JP2008305445A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase-change optical recording medium wherein a large capacity and high speed recording are possible and satisfactory rewrite property is obtained. <P>SOLUTION: An information recording medium is provided with: a substrate; a first dielectric layer provided on the substrate; a first interface layer which is provided on the first dielectric layer and formed of either a material containing hafnium oxide and stannic oxide or a material containing hafnium oxide and chrome oxide; a recording layer which is provided on the first interface layer and formed of a phase-change material; a second dielectric layer provided on the recording layer; and a reflection layer provided on the second dielectric layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an information recording medium on which information is recorded by laser beam irradiation, and more particularly to a phase change optical disc capable of high density recording.

  In recent years, the capacity of hard disk drives (HDD) has increased, the functionality of personal computers (PCs) has increased, the distribution of data and images using the Internet has become popular, the appearance of high-definition cameras capable of shooting high-resolution images, etc. As a result, the amount of data handled by a home video recorder equipped with a PC or HDD has increased dramatically. Accordingly, there is an increasing need for a large-capacity removable medium necessary for backup of data stored in the HDD.

  There is a phase change optical recording medium as one of removable and rewritable information recording media. A phase change optical recording medium includes a recording layer in which an atomic arrangement reversibly changes between two different states (between amorphous and crystal) by irradiation with a light beam, and the two different atomic arrangement states of the recording layer Information is recorded.

  Phase change type optical recording media are particularly inexpensive among rewritable media, and thus are widely used as consumer media. In particular, they are rapidly spreading as home video recording media such as DVD recorders. A video recording medium that has been a tape until now is replaced with a phase-change optical recording medium, thereby enabling a new function such as follow-up reproduction. Therefore, in such an application, advanced characteristics more than those of the phase change type optical recording medium that has been necessary as a backup medium for computers are required.

  For example, when the follow-up playback is performed, it is necessary to switch back and forth between recording and playback at a constant time since it is necessary to playback the image just recorded during the recording. For this purpose, it is necessary to increase the access speed for recording and reproducing information. Furthermore, a rewritable phase change recording medium capable of high-speed recording is required to record information satisfactorily in conventional low-speed recording as well as to enable high-speed recording of information. For example, in the case of a 4.7-GB DVD-RAM using the current red laser, the recording linear velocity (double speed) defined in the standard is 8.2 m / s, but it is compatible with five-times speed recording. In the DVD-RAM, it is required to have good recording performance in a very wide linear velocity range of 8.2 m / s to 20.5 m / s. Also, in the broadcasting field, digitalization and high-definition are being promoted. In such applications, recorded images have higher definition. Therefore, as a recording medium, not only high-speed information recording described above but also large-scale recording is possible. Capacity is also required.

As a phase change recording layer material capable of high-speed recording, a Ge—Sb—Te-based material having a composition on a line connecting GeTe and Sb ₂ Te ₃ in a triangular composition diagram having Ge, Sb and Te as vertices, It is often used because of its high crystallization speed. Furthermore, it has been conventionally known that the crystallization speed is further increased by replacing GeTe in the Ge—Sb—Te phase change material with SnTe. However, for example, according to Japanese Patent Laid-Open No. 2006-182005, when GeTe in a Ge—Sb—Te phase change material is replaced with SnTe, the recording layer in a crystalline state and an amorphous state (amorphous state) as Sn increases. Crystal growth from the outer edge of the molten region during the cooling process immediately after the recording layer is heated to the melting point or higher by the laser beam because the difference in refractive index is small or the recording layer is crystallized too fast on the low linear velocity side. Occurs, so-called recrystallization occurs, which reduces the recording mark size. Thus, when recrystallization occurs on the low linear velocity side, there arises a problem that the reproduction signal becomes small, and it becomes difficult to satisfy the characteristics in a wide linear velocity range from low speed to high speed.

  In addition, a Bi—Ge—Te phase change material has been proposed as a recording layer material capable of high-speed recording and capable of dealing with a wide linear velocity range (see, for example, Patent Document 1). Patent Document 1 also describes a composition range of a Bi—Ge—Te phase change material capable of high-speed recording and capable of dealing with a wide linear velocity range.

  On the other hand, as a technology for increasing the capacity of the phase change optical recording medium, the red laser used in the conventional DVD is changed to a blue laser, that is, the wavelength of light is shortened from about 650 nm to about 405 nm, There is a method for recording higher density information by reducing the laser spot diameter. Currently, Blu-ray Disc and HD-DVD have been proposed and standardized as disks using blue laser light having a wavelength of 405 nm.

  In general, it is known that the spot diameter of a laser beam is proportional to λ / NA when the laser wavelength is λ and the lens numerical aperture NA. Blu is used using a semiconductor laser having a wavelength of 405 nm and an objective lens having a numerical aperture NA of 0.85. In the case of -ray Disc, the laser spot diameter is about half of the laser spot diameter (semiconductor laser having a wavelength of 650 nm, objective lens having a numerical aperture NA of 0.60) used in a conventional DVD. Also, in the case of HD DVD using a semiconductor laser having a wavelength of 405 nm and an objective lens having a numerical aperture NA of 0.65, the laser spot diameter is as small as about 60% of that in the case of a conventional DVD.

Furthermore, the rewritable phase change optical recording medium has repeated rewriting durability as an important characteristic required in addition to the above-described high speed and large capacity. In the phase change type optical recording medium, the recording layer is heated to the melting point or higher by a laser beam at the time of recording, and then cooled. Therefore, when information is rewritten repeatedly, the recording layer and ZnS-SiO ₂ adjacent to the recording layer are used. The constituent elements of both layers invade and diffuse into each other's layers, and the constituent elements of both layers cause a chemical reaction with each other. When rewriting is performed repeatedly, there arises a problem that characteristics deteriorate.

In order to prevent the intrusion, diffusion and chemical reaction of the constituent elements between the two layers, conventionally, an interface layer has been provided between the recording layer and the protective layer to prevent chemical reaction and atomic diffusion between the protective layer and the recording layer, and rewrites repeatedly. An information recording medium having a structure for improving durability has been proposed (see, for example, Patent Documents 2 to 6). In Patent Documents 2 to 4, a mixture of Ta ₂ O ₅ and Cr ₂ O ₃ is formed in the interface layer on the laser beam incident side of the recording layer. Patent Document 5 proposes a rewritable phase change optical recording medium for blue laser, a recording layer is formed of a Ge—Sb—Te phase change material, and a film containing hafnium oxide in an interface layer; More specifically, an HfO ₂ film or a film formed of a material obtained by mixing CeO ₂ , TiO ₂ , and ZrO ₂ with HfO ₂ is used. Further, Patent Document 6 proposes a rewritable phase change optical recording medium in which the interface layer is formed of a film containing hafnium, oxygen and nitrogen.

JP 2004-155177 A JP 2003-178487 A JP 2005-285165 A JP 2006-182005 A JP 2004-171724 A JP 2006-103067 A

In the above-mentioned patent document 1, the present inventors use BiGeTe suitable for high speed as the recording layer material in the rewritable DVD using the conventional red laser, and Cr ₂ O ₃ and Ta ₂ O _{5 as the} interface layer material. It was confirmed that high-speed recording was possible and sufficient rewriting characteristics were obtained when this mixture was used. Therefore, the present inventors use a Bi—Ge—Te-based material as the recording layer material in order to further increase the capacity, and Cr ₂ O ₃ —Ta ₂ O as the first interface layer material on the light incident side. _When information was recorded / reproduced using a blue laser on a rewritable phase change recording medium using the ₅ mixture, rewriting durability equivalent to that obtained using a conventional red laser could not be obtained.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a large-capacity phase-change optical recording medium capable of high-speed recording and obtaining good rewriting characteristics. is there.

  According to an aspect of the present invention, there is provided an information recording medium, a substrate, a first dielectric layer provided on the substrate, a hafnium oxide provided on the first dielectric layer, and a tin oxide. Alternatively, a first interface layer formed of a material containing chromium oxide, a recording layer formed on the first interface layer and formed of a phase change material, and a second dielectric provided on the recording layer There is provided an information recording medium including a layer and a reflective layer provided on the second dielectric layer.

As described above, the present inventors use a Bi—Ge—Te-based material that can record at high speed and can correspond to a wide linear velocity range as the recording layer material, and Cr ₂ is used as the first interface layer material on the light incident side. When information was recorded / reproduced using a blue laser on a rewritable phase change recording medium using an O ₃ —Ta ₂ O ₅ mixture, the rewriting durability was the same as when a conventional red laser was used. It was not obtained. This is considered due to the following causes.

  Even in the case of a medium having an interface layer between the recording layer and the dielectric layer (protective layer), the characteristic deterioration due to rewriting is caused by repeated rewriting and the portion irradiated with the laser beam. Since the thermal expansion and contraction are repeated between and the other parts, a crack occurs in the interface layer, and the intrusion, diffusion and chemical reaction of constituent elements occur between the recording layer and the dielectric layer through the crack. It may have occurred. In particular, when a blue laser is used, the beam spot diameter is smaller than that of a red laser, and the energy intensity at the center of the beam is increased. Therefore, when repeated rewriting is performed using a blue laser, the recording layer is repeatedly melted and cooled more locally and at a higher temperature. It is done.

Further, as disclosed in Patent Document 1, the composition of the Bi—Ge—Te rough change material that is suitable for high-speed recording and can correspond to a wide linear velocity range is in the vicinity of Ge ₅₀ Te ₅₀ , Bi ₂ Te ₃ is added, and there is more Ge than the linear composition connecting Ge ₅₀ Te ₅₀ and Bi ₂ Te ₃ on the triangular composition diagram with Bi, Ge, and Te as vertices. The composition of the region. However, since Ge ₅₀ Te _{50 has} a high melting point of about 725 ° C. and Ge has a high melting point of about 937 ° C., the melting point of the Bi—Ge—Te coarse change material having the above composition is at least 700 ° C. or more. On the other hand, the melting point of the conventional Ge—Sb—Te or Ge—Sb—Sn—Te phase change material is about 650 ° C. Therefore, when information is recorded on the recording layer made of a Bi—Ge—Te phase change material, the information recording is performed on the recording layer made of a Ge—Sb—Te type or Ge—Sb—Sn—Te type phase change material. It is necessary to heat the recording layer to a higher temperature than in the case of performing the above, and it is considered that the influence of the above-described thermal stress is greater than in the conventional case. That is, the Bi—Ge—Te based coarse change material is a material that is disadvantageous in repeated rewriting durability as compared with the conventional recording layer material.

  From the above, when information recording is performed on a recording layer made of a Bi—Ge—Te phase change material using a blue laser, it is considered that the influence of the above-described thermal stress becomes very large. It is considered that sufficient rewriting durability could not be obtained with the interface layer material used in the phase change optical recording medium compatible with the red laser.

In addition, the inventors of the present invention use a conventionally used HfO ₂ film or HfO ₂ with CeO ₂ , TiO _{2 in a} phase change optical recording medium having a recording layer made of a Bi—Ge—Te phase change material. , ZrO ₂ mixed material was used as the first interface layer on the light incident side, and a recording medium was evaluated using a blue laser. However, although sufficient characteristics were obtained as initial characteristics after overwriting 10 times, the characteristics deteriorated rapidly when rewriting was repeated, and sufficient rewriting durability as a rewritable phase change recording medium was obtained. I found it impossible.

  Therefore, in order to solve the above-mentioned problems, the present inventors are made of a phase change material capable of high-speed recording (for example, a phase change material such as Bi—Ge—Te, Ge—Sb—Sn—Te). In a phase change optical recording medium having a recording layer, studies have been made on the formation material of the first interface layer located on the light incident side of the recording layer. As the formation material of the first interface layer, hafnium oxide and tin oxide are used. It has been found that a phase change optical recording medium compatible with a blue laser can be provided, which can provide good rewriting characteristics when a material containing, or a material containing hafnium oxide and chromium oxide is used. That is, by using a material containing hafnium oxide and tin oxide or a material containing hafnium oxide and chromium oxide as a material for forming the first interface layer, high-speed recording is possible and good rewriting characteristics are obtained. It was found that the obtained large-capacity phase change optical recording medium can be obtained.

  In the information recording medium of the present invention, the first interface layer is preferably formed of a material containing hafnium oxide and tin oxide, and the ratio of tin oxide contained in the material is preferably 5 to 15 mol%.

  In the information recording medium of the present invention, the first interface layer is formed of a material containing hafnium oxide and chromium oxide, and the ratio of the chromium oxide contained in the material is 2.5 to 10 mol%. Is preferred.

The hafnium oxide contained in the first interface layer of the present invention is represented as HfO _{2 in the} stoichiometric composition, but it is difficult to increase the purity of HfO ₂ in the purification process of Hf, which is a raw material base material. Zirconium (Zr), titanium (Ti), and the like are mixed as an impurity element in an amount of about 1 to 2%. However, even if the impurity element or the oxide thereof is contained in this amount in this amount in the first interface layer, it does not affect the effect of the present invention and does not depart from the scope of the present invention.

  In the information recording medium of the present invention, the recording layer is preferably formed of a phase change material containing Bi, Ge, and Te. As described above, the Bi-Ge-Te phase change material is suitable for high-speed recording and can be used in a wide linear velocity range. Therefore, the present invention has a recording layer formed of a Bi-Ge-Te phase change material. In this information recording medium, it is possible to deal with a wide linear velocity range and to obtain good rewriting characteristics. As a material for forming the recording layer, a phase change material such as a Ge—Sb—Te system or a Ge—Sb—Sn—Te system may be used other than the Bi—Ge—Te system.

In the information recording medium of the present invention, it is preferable that a second interface layer is further provided between the recording layer and the second dielectric layer. As the material for forming the second interface layer, any material can be used as long as it can prevent the intrusion, diffusion and chemical reaction of the constituent elements between the recording layer and the second dielectric layer. For example, as the material for forming the second interface layer, a material (such as Cr ₂ O ₃ ) conventionally used for a phase change optical recording medium compatible with a red laser may be used.

  According to the information recording medium of the present invention, the first interface layer disposed on the light incident side of the recording layer is formed of a material containing hafnium oxide and tin oxide, or a material containing hafnium oxide and chromium oxide. Thus, it is possible to provide a large-capacity phase-change optical recording medium capable of high-speed recording and obtaining good rewriting characteristics.

  Examples of the information recording medium of the present invention will be specifically described below, but the present invention is not limited thereto.

[Optical disk and manufacturing method thereof]
A schematic cross-sectional view of the phase change type optical disc (sample No. 1) produced in Example 1 is shown in FIG. As shown in FIG. 1, an optical disc 100 manufactured in this example has a first dielectric layer 2, a first interface layer 3, a recording layer 4, a second interface layer 5, and a second dielectric layer 6 on a substrate 1. The blocking layer 7, the reflective layer 8, the protective layer 9, and the dummy substrate 10 are stacked in this order. In the optical disc 100 of this example, as shown in FIG. 1, a laser beam 200 is incident from the substrate 1 side.

  In addition, the optical disc 100 manufactured in this example is a medium in which a relationship of Rc> Ra is established between the reflectance Rc of the crystal part which is an unrecorded part and the reflectance Ra of the amorphous part which is a recording part. This is a so-called High-to-Low medium.

  Next, a manufacturing method of the optical disc 100 of this example will be described. First, a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.6 mm was prepared as the substrate 1. The substrate 1 was produced by injection molding, and grooves having a depth of 30 nm were formed on the substrate 1 at a pitch of 0.4 μm. Next, the substrate 1 is set in a sputtering apparatus capable of reducing the film thickness distribution and having high reproducibility, and the first dielectric layer 2 to the reflective layer 8 are formed on the surface of the substrate 1 on which the grooves are formed by sputtering. Formed. As the sputtering apparatus, a plurality of sputtering chambers were provided, and each sputtering chamber was equipped with a plurality of sputtering targets, and an apparatus capable of simultaneous sputtering was used.

A (ZnS) _80- (SiO ₂ ) ₂₀ [mol%] film having a thickness of 60 nm was formed on the substrate 1 as the first dielectric layer 2.

Next, an HfO ₂ —SnO ₂ film having a thickness of 5 nm was formed as the first interface layer 3 on the first dielectric layer 2. At this time, HfO ₂ and SnO ₂ were used as the sputtering target, and the first interface layer 3 was formed by simultaneous sputtering. In this example, the mixing ratio of HfO ₂ and SnO _{2 in} the first interface layer 3 is HfO ₂ : SnO ₂ = 95: 5 mol%, that is, included in the forming material of the first interface layer 3. The sputtering power applied to each sputtering target was adjusted so that the ratio of SnO ₂ to be 5 mol%.

Next, a Bi ₅ Ge _44.2 Te _50.8 (at%) film having a thickness of 12.5 nm was formed as the recording layer 4 on the first interface layer 3. Next, a Cr ₂ O ₃ film having a thickness of 3 nm was formed as the second interface layer 5 on the recording layer 4. Next, a (ZnS) _80- (SiO ₂ ) ₂₀ [mol%] film having a thickness of 14 nm was formed as the second dielectric layer 6 on the second interface layer 5. Next, a Cr ₂ O ₃ film having a thickness of 3 nm was formed as the blocking layer 7 on the second dielectric layer 6. Next, an AgCu (1 wt%) Ca (500 ppm) film having a thickness of 100 nm was formed on the blocking layer 7 as the reflective layer 8. In this example, when the layers other than the first interface layer 3 are formed by sputtering, a sputtering target having a composition corresponding to the film to be formed is used.

  Next, the disk on which the first dielectric layer 2 to the reflective layer 8 were formed on the substrate 1 was taken out from the sputtering apparatus. Next, an ultraviolet curable resin was applied as a protective layer 9 on the reflective layer 8, and a polycarbonate dummy substrate 10 having a thickness of 0.6 mm was placed thereon. Subsequently, the dummy substrate 10 was bonded together by irradiating the dummy substrate 10 with ultraviolet rays and curing the ultraviolet curable resin. In this example, the optical disk 100 having the structure shown in FIG. 1 was produced as described above.

  In this example, the film thicknesses of the first dielectric layer 2 and the second dielectric layer 6 are in the range where the reflectance R in the unrecorded state is 11 to 15% in accordance with the optical constant of the first interface layer 3. In addition, the film thickness was adjusted so that the modulation degree of the recording / reproducing signal was 0.45 or more. In the optical disc 100 manufactured in this example, the reflectance R in the unrecorded state was 13.6%, and the degree of modulation was 0.54.

  Next, the optical disc 100 obtained by the above manufacturing method is mounted on an initialization apparatus (not shown), and an elliptical laser beam having a wavelength of 810 nm, a beam spot major axis of 100 μm, and a minor axis of 1 μm is applied to the entire surface of the optical disc 100. The recording layer 4 was initially crystallized.

In this example, as described above, the first dielectric layer 2 and the second dielectric layer 6 are formed of a mixture of (ZnS) ₈₀ (SiO ₂ ) ₂₀ , but the present invention is not limited to this, for example, A material in which the mixture ratio of the mixture of ZnS and SiO ₂ is changed, an oxide such as SiO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , or a nitride such as Si—N, Al—N, Ge—N, etc. is used. obtain.

In this example, the second interface layer 5 is formed of a Cr ₂ O ₃ film. However, the present invention is not limited to this, and the diffusion of constituent elements between the recording layer 4 and the second dielectric layer 6 can be improved. Any material can be used as long as the material has an effect of preventing entry and reaction. When the second dielectric layer 6 is formed of a material that does not react with the recording layer 4 or has a low reactivity (for example, a material that does not contain S), the second interface layer 5 is not provided. Also good.

  In this example, an AgCu (1 wt%) Ca (500 ppm) film is used as the reflective layer 8, but the present invention is not limited to this. For example, the composition ratio of the AgCaCu film is changed, and Ag is the main component. An alloy or an alloy containing Al as a main component can be used.

The blocking layer 7 reacts with Ag in the Ag alloy film used as the reflective layer 8 and S (sulfur) in the mixture of the (ZnS) ₈₀ (SiO ₂ ) ₂₀ film used in the second dielectric layer 6. This layer is provided in order to prevent the recording characteristics from being deteriorated by the recording. In this example, Cr ₂ O ₃ is used as a material for forming the blocking layer 7, but the present invention is not limited to this, and reaction between Ag in the reflective layer 8 and S in the second dielectric layer 6 is prevented. In addition, any material can be used as long as the material is excellent in adhesion between the Ag alloy film of the reflective layer 8 and the (ZnS) ₈₀ (SiO ₂ ) ₂₀ film of the second dielectric layer 6. If the second dielectric layer 6 and the reflective layer 8 do not react with each other or are made of a material with low reactivity, the blocking layer 7 may not be formed.

In the optical disk of Example 2 (Sample No. 2), the first interface layer 3 was formed of a 5 nm thick HfO ₂ —Cr ₂ O ₃ film. At this time, HfO ₂ and Cr ₂ O ₃ were used as the sputtering target, and the first interface layer 3 was formed by simultaneous sputtering. In this example, the sputtering power applied to each sputtering target so that the mixing ratio of HfO ₂ and Cr ₂ O ₃ in the first interface layer 3 is HfO ₂ : Cr ₂ O ₃ = 95: 5 mol%. Adjusted. The optical disc of this example has the same configuration as that of Example 1 except that the material for forming the first interface layer 3 is changed. In the optical disc 100 manufactured in this example, the reflectance R in an unrecorded state was 13.2%, and the modulation factor was 0.50.

In the optical disc of Example 3 (sample No. 3), the recording layer 4 was formed of a Ge ₂₄ Sb ₁₀ Sn ₁₄ Te ₅₂ (at%) film having a thickness of 11 nm. In this example, the second dielectric layer 6 is formed of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of 10 nm. In this example, the configuration of the optical disk other than the recording layer 4 and the second dielectric layer 6 is the same as that of the first embodiment. In the optical disc 100 manufactured in this example, the reflectance R in the unrecorded state was 14.3%, and the modulation factor was 0.50.

In the optical disk of Example 4 (sample No. 4), the recording layer 4 was formed of a Ge ₂₄ Sb ₁₀ Sn ₁₄ Te ₅₂ (at%) film having a thickness of 11 nm. In this example, the second dielectric layer 6 is formed of a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of 10 nm. In this example, the configuration of the optical disk other than the recording layer 4 and the second dielectric layer 6 is the same as that of the second embodiment. In the optical disc 100 manufactured in this example, the reflectance R in the unrecorded state was 14.0%, and the modulation factor was 0.47.

[Comparative Example 1]
In the optical disk of Comparative Example 1, the first interface layer 3 was formed of a Cr ₂ O ₃ —Ta ₂ O ₅ film having a thickness of 5 nm. At this time, Cr ₂ O ₃ and Ta ₂ O ₅ were used as the sputtering target, and the first interface layer 3 was formed by simultaneous sputtering. In this example, each sputter target is mixed so that the mixing ratio of Cr ₂ O ₃ and Ta ₂ O ₅ in the first interface layer 3 is Cr ₂ O ₃ : Ta ₂ O ₅ = 60: 40 mol%. The sputtering power to be applied was adjusted. The optical disc of this example has the same configuration as that of Example 1 except that the material for forming the first interface layer 3 is changed. In the optical disc 100 manufactured in this example, the reflectance R in an unrecorded state was 13.0%, and the degree of modulation was 0.48. The material for forming the first interface layer 3 used in this example is a material used in a conventional rewritable DVD compatible with a red laser. In the rewritable DVD compatible with a red laser, the first interface layer 3 has a Cr layer in the first interface layer. Sufficient rewriting durability is obtained by using the ₂ O ₃ —Ta ₂ O ₅ film.

[Comparative Example 2]
In the optical disc of Comparative Example 2, the first interface layer 3 was formed of a 5 nm thick HfO ₂ film. At this time, HfO ₂ was used as a sputtering target. The optical disc of this example has the same configuration as that of Example 1 except that the material for forming the first interface layer 3 is changed. In the optical disc 100 manufactured in this example, the reflectance R in an unrecorded state was 14.0%, and the degree of modulation was 0.54. In addition, HfO ₂ is a material conventionally used as a material for forming an interface layer of a rewritable phase change medium compatible with a blue laser in, for example, Patent Document 5 described above.

[Characteristic evaluation]
Next, characteristics evaluation of the optical disc 100 manufactured in Examples 1 to 4 and Comparative Examples 1 and 2 was performed using a disc evaluation apparatus ODU-1000 manufactured by Pulstec Industrial Co., Ltd. This evaluation apparatus includes a blue-violet semiconductor laser having a wavelength of 405 nm and an objective lens having a numerical aperture NA of 0.65. Further, in the evaluation method of this example, a method of recording information on a portion that becomes a convex portion of the substrate 1 when viewed from the light incident side, that is, a so-called groove recording method is adopted. The recording conditions were set so that the linear velocity was 6.61 m / s and the channel bit length T = 0.102 μm.

  In this example, the bit error rate bER (initial bER characteristic) after 10 overwrite recordings was evaluated as the initial characteristic. In addition, as the repeated rewrite characteristics, the number of rewrites when the bit error rate deteriorated by two digits was evaluated from the bit error rate bER after 2000 rewrites and the initial bER characteristic. In this example, it is assumed that the number of rewrites causing no problem in actual use is 2000. In addition, when the deterioration of the bER from the initial bER after 2000 rewrites is less than 2 digits, the number of rewrites in which the bER deteriorates by 2 digits is set to 2000 or more.

  In the above evaluation, the bit error rate bER was measured as follows. First, a random pattern of RLL (1, 10) modulation method including patterns from 2T to 13T is randomly recorded on the measurement track, and then the same random pattern is recorded on the adjacent tracks on both sides of the measurement track. Returning to the measurement track, bER was measured.

  The evaluation results are shown in FIG. Sample No. 2 in FIG. 1 to 4 correspond to the optical disks of Examples 1 to 4, respectively. FIG. 2 also shows the film configuration (formation material, composition or mixing ratio, and film thickness) of each sample, the reflectance R in the unrecorded state, and the degree of modulation.

Moreover, although the comprehensive evaluation of the evaluation result of each sample was described by (double-circle), (circle), (triangle | delta), and x in the lowest stage of FIG. 2, these evaluation criteria are as follows.
◎: When the bER degradation after 2000 rewrites is less than 2 digits and the bER after 2000 rewrites is 5.0E-5 or less. ○: The bER degradation after 2000 rewrites is 2 digits or more. When bER after 2000 rewrites is 1.0E-04 or less and the number of rewrites when bER deteriorates by 2 digits is 1000 or more. Δ: bER after 2000 rewrites from 1.0E-4 Large and the number of rewrites when the bER deteriorates by two digits is 1000 or more x: The number of rewrites when the bER after 2000 rewrites is greater than 1.0E-4 and the bER deteriorates by two digits Is less than 1000 times

  Here, the content of the evaluation criteria will be described more specifically. At the current technical level, the error-correctable bER is practically 1.0E-4 or less. In consideration of manufacturing variations of optical disks, margins of recording conditions, and the like, the actual use level of bER is 5.0E-5 or less. Therefore, according to the above evaluation criteria, ◎ evaluation is when bER after 2000 rewrites is at the actual use level and has excellent rewrite endurance. ○ Evaluation shows that bER degradation after 2000 rewrites is 2 digits or more, but bER after 2000 rewrites is at a level where error correction is possible, and the number of rewrites when bER degrades by 2 digits is the conventional optical disc (For example, the optical disk of Comparative Examples 1 and 2) is increased. The evaluation is a case where the number of rewrites when the bER deteriorates by two digits increases compared to the conventional case, although the bER after 2000 rewrites exceeds the level capable of error correction. In addition, x evaluation is a case where the bER after 2000 rewrites exceeds a level capable of error correction, and the number of rewrites when the bER deteriorates by two digits is small.

As is clear from FIG. 2, good initial bER characteristics were obtained in any of the optical disks manufactured in Examples 1 to 4 and Comparative Examples 1 and 2, but both of the optical disks of Comparative Examples 1 and 2 were 2000. The number of rewrites in which the bER deteriorated by 2 digits or more after the rewrite and the bER deteriorated by 2 digits was 100 times and 300 times, respectively, and the overall evaluation was x. On the other hand, in each of the optical disks of Examples 1 to 4, the bER degradation after 2000 rewrites is less than 2 digits, the bER after 2000 rewrites is 5.0E-5 or less, and the bER is The number of rewrites when it deteriorated by two digits exceeded 2000, and the overall evaluation was ◎ evaluation. That is, from the evaluation results of FIG. 2, in the optical disk in which the recording layer is formed of a material suitable for high-speed recording in Examples 1 to 4, the first interface layer 3 is formed as an HfO ₂ —SnO ₂ film or an HfO ₂ —Cr ₂ O _3. It was found that a phase change optical disc compatible with a blue laser capable of high-speed recording and having excellent rewriting characteristics can be provided by forming the film. In particular, when a Bi-Ge-Te-based material is used as the phase change material of the recording layer, the Bi-Ge-Te-based material is a material capable of high-speed recording and compatible with a wide linear velocity range as described above. Therefore, it has been found that a blue laser compatible (large capacity) phase change optical disk capable of supporting a wide linear velocity range and obtaining good rewriting characteristics can be provided.

In Example 5, various optical disks were manufactured by changing the mixing ratio of HfO ₂ and SnO _{2 in} the first interface layer 3 in the optical disk 100 of Example 1.

Specifically, the proportion of SnO ₂ contained in the first interface layer 3 is 2.5 mol% (sample No. 5), 5 mol% (sample No. 1: optical disc of Example 1), 7.5 mol% (sample) No. 6) Various optical discs with 10 mol% (sample No. 7), 12.5 mol% (sample No. 8), 15 mol% (sample No. 9) and 17.5 mol% (sample No. 10). Produced. The first interface layer 3 was formed by co-sputtering using two sputter target HfO ₂ and SnO _2, adjustment of the mixing ratio of HfO ₂ and SnO ₂ of the first interface layer 3, use The sputtering power applied to each of the sputtering targets was adjusted. These various optical discs were manufactured in the same manner as in Example 1 except that the mixing ratio of HfO ₂ and SnO _{2 in} the first interface layer 3 was changed.

  Sample No. In the optical discs of 8 to 10, the thicknesses of the first dielectric layer 2 and the second dielectric layer 6 are in the range where the unrecorded reflectance R is 11 to 15% in accordance with the optical constants of the first interface layer 3. Further, the film thickness was changed from that of Example 1 so that the modulation degree of the recording / reproducing signal was 0.45 or more. Specifically, sample no. In 8-10 optical disks, the film thickness of the first dielectric layer 2 was 62 nm, and the film thickness of the second dielectric layer 6 was 13 nm.

  The rewriting characteristics were also evaluated for the various optical discs in the same manner as in Examples 1 to 4. The results are shown in FIG. The standard of comprehensive evaluation in FIG. 3 is the same as the standard of Examples 1-4. FIG. 3 also shows the film configuration of each sample, the reflectance R in the unrecorded state, and the degree of modulation.

  As is clear from FIG. 1 and no. In all of the optical discs 6 to 9, the bER deterioration after 2000 rewrites is less than 2 digits, the bER after 2000 rewrites is 5.0E-5 or less, and the bER deteriorates by 2 digits. The number of rewrites exceeded 2000, and the overall evaluation was ◎ evaluation.

  Sample No. 5 and no. In all of the 10 optical discs, although the bER degradation after 2000 rewrites is 2 digits or more, the bER after 2000 rewrites is 1.0E-04 or less (at a level where error correction is possible), and When the bER deteriorated by two digits, the number of rewrites was 1000 or more, which was a good evaluation.

From the result of FIG. 3, in the optical disk using the HfO ₂ —SnO ₂ film for the first interface layer 3, the ratio of SnO ₂ contained in the first interface layer 3 is 2.5 mol% to 17.5 mol%. It was found that good repeated rewriting characteristics (◎ and ○ evaluations) were obtained. In particular, it has been found that when the proportion of SnO ₂ contained in the first interface layer 3 is 5 mol% to 15 mol%, further excellent repeated rewriting characteristics (◎ evaluation) can be obtained.

In Example 6, various optical disks were prepared by changing the mixing ratio of HfO ₂ and Cr ₂ O ₃ in the first interface layer 3 in the optical disk 100 of Example 2.

Specifically, the ratio of Cr ₂ O ₃ contained in the first interface layer 3 is 2.5 mol% (sample No. 11), 5 mol% (sample No. 2: optical disc of Example 2), 7.5 mol%. (Sample No. 12), 10 mol% (Sample No. 13), 12.5 mol% (Sample No. 14), 15 mol% (Sample No. 15), and 17.5 mol% (Sample No. 16) An optical disc was produced. The first interface layer 3 was formed by co-sputtering using two sputter target HfO ₂ and _Cr 2 _{O 3,} the mixing ratio of the HfO ₂ and _Cr 2 _{O 3} of the first interface layer 3 Adjustment was performed by adjusting the sputtering power applied to each sputtering target used. These various optical disks were manufactured in the same manner as in Example 2 except that the mixing ratio of HfO ₂ and Cr ₂ O ₃ in the first interface layer 3 was changed.

  Sample No. In the 13-16 optical disks, the film thickness of the first dielectric layer 2 is in the range of the reflectance R in the unrecorded state of 11-15% in accordance with the optical constant of the first interface layer 3, and the recording / reproducing signal In order to make the degree of modulation of 0.45 or more, the film thickness was changed from that in Example 1. Specifically, sample no. The film thicknesses of the 13th to 16th first dielectric layers 2 were all set to 62 nm. Sample No. In the optical disks of 15 and 16, the thickness of the second dielectric layer 6 is set in the same manner as in Example 1 in consideration of the reflectance R in the unrecorded state and the modulation degree of the recording / reproducing signal as in the first dielectric layer 2. Changed the film thickness. Specifically, sample no. In the 15 and 16 optical disks, the thickness of the second dielectric layer 6 was 15 nm and 16 nm, respectively.

  The rewriting characteristics were also evaluated for the various optical discs in the same manner as in Examples 1 to 4. The results are shown in FIG. The standard of comprehensive evaluation in FIG. 4 is the same as the standard of Examples 1-4. FIG. 4 also shows the film configuration of each sample, the reflectance R in the unrecorded state, and the degree of modulation.

  As is clear from FIG. 2 and no. In any of the optical discs 12 to 14, the bER deterioration after 2000 rewrites is less than 2 digits, the bER after 2000 rewrites is 5.0E-5 or less, and the bER deteriorates by 2 digits. The number of rewrites exceeded 2000, and the overall evaluation was ◎ evaluation.

  Sample No. In the 11 optical disk, the bER degradation after 2000 rewrites is 2 digits or more, but the bER after 2000 rewrites is 1.0E-04 or less (at an error correction level), and the bER is 2 The number of rewrites when the digits deteriorated was 1000 or more, which was evaluated as “good”.

  Sample No. In both 15 and 16 optical discs, the bER degradation after 2000 rewrites was 2 digits or more and the bER after 2000 rewrites was greater than 1.0E-04, but the rewrite when the bER deteriorated by 2 digits The number of times was 1000 times or more, and a good number of times of rewriting was obtained as compared with, for example, Comparative Examples 2 and 3 (see FIG. 2).

From the result of FIG. 4, in the optical disk using the HfO ₂ —Cr ₂ O ₃ film for the first interface layer 3, the composition of Cr ₂ O ₃ in the first interface layer 3 is 2.5 mol% to 12.5 mol%. In some cases, it was found that good repeated rewriting characteristics (特性 and ○ evaluations) can be obtained. In particular, when the composition of the _Cr 2 _{O 3} of the first interface layer 3 to 5mol% ~12.5mol% It was found that more excellent repeated rewriting properties (◎ Evaluation) is obtained.

  In the information recording medium of the present invention, the first interface layer located on the light incident side of the recording layer is any one of a material containing hafnium oxide and tin oxide, and a material containing hafnium oxide and chromium oxide. By forming, excellent repeated rewriting characteristics can be obtained even when a blue laser is used for recording and reproduction. Therefore, the information recording medium of the present invention is suitable for a phase-change optical recording medium capable of increasing the capacity corresponding to a blue laser, such as HD DVD and Bru-ray Disc.

FIG. 1 is a schematic cross-sectional view of an optical disc according to the first embodiment. FIG. 2 is a diagram showing the evaluation results of the optical disks produced in Examples 1 to 4 and Comparative Examples 1 and 2. FIG. 3 is a diagram showing the evaluation results of the optical disc manufactured in Example 5. FIG. 4 is a diagram showing the evaluation results of the optical disc produced in Example 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 First dielectric layer 3 First interface layer 4 Recording layer 5 Second interface layer 6 Second dielectric layer 7 Blocking layer 8 Reflective layer 9 Protective layer 10 Dummy substrate 100 Optical disc

Claims (5)

An information recording medium,
A substrate,
A first dielectric layer provided on the substrate;
A first interface layer provided on the first dielectric layer and formed of a material containing hafnium oxide and tin oxide or chromium oxide;
A recording layer provided on the first interface layer and formed of a phase change material;
A second dielectric layer provided on the recording layer;
An information recording medium comprising: a reflective layer provided on the second dielectric layer. 2. The information recording according to claim 1, wherein the first interface layer is formed of a material containing hafnium oxide and tin oxide, and a ratio of tin oxide contained in the material is 5 to 15 mol%. Medium. The first interface layer is formed of a material containing hafnium oxide and chromium oxide, and the ratio of the chromium oxide contained in the material is 2.5 to 10 mol%. Information recording medium. The information recording medium according to any one of claims 1 to 3, wherein the recording layer is made of a phase change material containing Bi, Ge, and Te. The information recording medium according to claim 1, further comprising a second interface layer between the recording layer and the second dielectric layer.

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