JP2006221812A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium which can make CAV recording, wherein the reproduced signals does not deteriorate even after rewriting data for 100,000 times or more. <P>SOLUTION: This information recording medium has a base plate, and a recording layer to record information with phase changes made by irradiation with a laser beam. Further, it has a recording layer which contains at least Ge, Sb, Te and Bi and that contains Bi in the amount of 1-9%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an information recording medium on which information is recorded by irradiation with an energy beam, and more particularly to a phase change optical disk such as a DVD-RAM and a DVD-RW.

  In recent years, the market for read-only optical disks such as DVD-ROM and DVD-Video has been expanded. In addition, rewritable DVDs such as 4.7 GB DVD-RAM and 4.7 GB DVD-RW have been put on the market, and the market is rapidly expanding as computer backup media and video recording media replacing VTRs. Furthermore, in recent years, market demands for improving the transfer rate and access speed for recordable DVDs have increased.

  A recordable DVD medium such as DVD-RAM and DVD-RW that can be recorded and erased employs a phase change recording method. In the phase change recording method, basically, information of “0” and “1” is recorded in correspondence with crystal and amorphous. In addition, since the refractive index of crystal and amorphous is different, the refractive index and film thickness of each layer are designed so that the difference in reflectance between the portion changed to crystal and the portion changed to amorphous is maximized. By irradiating the crystallized part and the amorphous part with a laser beam and reproducing the reflected light, recorded “0” and “1” can be detected.

  Also, in order to make the predetermined position amorphous (usually this operation is called “recording”), the temperature of the recording layer becomes higher than the melting point of the recording layer material by irradiating a relatively high power laser beam. In order to make the crystal in a predetermined position (usually this operation is called “erasing”), the temperature of the recording layer is changed by irradiating a relatively low power laser beam. To a temperature near the crystallization temperature below the melting point. By doing so, the amorphous state and the crystalline state can be reversibly changed.

  In order for the recordable DVD to meet the demand for an improvement in transfer rate, a method of increasing the number of rotations of the medium and performing recording / erasing in a short time is general. At this time, the problem is recording / erasing characteristics when information is overwritten on the medium. The above problems will be described in detail below.

  Consider changing a given position from amorphous to crystalline. When the rotation speed of the medium is increased, the time for passing the laser beam and the predetermined position is shortened, and at the same time, the time for which the predetermined position is maintained at the crystallization temperature is also shortened. If the time for maintaining the temperature at the crystallization temperature is too short, the crystal cannot be sufficiently grown, so that amorphous remains. This is reflected in the reproduction signal, and the reproduction signal quality deteriorates.

  As a method for solving this problem, 1. 1. Increase the crystallization speed by changing the recording film composition. Two methods are conceivable: an interface layer in contact with the recording film and a material that promotes crystallization of the recording film.

  For example, in Japanese Patent Laid-Open No. 2001-322357, high-density recording is possible by using a material obtained by adding a metal such as Ag, Al, Cr, or Mn to a Ge—Sn—Sb—Te-based material as a recording material. It is said that an information recording medium having excellent repeated rewriting performance and little deterioration of crystallization sensitivity with time can be obtained. Japanese Patent Laid-Open No. 2-14289 also describes a Ge—Sn—Sn—Te based recording film material.

Japanese Patent Laid-Open No. 5-342629 discloses that the recording layer can be crystallized in a short time by introducing an interface layer that contacts the recording layer and promotes crystallization of the recording layer such as Sb ₄₀ Te ₁₀ Se ₅₀ . Further, in Japanese Patent Laid-Open No. 9-161316, an initial crystallization process can be performed at extremely high speed by providing a layer made of, for example, Sb ₂ Te ₃ as an interface layer (crystallization promoting layer). Furthermore, Japanese Patent Laid-Open No. 2001-273673 provides an information recording medium in which the crystallization speed does not decrease even after long-term storage by providing a layer made of SnTe, PbTe or the like as an interface layer (crystal nucleation layer). Yes.

  When information is recorded on an optical disk employing a phase change recording method, the rotational speed of the optical disk is usually controlled by a CLV (Constant Linear Velocity) method. That is, the control method is such that the relative speed between the laser beam and the optical disk is always constant. On the other hand, in the CAV (Constant Angular Velocity) method, there is a method of controlling the rotation with a constant angular velocity when rotating the optical disk.

  The features of the CLV method are as follows. 1. Since the data transfer rate during recording and reproduction is always constant, the signal processing circuit can be greatly simplified. Since the relative speed between the laser beam and the optical disk can be kept constant, the temperature history of the recording layer at the time of recording / erasing is made constant, so the load on the medium is small. 3. When the laser beam is moved in the radial direction of the optical disk, it is necessary to control the number of rotations of the motor again according to the radial position. For this reason, the access speed is greatly reduced.

  The features of the CAV method are: 1. Since the data transfer rate at the time of recording / reproduction varies depending on the radial position, the signal processing circuit increases. 2. Since the relative speed of the laser beam and the optical disk differs depending on the radial position, the temperature history of the recording layer at the time of recording / erasing largely depends on the radial position, and an optical disk having a special configuration is required. When the laser beam is moved in the radial direction of the optical disk, it is not necessary to re-control the number of rotations of the motor in accordance with the radial position, so that high speed access is possible.

  By using the recording layer material and the interface layer material disclosed in the conventional examples, extremely good recording / reproducing characteristics can be realized even when the disk linear velocity is high. However, since the conventional example does not sufficiently consider the problems in performing CAV recording, when CAV recording is performed, a reproduction signal reproduced from recorded information at the inner periphery of the information recording medium. There was a problem that quality deteriorated significantly.

In addition, the interface layer made of Sb ₄₀ Te ₁₀ Se ₅₀ , Sb ₂ Te ₃ , SnTe, PbTe, etc. shown in the conventional example is melted into the recording film by rewriting about 100,000 times, and the reproduction signal is transmitted. The problem of deteriorating occurred.

  Accordingly, an object of the present invention is to provide an information recording medium that can perform CAV recording and that does not deteriorate the reproduction signal even when rewriting is performed many times about 100,000 times.

  The problems of the above-described conventional example for obtaining an information recording medium that can perform CAV recording and that does not deteriorate the reproduction signal even when rewritten many times about 100,000 times will be summarized.

  The problems to be solved by the present invention are the following two points.

1) Suppression of melting of interface layer material into recording layer at the time of rewriting many times 2) Suppression of reproduction signal deterioration in inner peripheral part at the time of CAV recording Hereinafter, the causes of 1) and 2) will be described sequentially. Here, the description will be made on the premise of the information recording medium having the structure of FIG. That is, a first protective layer, a first interface layer, a recording layer, a second interface layer, a second protective layer, an absorptivity control layer, a thermal diffusion layer, and an ultraviolet curable protective layer are sequentially laminated on the substrate. . The effects of the present invention are not necessarily limited to the information recording medium having the structure shown in FIG.

1) Cause of interfacial layer material penetration into recording layer This phenomenon will be described with reference to FIG. FIG. 2 shows a recording layer of an information recording medium when the interface layer material such as Sb ₄₀ Te ₁₀ Se ₅₀ , Sb ₂ Te ₃ , SnTe, or PbTe shown in the conventional example is adopted as the first interface layer and the second interface layer. It is sectional drawing of a periphery part. The laser beam focused by the lens focuses on the recording film as shown in the figure. At this time, the laser beam is absorbed mainly on the surface of the recording layer on the first interface layer side. As a result, the recording layer generates heat on the surface of the recording layer in contact with the first interface layer. Thus, in the case of the configuration as shown in the figure, the temperature on the first interface layer side of the recording layer always tends to be higher than that on the second interface layer side of the recording layer.

Usually, the interface layer material that promotes the crystallization of the recording layer as described above has a lower melting point than that of Ge ₃ N ₄ , Cr ₂ O ₃ or the like generally used as the interface layer. When rewriting is repeated many times about 10,000 times, the interface layer material selectively dissolves in the recording layer from the first interface layer side. The inventors have also clarified that Bi ₂ Te ₃ also exhibits extremely good performance as a layer for promoting crystallization of the recording layer. However, since the melting point of Bi ₂ Te ₃ is as low as about 600 ° C., problems similar to those of the conventional material have occurred. In addition, the inventors simply use elements such as Sn, Pb, and Bi without using a compound such as Sb ₄₀ Te ₁₀ Se ₅₀ , Sb ₂ Te ₃ , SnTe, or PbTe as the interface layer as in the conventional example. The crystallization promoting effect of the recording layer can be obtained simply by adding to the interface layer material. This is because Te contained in the recording layer and elements such as Sn, Pb, and Bi are combined to generate crystalline compounds such as SnTe, PbTe, and Bi ₂ Te ₃ , respectively. As a result, the crystallization of the recording layer is promoted by using the crystalline compound as a crystal nucleus on the surface of the interface layer. For example, as an interface layer material, an oxide compound of the element such as SnO ₂ , PbO ₂ , Bi ₂ O _3, a sulfide of the element such as SnS ₂ , PbS, Bi ₂ S ₃ , or SnSe ₂ , PbSe, Bi _{Even when} a selenide of the element such as ₂ Se ₃ is used, the liberated element is combined with Te in the recording layer to form a crystalline compound, so that an effect of promoting crystallization of the recording layer is obtained. It is done. However, since the oxides, sulfides, and selenides are also thermally unstable, there arises a problem that the element is dissolved in the recording layer and the reproduction signal is deteriorated.

On the other hand, only the first interface layer is made of an interface layer material that has a high melting point such as Cr ₂ O ₃ or Ge ₃ N ₄ but has no effect of promoting crystallization of the recording layer. When the interface layer material such as Sb ₄₀ Te ₁₀ Se ₅₀ , Sb ₂ Te ₃ , SnTe, PbTe shown in the conventional example is used for the _two interface layers, such a problem does not occur. This indicates that the interface layer material is selectively dissolved in the recording layer from the first interface layer side. As described above, the cause of the melting of the interface layer material into the recording layer is that the temperature of the portion of the recording layer on the first interface layer side increases, so that the interface layer material melts into the recording layer from the first interface layer. . As described above, when the interface layer material that does not promote the crystallization of the recording film is used for the first interface layer, there arises a problem that the crystallization is not sufficiently performed during high-speed recording.

2) Cause of reproduction signal deterioration in the inner periphery during CAV recording First, the crystal state of the periphery of the amorphous mark in the outer periphery where the reproduction signal is not deteriorated will be described (FIG. 3). FIG. 3A is a diagram showing an amorphous mark when an amorphous mark is recorded on a crystal and a crystal state around the amorphous mark. What is characteristic is that the molten region is an amorphous mark as it is. Further, as shown in FIG. 2B, even when a new amorphous mark is overwritten on FIG. 3A, the amorphous mark of FIG. 3A is completely crystallized. .

  Next, the cause of reproduction signal deterioration in the inner periphery will be described with reference to FIG. FIG. 4A is a diagram schematically showing the crystal state of the periphery of the amorphous mark when the amorphous mark is recorded on the inner periphery of the conventional information recording medium. A characteristic point is that the amorphous mark is significantly smaller than the melting region. This is because, during recording of the amorphous mark, a crystal grows from the outer edge of the melted region melted by the laser beam, and the phenomenon that the recording mark shrinks (recrystallization) occurs. The reason for this will be described below. In CAV recording, the disk linear velocity at the inner periphery is slow. For this reason, the cooling rate of the melted region becomes slow due to the influence of heat by the laser beam that has passed, and as a result, the amorphous region is recrystallized.

  For this reason, the size of the finally generated amorphous mark becomes smaller than that of the melted region, and the reproduction signal amplitude decreases (problem 1). In addition, the crystal grain size of the recrystallization region that causes shrinkage is larger than that of the normal crystallization region. Further, as shown in FIG. 3B, when information is newly overwritten on FIG. 3A, crystals having different crystal grain sizes remain between the amorphous marks. Since the reflectance is different when the crystal grain size is different, the dispersion of the crystal grain size causes the dispersion of the reflectance, and as a result, the noise of the reproduction signal is increased (Problem 2). Further, the dispersion of the crystal grain size causes dispersion of the thermal conductivity, the melting point, and the crystal growth rate. As a result, the amorphous mark shape is affected by the dispersion of the crystal grain size, and the reproduction signal is deteriorated (Problem 3). As described above, the main causes of reproduction signal deterioration in the inner periphery are problems 1 to 3 caused by recrystallization.

  Next, specific solutions for the problems 1) and 2) will be described.

1) Suppression of melting of interface layer material into recording layer during multiple rewrites In order to solve the above problem, the first interface layer and the second interface layer have an effect of promoting the crystallization of the recording layer. In order to contain elements such as Bi, Sn, and Pb, and to prevent the low-melting-point elements from dissolving into the recording layer, the sum of the contents of Bi, Sn, and Pb contained in the first interface layer is determined. The amount may be less than that of the second interface layer.

Alternatively, since Te also has a low melting point, when using a Te compound such as SnTe, PbTe, Bi ₂ Te ₃ as the first interface layer or the second interface layer, the Bi, The sum of the contents of Sn, Pb, Te, etc. may be reduced as compared with the second interface layer.

  Here, as a method of reducing the content of Bi, Sn, Pb, Te, or the like contained in the interface layer, a method of adding a thermally and chemically stable Ge—N-based material to the interface layer is preferable. This is because Ge is in the same family as Sn and Pb, and Bi and Te can easily form a compound. In addition, Bi, Sn, Pb, and Te are difficult to bond with nitrogen, so that it is possible to avoid a decrease in the crystallization promoting effect of the recording layer due to the addition of Ge—N.

  As the method for producing the interface layer, the following method can reduce the price of the sputtering target, can use DC sputtering that can reduce the thermal damage to the substrate and can reduce the price of the sputtering apparatus, and is more uniform. It is excellent because Ge—N can be added. That is, by performing sputtering using a sputtering target containing Te and Ge, and further containing any one element of Bi, Sn, and Pb and a sputtering gas containing nitrogen, This is a method of forming an interface layer.

  In addition to the addition of the Ge—N-based material, a transition metal oxide or a transition metal nitride may be added. Since transition metals easily change their valence, even if elements such as Bi, Sn, and Pb are liberated, the transition metal changes its valence, and bonding occurs between the transition metal and Bi, Sn, and Pb. This is because a thermally stable compound is produced. In particular, Cr, Mo, and W are excellent materials because they have a high melting point, easily change their valence, and easily form a thermally stable compound with the metal.

In addition, when the first interface layer has to be made as thin as 3 nm or less in order to control the crystallization of the recording film due to optical demands, the first interface layer is not layered but formed in spots. Sometimes. Even in this case, the effect of promoting the crystallization of the recording layer is not lost, but sulfur in ZnS-SiO ₂ used for the first protective layer may pass through the first interface layer and dissolve into the recording layer. is there. In such a case, instead of ZnS—SiO ₂ , a material containing SnO ₂ containing Sn that is more thermally stable than ZnS—SiO ₂ and that promotes crystallization of the recording layer may be used. Good.

Further, the thermal load on the second interface layer during information recording is smaller than that of the first interface layer. However, the second interface layer is used in order to control the crystallization of the recording film because of optical requirements. When the thickness of the second interface layer must be reduced to 1 nm or less, the second interface layer may not be layered and may be formed in spots. Even in this case, the effect of promoting the crystallization of the recording layer is not lost, but sulfur in ZnS-SiO ₂ used for the second protective layer may pass through the second interface layer and dissolve into the recording layer. is there. Even in such a case, instead of ZnS—SiO ₂ , a material such as SnO ₂ containing Sn that is more thermally stable than ZnS—SiO ₂ and promotes crystallization of the recording layer may be used. .

2) Suppression of reproduction signal deterioration in inner periphery during CAV recording Next, a specific measure for suppressing reproduction signal deterioration in the inner periphery during CAV recording will be described. As described above, the reproduction signal deterioration in the inner periphery during CAV recording is caused by the phenomenon that the crystal grows from the outer edge of the melted region melted by the laser beam during recording of the amorphous mark and the recording mark shrinks ( This is because recrystallization occurs. Therefore, recrystallization should be suppressed to solve the above problem. In order to suppress recrystallization, a material that is difficult to grow crystals, that is, a material having a slow crystal growth rate may be used as the recording layer material. However, when such a material is used, when the disk linear velocity increases at the outer peripheral portion, the heating time by the laser beam becomes insufficient, and the time for the recording layer to be maintained at the crystallization temperature is insufficient. Therefore, there arises a problem that the amorphous mark to be crystallized is not sufficiently crystallized.

  Therefore, the inventors have intensively studied how this problem can be solved, and have come up with a method for solving an essential problem. The said solution is demonstrated in detail using FIGS.

  FIG. 5 is a diagram for explaining a mechanism in which recrystallization of a conventional medium occurs. In general, it can be explained that the crystallization of the recording layer is constituted by two kinds of phenomena. Nucleation and crystal growth. The speed of nucleation and crystal growth is a function of temperature as shown in FIG. That is, the crystal growth rate is maximized immediately below the melting point of the recording layer material, and the nucleation rate is maximized on the lower temperature side than the temperature at which the crystal velocity is maximized.

  Incidentally, as described above, in the phase change recording, the amorphous mark is crystallized by heating the recording layer material to near the crystal growth temperature below the melting point. At this time, crystal nuclei are generated in the recording layer because the temperature passes through a temperature at which the nucleation rate becomes maximum when the temperature is raised. Further, since the crystal growth rate increases as the temperature rises further, the crystal grows around the crystal nucleus generated on the low temperature side, and the entire amorphous mark can be crystallized.

  On the other hand, when recording an amorphous mark, the temperature of the recording layer is heated above the melting point of the recording layer material. At this time, at the center of the amorphous mark, the recording layer is made amorphous with cooling. However, at the outer edge portion of the melted region, when the temperature of the outer edge portion is cooled to a temperature range where the crystal growth rate immediately below the melting point is maximized, crystals from the outer edge portion toward the center of the molten region are formed. As a result of the growth, the size of the finally recorded amorphous mark is reduced (FIG. 6). This is the mechanism by which recrystallization occurs.

  In order to solve the problem of recrystallization, the maximum value of the crystal growth rate is decreased and the maximum value of the crystal growth rate is increased as shown in FIG. By doing so, crystal growth can be suppressed from the outer edge of the molten region during recording of the amorphous mark (FIG. 8). Further, when crystallizing the amorphous mark, a large number of crystal nuclei are formed as compared with the case of FIG. 5, so that even if the crystal growth rate is reduced, the entire amorphous mark can be crystallized. It becomes possible.

  As shown in FIG. 7, the inventors have clarified that there are two methods for increasing the nucleation rate and decreasing the crystal growth rate. That is, the following method.

Method A: A material having a low nucleation rate and a crystal growth rate is used as the recording layer material, and a material that increases the nucleation rate is used at the interface.

Method B: A material having a high nucleation rate and a low crystal growth rate is used as the recording layer material.

  Methods A and B will be described in detail below.

In the case of Method A, elements such as Sn, Pb and Bi may be included as the interface layer material. In addition, this interface layer should just contain said element in either 1st, 2nd, or both. In this case, as the interface layer material, an oxide compound of the element such as SnO ₂ , PbO ₂ , Bi ₂ O _3, a sulfide of the element such as SnS ₂ , PbS, Bi ₂ S ₃ , or SnSe ₂ , PbSe, A chalcogenide compound of Sn, Pb, Bi such as a selenide of the element such as Bi ₂ Se ₃ or a telluride such as SnTe, PbTe, Bi ₂ Te ₃ may be used. What is important is that the crystallization temperature of SnTe, PbTe, Bi ₂ Te ₃ or the like on the surface of the interface layer is extremely low (the crystallization temperature is below room temperature) due to the combination of Te, Sn, Pb, and Bi in the recording layer. When the recording film is crystallized, a compound that promotes crystal nucleation of the recording film is generated. Of course, when the telluride of Sn, Pb, Bi is contained in the interface layer, the effect of generating the crystal nuclei of the recording film is maximized, but the Sn, Pb, Bi oxides, sulfides, selenides are effective. Since the melting point is higher, the effect of suppressing the phenomenon that Sn, Pb, Bi is dissolved in the recording film is higher. In addition, compared with tellurides of Sn, Pb, and Bi, oxides, sulfides, and selenides of Sn, Pb, and Bi are more convenient because the absorptance is low and the degree of freedom in optical design is expanded. Ideally, as shown above, by using a material obtained by mixing telluride of Sn, Pb, Bi and a high melting point compound such as Ge ₃ N ₄ , Cr ₂ O ₃ as an interface layer, Since the element can be prevented from being dissolved into the recording layer by rewriting many times, and the absorptance of the interface layer can be reduced, the degree of freedom in optical design is increased.

Further, as the recording layer material, a recording layer material having a composition ratio in which Sb is excessively added to a GeSbTe-based recording layer material in which GeTe and Sb ₂ Te ₃ which are conventionally known are mixed at an appropriate ratio is used. good. Specifically, the recording layer material in the range represented by the following composition formula is excellent. (Atomic%)
Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y
20 <X <45, 0.5 <Y <5
Besides adding an excessive amount of Sb, an element that lowers the nucleation rate and the crystal growth rate may be added. Specifically, the recording layer material in the range represented by the following composition formula is excellent.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y ) _100-Z M _Z
20 <X <45, 0.5 <Y <5, 0.5 <Z <5
However, M is an element selected from Ag, Cr, Si, Ga, Al, In, B, and N.

  Further, the crystal growth rate of the recording layer material is preferably as low as possible, but if it is too slow, there arises a problem that the amorphous mark is not sufficiently crystallized in the outer peripheral portion of the information recording medium. In order to avoid this problem, a material that promotes crystallization of the recording layer material may be added to both the first interface layer and the second interface layer as much as possible. However, if many elements such as Sn, Pb, Bi, etc. are added to the first interface layer, there arises a problem that these elements are dissolved in the recording layer at the time of many rewrites. It is better that the amount of elements is smaller than that of the second interface layer.

  Next, method B will be described in detail.

The inventors have improved the nucleation speed by adding Bi ₂ Te ₃ to a GeSbTe-based recording layer material in which GeTe and Sb ₂ Te ₃ are mixed at an appropriate ratio, so that the nucleation speed can be improved. In addition, it was clarified that good recording / reproducing characteristics can be obtained from the inner circumference to the outer circumference of the information recording medium. The GeSnSbTe-based material shown in the above-mentioned conventional example is also a material with a very good nucleation rate, but according to the experiments by the inventors, the addition of Bi ₂ Te ₃ increases the crystal growth rate. Since the effect is large and the difference in refractive index between amorphous and crystal is large, the reproduction signal amplitude can be improved. Specifically, the Bi content may be 1 to 9%. Furthermore, the recording layer material in the range represented by the following composition formula is excellent.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2XY ) _100-Z (Bi ₂ Te ₃ ) _Z
20 <X <45, -2 <Y <2, 2.5 <Z <25
If the relationship between the four elements is within the range expressed by the composition formula, even if impurities are mixed, the effect of the present invention is not lost if the atomic% of impurities is within 1%. .

  In the present invention, the information recording medium may be expressed as a phase change optical disk or simply an optical disk. However, in the present invention, heat is generated by irradiation of an energy beam, and the atomic arrangement is changed by this heat. Since the present invention can be applied to any information recording medium on which information is recorded, the present invention can be applied to information recording media other than a disk-shaped information recording medium such as an optical card, regardless of the shape of the information recording medium.

  Further, in the present specification, the above-described energy beam is sometimes expressed as a laser beam, or simply laser light or light. However, as described above, the present invention is an energy capable of generating heat on an information recording medium. Since an effect can be obtained with a beam, the effect of the present invention is not lost even when an energy beam such as an electron beam is used. The present invention was invented for an information recording medium for a red laser (wavelength 645 to 660 nm), but is not particularly based on the wavelength of the laser, but a relatively short wavelength laser such as a blue laser or an ultraviolet laser. The present invention is also effective for information recording media on which recording is performed.

  In the present invention, it is assumed that the substrate is disposed on the light incident side of the recording layer. However, the substrate is disposed on the opposite side of the recording layer from the light incident side. Even when a protective material such as a thin protective sheet is disposed, the effect of the present invention is not lost.

  The first interface layer and the second interface layer contain elements such as Bi, Sn, and Pb that have an effect of promoting crystallization of the recording layer, and further suppress the melting of the low melting point element into the recording layer. Therefore, by reducing the sum of the contents of Bi, Sn, Pb, etc. contained in the first interface layer as compared with the second interface layer, the nucleation speed of the recording layer is improved and at the same time the interface layer It is possible to suppress the deterioration of the reproduction signal at the time of rewriting many times due to the material being dissolved in the recording layer.

Further, as the recording layer material, a recording layer material having a composition ratio in which Sb is excessively added to a GeSbTe-based recording layer material in which GeTe and Sb ₂ Te ₃ which are conventionally known are mixed at an appropriate ratio is used. good. By doing so, even if the CAV recording is performed, problems caused by recrystallization at the inner periphery can be suppressed.

Further, by adding Bi ₂ Te ₃ to a GeSbTe recording layer material in which GeTe and Sb ₂ Te ₃ are mixed at an appropriate ratio, the nucleation speed is improved and the inner circumference of the information recording medium can be improved even during CAV recording. Good recording / reproduction characteristics can be obtained from the outer periphery to the outer periphery. Since the recording film added with Bi ₂ Te ₃ has a large refractive index difference between amorphous and crystalline, the reproduction signal amplitude can be improved.

Various experimental examples are shown below, and examples of the present invention are clarified. Incidentally, in measuring the various performances of the information recording medium shown in each experimental example, the evaluation conditions and the information recording apparatus described later (FIG. 13), a random signal at the inner peripheral portion jitter (inner peripheral portion 10 times Jitter after recording) and outer periphery jitter (jitter after recording a random signal 10 times on the outer periphery) were measured. Further, in order to investigate the effect of the penetration of the interface layer material into the recording layer, the difference between the 11T amplitude after 10 times recording and the 11T amplitude after 10,000 times recording (hereinafter referred to as “amplitude degradation”) in the inner periphery. It was measured. In this information recording medium, land-groove recording is adopted. For this reason, the average value when information is recorded on the land and groove is shown here. The target values for each performance are as follows.

The inner peripheral portion jitter: 9% or less outer periphery jitter: 9% or less amplitude deterioration: 2 dB below Incidentally, the evaluation results of the experimental example in FIG. 9, 10 ◎, 〇 will be denoted by ×, criterion following Street.

A: Inner periphery jitter, outer periphery jitter is 8% or less, or amplitude deterioration is 1 dB or less.

◯: Inner periphery jitter, outer periphery jitter is 9% or less, or amplitude deterioration is 2 dB or less.

X: The inner peripheral jitter and the outer peripheral jitter are higher than 9%, or the amplitude deterioration is larger than 2 dB.

  FIG. 1 shows a basic configuration of an information recording medium according to an experimental example. That is, a first protective layer, a first interface layer, a recording layer, a second interface layer, a second protective layer, an absorptivity control layer, a thermal diffusion layer, and an ultraviolet curable protective layer are sequentially laminated on the substrate. . Here, a substrate made of polycarbonate having a thickness of 0.6 mm is used as the substrate, and a groove shape and a pre-pit shape in the same format as the 4.7 GB DVD-RAM are formed in advance on the substrate. Each of the layers was formed using the sputtering apparatus shown in FIG. 11 under the conditions shown in FIG.

<Experimental example 1>
First, as a comparison, the result of making a prototype of an information recording medium having a conventional structure and evaluating it is shown. First, by sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer, Cr ₂ O ₃ is 3 nm as the first interface layer, and Ge ₃₃ . ₃ Sb ₁₃ . ₃ Te ₅₃ . ₄ is 8 nm, Cr ₂ O ₃ is 1.5 nm as the second interface layer, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as the second protective layer, and Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is used as the absorptance control layer. A film of Al ₉₉ Ti ₁ having a thickness of 35 nm and a thermal diffusion layer of 60 nm was formed.

  As a result of evaluating the information recording medium, as indicated by reference numeral 1 in FIG. 9, the inner peripheral jitter and amplitude deterioration satisfied the target, but the outer peripheral jitter did not reach the target.

Next, when the first interface layer and the second interface layer were Sb ₂ Te ₃ , all items did not reach their targets as indicated by number 2 in FIG.

  Next, when SnTe is used for the first interface layer and the second interface layer, as shown by number 3 in FIG. 9, the outer peripheral jitter satisfies the target, but the inner peripheral jitter and amplitude deterioration are the targets. It was not achieved.

  Next, when the first interface layer and the second interface layer are made of PbTe, as shown by the number 4 in FIG. 9, the outer peripheral jitter satisfies the target, but the inner peripheral jitter and amplitude deterioration are the targets. It was not achieved.

Next, when the first interface layer and the second interface layer are Bi ₂ Te ₃ , the outer peripheral jitter satisfied the target as shown by number 5 in FIG. 9, but the inner peripheral jitter and amplitude Deterioration was not achieved.

  As described above, the configurations of numbers 1 to 5 in FIG. 9 cannot achieve both the reproduction signal quality during CAV recording and the amplitude deterioration during multiple rewrites. Each of these structures does not contain Bi in the recording layer, and thus corresponds to the conventional example of the present invention.

<Experimental example 2>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer, 3 nm as the first interface layer to be described later, and Ge ₃₃ . ₃ Sb ₁₃ . ₃ Te ₅₃ . ₄ is 8 nm, a second interface layer described later is 1.5 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer, Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is 35 nm as an absorptance control layer, heat As a diffusion layer, Al ₉₉ Ti ₁ was deposited to 60 nm.

Here, when the first interface layer is (SnTe) ₅₀ (Ge ₃ N ₄ ) ₅₀ and the second interface layer is SnTe, the inner peripheral jitter does not reach the target as shown by number 6 in FIG. However, the outer peripheral jitter and amplitude deterioration satisfied the targets.

Next, when the first interface layer is (PbTe) ₅₀ (Ge ₃ N ₄ ) ₅₀ and the second interface layer is PbTe, the inner peripheral jitter does not reach the target as shown by number 7 in FIG. However, the outer peripheral jitter and amplitude deterioration satisfied the targets.

Next, when the first interface layer is (Bi ₂ Te ₃ ) ₅₀ (Ge ₃ N ₄ ) ₅₀ and the second interface layer is Bi ₂ Te ₃ , as shown in the number 8 of FIG. The target of jitter was not achieved, but the outer peripheral jitter and amplitude deterioration satisfied the target.

  As described above, by making the content of Sn, Pb, Bi contained in the first interface layer smaller than that in the second interface layer, it is possible to suppress amplitude deterioration due to the interface layer material being dissolved in the recording layer. . However, in the configurations of Nos. 6 to 8 in FIG. 9, the inner peripheral jitter at the time of CAV recording could not be sufficiently reduced. Each of these structures does not contain Bi in the recording layer, and thus corresponds to the conventional example of the present invention.

<Experimental example 3>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer, 3 nm as the first interface layer to be described later, and Ge ₃₃ . ₃ Sb ₁₃ . ₃ Te ₅₃ . ₄ is 8 nm, a second interface layer described later is 1.5 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer, Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is 35 nm as an absorptance control layer, heat As a diffusion layer, Al ₉₉ Ti ₁ was deposited to 60 nm.

Here, when the first interface layer is SnTe and the second interface layer is (SnTe) ₅₀ (Ge ₃ N ₄ ) ₅₀ , as shown by number 9 in FIG. 9, the outer peripheral jitter satisfies the target. However, the inner circumference jitter and amplitude degradation did not reach the targets.

Next, when the first interface layer is PbTe and the second interface layer is (PbTe) ₅₀ (Ge ₃ N ₄ ) ₅₀ , as shown in the number 10 in FIG. However, the inner circumference jitter and amplitude degradation did not reach the targets.

Next, when the first interface layer is Bi ₂ Te ₃ and the second interface layer is (Bi ₂ Te ₃ ) ₅₀ (Ge ₃ N ₄ ) ₅₀ , as shown by reference numeral 11 in FIG. Satisfied the target, but the inner periphery jitter and amplitude degradation did not reach the target.

  As described above, when the content of Sn, Pb, Bi contained in the first interface layer is made larger than that in the second interface layer, the amplitude deterioration due to the interface layer material dissolving into the recording layer becomes remarkable. Further, with the configurations of numbers 9 to 11 in FIG. 9, the inner peripheral jitter at the time of CAV recording could not be sufficiently reduced. Each of these structures does not contain Bi in the recording layer, and thus corresponds to the conventional example of the present invention.

<Experimental example 4>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer, 3 nm as the first interface layer described later, and Ge ₃₀ . ₃ Sb ₁₉ . ₃ Te ₅₀ . ₄ is 8 nm, a second interface layer described later is 1.5 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer, Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is 35 nm as an absorptance control layer, heat As a diffusion layer, Al ₉₉ Ti ₁ was deposited to 60 nm.

Here, when the first interface layer is (SnTe) ₅₀ (Ge ₃ N ₄ ) ₅₀ and the second interface layer is SnTe, all the performances satisfy the target as shown by reference numeral 12 in FIG. It was.

Next, when the first interface layer is (PbTe) ₅₀ (Ge ₃ N ₄ ) ₅₀ and the second interface layer is PbTe, all the performances satisfy the target as shown by number 13 in FIG. It was.

Next, when the first interface layer is (Bi ₂ Te ₃ ) ₅₀ (Ge ₃ N ₄ ) ₅₀ and the second interface layer is Bi ₂ Te ₃ , all the performances are obtained as indicated by reference numeral 14 in FIG. Was satisfied with the goal.

Next, when the first interface layer is (Sn ₅ Bi ₂ Te ₈ ) ₆₀ (Ge ₃ N ₄ ) ₄₀ and the second interface layer is Sn ₅ Bi ₂ Te ₈ , as indicated by reference numeral 15 in FIG. All performances met the target. In particular, the performance of the inner periphery jitter and the outer periphery jitter was excellent.

Next, when the first interface layer is (Pb ₄ Bi ₂ Te ₇ ) ₄₀ (Ge ₃ N ₄ ) ₆₀ and the second interface layer is Pb ₄ Bi ₂ Te ₇ , as indicated by reference numeral 16 in FIG. All performances met the target. In particular, the performance of the inner periphery jitter and the outer periphery jitter was excellent.

Next, when the first interface layer is (Sn ₅ Bi ₂ Te ₈ ) ₂₀ (Ge ₃ N ₄ ) ₈₀ and the second interface layer is (Sn ₅ Bi ₂ Te ₈ ) ₈₀ (Ge ₃ N ₄ ) ₂₀ , As indicated by numeral 17 in FIG. 9, all the performances met the target. Also, the inner peripheral jitter, outer peripheral jitter, and amplitude deterioration performance were all good.

Next, when the first interface layer is (Pb ₄ Bi ₂ Te ₇ ) ₄₀ (Ge ₃ N ₄ ) ₆₀ and the second interface layer is (Pb ₄ Bi ₂ Te ₇ ) ₈₀ (Ge ₃ N ₄ ) ₂₀ , As indicated by numeral 18 in FIG. 9, all the performances met the target. Also, the inner peripheral jitter, outer peripheral jitter, and amplitude deterioration performance were all good.

As described above, by making the content of Sn, Pb, Bi contained in the first interface layer smaller than that in the second interface layer, it is possible to suppress amplitude deterioration due to the interface layer material being dissolved in the recording layer. . Further, by adding excessive Sb to the recording layer, it is possible to suppress recrystallization of the recording layer material, so that the inner peripheral jitter during CAV recording can be sufficiently reduced. Furthermore, by using Sn-Bi-Te-based material or Pb-Bi-Te-based material for the interface layer, compared with the case where SnTe, PbTe, Bi ₂ Te ₃ are used alone as the second interface layer. In addition, the inner peripheral jitter and the outer peripheral jitter can be reduced. This is presumably because the similarity between the crystal structure of the recording film and the crystal structure of the interface layer material has increased. That is, the Ge—Sb—Te-based material used here is a mixture of GeTe and Sb ₂ Te _{3 in} an appropriate ratio, and Sb or the like is added excessively. Here, the crystal system of SnTe and PnTe is the same system as GeTe, and the crystal system of Bi ₂ Te ₃ is the same system as Sb ₂ Te ₃ . This is because Ge, Sn, and Pb, and Sb and Bi are homologous elements. Therefore, the Sn—Bi—Te-based material or the Pb—Bi-Te-based material has a very high crystal structure similarity with the Ge—Sb—Te-based material and has a high crystallinity. The configurations of numbers 12 to 18 in FIG. 9 can achieve both the reproduction signal quality at the time of CAV recording and the amplitude deterioration at the time of many rewrites, but since the recording layer does not contain Bi, the reference example of the present invention. It corresponds to.

From the above results, it was found that the addition of a refractory dielectric material such as Ge ₃ N ₄ to the second interface layer is more effective in suppressing amplitude deterioration.

Further, the same information recording medium was prepared except the number 17 in FIG. 9 and the thickness of the first interface layer. The thickness of the first interface layer of this information recording medium was 0.5 nm, but in this case, the amplitude deterioration was greatly deteriorated. Therefore, when (SnO ₂ ) ₈₀ (Cr ₂ O ₃ ) ₂₀ was used as the first protective layer, the amplitude deterioration was greatly improved and was suppressed below the target.

Further, the same information recording medium was prepared except the number 17 in FIG. 9 and the thickness of the second interface layer. The thickness of the second interface layer of this information recording medium was 0.5 nm, but in this case, the amplitude deterioration was greatly deteriorated. Therefore, when (SnO ₂ ) ₉₀ (ZnS) ₁₀ was used as the first protective layer, the amplitude deterioration was greatly improved and was suppressed below the target.

<Experimental example 5>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer, 3 nm as the first interface layer to be described later, and Ge ₃₂ . ₂ Sb ₁₅ . ₅ Te ₅₂ . ₃ is 8 nm, a second interface layer to be described later is 1.5 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer, Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is 35 nm as an absorptance control layer, heat As a diffusion layer, Al ₉₉ Ti ₁ was deposited to 60 nm.

Here, when the first interface layer is Cr ₂ O ₃ and the second interface layer is SnTe, as shown by number 19 in FIG. 9, the inner peripheral jitter and amplitude deterioration satisfied the target. The perimeter jitter was not achieved.

Next, when the first interface layer is Cr ₂ O ₃ and the second interface layer is PbTe, as shown by numeral 20 in FIG. 9, the inner peripheral jitter and the amplitude deterioration satisfy the target. The perimeter jitter was not achieved.

Next, when the first interface layer is made of Cr ₂ O ₃ and the second interface layer is made of Bi ₂ Te ₃ , the inner peripheral jitter and amplitude deterioration satisfy the targets as shown by reference numeral 21 in FIG. However, the perimeter jitter was not achieved.

  As described above, when the first interface layer does not contain an element such as Sn, Pb, Bi or the like that promotes crystallization of the recording film, the jitter at the outer peripheral portion has not reached the target. 9 corresponds to the conventional example of the present invention because Bi is not contained in the recording layer.

Next, when the first interface layer was (SnTe) ₃₀ (Cr ₂ O ₃ ) ₇₀ and the second interface layer was SnTe, all items met the target as indicated by reference numeral 22 in FIG.

Next, when the first interface layer was (SnTe) ₃₀ (Cr ₂ O ₃ ) ₇₀ and the second interface layer was PbTe, all items met the target, as indicated by reference numeral 23 in FIG.

Next, when the first interface layer is (Bi ₂ Te ₃ ) ₃₀ (Cr ₂ O ₃ ) ₇₀ and the second interface layer is Bi ₂ Te ₃ , all items are shown as indicated by reference numeral 24 in FIG. Satisfied the goal.

As described above, by making the content of Sn, Pb, Bi contained in the first interface layer smaller than that in the second interface layer, it is possible to suppress amplitude deterioration due to the interface layer material being dissolved in the recording layer. . Further, by adding excess Sb to the recording layer, it is possible to suppress recrystallization of the recording layer material, so that the inner peripheral jitter during CAV recording can be sufficiently reduced. Further, it has been found that it is effective to add a transition metal oxide such as Cr ₂ O ₃ as a means for reducing elements such as Sn, Pb, and Bi contained in the first interface layer. The configurations of numbers 22 to 24 in FIG. 9 can achieve both the reproduction signal quality at the time of CAV recording and the amplitude deterioration at the time of many rewrites, but since the recording layer does not contain Bi, the reference example of the present invention. It corresponds to.

Next, when the first interface layer is SnTe and the second interface layer is (SnTe) ₃₀ (Cr ₂ O ₃ ) ₇₀ , as shown by reference numeral 25 in FIG. 9, the inner peripheral jitter and the outer peripheral jitter are The target was satisfied, but the amplitude deterioration was not achieved.

Next, when the first interface layer is PbTe and the second interface layer is (SnTe) ₃₀ (Cr ₂ O ₃ ) ₇₀ , as shown by reference numeral 26 in FIG. 9, the inner peripheral jitter and the outer peripheral jitter are The target was satisfied, but the amplitude deterioration was not achieved.

Next, when the first interface layer is Bi ₂ Te ₃ and the second interface layer is (Bi ₂ Te ₃ ) ₃₀ (Cr ₂ O ₃ ) ₇₀ , as shown by the number 27 in FIG. Jitter and jitter at the outer periphery satisfied the target, but the amplitude degradation did not reach the target.

  As described above, if the content of Sn, Pb, Bi contained in the first interface layer is larger than that in the second interface layer, amplitude deterioration occurs due to the first interface layer material being dissolved in the recording layer. By adding excess Sb in the layer, recrystallization of the recording layer material can be suppressed, so that the inner peripheral jitter during CAV recording can be sufficiently reduced. Each configuration of numbers 25 to 27 in FIG. 9 corresponds to the conventional example of the present invention because Bi is not contained in the recording layer.

Next, when the first interface layer was (SnTe) ₃₀ (CrN) ₇₀ and the second interface layer was SnTe, all items met the target, as indicated by reference numeral 28 in FIG.

Next, when the first interface layer was (SnTe) ₃₀ (CrN) ₇₀ and the second interface layer was PbTe, all items met the target, as indicated by reference numeral 29 in FIG.

Next, when the first interface layer is (Bi ₂ Te ₃ ) ₃₀ (CrN) ₇₀ and the second interface layer is Bi ₂ Te ₃ , all items are targeted as shown by number 30 in FIG. Satisfied.

  As described above, by making the content of Sn, Pb, Bi contained in the first interface layer smaller than that in the second interface layer, it is possible to suppress amplitude deterioration due to the interface layer material being dissolved in the recording layer. . Further, by adding excess Sb to the recording layer, it is possible to suppress recrystallization of the recording layer material, so that the inner peripheral jitter during CAV recording can be sufficiently reduced. Further, it has been found that it is effective to add a transition metal nitride such as CrN as a means for reducing elements such as Sn, Pb and Bi contained in the first interface layer. 9 can achieve both reproduction signal quality during CAV recording and amplitude deterioration during multiple rewrites, but does not contain Bi in the recording layer, so the conventional example of the present invention. It corresponds to.

<Experimental example 6>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer and (Sn ₅ Bi ₂ Te ₈ ) ₂₀ (Ge ₃ N ₄ ) ₈₀ is 3 nm as the first interface layer on the substrate. A recording layer described later is 8 nm, (Sn ₅ Bi ₂ Te ₈ ) ₈₀ (Ge ₃ N ₄ ) ₂₀ is 1.5 nm as a second interface layer, and (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer. A Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ film of 35 nm was formed as an absorptance control layer, and an Al ₉₉ Ti ₁ film of 60 nm was formed as a thermal diffusion layer.

Here, the recording layer is made of Ge ₃₃ . ₃ Sb ₁₃ . ₃ Te ₅₃ . _In the case of ₄ , the outer peripheral jitter and amplitude degradation satisfied the target as shown by reference numeral 31 in FIG. 10, but the inner peripheral jitter did not reach the target. The configuration of number 31 in FIG. 10 corresponds to the conventional example of the present invention because the recording layer does not contain Bi.

Next, the recording layer is made of Ge ₃₂ . ₇ Sb ₁₄ . ₅ Te ₅₂ . _In the case of ₈ , as shown by the number 32 in FIG.

Next, the recording layer is made of Ge ₃₀ . ₃ Sb ₁₉ . ₃ Te ₅₀ . _In the case of ₄ , the target was satisfied in all items as indicated by reference numeral 33 in FIG. In addition, both the inner peripheral jitter and the outer peripheral jitter were 1% or more below the target and showed good values.

Next, the recording layer is made of Ge ₂₈ . ₈ Sb ₂₂ . ₄ Te ₄₈ . _In the case of ₈ , as shown in the number 34 in FIG. The configurations of numbers 32 to 34 in FIG. 10 can achieve both reproduction signal quality at the time of CAV recording and amplitude deterioration at the time of many rewrites, but since the recording layer does not contain Bi, a reference example of the present invention. It corresponds to.

Next, the recording layer is made of Ge ₂₇ . ₈ Sb ₂₄ . ₄ Te ₄₇ . _In the case of ₈ , as shown by reference numeral 35 in FIG. 10, the inner peripheral jitter and amplitude deterioration satisfied the target, but the outer peripheral jitter did not reach the target. The configuration of number 35 in FIG. 10 corresponds to the conventional example of the present invention because the recording layer does not contain Bi.

As described above, when the recording layer does not contain excessive Sb with respect to the mixed composition of GeTe and Sb ₂ Te ₃ , the inner peripheral jitter cannot be sufficiently reduced. However, if the amount of Sb is added too much, the jitter at the outer periphery is increased. Therefore, in the following composition formula, Y is preferably about 0.5 to 5.

Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y (20 <X <45, 0.5 <Y <5)
<Experimental example 7>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer and (Sn ₅ Bi ₂ Te ₈ ) ₂₀ (Ge ₃ N ₄ ) ₈₀ is 3 nm as the first interface layer on the substrate. A recording layer described later is 8 nm, (Sn ₅ Bi ₂ Te ₈ ) ₈₀ (Ge ₃ N ₄ ) ₂₀ is 1.5 nm as a second interface layer, and (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer. A Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ film of 35 nm was formed as an absorptance control layer, and an Al ₉₉ Ti ₁ film of 60 nm was formed as a thermal diffusion layer.

Here, the recording layer is made of Ge ₄₈ Sb ₂ . ₈ Te ₄₉ . _In the case of ₂ , the outer peripheral jitter and amplitude degradation satisfied the target as indicated by reference numeral 36 in FIG. 10, but the inner peripheral jitter did not reach the target. The configuration of number 36 in FIG. 10 corresponds to the conventional example of the present invention because the recording layer does not contain Bi.

Next, the recording layer was made of Ge ₄₃ Sb ₆ . ₈ Te ₅₀ . _In the case of ₂ , the target was satisfied in all items as indicated by reference numeral 37 in FIG.

Next, the recording layer is formed of Ge ₂₀ Sb ₂₅ . ₂ Te ₅₄ . _In the case of ₈ , as shown by reference numeral 38 in FIG. The configurations of numbers 37 to 38 in FIG. 10 can achieve both the reproduction signal quality at the time of CAV recording and the amplitude deterioration at the time of many rewrites, but since the recording layer does not contain Bi, the reference example of the present invention. It corresponds to.

Next, the recording layer is formed of Ge ₁₈ . ₅ Sb ₂₆ . ₄ Te ₅₅ . _In the case of ₁ , the amplitude degradation satisfied the target as indicated by reference numeral 39 in FIG. 10, but the inner peripheral jitter and outer peripheral jitter did not reach the target. The configuration of number 39 in FIG. 10 corresponds to the conventional example of the present invention because the recording layer does not contain Bi.

As described above, it was found that the composition ratio of mixing GeTe and Sb ₂ Te ₃ in the recording layer is good when X is between 20 and 45 in the following composition formula.

Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y (20 <X <45, 0.5 <Y <5)
This is because if the amount of GeTe is too large, the crystal growth rate increases and recrystallization occurs. If the amount of GeTe is too small, the difference in refractive index between the crystal and the amorphous phase decreases, so that the reproduction signal amplitude is sufficiently high. This is because it cannot be made large.

<Experimental Example 8>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer and (Sn ₅ Bi ₂ Te ₈ ) ₂₀ (Ge ₃ N ₄ ) ₈₀ is 3 nm as the first interface layer on the substrate. A recording layer described later is 8 nm, (Sn ₅ Bi ₂ Te ₈ ) ₈₀ (Ge ₃ N ₄ ) ₂₀ is 1.5 nm as a second interface layer, and (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as a second protective layer. A Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ film of 35 nm was formed as an absorptance control layer, and an Al ₉₉ Ti ₁ film of 60 nm was formed as a thermal diffusion layer.

Here, the recording layer is made of Ag ₁ Ge ₃₁ . ₃ Sb ₁₅ . ₄ Te ₅₂ . _In the case of ₃ , the target was satisfied in all items as indicated by reference numeral 40 in FIG.

Next, the recording layer is made of Ag ₄ Ge ₃₁ Sb ₁₄ . ₇ Te ₅₀ . _In the case of ₂ , the target was satisfied in all items as indicated by reference numeral 41 in FIG. As described above, the configurations of numbers 40 to 41 in FIG. 10 can achieve both the reproduction signal quality at the time of CAV recording and the amplitude deterioration at the time of many rewrites, but the recording layer does not contain Bi. This corresponds to a reference example of the invention.

Next, the recording layer is made of Ag ₅ . ₅ Ge ₃₀ . ₅ Sb ₁₄ . ₅ Te ₄₉ . _In the case of ₅ , as shown by reference numeral 42 in FIG. 10, the inner peripheral jitter and amplitude degradation satisfied the target, but the outer peripheral jitter did not reach the target. The configuration of number 42 in FIG. 10 corresponds to the conventional example of the present invention because the recording layer does not contain Bi.

As described above, even when a mixed composition system of GeTe and Sb ₂ Te ₃ is used for the recording layer and a metal such as Ag is added in an amount of about 1 to 5%, good performance can be obtained. In addition to Ag, Cr, Si, Ga, Al, In, B, and N exhibit good performance in the same manner as Ag. As described above, it has been found that Z is about 0.5 to 5% in the following composition formula.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y ) _100-Z M _Z (20 <X <45, 0.5 <Y <5, 0.5 <Z <5)
(Where M is Ag, Cr, Si, Ga, Al, In, B, N)
<Experimental Example 9>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as the first protective layer, Ge ₃ N ₄ is 3 nm as the first interface layer, 8 nm is the recording layer described later, and 2 nm is the second interface layer. Ge ₃ N ₄ is 1.5 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as the second protective layer, Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is 35 nm as the absorption control layer, and Al ₉₉ Ti is used as the thermal diffusion layer. ₁ was formed into a film of 60 nm.

Here, the recording layer is set to Bi ₀ . ₈ Ge ₃₂ . ₆ Sb ₁₃ . ₁ Te ₅₃ . _In the case of ₅ , as shown by reference numeral 43 in FIG. 10, the inner peripheral jitter and amplitude deterioration satisfied the target, but the outer peripheral jitter did not reach the target. The structure of number 43 in FIG. 10 contains Bi, Ge, Sb, and Te in the recording layer, but its content is not within the range of 1 to 9%, and therefore corresponds to a comparative example of the present invention.

Next, the recording layer is Bi ₁ . ₂ Ge ₃₂ . ₃ Sb ₁₃ Te ₅₃ . _In the case of ₅ , the target was satisfied in all items as indicated by reference numeral 44 in FIG.

Next, the recording layer is formed of Bi ₅ Ge ₂₉ . ₁ Sb ₁₁ . ₇ Te ₅₄ . _In the case of ₂ , the target was satisfied in all items as indicated by reference numeral 45 in FIG.

Next, the recording layer is Bi ₈ . ₈ Ge ₂₆ Sb ₁₀ . ₄ Te ₅₄ . _In the case of ₈ , the target was satisfied in all items, as indicated by reference numeral 46 in FIG. As described above, the configurations of Nos. 44 to 46 in FIG. 10 contain Bi, Ge, Sb, Te in the recording layer, the content ratio is within a range of 1 to 9%, and the reproduction signal quality at the time of CAV recording. Corresponds to the embodiment of the present invention.

Next, the recording layer is Bi ₉ . ₈ Ge ₂₅ . ₁ Sb ₁₀ . _{In the case of 1} Te ₅₅ , as indicated by reference numeral 47 in FIG. 10, the outer peripheral jitter and amplitude deterioration satisfied the target, but the inner peripheral jitter did not reach the target. The configuration of number 47 in FIG. 10 contains Bi, Ge, Sb, and Te in the recording layer, but the content is not in the range of 1 to 9%, and therefore corresponds to a comparative example of the present invention.

As described above, when Bi ₂ Te ₃ is added to the mixed composition system of GeTe and Sb ₂ Te ₃ to the recording layer, the crystals of the recording layer such as Sn, Pb, and Bi are added to the first interface layer and the second interface layer. Even without the addition of a material that promotes the conversion, extremely good CAV recording performance can be obtained. From the above results, it was found that Z is preferably between 2.5 and 25% in the following composition formula.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y ) _100-Z (Bi ₂ Te ₃ ) _Z (20 <X <45, -2 <Y <2, 2.5 <Z < 25)
<Experimental example 10>
By sputtering process, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 120 nm as a first protective layer, Cr ₂ O ₃ is 3 nm as a first interface layer, a recording layer described later is 8 nm, and a second interface layer is formed on the substrate. Cr ₂ O ₃ is 1.5 nm, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is 30 nm as the second protective layer, Cr ₉₀ (Cr ₂ O ₃ ) ₁₀ is 35 nm as the absorptivity control layer, and Al ₉₉ Ti is used as the thermal diffusion layer. ₁ was formed into a film of 60 nm.

Next, the recording layer is formed of Bi ₅ Ge ₁₆ . ₆ Sb ₂₁ . ₇ Te ₅₆ . _In the case of ₇ , the inner jitter and the outer jitter did not reach the target as indicated by reference numeral 48 in FIG. The configuration of number 48 in FIG. 10 contains Bi, Ge, Sb, and Te in the recording layer, but the content is not in the range of 1 to 9%, and therefore corresponds to the comparative example of the present invention.

Next, the recording layer is formed of Bi ₅ Ge ₁₈ . ₄ Sb ₂₀ . ₃ Te ₅₆ . _In the case of ₃ , the target was satisfied in all items as indicated by reference numeral 49 in FIG.

Next, the recording layer is formed of Bi ₅ Ge ₃₈ . ₅ Sb ₄ . ₂ Te ₅₂ . _In the case of ₃ , the target was satisfied in all items as indicated by reference numeral 50 in FIG. As described above, the configurations of numbers 49 to 50 in FIG. 10 contain Bi, Ge, Sb, and Te in the recording layer, the content is in the range of 1 to 9%, and the reproduction signal at the time of CAV recording Since both the quality and the amplitude deterioration at the time of many rewrites can be achieved, this corresponds to the embodiment of the present invention.

Next, the recording layer is formed of Bi ₅ Ge ₄₀ . ₂ Sb ₂ . _{In the case of 8} Te ₅₂ , as shown by reference numeral 51 in FIG. 10, the outer peripheral jitter satisfied the target, but the inner peripheral jitter did not reach the target. The configuration of number 51 in FIG. 10 contains Bi, Ge, Sb, and Te in the recording layer, but the content is not in the range of 1 to 9%, and therefore corresponds to the comparative example of the present invention.

As described above, when Bi ₂ Te ₃ is added to the mixed composition system of GeTe and Sb ₂ Te ₃ to the recording layer, the crystals of the recording layer such as Sn, Pb, and Bi are added to the first interface layer and the second interface layer. Even without the addition of a material that promotes the conversion, extremely good CAV recording performance can be obtained. Further, in this case, the range of the composition ratio of GeTe and Sb ₂ Te ₃ was found to be good when X is about 20 to 45 in the following composition formula from the above results.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y ) _100-Z (Bi ₂ Te ₃ ) _Z (20 <X <45, -2 <Y <2, 2.5 <Z < 25)
Furthermore, when the recording layer was Bi ₅ Ge ₂₇ Sb ₁₆ Te ₅₂ , as indicated by numeral 52 in FIG. 10, the inner peripheral jitter satisfied the target, but the outer peripheral jitter did not reach the target. The structure of number 52 in FIG. 10 contains Bi, Ge, Sb, and Te in the recording layer, but the content is not in the range of 1 to 9%, and therefore corresponds to the comparative example of the present invention.

Next, the recording layer is formed of Bi ₅ Ge ₂₇ . ₇ Sb ₁₄ . ₅ Te ₅₂ . _In the case of ₈ , the target was satisfied in all items as indicated by reference numeral 53 in FIG.

Next, the recording layer is formed of Bi ₅ Ge ₃₀ . ₅ Sb ₉ . ₁ Te ₅₅ . _In the case of ₅ , the target was satisfied in all items as indicated by numeral 54 in FIG. As described above, the configurations of Nos. 53 to 54 in FIG. 10 contain Bi, Ge, Sb, Te in the recording layer, the content is in the range of 1 to 9%, and the reproduction signal at the time of CAV recording. Although quality and amplitude deterioration at the time of many rewrites can be made compatible, it corresponds to an embodiment of the present invention.

Next, the recording layer is formed of Bi ₅ Ge ₃₁ . ₃ Sb ₇ . ₃ Te ₅₆ . _In the case of ₄ , the inner peripheral jitter satisfied the target as indicated by reference numeral 55 in FIG. 10, but the outer peripheral jitter target was not achieved. The configuration of number 55 in FIG. 10 contains Bi, Ge, Sb, and Te in the recording layer, but the content is not in the range of 1 to 9%, and therefore corresponds to the comparative example of the present invention.

As described above, when Bi ₂ Te ₃ is added to the mixed composition system of GeTe and Sb ₂ Te ₃ to the recording layer, the crystals of the recording layer such as Sn, Pb, and Bi are added to the first interface layer and the second interface layer. Even without the addition of a material that promotes the conversion, extremely good CAV recording performance can be obtained. Further, in this case, the range of the composition ratio of GeTe and Sb ₂ Te ₃ was found from the above results that Y was good between about −2 and 2 in the following composition formula.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y ) _100-Z (Bi ₂ Te ₃ ) _Z (20 <X <45, -2 <Y <2, 2.5 <Z < 25)
(Sputtering equipment)
The sputtering apparatus for producing the information recording medium of the present invention has a plurality of chambers, each chamber is provided with one sputter target, and the substrate for the information recording medium is sequentially transported between the chambers. A so-called single-wafer sputtering apparatus is suitable.

  Here, the structure of the sputtering apparatus used for manufacturing the information recording medium of the present invention will be described with reference to FIG. The sputtering apparatus is provided with a total of nine chambers. Among these, the process chamber used for the process for film formation is provided with eight chambers of the 1st chamber to the 8th chamber. In addition, a load lock chamber is provided for transporting the substrate to the sputtering apparatus and carrying out the information recording medium after film formation from the sputtering apparatus. The sputtering apparatus is provided with the same number of carriers as the number of chambers, and the carrier rotates in the direction of the arrow with the center of the carrier as an axis, thereby serving to transport the substrate to each chamber.

  Each process chamber is provided with a sputtering power source suitable for forming each layer, a plurality of sputtering gas pipes, a mass flow controller for controlling the sputtering gas flow rate, and the like. When each substrate is set in each chamber, a sputtering gas suitable for each chamber is introduced, and then sputtering is performed in each chamber. A carrier for transporting each substrate is provided with a small vacuum motor for rotating the substrate. Since a power cable cannot be used for the power source of this motor, consideration is given to supplying power from the contact portion with each chamber at the same time that each carrier is set in each chamber. By performing this substrate rotation, the composition uniformity and film thickness uniformity of each layer formed on the substrate are greatly improved. In addition, since this sputtering apparatus has a structure in which He gas for cooling the substrate is introduced between the substrate and the carrier in order to prevent overheating of the substrate during sputtering, it is usually caused by overheating of the substrate. It is devised to prevent substrate deformation.

(Production example of information recording medium)
The track pitch is 0.615 μm, the groove depth is 65 nm, and address information for recording information on both the land and the groove is provided at the head of each sector. On the substrate, each thin film (first protective layer: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (124 nm), first interface layer: (Ge ₃ N ₄ ) ₈₀ (SnTe) ₂₀ (3 nm), recording layer: Ge _{32 .2} Sb _15.5 Te _52.3 (9 nm), second interface layer: (SnTe) ₈₀ (Ge ₃ N ₄ ) ₂₀ (1.5 nm), second protective layer: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (30 nm), the absorption rate control _{layer: Cr 90 (Cr 2 O 3} ) 10 (35nm), the thermal diffusion _layer:. Al ₉₉ was formed Ti 1 a (60 nm) sputtering apparatus previously used for this time This is a sputtering apparatus for mass production having eight process chambers as described, and the sputtering conditions used at this time are summarized in Fig. 12. The characteristic point is the film formation of the first interface layer and the second interface layer. , Ge ₈₀ (SnTe) ₂₀ and Ge ₂₀ (Sn ₅ Bi ₂ Te ₈ ) ₈₀ are used as sputtering targets, and the first interface layer (Ge ₃ N ₄ ) ₈₀ ( SnTe) ₂₀ and the second interface layer (SnTe) ₈₀ (Ge ₃ N ₄ ) _20. By doing so, low melting point elements such as Sn, Pb, Bi and Ge ₃ N4 are formed. Can be easily mixed, and the amount of nitrogen in the interface layer can be easily controlled.

  According to the experiments by the inventors, increasing the amount of nitrogen in the sputtering gas not only suppresses the dissolution of Sn, Pb, Bi into the recording layer but also improves the transparency of the interface layer. Can do. However, the effect of promoting crystallization of the recording layer is reduced. In this case, for example, the nitrogen concentration in the sputtering gas is increased in the third chamber for forming the first interface layer, and the nitrogen concentration in the sputtering gas is decreased in the fifth chamber for forming the second interface layer. Take measures. As described above, since the amount of nitrogen added can be easily controlled, it is possible to respond very quickly when controlling the penetration of the interface layer element into the recording layer or when controlling the crystallization promoting effect of the recording layer. it can.

  The information recording / reproducing of the information recording medium of the present invention, and the operation of the apparatus will be described below with reference to FIG. As a motor control method for recording / reproducing, a CAV method is adopted in which the rotational speed of the disk is made constant regardless of the zone where recording / reproducing is performed. The disk linear velocity is 8.2 m / sec at the innermost circumference (radius 24 mm) and 20 m / sec at the outermost circumference (radius 58.5 mm). In the present invention, the “inner periphery” basically refers to a radius of about 24 mm, and the outer periphery refers to a radius of about 58.5 mm.

  Next, the recording / reproducing process will be described below. First, information from the outside of the recording apparatus is transmitted to the 8-16 modulator 13-8 in units of 8 bits. When information is recorded on an information recording medium (hereinafter referred to as an optical disc) 13-1, recording is performed using a so-called 8-16 modulation method that converts 8 bits of information into 16 bits. In this modulation method, information having a mark length of 3T to 14T corresponding to 8-bit information is recorded on the medium. The 8-16 modulator 13-8 in the figure performs this modulation. Here, T represents the clock cycle at the time of recording information, and here it is 17.1 ns at the innermost circumference and 7 ns at the outermost circumference.

  The digital signal of 3T to 14T converted by the 8-16 modulator 13-8 is transferred to the recording waveform generation circuit 13-6, the width of the high power pulse is set to about T / 2, and the high power level laser irradiation is performed. Laser irradiation at a low power level with a width of about T / 2 is performed, and a multi-pulse recording waveform is generated in which laser irradiation at an intermediate power level is performed between the series of high power pulses. At this time, the high power level for forming the recording mark and the intermediate power level at which the recording mark can be crystallized were adjusted to optimum values for each medium to be measured and the radial position. Further, in the recording waveform generating circuit 13-6, the signals of 3T to 14T are made to correspond to “0” and “1” alternately in time series, and in the case of “0”, the laser power of the intermediate power level is set. In the case of “1”, a series of high power pulse trains including high power level pulses are irradiated. At this time, the portion irradiated with the intermediate power level laser beam on the optical disc 13-1 becomes a crystal, and the portion irradiated with the laser beam of a series of high power pulse trains including a high power level pulse is amorphous (mark portion). To change. Further, in the recording waveform generation circuit 13-6, when forming a series of high power pulse trains including a high power level for forming the mark portions, the high power pulse trains according to the space lengths before and after the mark portions. Has a multi-pulse waveform table that supports a method (adaptive recording waveform control) that changes the first pulse width and the last pulse width of the signal, thereby eliminating the effects of thermal interference between marks as much as possible. Multi-pulse recording waveform that can be generated.

  The recording waveform generated by the recording waveform generating circuit 13-6 is transferred to the laser driving circuit 13-7, and the laser driving circuit 13-7 selects the semiconductor laser in the optical head 13-3 based on the recording waveform. Make it emit light. A semiconductor laser having an optical wavelength of 655 nm is used as an information recording laser beam in the optical head 13-3 mounted on the recording apparatus. Information was recorded by squeezing the laser beam onto the recording layer of the optical disc 13-1 with an objective lens having a lens NA of 0.6 and irradiating a laser beam corresponding to the recording waveform.

  In general, when laser light having a laser wavelength λ is condensed by a lens having a lens numerical aperture NA, the spot diameter of the laser beam is approximately 0.9 × λ / NA. Therefore, under the above conditions, the spot diameter of the laser beam is about 0.98 microns. At this time, the polarization of the laser beam was circularly polarized.

  The recording apparatus is compatible with a system (so-called land / groove recording system) for recording information on both the groove and the land (area between the grooves). In this recording apparatus, tracking for the land and the groove can be arbitrarily selected by the L / G servo circuit 13-9. The recorded information was also reproduced using the optical head 13-3. A reproduction signal is obtained by irradiating a laser beam onto a recorded mark and detecting reflected light from the mark and a portion other than the mark. The amplitude of the reproduction signal is increased by the preamplifier circuit 13-4 and transferred to the 8-16 demodulator 13-10. The 8-16 demodulator 13-10 converts the information into 8-bit information every 16 bits. With the above operation, the reproduction of the recorded mark is completed. When recording is performed on the optical disc 13-1 under the above conditions, the mark length of the 3T mark, which is the shortest mark, is approximately 0.42 μm, and the mark length of the 14T mark, which is the longest mark, is approximately 1.96 μm.

  When performing inner and outer peripheral jitter, a random pattern signal including 3T to 14T is recorded and reproduced, and the reproduced signal is subjected to waveform equalization, binarization, and PLL (Phase Locked Loop) processing. Jitter was measured. For measurement of amplitude deterioration, an 11T signal was recorded, and the difference between the amplitude after 10 times recording and the amplitude after 10,000 times recording was measured.

  The optimum composition and optimum film thickness of each layer used in the information recording medium of the present invention will be described.

(First protective layer)
The substance present on the light incident side of the first protective layer is a plastic substrate such as polycarbonate or an organic substance such as an ultraviolet curable resin. These refractive indexes are about 1.4 to 1.6. In order to effectively cause reflection between the organic material and the first protective layer, the refractive index of the first protective layer is preferably 2.0 or more. The first protective layer is optically higher in refractive index than the substance (corresponding to the substrate in this example) present on the light incident side, and preferably has a high refractive index in a range where light absorption does not occur. Specifically, the refractive index n is between 2.0 and 3.0, and it is a material that does not absorb light, and it is particularly desirable to contain a metal oxide, carbide, nitride, sulfide, or selenide. . Further, it is desirable that the thermal conductivity is at least 2 W / mk or less. In particular, a ZnS—SiO ₂ -based compound has a low thermal conductivity and is optimal as the first protective layer. Furthermore, SnO ₂ or SnO ₂ is a material obtained by adding a sulfide such as ZnS, CdS, SnS, GeS, PbS, or a material obtained by adding a transition metal oxide such as Cr ₂ O ₃ or Mo ₃ O4 to SnO _2. Since the thermal conductivity is low and it is more thermally stable than the ZnS—SiO ₂ -based material, even when the film thickness of the first interface layer is 2 nm or less, the melting into the recording film does not occur. In particular, it exhibits excellent characteristics as the first protective layer. In order to effectively use the optical interference between the substrate and the recording layer, the optimum thickness of the first protective layer is 110 nm to 135 nm when the wavelength of the laser is about 650 nm.

(First interface layer)
Wherein the first interface layer as described in detail in the experimental example Bi, Sn, that material that promotes crystallization of the recording layer of Pb or the like is contained desirable. In particular, Te, oxides of Bi, Sn, Pb, Te oxides of Bi, Sn, Pb, mixtures of oxides and germanium, or Te oxides of Bi, Sn, Pb, oxides and transition metal oxides A mixture with a transition metal nitride is desirable. Since transition metals easily change their valence, even if elements such as Bi, Sn, Pb, and Te are liberated, the transition metal changes the valence, and the transition metal is between Bi, Sn, Pb, and Te. This is because bonding occurs in order to produce a thermally stable compound. In particular, Cr, Mo, and W are excellent materials because they have a high melting point, easily change their valence, and easily form a thermally stable compound with the metal. The Bi, Sn, Pb Te compound and oxide content in the first interface layer is as much as possible in order to promote crystallization of the recording layer, but the first interface layer is different from the second interface layer. In comparison, the laser beam irradiation tends to cause high temperatures and the problem that the interfacial layer material dissolves into the recording film occurs. Therefore, the content of Te, Bi, Sn, and Pb oxides and oxides is suppressed to 70% or less. There is a need.

  The effect is exhibited if the thickness of the first interface layer is 0.5 nm or more. However, when the film thickness is 2 nm or less, the first protective layer material may pass through the first interface layer, dissolve in the recording layer, and deteriorate the reproduction signal quality after many rewrites. Therefore, it is desirable that it is 2 nm or more. Further, when the film thickness of the first interface layer is as thick as 10 nm or more, it adversely affects optically, and thus there are problems such as a decrease in reflectivity and a decrease in signal amplitude. Therefore, the film thickness of the first interface layer is preferably 2 nm or more and 10 nm or less.

(Recording layer)
Wherein As discussed in detail in the experimental example, the first interface layer, if Bi in both the second interface layer, Sn, is material that promotes crystallization of the recording layer such as Pb is added, the recording layer material For example, a recording layer material having a composition ratio in which Sb is excessively added to a GeSbTe-based recording layer material in which GeTe and Sb ₂ Te ₃ are mixed at an appropriate ratio may be used. Specifically, the recording layer material in the range represented by the following composition formula is excellent. (Atomic%)
Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y
20 <X <45, 0.5 <Y <5
Besides adding an excessive amount of Sb, an element that lowers the nucleation rate and the crystal growth rate may be added. Specifically, the recording layer material in the range represented by the following composition formula is excellent.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2X-Y ) _100-Z M _Z
20 <X <45, 0.5 <Y <5, 0.5 <Z <5
However, M is an element selected from Ag, Cr, Si, Ga, Al, In, B, and N.

Further, by adding Bi ₂ Te ₃ to a GeSbTe recording layer material in which GeTe and Sb ₂ Te ₃ are mixed at an appropriate ratio, the nucleation speed is improved and the inner circumference of the information recording medium can be improved even during CAV recording. Good recording / reproduction characteristics can be obtained from the outer periphery to the outer periphery. By adding Bi ₂ Te _3, the crystal growth rate is increased, and the difference in refractive index between amorphous and crystal is large, so that the reproduction signal amplitude can be improved. Specifically, the Bi content is 1 to 9%, and the recording layer material in the range represented by the following composition formula is excellent.

(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2XY ) _100-Z (Bi ₂ Te ₃ ) _Z
20 <X <45, -2 <Y <2, 2.5 <Z <25
If the relationship between the four elements is within the range expressed by the composition formula, even if impurities are mixed, the effect of the present invention is not lost if the atomic% of impurities is within 1%. .

  In the medium structure of the present invention, the film thickness of the recording layer is optically optimal from 5 nm to 15 nm. Particularly, when the thickness is 7 nm or more and 11 nm or less, it is convenient because deterioration of the reproduction signal due to the flow of the recording film at the time of many rewrites can be suppressed and the modulation degree can be optically optimized.

(Second interface layer)
Wherein the second interface layer as described in detail in the experimental example Bi, Sn, that material that promotes crystallization of the recording layer of Pb or the like is contained desirable. In particular, Te, oxides of Bi, Sn, Pb, Te oxides of Bi, Sn, Pb, mixtures of oxides and germanium, or Te oxides of Bi, Sn, Pb, oxides and transition metal oxides A mixture with a transition metal nitride is desirable. Since transition metals easily change their valence, even if elements such as Bi, Sn, Pb, and Te are liberated, the transition metal changes the valence, and the transition metal is between Bi, Sn, Pb, and Te. This is because bonding occurs in order to produce a thermally stable compound. In particular, Cr, Mo, and W are excellent materials because they have a high melting point, easily change their valence, and easily form a thermally stable compound with the metal. The Bi, Sn, Pb Te compound content and oxide content in the second interface layer is as much as possible thermally and chemically, and the effect of improving the crystallization speed of the recording layer, particularly the nucleation speed. There is.

  If the thickness of the second interface layer is 0.5 nm or more, the effect is exhibited. However, when the film thickness is 1 nm or less, the second protective layer material may pass through the second interface layer, dissolve in the recording layer, and deteriorate the reproduction signal quality after many rewrites. Therefore, it is desirable to be 1 nm or more. Further, when the thickness of the second interface layer is as thick as 3 nm or more, it adversely affects optically, so that there are adverse effects such as a decrease in reflectance and a decrease in signal amplitude. Therefore, the film thickness of the second interface layer is preferably 1 nm or more and 3 nm or less.

(Second protective layer)
The second protective layer is a material that does not absorb light, and particularly preferably contains a metal oxide, carbide, nitride, sulfide, or selenide. Further, it is desirable that the thermal conductivity is at least 2 W / mk or less. In particular, a ZnS—SiO ₂ -based compound has a low thermal conductivity and is optimal as the second protective layer. Furthermore, SnO ₂ or SnO ₂ is a material obtained by adding a sulfide such as ZnS, CdS, SnS, GeS, PbS, or a material obtained by adding a transition metal oxide such as Cr ₂ O ₃ or Mo ₃ O4 to SnO _2. Since the thermal conductivity is low and it is more thermally stable than the ZnS—SiO ₂ -based material, even when the thickness of the second interface layer is 1 nm or less, the melting into the recording film does not occur. In particular, it exhibits excellent characteristics as the second protective layer. In order to effectively use the optical interference between the recording layer and the absorptance control layer, the optimum thickness of the second protective layer is 25 nm to 45 nm when the wavelength of the laser is about 650 nm.

(Absorption rate control layer)
The absorptance control layer preferably has a complex refractive index n, k in the range of 1.4 <n <4.5, −3.5 <k <−0.5, particularly 2 <n <4, −3.0 <. A material with k <−0.5 is desirable. In the absorptivity control layer, a thermally stable material is preferable because it absorbs light. Desirably, the melting point is required to be 1000 ° C. or higher. In addition, when the sulfide is added to the protective layer, there was a particularly large cross erase reduction effect. However, in the case of the absorption control layer, the content of the sulfide such as ZnS is at least added to the protective layer. Desirably less than the content. This is because adverse effects such as a decrease in melting point, a decrease in thermal conductivity, and a decrease in absorption rate may appear. The composition of the absorptance control layer is preferably a mixture of metal and metal oxide, metal sulfide, metal nitride, and metal carbide, and a mixture of Cr and Cr ₂ O ₃ is particularly good in improving overwrite characteristics. Showed the effect. In particular, when Cr is 60 to 95 atomic%, a material having thermal conductivity and optical constant suitable for the present invention can be obtained. Specifically, the metals include Al, Cu, Ag, Au, Pt, Pd, Co, Ti, Cr, Ni, Mg, Si, V, Ca, Fe, Zn, Zr, Nb, Mo, Rh, Sn, Sb, Te, Ta, W, Ir, Pb, and mixtures thereof are desirable, and examples of the metal oxide, metal sulfide, metal nitride, and metal carbide include SiO ₂ , SiO, TiO ₂ , Al ₂ O ₃ , and Y ₂ O. ₃ , CeO, La ₂ O ₃ , In ₂ O ₃ , GeO, GeO ₂ , PbO, SnO, SnO ₂ , Bi ₂ O ₃ , TeO ₂ , MO ₂ , WO ₂ , WO ₃ , Sc ₂ O ₃ , Ta ₂ O ₅ and ZrO ₂ are preferred. In addition to Si-O-N-based materials, oxidized, such as CoO-based material such as Si-Al-O-N-based material, Cr-O-based material such as _{Cr 2 O 3,, Co 2} O 3, CoO , Si—N materials such as TaN, AlN, Si ₃ N ₄ , nitrides such as Al—Si—N materials (eg, AlSiN ₂ ), Ge—N materials, ZnS, Sb ₂ S ₃ , CdS, Sulfides such as In ₂ S ₃ , Ga ₂ S ₃ , GeS, SnS ₂ , PbS, Bi ₂ S ₃ , SnSe ₃ , Sb ₂ S ₃ , CdSe, ZnSe, In ₂ Se ₃ , Ga ₂ Se ₃ , GeSe , GeSe ₂ , SnSe, PbSe, Bi ₂ Se _3, etc., CeF ₃ , MgF ₂ , fluoride such as CaF ₂ , or an absorptance control layer using a composition close to the above materials It may be used.

  Further, the film thickness of the absorptance control layer is preferably 10 nm or more and 100 nm or less, and when it is 20 nm or more and 50 nm or less, a particularly good overwrite characteristic improvement effect appears. Moreover, when the sum of the film thicknesses of the protective layer and the absorptance control layer is equal to or greater than the groove depth, the effect of reducing the cross erase appears remarkably. As described above, the absorptance control layer has a property of absorbing light. For this reason, the absorptance control layer also absorbs light and generates heat, as the recording layer absorbs light and generates heat. Further, it is important that the absorptance in the absorptance control layer is larger when the recording layer is in the amorphous state than when the recording layer is in the crystalline state. Thus, by optical design, the effect of reducing the absorption rate Aa in the recording layer when the recording layer is in an amorphous state is smaller than the absorption rate Ac in the recording layer when the recording layer is in a crystalline state. This effect can greatly improve the overwrite characteristics. In order to obtain the above characteristics, it is necessary to increase the absorption rate in the absorption rate control layer to about 30 to 40%. The amount of heat generated in the absorptance control layer varies depending on whether the recording layer is in a crystalline state or an amorphous state. As a result, the flow of heat from the recording layer to the thermal diffusion layer changes depending on the state of the recording layer, and this phenomenon can suppress an increase in jitter due to overwriting.

  The above effects are manifested by the effect of blocking the flow of heat from the recording layer to the thermal diffusion layer when the temperature in the absorptance control layer increases. In order to make effective use of this effect, the sum of the film thicknesses of the protective layer and the absorptivity control layer is not less than the step between the land grooves (groove depth on the substrate, about 1/7 to 1/5 of the laser wavelength). There should be. When the sum of the thicknesses of the protective layer and the absorptivity control layer is equal to or less than the step between the land grooves, the heat generated when recording on the recording layer is transferred to the thermal diffusion layer, and the recording mark recorded on the adjacent track is Easier to erase.

(Thermal diffusion layer)
The heat diffusion layer is preferably a metal or alloy having high reflectivity and high thermal conductivity, and the total content of Al, Cu, Ag, Au, Pt, and Pd is desirably 90 atomic% or more. Further, a material having a high melting point such as Cr, Mo, W and the like, and an alloy of these materials, and alloys of these materials are also preferable because they can prevent deterioration due to the flow of the recording layer material at the time of rewriting many times. In particular, when a thermal diffusion layer containing 95 atomic% or more of Al is used, it is possible to obtain an information recording medium that is inexpensive, excellent in high CNR, high recording sensitivity, excellent in multiple rewriting, and extremely effective in reducing cross erase. . In particular, when the composition of the thermal diffusion layer contains 95 atomic% or more of Al, an information recording medium that is inexpensive and excellent in corrosion resistance can be realized. As additive elements for Al, Co, Ti, Cr, Ni, Mg, Si, V, Ca, Fe, Zn, Zr, Nb, Mo, Rh, Sn, Sb, Te, Ta, W, Ir, Pb, B and C is excellent in terms of corrosion resistance. However, when the additive element is Co, Cr, Ti, Ni, or Fe, there is a great effect in improving corrosion resistance. The film thickness of the thermal diffusion layer is preferably 30 nm or more and 100 nm or less. When the film thickness of the thermal diffusion layer is less than 30 nm, the heat generated in the recording layer is difficult to diffuse. Therefore, the recording layer is likely to deteriorate especially when rewritten about 100,000 times, and cross erase occurs. It may be easier. Further, since light is transmitted, it is difficult to use as a heat diffusion layer, and the reproduction signal amplitude may be reduced. Further, when the metal element contained in the absorptance control layer and the metal element contained in the thermal diffusion layer are the same, there is a great advantage in production. That is, two layers of the absorptance control layer and the thermal diffusion layer can be formed using the same target. That is, when forming an absorptance control layer, sputtering is performed with a mixed gas such as an Ar—O ₂ mixed gas or an Ar—N ₂ mixed gas, and an appropriate refractive index is obtained by reacting a metal element with oxygen or nitrogen during sputtering. An absorptivity control layer is prepared, and when a thermal diffusion layer is formed, a metal thermal diffusion layer having a high thermal conductivity is formed by sputtering with Ar gas.

  When the film thickness of the thermal diffusion layer is 200 nm or more, the productivity is poor, and the internal stress of the thermal diffusion layer may cause warpage of the substrate, and information recording / reproduction may not be performed accurately. Moreover, if the film thickness of the thermal diffusion layer is 30 nm or more and 90 nm or less, it is more preferable in terms of corrosion resistance and productivity.

It is a figure for demonstrating the structure of the information recording medium of this invention. It is a figure for demonstrating the principle of this invention. It is a figure for demonstrating the conventional problem. It is a figure for demonstrating the conventional problem. It is a figure for demonstrating the conventional problem. It is a figure for demonstrating the conventional problem. It is a figure for demonstrating the principle of this invention. It is a figure for demonstrating the principle of this invention. It is a figure which shows the structure and recording characteristic of the information recording medium which concern on an experiment example. It is a figure which shows the structure and recording characteristic of the information recording medium which concern on an experiment example. It is explanatory drawing of the sputtering device applied to manufacture of the information recording medium based on this invention. It is a figure which shows the conditions of the sputtering process applied to manufacture of the information recording medium based on this invention. It is a figure which shows the information recording / reproducing apparatus for evaluating the information recording medium based on this invention.

Explanation of symbols

13-1: Optical disk 13-2: Motor 13-3: Optical head 13-4: Preamplifier circuit 13-6: Recording waveform generation circuit 13-7: Laser drive circuit 13-8: 8-16 modulator 13-9: L / G servo circuit 13-10: 8-16 demodulator

Claims (2)

A substrate,
A recording layer in which information is recorded by a phase change reaction by irradiation of a laser beam, which can be rewritten a plurality of times, contains at least Ge, Sb, Te and Bi, and has a Bi content of 1 to 9%; An information recording medium comprising: The composition ratio of the recording layer is
(Ge _XY Sb _{40-0.8X + 2Y} Te _60-0.2XY ) _100-Z (Bi ₂ Te ₃ ) _Z
20 <X <45, -2 <Y <2, 2.5 <Z <25
The information recording medium according to claim 1, wherein:

Images