JP3729833B2 - Information recording medium - Google Patents

Description

  The present invention relates to an information recording medium capable of optically recording, erasing, rewriting and reproducing information.

  A phase change type information recording medium records, erases, and rewrites information using a recording layer that reversibly undergoes a phase transformation between a crystalline phase and an amorphous phase. When the recording layer is rapidly cooled after being irradiated with a high-power laser beam, the irradiated portion becomes an amorphous phase and a recording mark is formed. 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 crystalline phase and the recording mark is erased. Therefore, in a phase change type information recording medium, by irradiating a recording layer with a laser beam modulated between a high power level and a low power level, the previous information is erased and rewritten with new information. Can do.

  When information is rewritten, atoms move in the recording layer in accordance with the phase transformation between the crystalline phase and the amorphous phase. As a result, in the conventional information recording medium, when rewriting is repeated, there is a local bias of atoms, and the thickness of the recording layer is fluctuated to cause a decrease in signal quality. Such a decrease in repetitive rewriting performance increases especially as the recording density increases. This is because when the recording density is increased, the interval between adjacent recording marks is narrowed, and it is likely to be affected by the deviation of atoms of adjacent recording marks.

  In order to prevent the repeated rewrite performance from being lowered, it is necessary to reduce the thickness of the recording layer in order to suppress the movement of atoms. Further, 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 speed of the recording layer decreases because the atoms are less likely to move. When the crystallization speed is lowered, the signal quality is lowered in a high-density information recording medium in which a small recording mark must be recorded in a short time. Further, when the crystallization speed is lowered, the crystallization sensitivity is likely to deteriorate with time and the erasure rate is deteriorated with time. That is, as the recording density becomes higher, it becomes more difficult to achieve both the improvement of the repeated rewriting performance and the suppression of the deterioration with time of the crystallization sensitivity.

In order to improve repetitive rewriting performance, a recording layer containing Te, Ge, Sn, and Sb has been reported (see Patent Document 1).
Japanese Patent Laid-Open No. 2-147289

  However, although the conventional recording layer exhibits a high crystallization speed, the repeated rewriting performance and the long-term stability of the crystallization sensitivity in high-density recording are not sufficient.

  In order to solve the above problems, the present invention provides an information recording medium capable of high-density recording, excellent repetitive rewriting performance, and little deterioration with time in crystallization sensitivity, and a method for manufacturing the same.

Information recording medium of the present invention, by irradiating a laser beam, recording of information, Ri can der erasing and reproducing, recording and erasing of information, reversible phase between amorphous and crystalline phase An optical recording medium formed by change, wherein at least a first protective layer, a first interface layer, a recording layer, a second interface layer, a second protective layer, a light absorption correction layer, and a reflective layer are provided on a substrate. in this order, the composition of the recording layer is represented by the composition formula _{[(Ge 1-X Sn X} ) a Sb 2 Te 3 + a] 100-B M B
(However, M is at least one element selected from Ag, Al, Cr, Mn and N , and A, B and X are 0 <A ≦ 10, 0 <B ≦ 20, 0.07 <X <0. expressed in.) which is within the range of .69, the content of Sn in the recording layer is 20 atomic% or less 2 atomic% or more, the first interface layer and the second interface layer, respectively, nitride It is a layer mainly composed of at least one selected from an oxide or a nitrided oxide.

  According to the information recording medium of the present invention, it is possible to obtain an information recording medium having good repeated rewriting performance and little deterioration of crystallization sensitivity with time.

In the information recording medium, the recording layer is represented by the composition formula _{[(Ge, Sn) A Sb} 2 Te 3 + A] 100-B M B
However, it may be made of a material represented by 0 <A ≦ 10, 0 <B ≦ 20. By setting A ≦ 10, it is possible to prevent the repeated rewrite performance from being lowered. By setting B ≦ 20, it is possible to prevent the deterioration of crystallization sensitivity with time.

  The first interface layer is preferably a layer containing carbide as a main component.

  It is preferable that at least one of the first interface layer and the second interface layer is a layer containing carbon as a main component.

  It is preferable that at least one of the first interface layer and the second interface layer is a layer containing germanium nitride as a main component.

  In the information recording medium, the Sn content in the recording layer may be 2 atomic% or more and 20 atomic% or less. By setting the Sn content to 2 atomic% or more, the crystallization rate can be sufficiently increased. By setting the Sn content to 20 atomic% or less, the ratio of the reflected light amount when the recording layer is in the crystalline phase and the reflected light amount when the recording layer is in the amorphous phase can be increased.

  In the information recording medium, the recording layer may have a thickness of 5 nm to 15 nm. By setting the thickness of the recording layer to 5 nm or more, the recording layer can be easily made into a crystalline phase. By setting the recording layer to 15 nm or less, it is possible to prevent the repeated rewrite performance from being lowered.

  The information recording medium further includes a first protective layer, a second protective layer, and a reflective layer, wherein the first protective layer, the recording layer, the second protective layer, and the reflective layer are They may be formed in this order on the substrate. In this case, an interface layer disposed at at least one position selected from a position between the first protective layer and the recording layer and a position between the second protective layer and the recording layer is further provided. You may prepare. Furthermore, you may further provide the light absorption correction layer arrange | positioned between the said 2nd protective layer and the said reflection layer.

  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 are the substrate. They may be formed in this order. According to the above configuration, an information recording medium capable of particularly high-density recording can be obtained. In this case, an interface layer disposed at at least one position selected from a position between the first protective layer and the recording layer and a position between the second protective layer and the recording layer is further provided. You may prepare. Furthermore, you may further provide the light absorption correction layer arrange | positioned between the said reflection layer and the said 2nd protective layer.

  In order to manufacture the recording medium, the vapor deposition method may be at least one method selected from a vacuum deposition method, a sputtering method, an ion plating method, a chemical vapor deposition method, and a molecular beam epitaxy method. .

  In the manufacturing method, the vapor deposition method may be a sputtering method using a gas containing at least one gas selected from nitrogen gas and oxygen gas and one noble gas selected from argon and krypton. Good.

  In the above manufacturing method, the recording layer may be formed at a film formation rate of 0.5 nm / second or more and 5 nm / second or less. According to the above configuration, an amorphous recording layer can be formed.

  In the manufacturing method, the recording layer may have a thickness of 5 nm to 15 nm.

  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.

  A partial cross-sectional view of the information recording medium 10 of Embodiment 1 is shown in FIG. The information recording medium 10 includes a substrate 11 and a first protective layer 12a, a first interface layer 13a, a recording layer 14, a second interface layer 13b, a second protective layer 12b, which are sequentially stacked on the substrate 11. A light absorption correction layer 15 and a reflective layer 16 and a dummy substrate 18 bonded to the reflective 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 disposed above the substrate 11. The information recording medium 10 is irradiated with a recording / reproducing energy beam (generally, a laser beam) 19 from the substrate 11 side.

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

The recording layer 14 includes 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, Sn) _A Sb ₂ Te _{3 + A} ] _100-B M _B
(However, a material represented by 0 <A ≦ 10, 0 <B ≦ 20) can be used. This composition formula shows that Ge and Sn are contained in the recording layer 14 in a total of [(100−B) · A] / (2A + 5) atomic%. More preferably, A satisfies 2 ≦ A ≦ 8. Further, B preferably satisfies 2 ≦ B ≦ 15. In the material represented by this composition formula, the Sn content is preferably 2 atomic% or more and 20 atomic% or less.

The material represented by the above composition formula can be described as a material in which a part of Ge having a GeTe—Sb ₂ Te ₃ pseudo-binary composition is substituted with Sn and an element M is further added. The GeTe—Sb ₂ Te ₃ quasi-binary composition has been conventionally used as a material having a high crystallization rate. However, the crystallization rate can be further increased by dissolving SnTe or PbTe in this solution. SnTe and PbTe have a rock salt type crystal structure similarly to the GeTe-Sb ₂ Te ₃ pseudobinary system. SnTe and PbTe have a high crystallization rate and are easily dissolved in Ge—Sb—Te. In particular, SnTe is preferable as a material to be dissolved in the GeTe—Sb ₂ Te ₃ pseudobinary composition.

For example, GeTe—SnTe—Sb ₂ Te ₃ obtained by mixing SnTe with a GeTe—Sb ₂ Te ₃ pseudobinary composition is preferably used as the material of the recording layer 14. In this case, the crystallization speed is further increased by replacing part of Ge with Sn to obtain (Ge, Sn) Te—Sb ₂ Te ₃ .

  The element M contained in the recording layer 14 is considered to have a function of suppressing atomic movement. By using two elements of Al and Ag, Cr and Ag, or Mn and Ag as the element M, it is possible to improve the repeated rewriting performance, suppress the deterioration of crystallization sensitivity with time, and increase the signal amplitude. However, when increasing the concentration of the element M and the number of elements, it is preferable to increase the Sn concentration in the recording layer 14 in order not to decrease the crystallization speed. The concentration of the element M is preferably not more than the Sn concentration.

  The substrate 11 is a disk-shaped transparent substrate. As a material of the substrate 11, for example, a resin such as amorphous polyolefin or polymethyl methacrylate (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 as necessary. Of the surface of the substrate 11, the surface on which 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.

  The first and second protective layers 12 a and 12 b have a function of protecting the recording layer 14. By adjusting the thicknesses 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 by calculation based on, for example, a matrix method (for example, see 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 reflected light amount of the crystalline recording layer 14 and the reflected light amount of the amorphous recording layer 14 is large and the amount of light incident on the recording layer 14 is large. Can be determined.

The first and second protective layers 12a and 12b are made of a dielectric, for example. Specifically, for example, oxides such as SiO ₂ and Ta ₂ O ₅ , nitrides such as Si—N, Al—N, Ti—N, Ta—N, Zr—N, or Ge—N, ZnS, etc. Or sulfides such as SiC can be used. A mixture of these can also be used. Among these, ZnS-SiO _2, which is a mixture of ZnS and SiO ₂ is particularly excellent material. ZnS—SiO ₂ is amorphous, has a high refractive index, and good mechanical properties and moisture resistance. ZnS—SiO ₂ can be formed at a high film formation rate. The first protective layer 12a and the second protective layer 12b may be formed of the same material or different materials.

  The first and second interface layers 13a and 13b are disposed 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 movement of a substance generated between the first protective layer 12a and the recording layer 14 and between the second protective layer 12b and the recording layer 14. Have Examples of the material of the first and second interface layers 13a and 13b include nitrides such as Si—N, Al—N, Zr—N, Ti—N, Ge—N, and Ta—N, or these. The nitrided oxide containing 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 a material for the light absorption correction layer 15, it is preferable to use a material having a high refractive index and absorbing light appropriately. For example, a material having a refractive index n of 3 to 6 and an extinction coefficient k of 1 to 4 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. In addition, a crystalline metal, a semimetal, or a semiconductor material such as Si alloy, Te, Ti, Zr, Nb, Ta, Cr, Mo, W, SnTe, or PbTe can also be used.

  The reflective layer 16 has a function of increasing the amount of light absorbed by the recording layer 14. Furthermore, by forming the reflective layer 16, the heat generated in the recording layer 14 can be quickly diffused, and the recording layer 14 can be easily made amorphous. Furthermore, by forming the reflective layer 16, the laminated multilayer film can be protected from the use environment.

  As a material of the reflective layer 16, for example, a single metal having a high thermal conductivity such as Al, Au, Ag, or Cu can be used. Alternatively, an alloy such as Al—Cr, Al—Ti, Ag—Pd, Ag—Pd—Cu, or Ag—Pd—Ti may be used. In these alloys, 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 information recording conditions.

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

  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. Further, the laminated multilayer film is protected by the dummy substrate 18. The material described for the substrate 11 can be used for the material of the dummy substrate 18. 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.

  In the information recording medium 10 of Embodiment 1, 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 repetitive rewriting performance, and little deterioration with time in crystallization sensitivity.

  In the first embodiment, the information recording medium 10 including one recording layer 14 is shown. However, the information recording medium of the present invention may include two recording layers 14 (the same applies to the following embodiments). is there). For example, a double-sided information recording medium can be obtained by bonding the dummy substrates 18 of the two information recording media 10 together with an adhesive layer.

(Embodiment 2)
In Embodiment 2, another example of the information recording medium of the present invention will be described. In addition, about the part similar to the part demonstrated in Embodiment 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted (it is the same also in the following embodiment).

  A partial cross-sectional view of the information recording medium 20 of Embodiment 2 is shown in FIG. The information recording medium 20 includes a first substrate 21, a reflective layer 16, a light absorption correction layer 15, a second protective layer 12b, a second interface layer 13b, and a recording layer that are sequentially stacked on the first substrate 21. 14, a first interface layer 13 a, a first protective layer 12 a, and a second substrate 22 bonded to the first protective layer 12 a by an adhesive layer 17. That is, the information recording medium 20 includes a first substrate 21 and a recording layer 14 disposed 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.

  As the first substrate 21, a substrate similar to 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 as necessary. Of the surface of the second substrate 22, the surface on which 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 about 0.05 mm to 0.5 mm, for example.

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, when the wavelength of the energy beam 19 is λ and the numerical aperture of the objective lens is NA, the size w of the beam spot is
w = k · λ / NA (where k is a constant)
Given in. The spot size w becomes smaller as the wavelength λ is shorter and as the numerical aperture NA is larger. Therefore, the information recording medium 20 capable of increasing the numerical aperture of the objective lens can perform recording with higher density than the information recording medium 10. For example, it is reported that an objective lens with NA = 0.6 can be used for a substrate with a thickness of 0.6 mm, and an objective lens with NA = 0.85 can be used with 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 Data Storage '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 the information recording medium 10 can be obtained.

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

  First, a substrate 11 is prepared, and the substrate 11 is placed in a film forming apparatus. As the film forming apparatus used in Embodiment 3, 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 a plurality of power supplies are provided in one vacuum chamber is used. be able to. Note that the following layers may be formed by the same film forming apparatus or may be formed by different film forming apparatuses.

  Then, on the substrate 11, the first protective layer 12a, the first interface layer 13a, the recording layer 14, the second interface layer 13b, the second protective layer 12b, the light absorption correction layer 15, and the reflective layer 16 are formed. Sequentially formed. 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 where the groove is formed.

  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, a base material made of a compound may be sputtered in an Ar gas atmosphere or a mixed gas atmosphere of Ar gas and a reactive gas. Alternatively, a reactive sputtering method in which a metal base material is sputtered in a mixed gas atmosphere of Ar gas and reactive gas may be used.

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

  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 noble gas selected from argon and krypton. As said mixed gas, the mixed gas of nitrogen gas and argon, the mixed gas of nitrogen gas and krypton, or the mixed gas which added oxygen gas to these can be used, for example. Specifically, the recording layer 14 can be formed by sputtering a base material (target) containing Ge, Sb, Te, Sn, and the element M in the mixed gas atmosphere. As a base material, five base materials corresponding to each of Ge, Sb, Te, Sn, and element M may be used, or a binary base material or a ternary base material combining several elements. May be used. Further, when the element M is composed only of 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) _A Sb ₂ Te _{3 + A} ] _100-B M _B
(However, the recording layer represented by 0 <A ≦ 10, 0 <B ≦ 20) can be easily formed.

  The recording layer 14 is preferably formed at a film formation rate of 0.5 nm / second or more and 5 nm / second or less (more preferably 0.8 nm / second to 3 nm / second).

  After forming the second protective layer 12b, the light absorption correction layer 15 and the reflective 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.

  Next, the 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 process for crystallizing the entire surface of the recording layer 14 may be performed. The initialization process can be performed before the dummy substrate 18 is bonded or after the dummy substrate 18 is bonded.

  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 by the same method as each layer of the information recording medium 10. Further, the second substrate 22 can be adhered to the first protective layer 12 a by the adhesive layer 17, similarly to the dummy substrate 18. Also in the manufacturing method of the information recording medium 20, an initialization process is performed as necessary. The initialization process 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.

  According to the manufacturing method of Embodiment 3, the information recording medium of the present invention can be easily manufactured.

  Hereinafter, the present invention will be described in more detail with reference to examples.

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

First, as the substrate 11, a polycarbonate substrate (thickness: 0.6 mm) on which spiral guide grooves were formed was prepared. On this polycarbonate substrate, a ZnS—SiO ₂ layer (first protective layer 12a, thickness 140 nm), a Ge—N layer (first interface layer 13a, thickness: 5 nm), a recording layer (recording layer 14), Ge—N layer (second interface layer 13b, thickness: 3 nm), ZnS—SiO ₂ layer (second protective layer 12b, thickness: 40 nm), GeCr layer (light absorption correction layer 15, thickness: 40 nm) ) And an Ag alloy layer (reflection layer 16, thickness: 80 nm) were formed in this order by a sputtering method. The thicknesses of the first protective layer 12a and the second protective layer 12b were adjusted so that the signal amplitude (change in the amount of reflected light) at a wavelength of 660 nm was increased and the amount of light incident on the recording layer was increased. . These thicknesses were determined using calculations based on the matrix method.

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

  Thereafter, 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 adhered to the Ag alloy layer and irradiated with ultraviolet rays to bond the Ag alloy layer and the dummy substrate.

  In Example 1, after bonding the dummy substrate, the entire information recording medium was irradiated with a laser beam to crystallize the entire recording layer. Thus, 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 produced.

On the other hand, as a comparative example, an information recording medium was produced in the same manner as in the above example except that the material of the recording layer was changed. In this comparative example, the recording layer was formed using a material represented by the composition formula Ge ₄ Sb ₂ Te ₇ . Also for this comparative example, eight types of information recording media C-11 to C-18 having different recording layer thicknesses were produced.

  The above 16 types of information recording media were evaluated for repeated rewriting performance and aging sensitivity deterioration over time. These evaluation methods will be described later. The evaluation results are shown in Table 1.

  The larger the “number of rewritable times” in Table 1, the better the repeated rewritability. A1 to D1 each indicate the lower range of the table. E1 indicates that rewriting could not be performed. The smaller the “jitter value change” in Table 1, the smaller the deterioration of crystallization sensitivity with time. A2 to D2 each indicate the lower range of the table. E2 indicates that evaluation was not possible because the jitter value before the standing test exceeded 13% between the front end of the recording mark and between the rear end of the recording mark. The meanings of A1 to E1 and A2 to E2 are the same in the following tables.

  As shown in Table 1, in the information recording media C-11 to C-18 of the comparative examples, there were cases where the characteristics of A or B were not shown for both the rewritable count and the jitter value change. 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 rewritable count and the jitter value change.

In addition, the information recording medium of Example 1 had, on average, better rewriting performance and less aging sensitivity deterioration over time as compared with Comparative Examples C-11 to C-18. The improvement of the repeated rewriting performance is considered to be due to the addition of nitrogen. In addition, it is considered that the suppression of the aging deterioration of the crystallization sensitivity with time is due to an increase in the crystallization speed by replacing a part of Ge in Ge ₄ Sb ₂ Te ₇ with Sn.

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

An information recording medium was produced in the same manner as in Example 1 except that the thickness of the recording layer was fixed to 7 nm and the Sn content of the recording layer was changed. In the information recording medium of Example 2, the recording layer was formed using a material represented by the composition formula [(Ge, Sn) ₄ Sb ₂ Te ₇ ] ₉₅ N ₅ . Then, the eight types of information recording media 10-21 to 10- in which the Sn content was changed between 2 atom% and 25 atom% and the Ge content was changed between 27 atom% and 4 atom%. 28 was produced. 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 not containing Sn was produced in the same manner.

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

  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 manufactured by changing the element M will be described.

An information recording medium was produced in the same manner as in Example 1 except that the element M was changed and the thickness of the recording layer was fixed to 11 nm. In the information recording medium of Example 3, the recording layer was formed using a material represented by the composition formula [(Ge, Sn) ₄ Sb ₂ Te ₇ ] ₉₅ M ₅ . 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 produced. In addition, as a comparative example, an information recording medium C-31 not containing the element M was produced in the same manner.

  These information recording media 10-31 to 35 and C-31 were repeatedly evaluated for rewriting performance by the method described later. The evaluation results are shown in Table 3.

  As shown in Table 3, the rewrite performance was improved by using Mn, Ag, Cr, Al, or N as the element M. This effect was particularly great with 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 marks and the jitter value between the rear ends of the recording marks were improved.

(Example 4)
In Example 4, an example in which the information recording medium 10 is manufactured using Mn as the element M will be described. An information recording medium was produced 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 was formed using a material represented by the composition formula [(Ge, Sn) ₄ Sb ₂ Te ₇ ] ₉₅ Mn ₅ . 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 produced.

  For these information recording media 10-41 to 10-48, repeated rewriting performance and aging sensitivity deterioration with time were evaluated by the methods described later. The evaluation results are shown in Table 4.

  As shown in Table 4, by using Mn as the element M, it is possible to obtain an information recording medium having good repetitive rewriting performance and little deterioration with time in crystallization sensitivity. These two characteristics were good when the thickness of the recording layer was 7 nm or more and 13 nm or less. In addition, when the random signal recorded before being left alone was reproduced after being left alone, it was confirmed that there was no problem in record storability because the jitter value did not change.

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

An information recording medium was produced 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 was formed using a material represented by the composition formula [(Ge, Sn) ₄ Sb ₂ Te ₇ ] ₉₅ Cr ₅ . The Sn content was changed from 0 to 25 atom%, and the Ge content was changed from 29 atom% to 4 atom%. The thickness of the recording layer was 9 nm.

  With respect to the plurality of information recording media thus produced, repeated rewriting performance and aging sensitivity deterioration with time were evaluated by the method described later. As a result of the evaluation, a range where particularly preferable results are obtained is indicated by * in Table 5.

  * Indicates that the number of rewritable times was 100,000 or more and the jitter value change was + 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%, repetitive rewriting performance is good, and crystallization sensitivity. An information recording medium with little deterioration over time was obtained.

  Further, when a similar experiment was performed 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.

  Furthermore, the same experiment was conducted 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 atom% to 20 atom% and the Mn, Al, or Cr content to 1 atom% to 13 atom%.

(Example 6)
In Example 6, an example of manufacturing the information recording medium 20 will be described.

First, as the first substrate 21, a polycarbonate substrate (thickness: 1.1 mm) having spiral guide grooves formed on the surface was prepared. Next, an Ag alloy layer (reflective layer 16, thickness: 80 nm), a Te compound layer (light absorption correction layer 15, thickness: 20 nm), a ZnS-SiO ₂ layer (second protective layer 12b) on a polycarbonate substrate. , 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 5 nm), A ZnS—SiO ₂ layer (first protective layer 12a, thickness: 60 nm) was formed in this order by a sputtering method. The thicknesses of the first protective layer 12a and the second protective layer 12b were adjusted so that the signal amplitude (change in reflected light amount) at a wavelength of 405 nm was increased and the incident light amount to the recording layer was increased. . These thicknesses were determined using calculations based on the matrix method.

The recording layer was formed using a material represented by the composition formula [(Ge, Sn) ₄ Sb ₂ Te ₇ ] ₉₅ Mn ₅ . The Ge content was 19 atomic% and the Sn content was 10 atomic%.

  Thereafter, an ultraviolet curable resin was applied as an adhesive layer 17 on the first protective layer. 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. .

  In Example 6, after bonding the second substrate, the entire information recording medium was irradiated with a laser beam to crystallize the entire recording layer. In this manner, an information recording medium of Example 6 was produced. In Example 6, seven types of information recording media 20-1 to 20-7 having different recording layer thicknesses were produced. With respect to these information recording media, repeated rewriting performance and deterioration with time of crystallization sensitivity were evaluated by an 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.

Even in high-density recording, as shown in Table 6, it was possible to obtain an information recording medium having good repetitive rewriting performance and little deterioration in crystallization sensitivity over time. This is presumably because part of Ge in Ge ₄ Sb ₂ Te ₇ was replaced with Sn, and Mn was added as the element M.

  Further, when a similar experiment was performed 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.

  Furthermore, the same experiment was conducted 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 rewrite performance)
Hereinafter, a method for evaluating repetitive rewriting performance will be described.

  A schematic diagram of the recording / reproducing apparatus used for the evaluation is shown in FIG. The recording / reproducing apparatus includes a spindle motor 32 that rotates the information recording medium 31, an optical head 34 that includes a semiconductor laser 33, and an objective lens 35. A laser beam 36 emitted from the semiconductor laser 33 is condensed by the objective lens 35 and applied to the recording layer of the information recording medium 31. As the information recording medium 31, the information recording medium produced in the example is used.

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

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

(Evaluation of aging sensitivity over time)
Hereinafter, a method for evaluating the deterioration of crystallization sensitivity with time will be described.

  First, a random signal was recorded 10 times on the information recording medium by the same method as the evaluation of the repeated 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, a random signal was overwritten once on the signal recorded before being left. Thereafter, 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.

  (Jitter value change (%)) in the table is a value given by (jitter value change (%)) = (jitter value (%) after being left) − (jitter value (%) before being left).

  If there is no change in crystallization sensitivity before and after standing, there is almost no change in jitter value. Conversely, when the crystallization sensitivity decreases before and after standing, the jitter value change increases. For this reason, it can be seen that the smaller the jitter value change, the less the deterioration of crystallization sensitivity with time. Practically, it is preferable that the worse one 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.

  Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

It is a partial cross section figure which shows an example about the information recording medium of this invention. It is a partial cross section figure which shows another example about the information recording medium of this invention. It is the schematic of the recording / reproducing apparatus used for evaluation of 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

Claims (4)

By irradiating laser light, the recording of information, Ri can der erasing and reproducing, recording and erasing of information, the optical recording medium performed by reversible phase change between the amorphous phase and a crystalline phase There,
On the substrate, at least the first protective layer, the first interface layer, the recording layer, the second interface layer, the second protective layer, the light absorption correction layer, and the reflective layer are provided in this order,
The composition of the recording layer is represented by the composition formula _{[(Ge 1-X Sn X} ) A Sb 2 Te 3 + A] 100-B M B
(However, M is at least one element selected from Ag, Al, Cr, Mn and N , and A, B and X are 0 <A ≦ 10, 0 <B ≦ 20, 0.07 <X <0. .69)) ,
The Sn content in the recording layer is 2 atomic% or more and 20 atomic% or less ,
An information recording medium, wherein each of the first interface layer and the second interface layer is a layer containing at least one selected from nitride or nitride oxide as a main component.   The information recording medium according to claim 1, wherein at least one of the first interface layer and the second interface layer is a layer mainly composed of germanium nitride.   The information recording medium according to claim 1, wherein a thickness of the recording layer is larger than 5 nm and smaller than 15 nm.   The information recording medium according to claim 1, wherein the recording layer has a thickness of 7 nm to 13 nm.

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