JP3912954B2 - Information recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an information recording medium on which information is recorded by irradiation with a laser beam, and to the information recording medium, and more particularly to a phase change optical disk such as DVD-RAM and DVD-RW, or a light such as MD and MO. The present invention relates to a recordable optical disc such as a magnetic disc and a write-once optical disc such as a DVD-R.
[0002]
In the present invention, the information recording medium may be expressed as a phase change optical disk, a magneto-optical disk, or simply an optical disk. However, in the present invention, heat is generated by irradiation with a laser beam, and this heat generates an atomic arrangement or magnetic field. Since it is applicable to any information recording medium in which information is recorded by causing a change in moment, the information recording medium other than the disk-shaped information recording medium such as an optical card is applicable regardless of the shape of the information recording medium. Is also effective.
[0003]
In addition, the laser beam described above may be simply expressed as laser light or light. However, as described above, the present invention is a laser beam capable of generating heat on an information recording medium, and has a plurality of refractive indexes. The effect can be obtained if the laser beam has multiple interference effects due to different interference layers. Further, the present invention was invented by a red laser (wavelength 645 to 660 nm), but not particularly by the wavelength of the laser, and a high density optical disk using a relatively short wavelength laser such as a blue laser or an ultraviolet laser. Also effective against.
[0004]
[Prior art]
In recent years, phase change optical discs such as 2.6 GB DVD-RAM have been commercialized by taking advantage of their excellent reproduction compatibility with read-only optical discs such as DVD-ROM and DVD-Video. However, since 2.6 GB DVD-RAM cannot sufficiently meet the demands of consumers in terms of recording capacity, expectations for 4.7 GB DVD-RAM and 4.7 GB DVD-RW are increasing. That is, these phase change optical discs are the same in terms of recording capacity as DVD-Video, so that an optical disc for video recording replacing VTR is realized.
[0005]
In order to realize the 4.7 GB DVD-RAM, it is necessary to solve many problems. Among these, suppression of cross erase is a main problem.
[0006]
Generally, when the track pitch of the information recording medium is narrowed to about 80% of the laser beam spot, the reproduction signal leaks from the adjacent information recording track. This leakage of the reproduction signal from the information recorded on the adjacent information recording track is called crosstalk. In order to solve this problem, a land groove recording system described below has been developed.
[0007]
In a rewritable optical disc, a concavo-convex shape (groove shape) for tracking a laser beam is provided on a plastic substrate, and a method of recording information in a concave portion or a convex portion is generally used. However, for the purpose of improving the recording density (narrow track pitch), in recent years, a method of recording information on each of the concave and convex portions using the above-described concave and convex shape has been developed. Here, the concavo-convex convex portions and concave portions are referred to as lands and grooves. Generally, when the track pitch of the information recording medium is narrowed to about 80% of the laser beam spot and information is recorded on both the land and the groove, the adjacent information recording track (the groove for the land or the land for the groove) From the playback signal. For example, when information recorded on the land is reproduced, a reproduction signal from the information recorded on the groove leaks, and there is a problem that the information recorded on the land cannot be reproduced accurately.
[0008]
In order to solve this problem, Japanese Patent Laid-Open No. 6-338064 (hereinafter referred to as “Document 1”) describes that the groove depth is λ / 7 or more and λ / 5 or less (λ: laser) in the land groove recording method. Wavelength). The feature of this method is that even when the track pitch is narrowed to about 60% of the laser beam spot, the crosstalk from the adjacent information recording track (the leakage of the signal from the adjacent information recording track) can be canceled.
[0009]
On the other hand, as a method for improving the reflectivity, as described in the 5th Phase Change Recording Society Symposium Proceedings, pp9-14, 1993 (hereinafter referred to as “Document 2”), the energy of the recording layer is described. ZnS-SiO on the beam incident side ₂ Layer, SiO ₂ There is known a method of providing an interference layer having a different refractive index called a layer and improving the reflectance by the effect of multiple interference.
[0010]
[Problems to be solved by the invention]
In Document 1, sufficient consideration is given to a method for suppressing the phenomenon (so-called cross erase) that the recording mark recorded on the adjacent information recording track (adjacent groove at the time of land recording or adjacent land at the time of groove recording) is erased. It has not been.
[0011]
For example, in Document 1, since the distance between the recording layer and the heat diffusion layer (reflection layer) is as small as 18 nm, heat is diffused to the adjacent information recording track via the heat diffusion layer during information recording, and cross erase occurs. It has been found that there is a problem that it becomes easy to do (Problem 1).
[0012]
In order to solve this problem, as described in Japanese Patent Application No. 10-285008, which is a prior application of the present application, it is important to keep the distance between the recording layer and the thermal diffusion layer to be greater than the groove depth. . However, when the distance between the recording layer and the thermal diffusion layer is separated to such an extent that the cross erase is sufficiently suppressed (65 nm or more when the laser wavelength is about 645 to 660 nm), the reflectance is lowered due to the effect of optical interference. (Problem 2).
[0013]
In order to improve the reflectance, it is conceivable to use the method disclosed in Document 2. However, in this method, the recording layer and the ZnS-SiO ₂ When the recording is repeated several thousand times, ZnS-SiO ₂ There arises a problem that the S element in the layer diffuses into the recording layer and the reflectance decreases (Problem 3).
[0014]
In order to avoid such a decrease in reflectivity, as described in JP-A-10-228676 (hereinafter referred to as “Document 3”), the recording layer and ZnS—SiO ₂ SiO between dielectric protective layers ₂ , Al ₂ O _Three A method of providing an interface layer made of a high melting point dielectric compound such as the above is known. However, it has been clarified that the above method may cause peeling between the recording layer and the interface layer when a high temperature humidification test or the like is performed (Problem 4).
[0015]
In order to suppress this peeling, as described in the above-mentioned Japanese Patent Application No. 10-285008, Al ₂ O _Three , SiO ₂ A dielectric such as a Cr—O-based material or a Ge—N-based material may be provided as an interface layer instead of the high melting point dielectric compound. However, the inventors have said that the Cr—O-based material, Ge—N-based material and the like are strong against peeling, but absorb the laser beam, thereby inhibiting the effect of multiple interference, resulting in a reflectivity. It has been clarified that this causes a problem of lowering (similar to problem 2). In this case, if the thickness of the interface layer is reduced, the above problem can be suppressed to some extent. However, if the thickness of the interface layer is 5 nm or less, ZnS-SiO ₂ It was found that the diffusion of S atoms from the dielectric protective layer could not be sufficiently suppressed (Problem 3 occurred).
[0016]
Further, when Document 2 and Document 3 are combined, a thin film of four layers exists on the laser beam incident side of the recording layer, which is not preferable for production because the total number is too large. Further, in the above-mentioned Document 1, Document 2, and Document 3, cross erase is not sufficiently considered, and when the track pitch is narrowed, there is a problem that cross erase occurs depending on the film thickness of each layer (Problem 1). the same as).
[0017]
Therefore, the problems of the present invention are cross erase suppression (problem 1 countermeasure), reflectivity improvement (problem 2 countermeasure), reflectivity decrease suppression during multiple rewrites (problem 3 countermeasure), and defect suppression by peeling (problem 4 countermeasure). The purpose of this is to clarify the structure of an information recording medium that satisfies both requirements and to provide it.
[0018]
[Means for Solving the Problems]
In order to solve the above-described problems in the prior art, the following information recording medium may be used. (1) In an information recording medium on which information is recorded by atomic arrangement change or / and electronic state change by laser beam irradiation, at least a substrate having a groove shape with a groove depth dg and a shape reflecting the groove shape An information recording medium comprising three thin films having different compositions of a first interference layer, a second interference layer, and a first interface layer in order from the laser beam incident side of the recording layer. The thermal conductivity of the layer is lower than the thermal conductivity of the second interference layer, the refractive index of the second interference layer is smaller than the refractive index of either the first interference layer or the recording layer, and the second interference layer and the recording layer An information recording medium comprising a first interface layer in contact with the recording layer therebetween, wherein a distance between the first interference layer and the recording layer is dg or less.
[0019]
As will be described in detail in the embodiments, the reflectance is improved when the refractive index of the first interference layer is larger than the refractive index of the second interference layer.
[0020]
Here, it is preferable that the first interference layer has a refractive index larger than the refractive index of the substance existing at least in contact with the laser beam incident side of the first interference layer. Usually, the substance present on the laser beam incident side of the first interference 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 reflect light effectively between the organic material and the first interference layer, the refractive index of the first interference layer is desirably 2.0 or more. Specifically, ZnS and SiO can be realized in that a high refractive index of 2.0 or more can be realized, a film forming rate is high and noise is not generated, and a thermal conductivity is extremely small. ₂ A mixture of is good.
[0021]
The refractive index of the second interference layer is required to be 2.0 or less, preferably 1.8 or less. Therefore, specifically, the second interference layer has, for example, SiO 2 in that the refractive index is extremely small. ₂ , Al ₂ O _Three It is desirable to contain a low refractive index oxide such as MgO.
[0022]
The inventors have clarified that the second interference layer made of such a low refractive index oxide easily peels from the recording layer. In order to suppress such peeling, a first interface layer may be provided between the recording layer and the second interference layer. Since the first interface layer exists in contact with the recording film, at least the melting point is required to be higher than the melting point of the recording layer. Further, the first interface layer is preferably a substance having good adhesion between the recording layer and the second interference layer.
[0023]
Furthermore, as described in the examples, the inventors have excellent adhesion to substances that easily become non-stoichiometric compounds such as oxides and nitrides of transition metals, or semiconductor element nitrides such as Ge and Si. However, since it is a non-stoichiometric compound, it has been clarified that free electrons exist, light absorption due to this occurs, and the reflectance is lowered.
[0024]
However, by combining the first interference layer, the second interference layer, and the first interface layer, the disadvantages of each layer as described above are complemented, cross-erasure suppression, improved reflectivity, and reflectivity during multiple rewrites It is possible to obtain an information recording medium that achieves both suppression of deterioration and suppression of defects due to peeling.
[0025]
Furthermore, the inventors use SiO used in the second interference layer, as will be explained in detail in the examples. ₂ , Al ₂ O _Three The thermal conductivity of low refractive index compounds such as MgO is ZnS-SiO used for the first interference layer. ₂ It has been clarified that cross erase is likely to occur due to the diffusion of heat to adjacent tracks because of its large size compared to such compounds. In order to avoid this, it has been clarified that the distance between the first interference layer and the recording layer should be smaller than the groove depth dg.
[0026]
There is an optimum value for the composition of each layer. That is, the information recording medium as described below.
[0027]
(2) In an information recording medium on which information is recorded by an atomic arrangement change or / and an electronic state change by laser beam irradiation, at least a substrate having a groove shape with a groove depth dg and a shape reflecting the groove shape An information recording medium comprising three thin films having different compositions of a first interference layer, a second interference layer, and a first interface layer in order from the laser beam incident side of the recording layer, the composition of ZnS ZnS and SiO having a ratio of 50% to 95% ₂ When the sum of the composition ratio of O, N, S, and C is X, the composition ratio of O is 50% or more of X, and the composition ratio of Al, Si, and Mg In the second interference layer whose sum is 70% or more of 1-X, and between the second interference layer and the recording layer, in contact with the recording layer, an oxide, nitride, or Si, Ge of transition metal element An information recording medium comprising: a first interface layer made of the above nitride or a mixture containing these, wherein the distance between the first interference layer and the recording layer is dg or less.
[0028]
The above configuration is particularly effective when the reflectivity is reduced due to the effect of optical interference. In other words, it is effective in a configuration in which the reflectance must be sacrificed in order to solve a thermal problem such as cross erase. Specifically, this is a case where a thermal diffusion layer is provided on the side opposite to the laser beam incident side of the recording layer, and the distance between the thermal diffusion layer and the recording layer is set to the groove depth dg or more.
[0029]
As described in detail in the examples, the provision of the thermal diffusion layer on the side opposite to the laser beam incident side of the recording layer quickly releases the heat generated during recording, and suppresses damage to the recording layer. Although effective, there is an adverse effect that the heat diffused in the heat diffusion layer reaches an adjacent track and causes cross erase. In order to avoid this problem, a layer (third interference layer) having a thermal conductivity smaller than that of the thermal diffusion layer is provided between the recording layer and the thermal diffusion layer as shown below, and the recording layer and the thermal diffusion layer are provided. Is set to a groove depth dg or more. However, in the case of such a structure, the reflectance is rapidly reduced.
[0030]
Even in such a case, a decrease in reflectivity can be suppressed by using the structure as shown in (1) and (2). Therefore, a practical low cross erase medium with high reflectivity as described below is realized.
[0031]
(3) The information recording medium according to (1) (2), comprising at least one thermal diffusion layer on the side opposite to the laser beam incident side of the recording layer, and between the recording layer and the thermal diffusion layer. An information recording medium comprising at least one third interference layer, wherein a distance between the recording layer and the thermal diffusion layer is not less than the above dg.
[0032]
Further, it has been found that the composition of the third interference layer has an optimum composition as shown in (4).
[0033]
(4) The information recording medium according to (3), wherein the third interference layer has a ZnS composition ratio of 50% to 95%. ₂ An information recording medium comprising a mixture of
[0034]
When such a composition is used, there arises a problem that S atoms contained in the third interference layer are diffused into the recording layer at the time of rewriting many times, and the reflectance is lowered. In such a case, as shown in (5), a second interface layer may be provided between the recording layer and the third interference layer. As already described, the interface layer material used in the second interface layer is preferably a transition metal element oxide or nitride, or a nitride of a semiconductor element such as Ge or Si, as in the first interface layer. However, as described above, since these compounds easily absorb light, the effect of multiple interference is hindered and the reflectance is easily lowered. Even in such a case, a decrease in reflectivity can be suppressed by using the structure as shown in (1) and (2). Needless to say, as shown in (5), it is important that the S element contained in the second interface layer is smaller than the S element contained in the third interference layer.
[0035]
(5) The information recording medium according to (4), wherein the second interface layer is present in contact with the recording layer between the third interference layer and the recording layer, and the composition ratio of the S element in the second interface layer Is smaller than the third interference layer.
[0036]
Further, when land / groove recording is performed as shown in (6), cross erase is a problem. Even in such a case, by using an information recording medium having a configuration as shown in (3). Thus, an information recording medium with extremely small cross erase can be realized.
[0037]
(6) The information recording medium according to (3), wherein information is recorded both in a groove (groove) and between grooves (land).
[0038]
The first interface layer, the second interface layer, the recording layer, and the like described above are usually extremely thin, about several nm. In such a case, a phenomenon that the film is not necessarily formed in a layer but is present in an island shape (a mottle) occurs (island formation of a thin film). Even in such a case, if the distance between the island-shaped thin films is about one-tenth of the wavelength of the laser beam, it is optically negligible and there is a layer having an average film thickness of the island-shaped thin films. Even if it thinks, the effect of the present invention is not lost. For example, even if the interface layer such as the second interface layer exists in an island shape, the effect of preventing the diffusion of each interference layer element into the recording layer is not sufficient, but is manifested. Also, the main purpose of the first interface layer is to prevent peeling that occurs between the second interference layer and the recording layer. Therefore, regarding the first interface layer, if the material used for the second interference layer is difficult to diffuse into the recording layer, it may be present even if it exists in an island shape.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
The invention is illustrated in detail by the following examples.
[0040]
FIG. 1 shows the basic structure of the information recording medium of the present invention. The first information recording member includes a first interference layer 1-2, a second interference layer 1-3, a first interface layer 1-4, and a recording layer 1 on a substrate 1-1 on which a groove-shaped information recording track is provided. -5, the second interface layer 1-6, the third interference layer 1-7, the thermal buffer layer 1-8, and the thermal diffusion layer 1-9 are sequentially stacked. Moreover, the information recording member of the same structure is bonded through the adhesive 1-10.
[0041]
A plastic transparent substrate such as polycarbonate is used as the substrate 1-1.
[0042]
Usually, the refractive index of such a transparent substrate is about 1.5 to 1.6. It is desirable that the optical characteristics to be satisfied of the first interference layer 1-2 have a refractive index larger than that of the substrate 1-1 and the refractive index is 2.0 or more. As a result, light is reflected between the substrate 1-1 and the first interference layer 1-2, and the reflectance change between the unrecorded portion (crystal) and the recorded portion (amorphous) due to the optical interference effect using this reflection. Can be increased.
[0043]
The refractive index of the second interference layer 1-3 is smaller than the refractive index of the first interference layer 1-2, and further smaller than the refractive index of the recording layer 1-5. The first interface layer 1-4 suppresses peeling between the recording layer 1-5 and the second interference layer 1-3. The refractive index of the first interface layer 1-4 is desirably as high as possible as that of the second interference layer 1-3. If the refractive index of the first interface layer 1-4 is as large as the first interference layer 1-2, In the range that does not affect the peeling suppression effect, it is preferable to be as thin as possible. The third interference layer 1-7 needs an appropriate film thickness in order to control the cross erase by appropriately separating the distance between the thermal diffusion layer 1-9 and the recording layer 1-5. At least the film thickness is 35 nm or more, and desirably a thickness greater than the groove depth. Moreover, it is requested | required that heat conductivity is moderately low. The second interface layer 1-6 mainly plays a role of suppressing peeling occurring between the recording layer 1-5 and the third interference layer 1-7 and suppressing diffusion of the third interference layer element to the recording layer. Yes. The thermal buffer layer 1-8 controls the flow of heat from the recording layer 1-5 to the thermal diffusion layer 1-9 at the same time as controlling the absorption rate when the recording layer 1-5 is crystalline or amorphous. Have a role. The optical constants (n, k) are preferably in the range of 1.4 <n <4.5 and −3.5 <k <−0.5, particularly 2 <n <4, −3.0 <k <−0. A material of .5 is desirable. The thermal diffusion layer 1-9 has a role of quickly diffusing heat generated in the recording layer 1-5 and suppressing thermal damage of the recording layer 1-5 during recording. For this reason, it is required that the thermal conductivity is moderately high. For this reason, a film thickness of at least 30 nm or more is necessary.
[0044]
The basic concept of the present invention is shown below. Here, for the sake of simplicity, description will be made using only the first interference layer, the second interference layer, the recording layer, the third interference layer, and the thermal diffusion layer, which are particularly important optically. FIG. 2 is a diagram schematically showing the refractive index of each layer with and without the second interference layer. The vertical axis represents the refractive index, and the horizontal axis represents the distance in the light incident direction from a certain point in the substrate. Here, the structure 1 is a structure in which a first interference layer, a recording layer, a third interference layer, and a reflection layer are sequentially laminated on a base plate. In the case of such a structure, optical design is mainly performed using a multiple interference effect using four reflecting surfaces. That is, the reflection surface A between the substrate and the first interference layer, the reflection surface B between the first interference layer and the recording layer, the reflection surface C between the recording layer and the third interference layer, and the reflection surface D between the third interference layer and the heat diffusion layer. is there. In such a case, there are six types of optical paths that can be used for optical design: A-B, A-C, A-D, B-C, B-D, and C-D. In contrast, when a second interference layer having a refractive index smaller than that of the first interference layer is inserted between the first interference layer and the recording layer (Structure 2), a reflection surface E that can be used for multiple interference is newly added. Is done. In such a case, optical paths that can be used for optical design are A-B, A-C, A-D, A-E, B-C, B-D, B-E, C-D. There are 10 types of between, CE, and DE, and the degree of freedom in optical design is dramatically improved. Moreover, it becomes easy to improve a reflectance by utilizing the reflection of the reflective surface E effectively.
[0045]
There are two reasons why the refractive index of the second interference layer is preferably smaller than that of the first interference layer.
[0046]
First, the refractive index of the substrate is limited to materials that can be selected in order to satisfy various properties required for the substrate, and the refractive index is about 1.5 to 1.6. Therefore, in order to increase the reflection coefficient at the reflection surface A, it is necessary to reduce or increase the refractive index of the first interference layer as much as possible. Considering that the refractive index of a normal inorganic dielectric material that can be used for the first interference layer is at least about 1.4, it is not practical to reduce the refractive index of the first interference layer. Therefore, the refractive index of the first interference layer needs to be as large as possible than the refractive index of the substrate. However, since a material having a refractive index of 2.5 or more normally absorbs light normally, the refractive index of the first interference layer is actually suppressed to about 2-2.2. Similarly, in order to increase the reflection coefficient at the reflection surface E, either the refractive index of the second interference layer is made larger or smaller than the refractive index of the first interference layer. When the refractive index of the second interference layer is made larger than the refractive index of the first interference layer, two problems occur. One is that it is very difficult to obtain a transparent material having a refractive index of 3 or more, for example, and the other is a refractive index between the recording layer (refractive index is about 4) and the second interference layer. It is to reduce the difference.
[0047]
As a result, the reflection coefficient on the reflection surface B is reduced. Therefore, the refractive index of the second interference layer is preferably smaller than the refractive index of the first interference layer. Further, the first interface layer is necessary mainly for suppressing peeling that occurs between the recording layer and the second interference layer. The refractive index of the first interface layer is desirably as high as possible as that of the second interference layer. However, when the refractive index becomes as large as the first interference layer, the range that does not affect the above-described peeling suppression effect. However, it is better to be as thin as possible.
[0048]
Next, optical calculation results are shown.
The optical constants (n, k) used for the calculation are shown below.
First interference layer: (2.16, 0.00)
Second interference layer: (1.4 to 2.2, 0.00)
First interface layer: (2.6, -0.09)
Recording layer (crystal): (4.57, -5.46)
Recording layer (amorphous): (4.51, -2.22)
Second interface layer: (2.6, -0.09)
Third interference layer: (2.16, 0.00)
Thermal buffer layer: (4.09, -2.88)
Thermal diffusion layer: (1.84, -5.74)
Moreover, the film thickness of each layer is shown below.
First interference layer: 0 to 150 nm
Second interference layer: 0 to 80 nm
First interface layer: 1 nm
Recording layer: 6.3 nm
Second interface layer: 10 nm
Third interference layer: 45 nm
Thermal buffer layer: 35 nm
Thermal diffusion layer: 60 nm
FIG. 3 shows the film of the first interference layer so that the ratio (Rc−Ra) / Rc of the crystal reflectance Rc and the amorphous reflectance Ra is 90% or more, with the second interference layer thickness and the refractive index as variables. It is a calculation result when the thickness is optimized. When the refractive index of the second interference layer is larger than the refractive index of the first interference layer (n = 2.2), the reflection of the crystal when the thickness of the second interference layer is 0 or more (that is, when the second interference layer exists) However, when the refractive index of the second interference layer is 2.0 or less, which is smaller than the refractive index of the second interference layer, the effect of improving the reflectance is exhibited. The target reflectance is 15% or more as described in the 4.7 GB DVD-RAM standard. Since this calculation does not take into account the effect of the laser beam reflected on the substrate surface, the calculation result of this calculation is substantially larger by about 4%. Therefore, the target value of the reflectance in this calculation is 19% or more. The refractive index of the second interference layer that satisfies this condition is 1.4 to 1.8. Even if the refractive index of the second interference layer is any value between 1.4 and 1.8, the above condition can be satisfied if the thickness of the second interference layer is 20 nm or more and 78 nm. Accordingly, the refractive index of the second interference layer is at least smaller than the refractive index of the first interference layer, desirably 1.8 or less, and the film thickness is preferably 20 nm or more and 78 nm or less. The range of film thickness and refractive index is the case where the target value of reflectivity is 19%. However, practically, the reflectivity is about 3% considering the uniformity in the optical disk surface, the yield during mass production, and the like. Need to be raised. Therefore, practically, the target is a reflectance of 22% or more. In this case, the target is satisfied when the refractive index of the second interference layer is 1.4 to 1.6 and the film thickness is 20 nm to 70 nm.
[0049]
Next, FIG. 4 shows calculation results of the second interference layer thickness and the refractive index dependence of the reproduction signal when the thickness of the first interference layer is optimized so that the crystal reflectance Rc is 20% or more. Shown in When the refractive index of the second interference layer is larger than the refractive index of the first interference layer (n = 2.2), when the thickness of the second interference layer is 0.0 or more (that is, when the second interference layer exists), Although the reproduction signal amplitude is reduced, when the refractive index of the second interference layer is 2.0 or less, which is smaller than the refractive index of the second interference layer, the effect of improving the reproduction signal amplitude is exhibited. In particular, when the thickness of the second interference layer is 20 nm or more, the reproduction signal amplitude improvement effect of 1 dB or more is exhibited even when the refractive index is 2.0. The optimum thickness of the second interference layer is about 45 nm ± 25 nm. Therefore, the refractive index of the second interference layer is at least smaller than the refractive index of the first interference layer, and the film thickness is preferably 20 nm or more. In particular, when the refractive index of the second interference layer is 1.8 or less and the film thickness is 20 nm or more and 78 nm or less, the reproduction signal amplitude can be improved by 2 dB or more.
[0050]
FIG. 5 is a diagram showing the relationship between the thickness and refractive index of the second interference layer and the optimum thickness of the first interference layer when the calculation of FIG. 3 is performed. The sum of the thicknesses of the first interference layer and the second interference layer is suitably 130 ± 20 nm, and especially when 130 ± 10 nm, the optimum values are concentrated. It is important to maintain this relationship. Recognize.
[0051]
The above calculation is performed when the wavelength of the reproduction laser is 660 nm. For example, when using a reproduction laser of another wavelength, when the laser wavelength is λ, the thickness of the second interference layer is λ / 40˜ It may be about λ / 10, more preferably λ / 30 to λ / 10. Further, the sum of the film thicknesses of the first interference layer and the second interference layer may be about λ / 5 ± λ / 30, more preferably about λ / 5 ± λ / 60.
[0052]
Next, by making the thermal conductivity of the first interference layer lower than the thermal conductivity of the second interference layer and setting the distance between the first interference layer and the recording layer to be equal to or less than the groove depth dg, cross erase is performed. The reason why it can be suppressed will be described. In order to suppress the cross erase, it is extremely important to reduce the heat flow toward the adjacent track. FIG. 6 shows the heat at the time of groove recording when the thermal conductivity of the second interference layer is larger than the thermal conductivity of the first interference layer and the distance between the first interference layer and the recording layer is larger than the groove depth dg. Showed the flow. In such a case, the second interference layer 6-2 having a high thermal conductivity mainly exists in the adjacent track direction of the heat generating portion 6-11 during groove recording. Therefore, heat is likely to diffuse in the direction of the adjacent track, resulting in cross erase. On the other hand, as shown in FIG. 7, the thermal conductivity of the first interference layer 7-1 is lower than the thermal conductivity of the second interference layer 7-2, and the first interference layer 7-1 and the recording layer 7- When the distance between 4 is equal to or less than the groove depth dg, the first interference layer 7-1 having a low thermal conductivity exists mainly in the adjacent track direction of the heat generating portion 7-11 during groove recording. Therefore, the heat flow 7-8 is reduced, and cross erase is suppressed. As described above, the heat flow 7-8 in the direction of the adjacent track of the heat generating portion 7-11 during groove recording greatly depends on the distance between the first interference layer 7-1 and the recording layer 7-4. .
[0053]
In the above description, the flow of heat from the groove to the land during groove recording has been described. However, the thickness of the third interference layer is important for controlling the flow of heat from the land to the groove. This phenomenon will also be described with reference to FIGS. When the thermal conductivity of the thermal diffusion layer 6-7 is higher than that of the third interference layer 6-6, and the distance between the thermal diffusion layer 6-7 and the recording layer 6-4 is equal to or less than the groove depth dg (FIG. 6) Since the heat diffusion layer 6-7 is mainly present in the adjacent track direction of the heat generating portion 6-12 at the time of land recording, heat easily flows in the adjacent track direction. In contrast, as in the case of FIG. 7, the thermal conductivity of the thermal diffusion layer 7-7 is higher than that of the third interference layer 7-6, and the thermal diffusion layer 7-7 and the recording layer 7- When the distance 4 is equal to or greater than the groove depth dg, the third interference layer 7-6 having a low thermal conductivity exists in the adjacent track direction of the heat generating portion 7-12 during land recording. It becomes difficult for heat to flow, and as a result, cross erase can be suppressed.
[0054]
Based on the above optical and thermal considerations, the sum of the thermal conductivity and the refractive index of the first interference layer and the second interference layer, and the thickness of the second interference layer and the first interface layer (the first interference layer and the first interference layer) (Corresponding to the distance between the recording layers) and the presence or absence of the first interface layer are shown in FIG.
[0055]
Structures A and K are the only structures that have good reflectivity, cross erase, and peeling defects. The difference between the structure A and the structure K is that the relationship between the thermal conductivity κ1 of the first interference layer and the thermal conductivity κ2 of the second interference layer and the film thicknesses of the second interference layer and the first interface layer with respect to the groove depth dg. The magnitude relationship of the sum d2 + ds (corresponding to the distance between the first interference layer and the recording layer). When the structure A and the structure K are compared, the structure K is more realistic for the following reason. In the present invention, the low refractive index material used for the second interference layer is SiO in consideration of heat resistance, productivity, etc. ₂ , Al ₂ O _Three Since it is a material having a relatively high thermal conductivity such as MgO, it is practically difficult to make the thermal conductivity of the second interference layer below the thermal conductivity of the first interference layer as in the structure A. It is.
[0056]
From the optical calculation results shown above, there was an effect even when the thickness of the second interference layer was increased to about λ / 4. Usually, in the case of land groove recording, the groove depth is about λ / 6. Therefore, the upper limit of the film thickness of the second interference layer is limited by the groove depth dg.
[0057]
An embodiment of the present invention will be shown below.
[0058]
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. Each thin film (first interference layer: (ZnS) on the substrate ₈₀ (SiO ₂ ) ₂₀ (100 nm), second interference layer: Al ₂ O _Three (35 nm), first interface layer: Cr ₂ O _Three (2 nm), recording layer 3: Ge ₂₈ Sb ₁₈ Te ₅₄ (7 nm), second interface layer: Cr ₂ O _Three (5 nm), third interference layer: (ZnS) ₈₀ (SiO ₂ ) ₂₀ (40 nm), thermal buffer layer: Cr ₇₅ (Cr ₂ O _Three ) _{twenty five} (60 nm), thermal diffusion layer: Al ₉₈ Ti ₂ (100 nm) were sequentially formed by a sputtering process.
[0059]
Moreover, the information recording member which has the same structure was bonded together through the adhesive agent. The information recording medium having the above configuration is called an optical disc A. The refractive index of the polycarbonate substrate was 1.58. There are 35 user recording zones in the radial direction of the optical disc, and there are 25 to 59 sectors in one circumference of the zone. The track pitch is 0.615 μm.
[0060]
Information was recorded / reproduced on the optical disc A by the information recording / reproducing apparatus shown in FIG. The operation of the information recording / reproducing apparatus will be described below. As a motor control method for recording / reproducing, a ZCLV (Zone Constant Linear Velocity) method for changing the number of rotations of the disk for each zone for recording / reproducing is adopted. The disk linear velocity is about 8.2 m / s.
[0061]
Information from outside the recording apparatus is transmitted to the 8-16 modulator 8-8 in units of 8 bits. When information was recorded on the optical disc 8-1, recording was performed using a modulation system that converts 8 bits of information into 16 bits, a so-called 8-16 modulation system.
[0062]
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 8-8 in the figure performs this modulation. Here, T represents the clock cycle at the time of information recording, and here it was 17.1 ns.
[0063]
The digital signal of 3T to 14T converted by the 8-16 modulator 8-8 is transferred to the recording waveform generation circuit 8-6, the width of the high power pulse is set to about T / 2, and the high power level laser irradiation interval Then, a low power level laser irradiation having a width of about T / 2 is performed, and a multi-pulse recording waveform is generated in which the intermediate power level laser irradiation is performed between the series of high power pulses. At this time, the high power level for forming the recording mark was set to 10.0 mW, and the intermediate power level capable of erasing the recording mark was set to 4.0 mW. Further, in the recording waveform generation circuit 8-6, 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 disk 1 becomes a crystal (space portion), and the portion irradiated with a series of high power pulse trains including a high power level pulse is amorphous. Changes to (marked part). Further, in the recording waveform generation circuit 8-6, when forming a series of high power pulse trains including a high power level for forming the mark portion, according to the length of the space portion before and after the mark portion, It has a multi-pulse waveform table corresponding to a method (adaptive recording waveform control) that changes the first pulse width and the last pulse width of a multi-pulse waveform, and this affects the effect of thermal interference between marks. The multi-pulse recording waveform that can eliminate as much as possible is generated.
[0064]
The recording waveform generated by the recording waveform generating circuit 8-6 is transferred to the laser driving circuit 8-7. The laser driving circuit 8-7 uses the recording waveform to scan the semiconductor laser in the optical head 8-3. Make it emit light.
[0065]
In the optical head 8-3 mounted on the recording apparatus, a semiconductor laser having an optical wavelength of 655 nm is used as an information recording laser beam. Information was recorded by narrowing down the laser beam onto the recording layer of the optical disc 8-1 with an objective lens having a lens NA of 0.6 and irradiating a laser beam corresponding to the recording waveform.
[0066]
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, in the case of 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.
[0067]
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, the tracking for the land and groove can be arbitrarily selected by the L / G servo circuit 8-9.
[0068]
The recorded information was also reproduced using the optical head 8-3. 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 reproduced signal is increased by the preamplifier circuit 8-4 and transferred to the 8-16 demodulator 8-10. The 8-16 demodulator 8-10 converts the information into 8-bit information every 16 bits. With the above operation, the reproduction of the recorded mark is completed.
[0069]
When recording is performed on the optical disc 8-1 under the above conditions, the mark length of the 3T mark which is the shortest mark is about 0.42 μm, and the mark length of the 14T mark which is the longest mark is about 1.96 μm.
[0070]
As a result of measuring the reflectance of the crystal and the degree of modulation in the land groove (a value obtained by normalizing the difference between the reflectance of the crystal and the reflectance of the amorphous by the reflectance of the crystal) using the above apparatus, 22% and 55%, respectively. (Land), 56% (groove), and it was found that a good reproduction signal was obtained. The values after 100,000 rewrites were 20.2%, 54% (land), and 54% (groove), respectively, and were values that could sufficiently withstand practical use. Further, as a result of an accelerated storage life test under the condition of 90 ° C. and 80% humidity, it was found that no peeling defect occurred even after 200 hours.
[0071]
Further, when the composition and film thickness of the first interference layer, the second interference layer, the first interface layer, and the first interface layer of the disk A are changed, the refractive index and heat conduction of the first interference layer and the second interference layer are changed. FIG. 16 shows the relationship between the reflectance and the reflectance, the presence / absence of cross-erase, and the presence / absence of peeling defects.
[0072]
When the thermal conductivity of the second interference layer is larger than the thermal conductivity of the first interference layer and the sum of the film thicknesses of the second interference layer and the first interface layer is larger than the groove depth (65 nm), In C, when there is no first interface layer, in the disk D, the thermal conductivity of the first interference layer is larger than the thermal conductivity of the second interference layer, and the sum of the film thicknesses of the second interference layer and the first interference layer is the groove. When the depth is smaller than 65 nm, the disk E is a case where the refractive index of the second interference layer is larger than the refractive index of the first interference layer. These disks are not practical because of problems such as a decrease in reflectivity, cross erase, and peeling defects.
[0073]
Further, a disc having the same structure except for the disc A and the groove depth of the substrate was made as a prototype, and the presence / absence of cross erase was measured.
Groove depth (nm) Cross erase
25 Yes
30 Yes
37 None
65 None
76 None
As is clear from this result, when the sum of the film thicknesses of the second interference layer and the first interface layer (corresponding to the distance between the first interference layer and the recording film: 37 nm) is smaller than the groove depth, cross erase is performed. However, when the sum of the film thicknesses of the second interference layer and the first interface layer is equal to or greater than the groove depth, no cross erase occurs.
[0074]
As is clear from the above results, in the optical disk having a structure that does not satisfy any of the following conditions, any of problems such as a decrease in reflectivity, cross erase, and peeling defects occurred.
[0075]
(1) The thermal conductivity of the first interference layer is smaller than the thermal conductivity of the second interference layer, and the distance between the first interference layer and the recording layer is equal to or less than the groove depth.
(2) The refractive index of the second interference layer is larger than the refractive index of the first interference layer.
(3) A first interface layer is provided between the second interference layer and the recording layer.
[0076]
Also, the Cr of disk A ₂ O _Three Instead of this, the presence or absence of peeling defects when various materials were used as the first interface layer was examined, and the results are shown below.
First interface layer Existence of peeling defects
Ge _Three N _Four None
Si _Three N _Four None
SiO ₂ Yes
Al ₂ O _Three Yes
With MgO
TiO ₂ None
V ₂ O _Three None
Mn _Three O _Four None
Fe ₂ O _Three None
Mo ₂ O _Three None
W ₂ O _Three None
Co ₂ O _Three None
With AlN
As described above, when transition metal oxides such as Si, Ge nitride, Ti, V, Mn, Fe, Mo, W, and Co are used for the first interface layer, it is understood that no defects due to peeling occur. It was.
[0077]
Next, the optimum composition and the optimum film thickness of each layer will be described.
[0078]
Usually, the substance present on the light incident side of the first interference 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 substance and the first interference layer, the refractive index of the first interference layer is desirably 2.0 or more.
[0079]
The first interference layer is optically higher in refractive index than the substance existing on the light incident side (corresponding to the substrate in this embodiment), 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. Especially ZnS-SiO ₂ The compound of the system has a low thermal conductivity and is optimal as the first interference layer.
[0080]
FIG. 9 shows ZnS and SiO. ₂ The relationship between the composition ratio of ZnS and the refractive index when the composition ratio was changed was shown. In addition, the relationship between the composition ratio of ZnS and the thermal conductivity is shown below.
Composition ratio of ZnS Thermal conductivity
0 2W / mk
50 0.6 W / mk
70 0.5 W / mk
80 0.5W / mk
95 1W / mk
100 4W / mk
Also, as shown in FIG. 16, Al used as the second interference layer ₂ O _Three , SiO ₂ The thermal conductivity of MgO was 11 W / mk, 2 W / mk, and 4 W / mk, respectively.
[0081]
Therefore, when these materials are used as the second interference layer, when the composition ratio of ZnS is 50% or more and 95% or less, the thermal conductivity of the first interference layer is lower than the thermal conductivity of the second interference layer. In addition, since the refractive index is sufficiently large as 2.0 or more, the effect of the present invention is exhibited.
[0082]
As described above, the sum of the film thicknesses of the first interference layer and the second interference layer is preferably 130 ± 20 nm. The optimum film thickness of the second interference layer is 20 to 70 nm. From these, it can be seen that the thickness of the first interference layer is suitably 40 to 130 nm.
[0083]
The refractive index of the second interference layer is at least equal to or lower than the refractive index of the first interference layer, and is required to be 2.0 or less, preferably 1.8 or less.
[0084]
In particular, the material used for the second interference layer is Al. ₂ O _Three , SiO ₂ A low refractive index material such as MgO is suitable. Or these mixed materials may be sufficient. Al measured by the inventors ₂ O _Three , SiO ₂ MgO had refractive indexes of 1.65, 1.46, and 1.73, respectively. Moreover, the refractive index of the mixture changed in proportion to the mixing ratio, and all were 1.8 or less. Usually, when an oxide of any element of Al, Si, and Mg is contained, the refractive index decreases in proportion to the content of these oxides. Therefore, the sum of the contents of the oxides of Al, Si, and Mg contained in the second interference layer is required to be larger than the sum of the contents of the oxides contained in the first interference layer. .
[0085]
The characteristics required for the second interference layer are that the refractive index is equal to or lower than that of the first interference layer, and that it is thermally and chemically stable. Such a material contains any oxide of Al, Si, and Mg. In particular, when the sum of the composition ratios of O, N, C, and S in the second interference layer is X, the composition of O It is important that the ratio is 50% or more of X and the sum of the composition ratios of Al, Si, and Mg is 70% or more of 1-X. When the composition ratio of O is 50% or less of X, or when the composition ratio of Al, Si, and Mg is 50 or less of 1-X, the refractive index tends to increase, and the effects of the present invention are hardly exhibited. Because it becomes.
[0086]
As an example, FIGS. 10 and 11 show the relationship between the composition and refractive index of the second interference layer.
[0087]
Figure 10 shows SiO ₂ And Si _Three N _Four When the mixing ratio of Al is changed, and Al ₂ O _Three 5 is a graph showing the relationship between the composition ratio of O and the refractive index with respect to the sum X of the composition ratios of O and N when the mixing ratio of Al and AlN is changed. SiO ₂ And Si _Three N _Four Is mixed, the refractive index changes in proportion to the mixing ratio. The composition ratio of O to X at which the refractive index was 1.8 or less was 49% or more. Further, the composition ratio of O to X with a refractive index of 2.0 or less was 20% or more. Therefore, when the composition ratio of O to X is 50% or more, the effect of the present invention is sufficiently exhibited. Al ₂ O _Three Also when AlN is mixed with AlN, the refractive index changes in proportion to the mixing ratio. The composition ratio of O to X with a refractive index of 1.8 or less was 74% or more. Further, the composition ratio of O to X with a refractive index of 2.0 or less was 46% or more. Therefore, Al ₂ O _Three -AlN, SiO ₂ -Si _Three N _Four In both systems, when the composition ratio of O to X is 50% or more, the effects of the present invention are sufficiently exhibited.
[0088]
FIG. 11 shows Al. ₂ O _Three , SiO ₂ , MgO to Cr ₂ O _Three It is the result of investigating the relationship between the composition ratio and refractive index of Al, Si, Mg with respect to 1-X in the case of adding. Al ₂ O _Three -Cr ₂ O _Three In the system, when the composition ratio of Al with respect to the sum of the composition ratio of Cr and Al is 73% or more, SiO 2 ₂ -Cr ₂ O _Three In the system, when the composition ratio of Si with respect to the sum of the composition ratios of Cr and Si is 62% or more, MgO—Cr ₂ O _Three In the system, when the composition ratio of Mg with respect to the sum of the composition ratios of Cr and Mg was 88% or more, the refractive index was 1.8 or less. Al ₂ O _Three -Cr ₂ O _Three In the system, when the composition ratio of Al with respect to the sum of the composition ratio of Cr and Al is 54% or more, SiO 2 ₂ -Cr ₂ O _Three In the system, when the composition ratio of Si with respect to the sum of the composition ratios of Cr and Si is 46% or more, MgO—Cr ₂ O _Three In the system, when the composition ratio of Mg with respect to the sum of the composition ratios of Cr and Mg was 65% or more, the refractive index was 2.0 or less.
[0089]
Therefore, when the composition ratio of Al, Si, Mg to 1-X is 70% or more, the effect of the present invention is sufficiently exhibited. Moreover, as already shown, all of the oxides of Al, Si, and Mg have a low refractive index, and a mixture thereof also has a low refractive index. Therefore, even when other metal oxides or the like are added to these mixtures, the effect of the present invention is manifested when the sum of the composition ratios of Al, Si, and Mg to 1-X is 70% or more. Also, Cr as an additive metal ₂ O _Three The results of the addition of, but other metal oxides, metal nitrides, semiconductor oxides, semiconductor nitrides, etc. are also Cr ₂ O _Three Therefore, the effect of the present invention is manifested by adjusting the composition ratio so as to satisfy the above conditions.
[0090]
The second interference layer is usually a single compound or a mixture of stoichiometric compositions that are unlikely to absorb, but when such a compound is laminated adjacent to the recording layer, it is between the recording layer and the second interference layer. Defects due to film peeling are likely to occur. In such a case, an oxide or nitride of a transition metal element that is likely to become a non-stoichiometric compound as described below, or a mixture of these elements may be added to the second interference layer. In addition, even if the above measures are taken, if the effect of suppressing peeling is not sufficient, a first interface layer for improving the adhesion may be provided between the second interference layer and the recording layer. Usually, peeling easily occurs between the recording layer and the second interference layer depending on the content of oxides of Al, Si, and Mg. Therefore, the sum of the contents of Al, Si, Mg oxide contained in the first interface layer is smaller than the sum of the contents of the Al, Si, Mg oxide contained in the second interference layer. Is required. In addition, as the material for the first interface layer, oxides or nitrides of transition metal elements that are likely to become non-stoichiometric compounds, or mixtures of these elements are particularly excellent. In addition, oxides and nitrides of semiconductors such as Si and Ge are excellent because they easily become non-stoichiometric compounds.
[0091]
Specifically, oxides such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, La, and Ce, nitrides, or mixtures thereof Is suitable. Especially Cr-O-based material, Co ₂ O _Three , Oxides such as Co—O based materials such as CoO, Ta—N based materials, Al—N based materials, Si—N based materials, Al—Si—N based materials (for example, AlSiN ₂ ), Nitrides such as Ge—N-based materials, carbides such as SiC and GeC, and mixed materials thereof.
[0092]
Further, since the above materials usually absorb light, an optically good effect cannot be obtained.
[0093]
However, it is more practical to have the first interface layer because it has a great effect of suppressing film peeling, improving the storage life, and suppressing deterioration of many-time rewriting. Therefore, it is better that the thickness of the first interface layer is thin as long as the above effect is not lost. According to the examination results of the inventors, the film thickness of the first interface layer should be 0.5 nm or more. When the thickness is 5 nm or more, adverse effects such as a decrease in reflectivity and signal amplitude are likely to occur. When the thickness is 20 nm or more, the reflectivity decreases and the signal amplitude decreases, and the level is not practical. Therefore, the thickness of the first interface layer is 0.5 nm to 20 n, preferably 0.5 nm to 5 nm.
[0094]
Further, as the recording layer used in the present invention, a phase change recording material is particularly suitable, and the Ge layer used in the above examples is used. ₂₈ Sb ₁₈ Te ₅₄ As a material for the recording layer in place of the above, a composition in which Ge is in the range of 23 to 33 atomic%, Sb is in the range of 10 to 25 atomic%, and Te is in the range of 50 to 60 atomic%, particularly, the rewritable number of times is hardly reduced all right. In addition, AgSbTe ₂ When 1 to 7% is added, there is an effect of suppressing recording film flow that occurs at the time of rewriting many times.
[0095]
Furthermore, Ge other than the above ₂ Sb ₂ Te _Five , GeSb ₂ Te _Four , GeSb _Four Te ₇ , In _Three SbTe ₂ , In ₃₅ Sb ₃₂ Te ₃₃ , In ₃₁ Sb ₂₆ Te ₄₃ , GeTe, Ag-In-Sb-Te, Co-Ge-Sb-Te, V-Ge-Sb-Te, Ni-Ge-Sb-Te, Pt-Ge-Sb-Te, Si-Ge-Sb-Te Au-Ge-Sb-Te, Cu-Ge-Sb-Te, Mo-Ge-Sb-Te, Mn-Ge-Sb-Te, Fe-Ge-Sb-Te, Ti-Ge-Sb-Te, Bi Even if it is replaced with at least one of —Ge—Sb—Te, W—Ge—Sb—Te and compositions close thereto, or even if a part of Ge is replaced with In, similar characteristics can be obtained.
[0096]
When a recording layer containing 5 atomic% or less of nitrogen is used in each recording layer composition described above, the reproduction signal output is reduced, but there is an advantage in that the recording layer flow during multiple rewriting is suppressed.
[0097]
When the recording layer thickness is at least the level difference (groove depth) between the land and the groove, the cross erase reduction effect is large. Moreover, 4-20 nm has a large degree of modulation, and it is good that it does not flow easily. If it is 4-10 nm, it is still better. When the film thickness of the recording layer is less than 4 nm, the reflectivity, the signal amplitude, etc. are remarkably reduced, but the effect of suppressing the overwrite jitter and the effect of suppressing the recording film flow at the time of many rewrites are large. Further, when the thickness of the recording layer was greater than 10 nm, the reflectivity, the signal amplitude, and the like were good, but problems such as an increase in overwrite jitter and a flow of the recording film at the time of many rewrites appeared remarkably.
[0098]
FIG. 12 shows the relationship between the total recording film thickness and the reflectance when the recording layer film thickness of the disk A is changed. At this time, the thickness of each layer is optimized so that the degree of modulation is constant and the reflectance is as high as possible. When the recording layer film thickness is 4 nm or more, the reflectance is 18% or more, which is good. However, when the recording layer film thickness is less than 4%, the reflectance is drastically decreased to a target value of 15% or less. It was no longer right.
[0099]
FIG. 13 shows the relationship between the recording layer thickness and the amount of increase in jitter due to overwriting when the recording layer thickness of the disk A is changed. When the recording layer thickness is 10 nm or less, the amount of increase in jitter due to overwriting is about 1% or less, which is an allowable range. However, when the recording layer thickness is greater than 10 nm, jitter due to overwriting increases rapidly. Therefore, it was not practical.
[0100]
The recording layer in the present invention performs recording by changing the atomic arrangement. The atomic arrangement change refers to an atomic arrangement change that hardly accompanies a change in the outer shape of the film such as a phase change.
[0101]
In this embodiment, recording is performed on a phase change recording layer mainly composed of Ge, Sb, Te, In, Ag, etc. as an optical disk. However, the basis of the present invention is that heat is generated by a laser beam, This is to control the thermal characteristics (temperature distribution, cooling rate distribution) as well as the optical characteristics (reflectance, modulation degree) of the optical disk on which the recording mark is recorded by this heat. In addition, the present invention is also effective in recording on a magneto-optical recording layer mainly composed of Tb, Fe, Co, Dy, Gd and the like. Further, the present invention is not limited to a rewritable information recording medium. Further, in the case of organic dye recording in which recording is performed by changing the shape of the substrate or the recording layer, the change occurs only when a high power laser beam is irradiated, and this change is irreversible. The basis of the present invention is to control heat characteristics (temperature distribution, cooling rate distribution) as well as optical characteristics (reflectance, modulation degree) of an optical disc that records a recording mark by the heat generated by the laser beam. Therefore, the present invention is not limited to a rewritable optical disc, and can be applied to a write-once optical disc.
[0102]
As the material for the second interface layer, an oxide or nitride of a transition metal element that is likely to become a non-stoichiometric compound, or a mixture of these elements is preferable as in the first interface layer. In addition, oxides and nitrides of semiconductors such as Si and Ge are excellent because they easily become non-stoichiometric compounds.
[0103]
Specifically, oxides such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, La, and Ce, nitrides, or mixtures thereof Is suitable. Especially Cr-O-based material, Co ₂ O _Three , CoO-based oxides such as CoO, TaN, AlN, Si _Three N _Four Si-N-based materials such as Al-Si-N-based materials (for example, AlSiN ₂ ), Nitrides such as Ge—N-based materials, carbides such as SiC and GeC, and mixed materials thereof.
[0104]
Further, since the above materials usually absorb light, an optically good effect cannot be obtained.
[0105]
However, it has great effects of suppressing film peeling, improving the storage life, and suppressing deterioration of many-time rewriting. The difference between the first interface layer and the second interface layer is the difference in material existing on the side opposite to the adjacent surface to the recording layer. In the case of the first interface layer, the second interference layer exists on the surface opposite to the adjacent surface to the recording layer, whereas in the case of the second interface layer, on the surface opposite to the adjacent surface to the recording layer. Has a third interference layer. As described above, since the second interference layer is mainly composed of an oxide such as Al, Si, Mg, etc., it is extremely thermally and chemically stable. On the other hand, since the third interference layer is mainly composed of a sulfide such as ZnS as described above, it is unstable both thermally and chemically. In such a case, if the second interface layer is too thin, S atoms in the third interference layer diffuse into the recording layer at the time of many rewrites, causing deterioration such as a decrease in reflectance and a decrease in crystallization speed. Therefore, it is better that the thickness of the second interface layer is as thin as possible without losing the above effect. According to the examination results of the inventors, it was sufficient that the thickness of the second interface layer was 5 nm or more. When the thickness is 10 nm or more, adverse effects such as a decrease in reflectance and signal amplitude are likely to occur. When the thickness is 20 nm or more, the decrease in reflectance and signal amplitude is increased, and the level is not practical. Therefore, the thickness of the second interface layer is 5 nm to 20 nm, preferably 5 nm to 10 nm.
[0106]
The third interference layer is optically a material that does not absorb light, and is preferably as small as possible in terms of thermal conductivity. Specifically, the refractive index n is between 1.5 and 3.0, and it is a material that does not absorb light. In particular, it is desirable to contain a metal oxide, carbide, nitride, sulfide, or selenide. . In particular, the third interference layer is (ZnS) ₈₀ (SiO ₂ ) ₂₀ (Molar ratio) or ZnS and SiO ₂ Since the thermal conductivity is remarkably lowered particularly when the mixing ratio is changed (ZnS is 50 to 95 mol%), it is optimal as the third interference layer.
[0107]
The film thickness of the third interference layer is preferably about 35 to 200 nm. Desirably, it is better than the step between land grooves (groove depth on the substrate, about 1/7 to 1/5 of the laser wavelength) or more. Further, the sum of the film thicknesses of the third interference layer and the heat buffer layer may be greater than the step between the land grooves. When the film thickness of the third interference layer is 35 nm or less, or when the sum of the film thicknesses of the third interference layer and the thermal buffer layer is equal to or less than the step between the land grooves, the heat generated when recording on the recording layer is heated. Heat is transferred through the diffusion layer, and the recording marks recorded on the adjacent tracks are easily erased. That is, there arises a problem that cross erase is likely to occur. In addition, when the thickness of the third interference layer is 200 nm or more, the cooling rate in the recording layer during information recording becomes extremely small, which causes the problem that it becomes difficult to become amorphous (a recording mark is difficult to form) and at the same time, production Occasionally, the film thickness distribution of the third interference layer in the optical disk surface causes a problem such that the reflectance distribution in the disk surface becomes too large.
[0108]
FIG. 14 shows the relationship between the amount of increase in jitter due to cross erase and the thickness of the third interference layer when the thickness of the third interference layer of the optical disc A is changed. At this time, the thickness of the first interference layer is optimized so that the degree of modulation is constant. Further, a mark increase was recorded when a mark was recorded in advance and the mark recorded in the groove was reproduced when the adjacent track (land) was rewritten 1000 times. (The effect of cross erase is smaller when the lands and grooves in the above experiment are reversed.) When the thickness of the third interference layer is 35 nm or more (the thickness of the third interference layer, the second interface layer, and the thermal buffer layer) Cross erase did not occur at all, but the sum of the thickness of the third interference layer was less than 35 nm (thickness of the third interference layer, the second interface layer, and the thermal buffer layer). This is not practical because a cross erase occurs suddenly.
[0109]
The thermal buffer layer preferably has a complex refractive index n and k in the range of 1.4 <n <4.5 and −3.5 <k <−0.5, particularly 2 <n <4 and −3.0 <k. A material of <-0.5 is desirable. In order to absorb light in the thermal buffer layer, a thermally stable material is preferable, and it is desirable that the melting point is 1000 ° C. or higher.
[0110]
In addition, when sulfide is added to the third interference layer, there is a particularly large cross erase reduction effect. However, in the case of the thermal buffer layer, the content of sulfide such as ZnS is added to at least the third interference layer. Desirably less than the sulfide 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.
[0111]
The composition of the thermal buffer layer is preferably a mixture of metal and metal oxide, metal sulfide, metal nitride, metal carbide, Cr and Cr ₂ O _Three This mixture showed a particularly good effect of improving the overwrite property. 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, A mixture of Sb, Te, Ta, W, Ir, and Pb is desirable. Metal oxide, metal sulfide, metal nitride, and metal carbide are SiO. ₂ , SiO, TiO ₂ , Al ₂ O _Three , Y ₂ O _Three , CeO, La ₂ O _Three , In ₂ O _Three , GeO, GeO ₂ , PbO, SnO, SnO ₂ , Bi ₂ O _Three , TeO ₂ , MO ₂ , WO ₂ , WO _Three , Sc ₂ O _Three , Ta ₂ O _Five , ZrO ₂ Is preferred. In addition, Si-O-N materials, Si-Al-O-N materials, Cr ₂ O _Three , Etc. Cr-O-based materials, Co ₂ O _Three , CoO-based oxides such as CoO, TaN, AlN, Si _Three N _Four Si-N-based materials such as Al-Si-N-based materials (for example, AlSiN ₂ ), Nitrides such as Ge—N-based materials, ZnS, Sb ₂ S _Three , CdS, In ₂ S _Three , Ga ₂ S _Three , GeS, SnS ₂ , PbS, Bi ₂ S _Three , Etc., SnSe _Three , Sb ₂ S _Three , CdSe, ZnSe, In ₂ Se _Three , Ga ₂ Se _Three , GeSe, GeSe ₂ , SnSe, PbSe, Bi ₂ Se _Three Selenides such as CeF _Three , MgF ₂ , CaF ₂ A heat buffer layer using a fluoride such as the above or a composition close to the above material may be used.
[0112]
Further, the film thickness of the thermal buffer layer is preferably 10 nm or more and 100 nm or less. When the film thickness is 20 nm or more and 50 nm or less, a particularly excellent overwrite characteristic improvement effect appears. In addition, when the sum of the film thicknesses of the third interference layer, the second interface layer, and the thermal buffer layer is equal to or greater than the groove depth, the effect of reducing the cross erase appears remarkably.
[0113]
As described above, the thermal buffer layer has a property of absorbing light. For this reason, the thermal buffer 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 thermal buffer 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 to be smaller than the absorption rate Ac in the recording layer when the recording layer is in a crystalline state is exhibited. 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 thermal buffer layer to about 30 to 40%. The amount of heat generated in the thermal buffer 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.
[0114]
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 thermal buffer layer rises. In order to make effective use of this effect, the sum of the thicknesses of the third interference layer and the thermal buffer 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). Is better. When the sum of the thicknesses of the third interference layer and the heat buffer 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 recorded on the adjacent track. Becomes easier to erase.
[0115]
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% 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% or more of Al is used, an information recording medium that is inexpensive, excellent in high CNR, high recording sensitivity, excellent in multiple rewritability, and extremely effective in reducing cross erase can be obtained. . In particular, when the composition of the heat diffusion layer contains 95% or more of Al, an inexpensive information recording medium with excellent 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, but when the additive element is Co, Cr, Ti, Ni, Fe, or Cu, there is a great effect in improving corrosion resistance. The film thickness of the thermal diffusion layer is preferably 30 nm or more and 300 nm or less. When the thickness of the thermal diffusion layer is smaller than 30 nm, the heat generated in the recording layer is difficult to diffuse. Therefore, the recording layer is liable 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 reflective layer, and the reproduction signal amplitude may be reduced. Further, when the metal element contained in the thermal buffer 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 thermal buffer layer and the thermal diffusion layer can be formed using the same target. In other words, Ar-O during the thermal buffer layer formation ₂ Mixed gas, Ar-N ₂ Sputtering is performed with a mixed gas such as a mixed gas, and a thermal buffer layer having an appropriate refractive index is created by reacting a metal element with oxygen or nitrogen during sputtering. When forming a thermal diffusion layer, sputtering is performed with Ar gas. A metal thermal diffusion layer with high thermal conductivity is created.
[0116]
When the film thickness of the thermal diffusion layer is 300 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 70 nm or more and 150 nm or less, it is more preferable in terms of corrosion resistance and productivity.
[0117]
【The invention's effect】
As described above in detail, the effects of the present invention are remarkably exhibited when the following conditions are satisfied.
[0118]
(1) The thermal conductivity of the first interference layer is smaller than the thermal conductivity of the second interference layer, and the distance between the first interference layer and the recording layer is equal to or less than the groove depth.
(2) The refractive index of the second interference layer is larger than the refractive index of the first interference layer.
(3) A first interface layer is provided between the second interference layer and the recording layer.
Also, by combining the first interference layer, the second interference layer, and the first interface layer, the disadvantages of each layer are complemented, suppressing cross erase, improving the reflectance, suppressing the decrease in reflectance during multiple rewrites, and suppressing defects due to peeling. Even when it is possible to obtain a compatible information recording medium and have a structure that suppresses cross erase suppression, which is a problem during high-density recording, there is a decrease in reflectivity, a decrease in reflectivity during multiple rewrites, and defects due to peeling. Since it does not occur, a high-density information recording medium can be created very easily.
[Brief description of the drawings]
FIG. 1 is a structural diagram of an information recording medium of the present invention.
FIG. 2 is a conceptual diagram for explaining the principle of the present invention.
FIG. 3 is a diagram illustrating a calculation example of the present invention.
FIG. 4 is a diagram illustrating a calculation example of the present invention.
FIG. 5 is a diagram illustrating a calculation example of the present invention.
FIG. 6 is a conceptual diagram for explaining the principle of the present invention.
FIG. 7 is a conceptual diagram for explaining the principle of the present invention.
FIG. 8 is a block diagram of an information recording apparatus used in an embodiment of the present invention.
FIG. 9 is a diagram showing the relationship between the composition and refractive index of the first interference layer used in the present invention.
FIG. 10 is a diagram showing the relationship between the composition and refractive index of the second interference layer used in the present invention.
FIG. 11 is a diagram showing the relationship between the composition and refractive index of the second interference layer used in the present invention.
FIG. 12 is a diagram showing the relationship between the film thickness of the recording layer used in the present invention and the reflectance.
FIG. 13 is a diagram showing the relationship between the film thickness of a recording layer used in the present invention and the amount of jitter increase due to overwriting.
FIG. 14 is a diagram showing the relationship between the film thickness of the third interference layer used in the present invention and the amount of increase in jitter due to cross erase.
FIG. 15 is a diagram for considering characteristics of each structure;
FIG. 16 is a diagram summarizing the characteristics of each prototype structure.
[Explanation of symbols]
1-1, 1-1 ′: substrate
1-2, 1-2 ': Lower protective layer
1-3, 1-3 ′: Recording layer
1-4, 1-4 ′: Third interference layer
1-5, 1-5 ′: Thermal diffusion layer
1-6, 1-6 ′: Adhesive
1-7, 1-7 ′: Adhesive
1-8, 1-8 ′: Adhesive
1-9, 1-9 ′: Adhesive
1-10: Adhesive
6-0, 7-0: Substrate
6-1, 7-1: first interference layer
6-2, 7-2: Second interference layer
6-3, 7-3: First interface layer
6-4, 7-4: Recording layer
6-5, 7-5: Second interface layer
6-6, 7-6: Third interference layer
6-7, 7-7: Thermal diffusion layer
6-8, 7-8: Heat flow
6-9, 7-9: Objective lens
6-10, 7-10: Laser beam
6-11, 7-11: Heat generating part during groove recording
6-12, 7-12: Heat generating portion during land recording
8-1: Optical disc
8-2: Motor
8-3: Optical head
8-4: Preamplifier circuit
8-6: Recording waveform generation circuit
8-7: Laser drive circuit
8-8: 8-16 modulator
8-9: L / G servo circuit
8-10: 8-16 demodulator.

Claims (2)

An information recording medium on which information is recorded by the phase change of the recording layer by irradiation with a laser beam,
A first interference layer, a second interference layer, and a first interface layer are arranged in order from the side closer to the substrate between a substrate having a groove shape with a groove depth dg and the recording layer reflecting the groove shape. And
The thermal conductivity of the first interference layer is lower than the thermal conductivity of the second interference layer, and the refractive index of the second interference layer is smaller than the refractive index of the first interference layer and the refractive index of the recording layer. ,
A distance between the first interference layer and the recording layer is not more than the dg;
On the opposite side of the recording layer to the side in contact with the first interface layer, a thermal diffusion layer made of a metal element, and a third interference layer provided between the recording layer and the thermal diffusion layer,
The distance between the recording layer and the heat diffusion layer is not less than the dg,
An information recording medium, wherein a second interface layer is provided in contact with the recording layer between the third interference layer and the recording layer. The first and third interference layers are made of a mixture of ZnS and SiO ₂ having a composition ratio of ZnS of 50% or more and 90% or less, and the second interference layer has a sum of composition ratios of O, N, S, and C. In the case of X, the composition ratio of O is 50% or more of X, the sum of the composition ratios of Al, Si, and Mg is 70% or more of 1-X, and the first interface layer is an oxidation of a transition metal element. The information recording medium according to claim 1, wherein the information recording medium is made of a material, a nitride, a nitride of Si, Ge, or a mixture containing these.

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