polyethylene concentrations under the same conditions as in Example 1, and the cross erase characteristics were evaluated. FIG. 8 shows the dependency of the cross erase characteristic on the polyethylene concentration. From this figure, it can be seen that the polyethylene concentration is 0.5-6.
It can be seen that the cross-erasing characteristics were significantly improved in the range of vol%. Also in this embodiment, by adding polyethylene to the recording layer, GeSbTe having a columnar structure is formed.
It has been found that polyethylene can be preferentially precipitated at the crystal grain boundaries to reduce the thermal conductivity in the direction of the film surface of the recording layer, thereby improving the cross erase characteristics.

[0035]

As described above in detail, in the phase-change optical recording medium of the present invention, the organic compound is precipitated at the crystal grain boundaries of the recording layer to make the thermal conductivity smaller than within the crystal grains.
Even when the pitch of the land grooves is reduced, cross-erasing for erasing recording marks on adjacent tracks can be suppressed, and high-density recording can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a phase change optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a polyimide concentration of a recording layer of a phase change optical recording medium and cross erase characteristics in Example 1 of the present invention.

FIG. 3 is a diagram showing a relationship between a polyimide concentration and a thermal conductivity of a recording layer of a phase change optical recording medium according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a polyimide concentration distribution of a recording layer of a phase change optical recording medium according to the first embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the PTFE concentration of the recording layer of the phase change optical recording medium and the cross erase characteristic according to the second embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between a PTFE concentration of a recording layer of a phase change optical recording medium and cross erase characteristics in Embodiment 3 of the present invention.

FIG. 7 is a sectional view of a phase-change optical recording medium according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing the relationship between the polyethylene concentration of the recording layer of the phase change optical recording medium and the cross erase characteristic in Example 4 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Polycarbonate board 12 ... 1st dielectric protection layer 13 ... Phase change optical recording layer 14 ... 2nd dielectric protection layer 15 ... Reflection layer 16 ... Absorption rate correction layer

Claims (2)

[Claims] 1. A phase-change optical recording medium comprising a phase-change optical recording layer that transitions between a crystalline state and an amorphous state by light irradiation, wherein a crystal part of the phase-change optical recording layer has a film surface. A phase-change optical recording medium characterized by having a columnar structure perpendicular to a crystal grain and having a thermal conductivity at a crystal grain boundary smaller than a thermal conductivity within a crystal grain. 2. The phase change optical recording medium according to claim 1, wherein the crystal grain boundaries of the phase change optical recording layer are made of an organic compound.