Information recording medium and its manufacturing method

The present invention relates to an information recording medium capable of optically recording, erasing, rewriting, and reproducing information, and a method for manufacturing the same.

[0002] A phase-changing information recording medium uses a recording layer that reversibly undergoes a phase transformation between a crystalline phase and an amorphous phase to record, erase, and rewrite information. Do. When the recording layer is irradiated with a high-power laser beam and then rapidly cooled, the irradiated portion becomes an amorphous phase and a recording mark is formed. Further, when the amorphous portion of the recording layer is irradiated with a low-power laser beam and then slowly cooled, the irradiated portion becomes a crystal phase and the recording mark is erased. Therefore, in a phase-changing information recording medium, the recording layer is irradiated with a laser beam that is power-modulated between a high power level and a low power level, so that the previous information is erased and rewritten with new information. Can be done.

[0003] When rewriting the information, atoms move in the recording layer along with the phase transformation of the crystalline phase-amorphous phase. As a result, in the conventional information recording medium, when rewriting is repeated, atomic bias may occur locally to fluctuate the thickness of the recording layer, which may cause deterioration of signal quality. Such a decrease in repetitive rewriting performance becomes particularly large as the recording density increases. This is because as the recording density increases, the distance between adjacent recording marks becomes narrower, and it becomes more susceptible to the atomic bias of adjacent recording marks.

[0004] In order to prevent deterioration of repetitive rewriting performance, it is necessary to reduce the thickness of the recording layer in order to suppress the movement of atoms. In addition, reducing the thickness of the recording layer is a technique necessary for realizing a high-density information recording medium having two recording layers. However, if the thickness of the recording layer is reduced, the crystallization rate of the recording layer is lowered because the atoms are less likely to move. When the crystallization rate is reduced, the signal quality is deteriorated in a high-density information recording medium in which small recording marks must be recorded in a short time. Further, when the crystallization rate decreases, the crystallization sensitivity tends to deteriorate with time and the erasure rate tends to deteriorate with time. That is, the higher the density of recording, the more difficult it is to achieve both improvement in rewriting performance and suppression of deterioration of crystallization sensitivity over time.

[0005] In order to improve the rewriting performance repeatedly, a recording layer containing Te, Ge, Sn, and Sb has been reported (see Japanese Patent Application Laid-Open No. 2-147289).

[0006] [Problems to be Solved by the Invention] However, although the conventional recording layer exhibits a large crystallization rate, the long-term stability of the repetitive rewriting performance and the crystallization sensitivity in high-density recording is not sufficient.

[0007] In order to solve the above problems, the present invention provides an information recording medium capable of high-density recording, excellent in rewriting performance, and less deterioration of crystallization sensitivity with time, and a method for producing the same. The purpose.

[Means for Solving the Problems] In order to achieve the above object, the information recording medium of the present invention is an information recording medium including a substrate and a recording layer arranged above the substrate. The recording layer is a layer that reversibly undergoes a phase transformation between the crystalline phase and the amorphous phase by irradiation with an energy beam, and has a composition formula [(Ge)._1-XSn_X)_ASb₂Te_{3 + A}]_100-BM_B(However, M is at least one element selected from Ag, Al, Cr, Mn and N, and A, B and X satisfy 0 &lt;A10, 0 &lt;B20 and 0.07 &lt;X &lt;0.69, respectively. ), And the Sn content in the recording layer is 2 atomic%.<u style="single">that's all</u>It is characterized by having 20 atomic% or less. As used herein, the term "constituent element" refers to an element that is essential for the manifestation of one property of a substance containing it. The recording layer is essentially Ge, Sb, Te, Sn, and at least<u style="single">1</u>It preferably consists of one element M. According to the above-mentioned information recording medium, it is possible to obtain an information recording medium capable of high-density recording, excellent in rewriting performance repeatedly, and less deteriorated in crystallization sensitivity with time.

[0009] In the information recording medium, the recording layer<u style="single">Is the composition formula [</u>(Ge_1-XSn_X)_ASb₂Te_{3 + A}]_100-BM_B(However, M is at least one element selected from Ag, Al, Cr, Mn and N, and A, B and X satisfy 0 &lt;A10, 0 &lt;B20 and 0.07 &lt;X &lt;0.69, respectively. Includes materials represented by.)<u style="single">I'm sorry. Let A 10</u>As a result, it is possible to prevent the rewriting performance from being deteriorated repeatedly. By setting B 20, it is possible to prevent the crystallization sensitivity from deteriorating with time.

[0010] In the information recording medium, Sn in the recording layer<u style="single">of</u>Content is 2 atoms%<u style="single">that's all</u>20 atomic% or less. Sn content is 2 atomic%<u style="single">With the above</u>By doing so, the crystallization rate can be made sufficiently high. By setting the Sn content to 20 atomic% or less, the ratio of the reflected light amount when the recording layer is a crystalline phase and the reflected light amount when the recording layer is an amorphous phase can be increased.

[0011] In the information recording medium, the thickness of the recording layer is larger than 5 nm and smaller than 15 nm. By making the thickness of the recording layer larger than 5 nm, the recording layer can be easily made into a crystalline phase. By making the recording layer smaller than 15 nm, it is possible to prevent the repeated rewriting performance from deteriorating. The thickness of the recording layer is 7 nm or more and 13 nm or less.<u style="single">thing</u>Is more preferable.

[0012] The information recording medium further includes a first protective layer, a second protective layer, and a reflective layer, and the first protective layer, the recording layer, the second protective layer, and the reflective layer. However, they may be formed on the substrate in this order. In this case, the interface layer arranged at at least one position selected from the position between the first protective layer and the recording layer and the position between the second protective layer and the recording layer is further added. You may prepare. Further, a light absorption correction layer arranged between the second protective layer and the reflective layer may be further provided.

[0013] The information recording medium further includes a first protective layer, a second protective layer, and a reflective layer, and the reflective layer, the second protective layer, the recording layer, and the first protective layer. May be formed on the substrate in this order. According to the above configuration, an information recording medium capable of particularly high-density recording can be obtained. In this case, the interface layer arranged at at least one position selected from the position between the first protective layer and the recording layer and the position between the second protective layer and the recording layer is further added. You may prepare. Further, a light absorption correction layer arranged between the reflection layer and the second protective layer may be further provided.

[0014] The method for producing an information recording medium of the present invention includes a step of forming a recording layer on a substrate on which a phase transformation reversibly occurs between a crystalline phase and an amorphous phase by irradiation with an energy beam. , The recording layer has a composition formula [(Ge_1-XSn_X)_ASb₂Te_{3 + A}]_100-BM_B(However, M is at least one element selected from Ag, Al, Cr, Mn and N, and A, B and X satisfy 0 &lt;A10, 0 &lt;B20 and 0.07 &lt;X &lt;0.69, respectively. ), And the Sn content in the recording layer is 2 atomic%.<u style="single">that's all</u>It is characterized by having 20 atomic% or less. According to the above manufacturing method, the information recording medium of the present invention can be reasonably manufactured.

【0015】<u style="single">The recording layer</u>, Vacuum deposition, sputtering, ion plating, chemical vapor deposition, and molecular beam epitaxy.<u style="single">It is preferably formed by a vapor phase film forming method.</u>[0016] In the above production method, the vapor phase film forming method is a sputtering method using a gas containing at least one gas selected from nitrogen gas and oxygen gas and one rare gas selected from argon and krypton. There may be.

[0017] In the above manufacturing method, the recording layer may be formed at a film forming rate of 0.5 nm / sec or more and 5 nm / sec or less. According to the above configuration, a recording layer in an amorphous state can be formed.

[0018] In the above manufacturing method, the thickness of the recording layer is<u style="single">It is preferably larger than 5 nm and smaller than 15 nm, and more preferably 7 nm or more and 13 nm or less.</u>BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) In the first embodiment, an example of the information recording medium of the present invention will be described.

[0021] FIG. 1 shows a partial cross-sectional view of the information recording medium 10 of the first embodiment. The information recording medium 10 includes a substrate 11, a first protective layer 12a, a first interface layer 13a, a recording layer 14, a second interface layer 13b, and a second protective layer 12b, which are laminated on the substrate 11 in this order. A light absorption correction layer 15, a reflection layer 16, and a dummy substrate 18 bonded to the reflection layer 16 by an adhesive layer 17 are provided. That is, the information recording medium 10 includes a substrate 11 and a recording layer 14 arranged above the substrate 11. The information recording medium 10 is irradiated with an energy beam (generally, a laser beam) 19 for recording / reproduction from the substrate 11 side.

[0022] The recording layer 14 is a layer that reversibly undergoes a phase transformation between the crystalline phase and the amorphous phase by irradiation with the energy beam 19. Specifically, by irradiating the high-power energy beam 19, the crystal phase portion of the recording layer 14 can be changed to an amorphous phase. Further, by irradiating the energy beam 19 with low power, the amorphous phase portion of the recording layer 14 can be changed to the crystalline phase. The thickness of the recording layer 14 is preferably 5 nm or more and 15 nm or less.

[0023] The recording layer 14 contains at least one element M selected from Ag, Al, Cr, Mn and N, and Ge, Sb, Te and Sn as constituent elements. Specifically, the composition formula [(Ge_1-XSn_X)_ASb₂Te_{3 + A}]_100-BM_B(However, materials represented by 0 &lt;A 10, 0 &lt;B 20, 0.07 &lt;X &lt;0.69) can be used. This composition formula indicates that the recording layer 14 contains a total of [(100-B) · A] / (2A + 5) atomic% of Ge and Sn. It is more preferable that A satisfies 2 A 8. Further, it is more preferable that B satisfies 2 B 15. In the material represented by this composition formula, the Sn content is 2 atomic%.<u style="single">that's all</u>20 atomic% or less.

[0024] The material represented by the above composition formula is GeTe-Sb.₂Te₃It can be explained as a material in which a part of Ge having a pseudo-binary composition is replaced with Sn and the element M is further added. GeTe-Sb₂Te₃The pseudo-binary composition has been conventionally used as a material having a high crystallization rate, but the crystallization rate can be further increased by dissolving SnTe or PbTe in the material. SnTe and PbTe are GeTe-Sb₂Te₃Similar to the pseudo-binary system, the crystal structure is rock salt type. In addition, SnTe and PbTe have a high crystallization rate and are easily dissolved in Ge-Sb-Te. In particular, SnTe is GeTe-Sb₂Te₃It is preferable as a material to be dissolved in a pseudo-binary composition.

[0025] For example, GeTe-Sb₂GeTe-SnTe-Sb obtained by mixing SnTe with Te3 pseudo-binary composition₂Te₃Is preferably used as the material of the recording layer 14. In this case, replace part of Ge with Sn and (Ge, Sn) Te-Sb₂Te₃By doing so, the crystallization rate is further increased.

[0026] The element M contained in the recording layer 14 is considered to have a function of suppressing atomic movement. By using two elements, Al and Ag, Cr and Ag, or Mn and Ag, as the element M, the rewriting performance can be improved, the deterioration of the crystallization sensitivity with time can be suppressed, and the signal amplitude can be increased. However, when increasing the concentration of element M or the number of elements, it is preferable to increase the Sn concentration in the recording layer 14 in order not to reduce the crystallization rate. The concentration of element M is preferably equal to or less than the concentration of Sn.

[0027] The substrate 11 is a disk-shaped transparent substrate. As the material of the substrate 11, for example, a resin such as amorphous polyolefin or polymethylmethacrylate (PMMA), or glass can be used. A guide groove for guiding the energy beam 19 may be formed on the surface of the substrate 11 on the recording layer 14 side, if necessary. The surface of the substrate 11 on the side where the energy beam 19 is incident is generally smooth. The thickness of the substrate 11 is, for example, about 0.5 mm to 1.3 mm.

[0028] The first and second protective layers 12a and 12b have a function of protecting the recording layer 14. By adjusting the thickness of the first and second protective layers 12a and 12b, the amount of light incident on the recording layer 14 can be increased, and the signal amplitude (change in the amount of reflected light before and after recording) can be increased. can do. The thickness of the protective layer can be determined, for example, by calculation based on the matrix method (see, for example, Hiroshi Kubota, "Wave Optics", Iwanami Shinsho, 1971, Chapter 3). According to this calculation, the thickness of the protective layer is such that the difference between the amount of reflected light of the crystalline recording layer 14 and the amount of reflected light of the amorphous recording layer 14 is large and the amount of light incident on the recording layer 14 is large. Can be determined.

[0029] The first and second protective layers 12a and 12b are made of, for example, a dielectric. Specifically, for example, SiO₂And Ta₂O₅Oxides such as Si-N, Al-N, Ti-N, Ta-N, Zr-N, or Ge-N and other nitrides, ZnS and other sulfides, or SiC and other carbides can be used. .. A mixture of these can also be used. Among these, ZnS and SiO₂ZnS-SiO which is a mixture with₂Is a particularly good material. ZnS-SiO₂Is amorphous, has a high refractive index, and has good mechanical properties and moisture resistance. Also, ZnS-SiO₂Can form a film at a high film forming speed. The first protective layer 12a and the second protective layer 12b may be formed of the same material or may be formed of different materials.

[0030] The first and second interface layers 13a and 13b are arranged between the first protective layer 12a and the recording layer 14, and between the second protective layer 12b and the recording layer 14, respectively. .. The first and second interface layers 13a and 13b have a function of preventing mass transfer occurring between the first protective layer 12a and the recording layer 14 and between the second protective layer 12b and the recording layer 14. Has. The materials of the first and second interface layers 13a and 13b include, for example, nitrides such as Si-N, Al-N, Zr-N, Ti-N, Ge-N, or Ta-N, or these. Containing nitride oxides or carbides such as SiC can be used. In order to obtain good recording / erasing performance, the thickness of the first and second interface layers 13a and 13b is preferably in the range of 1 nm to 10 nm, and more preferably in the range of 2 nm to 5 nm. preferable.

The light absorption correction layer 15 adjusts the ratio between the light absorption rate when the recording layer 14 is in a crystalline state and the light absorption rate when the recording layer 14 is in an amorphous state. The light absorption correction layer 15 can prevent the shape of the recording mark from being distorted during rewriting. As the material of the light absorption correction layer 15, it is preferable to use a material having a high refractive index and appropriately absorbing light. For example, a material having a refractive index n of 3 or more and 6 or less and an extinction coefficient k of 1 or more and 4 or less can be used. Specifically, an amorphous Ge alloy such as Ge-Cr or Ge-Mo, or an amorphous Si alloy such as Si-Cr, Si-Mo, or Si-W can be used. Crystalline metal, metalloid or semiconductor materials such as Si alloys, Te compounds, Ti, Zr, Nb, Ta, Cr, Mo, W, SnTe, or PbTe can also be used.

[0032] The reflective layer 16 has a function of increasing the amount of light absorbed by the recording layer 14. Further, by forming the reflective layer 16, the heat generated in the recording layer 14 can be rapidly diffused, and the recording layer 14 can be easily amorphized. Further, by forming the reflective layer 16, the laminated multilayer film can be protected from the usage environment.

[0033] As the material of the reflective layer 16, for example, a simple substance metal having high thermal conductivity such as Al, Au, Ag, or Cu can be used. Further, alloys such as Al-Cr, Al-Ti, Ag-Pd, Ag-Pd-Cu and Ag-Pd-Ti may be used. With these alloys, the moisture resistance and thermal conductivity can be adjusted by changing the composition. The reflective layer 16 may be omitted depending on the material of the recording layer 14 and the information recording conditions.

[0034] The adhesive layer 17 is a layer for adhering the dummy substrate 18 to the reflective layer 16. The adhesive layer 17 is made of a material having high heat resistance and adhesiveness, and for example, a resin such as an ultraviolet curable resin can be used. Specifically, a material containing an acrylic resin as a main component or a material containing an epoxy resin as a main component can be used. Further, the adhesive layer 17 may be formed by using a resin film, a dielectric film, double-sided tape, or a combination thereof.

[0035] The dummy substrate 18 is a disk-shaped substrate. The dummy substrate 18 has a function of increasing the mechanical strength of the information recording medium 10. In addition, the dummy substrate 18 protects the laminated multilayer film. As the material of the dummy substrate 18, the material described for the substrate 11 can be used. The material of the dummy substrate 18 may be the same as or different from the material of the substrate 11. Further, the thickness of the dummy substrate 18 may be the same as or different from the thickness of the substrate 11.

[0036] In the information recording medium 10 of the first embodiment, the recording layer 14 contains the elements M, Ge, Sb, Te, and Sn as constituent elements. Therefore, according to the information recording medium 10, it is possible to obtain an information recording medium capable of high-density recording, excellent in rewriting performance repeatedly, and less deteriorated in crystallization sensitivity with time.

Although the information recording medium 10 including one recording layer 14 is shown in the first embodiment, the information recording medium of the present invention may include two recording layers 14 (in the following embodiments). The same is true). For example, for two information recording media 10, an information recording medium having a double-sided structure can be obtained by bonding the dummy substrates 18 to each other with an adhesive layer.

(Embodiment 2) In the second embodiment, another example of the information recording medium of the present invention will be described. The same parts as those described in the first embodiment are designated by the same reference numerals and duplicated explanations are omitted (the same applies to the following embodiments).

[0039] FIG. 2 shows a partial cross-sectional view of the information recording medium 20 of the second embodiment. The information recording medium 20 includes a first substrate 21, a reflection layer 16 laminated on the first substrate 21, a light absorption correction layer 15, a second protective layer 12b, a second interface layer 13b, and a recording layer. It comprises 14, a first interface layer 13a, a first protective layer 12a, and a second substrate 22 bonded to the first protective layer 12a by an adhesive layer 17. That is, the information recording medium 20 includes a first substrate 21 and a recording layer 14 arranged above the first substrate 21. The information recording medium 20 is irradiated with an energy beam (generally, a laser beam) 19 for recording / reproduction from the second substrate 22 side.

[0040] As the first substrate 21, the same substrate as the substrate 11 can be used. The second substrate 22 is a disk-shaped transparent substrate, and can be formed of the same material as the substrate 11. A guide groove for guiding the energy beam 19 may be formed on the surface of the second substrate 22 on the recording layer 14 side, if necessary. Of the surface of the second substrate 22, the surface on the side where the energy beam 19 is incident is preferably smooth. The second substrate 22 is thinner than the first substrate 21, and has a thickness of, for example, about 0.05 mm to 0.5 mm.

[0041] In the information recording medium 20, since the second substrate 22 is thinner than the first substrate 21, the numerical aperture of the objective lens can be increased. Here, assuming that the wavelength of the energy beam 19 is λ and the numerical aperture of the objective lens is NA, the beam spot size w is given by w = k · λ / NA (where k is a constant). The spot size w becomes smaller as the wavelength λ is shorter and the numerical aperture NA is larger. Therefore, the information recording medium 20 capable of increasing the numerical aperture of the objective lens can record at a higher density than the information recording medium 10. For example, it has been reported that an objective lens with NA = 0.6 can be used on a substrate with a thickness of 0.6 mm, and an objective lens with NA = 0.85 can be used on a substrate with a thickness of 0.1 mm (Kiyoshi Osato). , "A rewritable optical disk system with over 10 GB of capacity", Proc.SPIE.Optical DataStorage '98, 3401, 80-86 (1998)).

Since the information recording medium 20 uses the recording layer 14 made of the material described in the information recording medium 10, the same effect as that of the information recording medium 10 can be obtained.

(Embodiment 3) In the third embodiment, a method of manufacturing the information recording medium 10 will be described as an example of the method of manufacturing the information recording medium of the present invention. As described below, the manufacturing method of the third embodiment includes a step of forming the recording layer 14 by a vapor phase film forming method.

[0044] First, the substrate 11 is prepared, and the substrate 11 is arranged in the film forming apparatus. As the film forming apparatus used in the third embodiment, a single-wafer film forming apparatus in which one power source is provided in one vacuum chamber or an in-line film forming apparatus in which one vacuum chamber is provided with a plurality of power sources is used. be able to. The following layers may be formed by the same film forming apparatus or may be formed by different film forming apparatus.

[0045] Then, on the substrate 11, a first protective layer 12a, a first interface layer 13a, a recording layer 14, a second interface layer 13b, a second protective layer 12b, a light absorption correction layer 15, and reflection. Layer 16 is formed sequentially. When a groove for guiding the energy beam 19 is formed on the surface of the substrate 11, the first protective layer 12a is formed on the surface on which the groove is formed.

[0046] The first protective layer 12a, the first interface layer 13a, the second interface layer 13b, and the second protective layer 12b can be formed by, for example, a sputtering method. Specifically, the base material made of the compound may be sputtered in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reaction gas. Further, a reactive sputtering method in which a base metal made of a metal is sputtered in a mixed gas atmosphere of an Ar gas and a reaction gas may be used.

The recording layer 14 is made of the material described in the first embodiment and is formed by the Vapor Deposition Method. As the vapor phase deposition method, at least one selected from a vacuum vapor deposition method, a sputtering method, an ion plating method, a chemical vapor deposition method (Chemical Vapor Deposition), and a molecular beam epitaxy method can be used. ..

[0048] For example, the recording layer 14 can be formed by a sputtering method using a mixed gas containing at least one gas selected from nitrogen gas and oxygen gas and one rare gas selected from argon and krypton. As the mixed gas, for example, a mixed gas of nitrogen gas and argon, a mixed gas of nitrogen gas and krypton, or a mixed gas obtained by adding oxygen gas to these can be used. Specifically, the recording layer 14 can be formed by sputtering a base material (target) containing Ge, Sb, Te, Sn, and element M in the mixed gas atmosphere. As the base material, five base materials corresponding to Ge, Sb, Te, Sn, and element M may be used, or a binary base material or a ternary base material in which several elements are combined may be used. May be used. When the element M is composed of only nitrogen, the recording layer 14 can be formed by sputtering a target containing Ge, Sb, Te, and Sn in an atmosphere containing nitrogen gas.

According to the sputtering method, the composition formula [(Ge, Sn)_ASb₂Te_{3 + A}]_100-BM_B(However, the recording layer represented by 0 &lt;A 10, 0 &lt;B 20) can be easily formed.

[0050] The recording layer 14 is preferably formed at a film forming rate of 0.5 nm / sec or more and 5 nm / sec or less (more preferably 0.8 nm / sec to 3 nm / sec).

After forming the second protective layer 12b, the light absorption correction layer 15 and the reflection layer 16 are formed on the second protective layer 12b. The light absorption correction layer 15 and the reflection layer 16 can be formed by sputtering a base material made of metal in an Ar gas atmosphere.

[0052] Next, an adhesive layer 17 is formed on the reflective layer 16, and the reflective layer 16 and the dummy substrate 18 are bonded together. In this way, the information recording medium 10 can be manufactured. If necessary, an initialization step of crystallizing the entire surface of the recording layer 14 may be performed. The initialization step can be performed before the dummy substrates 18 are attached or after the dummy substrates 18 are attached.

[0053] The information recording medium 20 can also be manufactured by the same method as the information recording medium 10. Each layer of the information recording medium 20 can be formed in the same manner as each layer of the information recording medium 10. Further, the second substrate 22 can be adhered to the first protective layer 12a by the adhesive layer 17 in the same manner as the dummy substrate 18. Also in the manufacturing method of the information recording medium 20, an initialization step is performed as necessary. The initialization step can be performed before the second substrate 22 is bonded or after the second substrate 22 is bonded. In the information recording medium 20, since the energy beam 19 is incident from the second substrate 22 side, the thickness of the adhesive layer 17 is preferably uniform over the entire surface.

[0054] According to the manufacturing method of the third embodiment, the information recording medium of the present invention can be easily manufactured.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1) In Example 1, an example of the information recording medium 10 will be described. Hereinafter, a method for manufacturing the information recording medium according to the first embodiment will be described.

[0057] First, as the substrate 11, a polycarbonate substrate (thickness: 0.6 mm) having a spiral guide groove formed therein was prepared. ZnS-SiO on this polycarbonate substrate₂Layer (first protective layer 12a, thickness 140 nm), Ge-N layer (first interface layer 13a, thickness: 5 nm), recording layer (recording layer 14), Ge-N layer (second interface layer) 13b, thickness: 3nm), ZnS-SiO₂Sputtering layers (second protective layer 12b, thickness: 40 nm), GeCr layer (light absorption correction layer 15, thickness: 40 nm), and Ag alloy layer (reflection layer 16, thickness: 80 nm) in this order. Formed by law. The thickness of the first protective layer 12a and the second protective layer 12b was adjusted so that the signal amplitude (change in the amount of reflected light) at a wavelength of 660 nm was large and the amount of light incident on the recording layer was large. .. These thicknesses were determined using calculations based on the matrix method.

The recording layer has a composition formula [(Ge, Sn).₄Sb₂Te₇]₉₅N₅It was formed using the material represented by. This recording layer contains Ge and Sn in total 95 × 4 / (4 + 2 + 7) = 29 atomic%. Specifically, the Ge content was set to 24 atomic% and the Sn content was set to 5 atomic%.

[0059] After that, an ultraviolet curable resin was spin-coated on the Ag alloy layer as the adhesive layer 17. Finally, the dummy substrate (thickness: 0.6 mm) was brought into close contact with the Ag alloy layer and irradiated with ultraviolet rays to bond the Ag alloy layer and the dummy substrate.

[0060] In Example 1, after the dummy substrate was adhered, the entire information recording medium was irradiated with a laser beam to crystallize the entire recording layer. In this way, the information recording medium of Example 1 was produced. In Example 1, eight types of information recording media 10-11 to 10-18 having different recording layer thicknesses were prepared.

[0061] On the other hand, as a comparative example, an information recording medium was produced in the same manner as in the above embodiment except that the material of the recording layer was changed. In this comparative example, the composition formula Ge₄Sb₂Te₇A recording layer was formed using the material represented by. For this comparative example as well, eight types of information recording media C-11 to C-18 having different recording layer thicknesses were prepared.

[0062] With respect to the above 16 types of information recording media, the rewriting performance and the deterioration of the crystallization sensitivity with time were evaluated. These evaluation methods will be described later. The evaluation results are shown in Table 1.

[0063] [Table 1]<img file="JP3666854B2_D0001.tif" />[0064] The larger the "rewritable number" in Table 1, the better the rewrite performance. A1 to D1 indicate the range at the bottom of the table, respectively. E1 indicates that the rewrite could not be performed. The smaller the "jitter value change" in Table 1, the smaller the deterioration of the crystallization sensitivity over time. A2 to D2 indicate the range at the bottom of the table, respectively. E2 indicates that the jitter value before the neglected test could not be evaluated because it exceeded 13% between the front end of the recording mark and the rear end of the recording mark. The meanings of A1 to E1 and A2 to E2 are the same in the table below.

As shown in Table 1, the information recording media C-11 to C-18 of the comparative example did not show the characteristics of A or B with respect to both the number of rewritable times and the change in the jitter value. On the other hand, in the information recording media 10-13 to 10-16 of Example 1, the characteristics of A or B were shown for both the number of rewritable times and the change in the jitter value.

[0066] On average, the information recording medium of Example 1 had better rewriting performance and less deterioration of crystallization sensitivity with time than Comparative Examples C-11 to C-18. It is considered that the improvement of the rewriting performance is due to the addition of nitrogen. In addition, the suppression of deterioration of crystallization sensitivity over time is Ge.₄Sb₂Te₇It is considered that this is because the crystallization rate was increased by substituting a part of Ge with Sn.

(Example 2) In Example 2, an example in which the information recording medium 10 is produced by changing the Sn content of the recording layer will be described.

[0068] An information recording medium was prepared in the same manner as in Example 1 except that the thickness of the recording layer was fixed at 7 nm and the Sn content of the recording layer was changed. In the information recording medium of Example 2, the recording layer has a composition formula [(Ge, Sn).₄Sb₂Te₇]₉₅N₅It was formed using the material represented by. Then, eight kinds of information recording media 10-21 to 10- in which the Sn content was changed between 2 atomic% and 25 atomic% and the Ge content was changed between 27 atomic% and 4 atomic%. 28 was prepared. The information recording medium 10-22 is the same as the information recording medium 10-13. Further, as a comparative example, an information recording medium C-21 containing no Sn was also produced in the same manner.

[0069] With respect to these information recording media 10-21 to 28 and C-21, the deterioration of the crystallization sensitivity with time was evaluated by measuring the change in the jitter value by the method described later. The evaluation results are shown in Table 2.

[0070] [Table 2]<img file="JP3666854B2_D0002.tif" />As shown in Table 2, good characteristics were obtained when the Sn content was in the range of 2 atomic% to 20 atomic%.

(Example 3) In Example 3, an example in which the information recording medium 10 is produced by changing the element M will be described.

An information recording medium was prepared in the same manner as in Example 1 except that the element M was changed and the thickness of the recording layer was fixed at 11 nm. In the information recording medium of Example 3, the recording layer has a composition formula [(Ge, Sn).₄Sb₂Te₇]₉₅M₅It was formed using the material represented by. The Ge content was 24 atomic% and the Sn content was 5 atomic%. In Example 3, five types of information recording media 10-31 to 10-35 using Mn, Ag, Cr, Al, or N as the element M were prepared. Further, as a comparative example, an information recording medium C-31 containing no element M was also produced in the same manner.

[0074] The rewriting performance of these information recording media 10-31 to 35 and C-31 was evaluated repeatedly by the method described later. The evaluation results are shown in Table 3.

[0075] [Table 3]<img file="JP3666854B2_D0003.tif" />[0076] As shown in Table 3, the rewriting performance was improved by using Mn, Ag, Cr, Al, or N as the element M. This effect was particularly significant at Mn, Cr, Al, and N. When Ag was used as the element M, the signal amplitude was increased, and the jitter value between the front ends of the recording mark and the jitter value between the rear ends of the recording mark were improved.

[Example 4] In Example 4, an example in which the information recording medium 10 is produced using Mn as the element M will be described.

An information recording medium was prepared in the same manner as in Example 1 except that Mn was used as the element M. In the information medium of Example 4, the recording layer has a composition formula [(Ge, Sn).₄Sb₂Te₇]₉₅Mn₅It was formed using the material represented by. The Ge content was 24 atomic% and the Sn content was 5 atomic%. In Example 4, eight types of information recording media 10-41 to 10-48 in which the thickness of the recording layer was changed were prepared.

[0079] For these information recording media 10-41 to 10-48, the repetitive rewriting performance and the deterioration of the crystallization sensitivity with time were evaluated by the method described later. The evaluation results are shown in Table 4.

[0080] [Table 4]<img file="JP3666854B2_D0004.tif" />As shown in Table 4, by using Mn as the element M, it has become possible to obtain an information recording medium having good rewriting performance and little deterioration of crystallization sensitivity with time. When the thickness of the recording layer was 7 nm or more and 13 nm or less, these two characteristics became good. In addition, when the random signal recorded before being left unattended was only reproduced after being left unattended, there was no change in the jitter value, so it was confirmed that there was no problem in record preservation.

[Example 5] In Example 5, an example in which the information recording medium 10 is produced by changing the content of the element M and the content of Sn will be described.

[0083] An information recording medium was prepared in the same manner as in Example 1 except that Cr was used as the element M and the Sn content was changed. The recording layer has a composition formula [(Ge, Sn)₄Sb₂Te₇]₉₅Cr₅It was formed using the material represented by. The Sn content was changed from 0 to 25 atomic%, and the Ge content was changed from 29 atomic% to 4 atomic%. The thickness of the recording layer was 9 nm.

[0084] With respect to the plurality of information recording media thus produced, the rewriting performance and the deterioration of the crystallization sensitivity with time were evaluated by the method described later. As a result of the evaluation, the range in which particularly favorable results were obtained is shown by * in Table 5.

[0085] [Table 5]<img file="JP3666854B2_D0005.tif" />[0086] The * mark indicates that the number of rewritable times is 100,000 times or more and the jitter value change is + 2% or less. As shown in Table 5, by using a material having a Sn content of 5 atomic% to 20 atomic% and a Cr content of 2 atomic% to 15 atomic%, the rewriting performance is good and the crystallization sensitivity is good. An information recording medium with little deterioration over time was obtained.

Further, when the same experiment was carried out using Mn or Al as the element M, the same result as that of the information recording medium using Cr as the element M was obtained.

[0088] Further, similar experiments were carried out using Ag and Mn, or Ag and Al, or Ag and Cr as the element M. The Ag content was fixed at 1 atomic%. As a result, an information recording medium having excellent characteristics was obtained by setting the Sn content to 5 atomic% to 20 atomic% and the Mn, Al or Cr content to 1 atomic% to 13 atomic%.

[Example 6] In Example 6, an example in which the information recording medium 20 is produced will be described.

[0090] First, as the first substrate 21, a polycarbonate substrate (thickness: 1.1 mm) having a spiral guide groove formed on its surface was prepared. Next, on the polycarbonate substrate, an Ag alloy layer (reflection layer 16, thickness: 80 nm), a Te compound layer (light absorption correction layer 15, thickness: 20 nm), ZnS-SiO₂Layer (second protective layer 12b, thickness: 11 nm), Ge-N layer (second interface layer 13b, thickness: 3 nm), recording layer (recording layer 14), Ge-N layer (first interface) Layer 13a, thickness 5nm), ZnS-SiO₂Layers (first protective layer 12a, thickness: 60 nm) were formed in this order by sputtering. The thickness of the first protective layer 12a and the second protective layer 12b was adjusted so that the signal amplitude (change in the amount of reflected light) at a wavelength of 405 nm was large and the amount of light incident on the recording layer was large. .. These thicknesses were determined using calculations based on the matrix method.

The recording layer has a composition formula [(Ge, Sn).₄Sb₂Te₇]₉₅Mn₅It was formed using the material represented by. The Ge content was 19 atomic% and the Sn content was 10 atomic%.

[0092] After that, an ultraviolet curable resin was applied on the first protective layer as the adhesive layer 17. Finally, the second substrate (second substrate 22, thickness: 0.1 mm) was brought into close contact with the first protective layer and irradiated with ultraviolet rays to bond the first protective layer and the second substrate.

[0093] In Example 6, after the second substrate was adhered, the entire information recording medium was irradiated with a laser beam to crystallize the entire recording layer. In this way, the information recording medium of Example 6 was prepared. In Example 6, seven types of information recording media 20-1 to 20-7 having different recording layer thicknesses were prepared. With respect to these information recording media, the rewriting performance and the deterioration of the crystallization sensitivity with time were evaluated by the evaluation method described later. In the evaluation of Example 6, the characteristics were evaluated by performing high-density recording using a laser beam having a wavelength of 405 nm and an objective lens having NA = 0.8. The evaluation results are shown in Table 6.

[0094] [Table 6]<img file="JP3666854B2_D0006.tif" />[0095] As shown in Table 6, even in high-density recording, it has become possible to obtain an information recording medium having good rewriting performance and little deterioration of crystallization sensitivity with time. This is Ge₄Sb₂Te₇It is considered that this is because a part of Ge was replaced with Sn and Mn was added as an element M.

[0096] Further, when a similar experiment was carried out using Cr or Al as the element M, the same result as that of the information recording medium using Mn as the element M was obtained.

[0097] Further, a similar experiment was carried out using Ag and Mn, or Ag and Al, or Ag and Cr as the element M. The Ag content was 1 atomic%. The content of Mn, Al, or Cr was 4 atomic%. As a result, the same result as that of the information recording medium using Mn as the element M was obtained.

(Evaluation of Repeated Rewriting Performance) The method of evaluating the repeated rewriting performance will be described below.

FIG. 3 shows a schematic diagram of the recording / reproducing device used for the evaluation. The recording / reproducing device includes a spindle motor 32 for rotating the information recording medium 31, an optical head 34 including a semiconductor laser 33, and an objective lens 35. The laser beam 36 emitted from the semiconductor laser 33 is focused by the objective lens 35 and irradiated to the recording layer of the information recording medium 31. As the information recording medium 31, the information recording medium produced in the examples is used.

In the evaluation of Examples 1 to 5, a semiconductor laser 33 having a wavelength of 660 nm and an objective lens 35 having a numerical aperture of 0.6 were used, and the linear velocity was set to 8.2 m / sec. In the evaluation of Example 6, a semiconductor laser 33 having a wavelength of 405 nm and an objective lens 35 having a numerical aperture of 0.8 were used, and the linear velocity was set to 8.6 m / sec.

[0101] In order to evaluate the repetitive rewriting performance, the laser beam 36 was modulated into a high output peak power Pp and a low output bias power Pb, and a random signal was recorded. Then, the jitter value between the front ends of the recording mark and the jitter value between the rear ends of the recording mark were measured, and both were averaged to calculate the average jitter value. The repetitive rewriting performance was evaluated by the number of rewrites (the number of rewritable times in the table) until the average jitter value reached 13% by repeatedly recording the signal using the laser beams 36 of Pp and Pb. When the information recording medium is used as an external memory of a computer, the number of rewritable times is preferably 100,000 or more. When the information recording medium is used as an image / audio recorder, it can be said that 10,000 rewritable times is sufficient.

(Evaluation of aging deterioration of crystallization sensitivity) The method of evaluating aging deterioration of crystallization sensitivity will be described below.

[0103] First, a random signal was recorded 10 times on the information recording medium by the same method as the evaluation of the repetitive rewriting performance, and the jitter value between the front ends of the recording marks and the jitter value between the rear ends of the recording marks were measured. ..

Next, the information recording medium was left in an environment at 90 ° C. and a relative humidity of 20% for 24 hours. Then, after being left unattended, a random signal was overwritten once on the signal recorded before being left unattended. Then, the jitter value between the front ends of the recording mark and the jitter value between the rear ends of the recording mark were measured.

[0105] (Jitter value change (%)) in the table is a value given by (Jitter value change (%)) = (Jitter value (%) after leaving)-(Jitter value (%) before leaving). Is.

[0106] If there is no change in the crystallization sensitivity before and after leaving, there is almost no change in the jitter value. On the contrary, when the crystallization sensitivity decreases before and after leaving, the change in the jitter value becomes large. Therefore, it can be seen that the smaller the change in the jitter value, the smaller the deterioration of the crystallization sensitivity with time. Practically, it is preferable that the worse of the change in the jitter value between the front ends and the change in the jitter value between the rear ends is + 2% or less.

[0107] Although the embodiments of the present invention have been described above with reference to examples, the present invention is not limited to the above embodiments and can be applied to other embodiments based on the technical idea of the present invention. ..

[Effect of the Invention] As described above, according to the information recording medium of the present invention, an information recording medium having good rewriting performance and little deterioration of crystallization sensitivity with time can be obtained.

[0109] Further, according to the method for manufacturing an information recording medium of the present invention, the information recording medium of the present invention can be easily manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] FIG. 1 is a partial cross-sectional view showing an example of the information recording medium of the present invention.

FIG. 2 is a partial cross-sectional view showing another example of the information recording medium of the present invention.

FIG. 3 is a schematic view of a recording / reproducing device used for evaluating an information recording medium.

[Explanation of symbols] 10, 20, 31 Information recording medium 11 Substrate 12a First protective layer 12b Second protective layer 13a First interface layer 13b Second interface layer 14 Recording layer 15 Light absorption correction layer 16 Reflective layer 17 Adhesive layer 18 Dummy substrate 19 Energy beam 21 First substrate 22 Second substrate 32 Spindle motor 33 Semiconductor laser 34 Optical head 35 Objective lens 36 Laser beam