JP2001035010A - Optical disk and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical disk having a board use linear velocity region and high repeated durability. SOLUTION: This optical disk has a heat sink layer 5 consisting of a metallic film having an about several tens nm film thickness and a dielectric multi- layered reflection film 6 provided with dielectric alternatively-layered films of two or more layers having a central thickness of 1/4 of used wavelength laminated on a recording film of a disk base material, thereby, obtains a broad use linear velocity region and high repeated durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk and a method of manufacturing the optical disk, and more particularly, the present invention relates to an optical disk using a dielectric multilayer film.
More particularly, the present invention relates to an optical disk using a dielectric multilayer film as a reflection film and having a heat sink layer.

[0002]

2. Description of the Related Art Conventionally, optical recording disks can be classified into two types: write-once type and rewritable type. The write-once type is an optical disk that is permanently recorded when information is recorded once, while the rewritable type is an optical disk on which information can be repeatedly erased and written. Therefore, the write-once optical disk and the rewritable optical disk generally have different disk configurations.

FIG. 2 shows the configuration of a typical conventional rewritable optical disk. That is, the lower protective film 2 for protecting the recording film, the recording film 3 for retaining information, the protection of the recording film 3, and the like, by using some film forming means such as sputtering or vacuum deposition on the substrate 1. An upper protective film 4 corresponding to the thermal characteristics of the recording film 3 and a reflective film 5 are formed. As a material of the reflection film 5, a metal such as Al, Au, or Cu is generally used. This reflection film also has a role as a heat sink.

Here, the principle of writing on the phase change optical disk will be described. Now, it is assumed that the recording film 3 used in the optical disk shown in FIG. 2 records and reproduces information by utilizing a change in optical phase. When a laser beam is focused on the crystallized recording film 3 of the optical disc by a lens or the like, the temperature of the crystallized portion irradiated with the laser beam starts to rise. The situation is shown in the area indicated by 1 in the graph of FIG.

Next, as shown by a region 2 in the graph of FIG. 3, after the temperature is raised to a point exceeding the melting point Tm of the recording film 3 and then the laser power is lowered, the graph of FIG. As shown in a region indicated by 3 in the figure, the temperature of the crystallized portion starts to decrease. Therefore, by lowering the temperature sufficiently quickly to a certain temperature or less called the glass transition temperature Tg,
The recording film can be made amorphous. The amorphous state thus obtained is regarded as a recording mark. On the other hand, if the temperature is lowered sufficiently slowly, the crystal will not be in the amorphous state but will be in the original crystalline state. During the recording operation, when the linear velocity is low, the time during which the laser beam hits one area is long, so that slow cooling is likely to occur, and it is difficult to realize an amorphous state.

On the other hand, when the linear velocity of the optical disk is high, as described later, the temperature of the recording film rises to a relatively high temperature, causing a problem that the recording characteristics deteriorate.

Next, the principle of controlling the mark length will be described. When a writing operation is performed while irradiating an intensity-modulated laser beam onto a rotating optical disk, a mark is formed on a portion irradiated with a high laser power. The details will be described below.

FIG. 4 shows the maximum temperature distribution in the direction swept by the laser beam. Although the temperature of the portion irradiated with the laser beam rises, the amount of temperature rise increases in this direction because heat accumulates in the sweep direction. Only the part whose maximum temperature exceeds the melting point Tm is marked. If the optical disk has no heat sink, the recording film rises to a relatively high temperature when writing the same mark length because the heat easily accumulates, as shown in graph A of FIG. Therefore, the recording film and the substrate are easily deteriorated, and the repetition resistance of the disk is deteriorated.

Next, an optical design of a general phase change optical disk will be described. That is, when the laser light is incident on the disk, the light is not absorbed by the recording film, the metal film, or the like due to the nature of the light wave, and the reflectance reflecting the result of the optical interference is observed. That is,
The reflectance is determined as a result of interference of reflected light determined by the refractive index and absorptance of each film, the film thickness, and the wavelength of the light source. In addition, since the refractive index and the absorptivity of a substance generally have wavelength dispersion, an optical disc having a desired reflectance cannot be obtained with respect to the wavelength of the light source used.

For example, as shown in FIG. 5, the reflectivity of aluminum Al formed by sputtering differs greatly depending on the manufacturing method, as is clear from the graph showing the relationship between the wavelength of light and the reflectivity. Even if it is aluminum Al manufactured by the same manufacturing method, its reflectivity differs depending on the wavelength of light.

[0011]

As described above, when a metal film is used as the reflection film, the reflectance and the absorptance change when the wavelength of the laser used changes. Therefore, the first problem is that a desired reflectance may not be obtained when the wavelength of the laser used is changed. The reason is derived from the large wavelength dispersion of the metal's refractive index and absorption coefficient. As an example, as is clear from the wavelength dependence of the reflectance of Al shown in FIG. 5, the reflectance of aluminum Al obtained by sputtering shows a high reflectance of about 80% near 640 nm, but the shorter wavelength has a shorter wavelength. On the side, the reflectivity decreases, so that it cannot be used as a reflective film of an optical disk. Normally, if the reflectance is lower than about 75%, the film cannot be used as a reflection film. Therefore, for a wavelength shorter than 400 nm, some other measure must be taken.

In order to solve these problems, Japanese Patent Laid-Open Publication No. 4-137234 proposes an optical disk using a dielectric multilayer film as a reflection film. However, when a disk having this configuration is used, the temperature rises at low linear speed because there is no metal reflective film serving as a heat sink as shown in FIG. 2 described above. The second problem is that it cannot be used because it is too hard and that it has low repetition resistance.

Japanese Patent Application Laid-Open No. Hei 8-21176 discloses a phase-change optical recording medium. The structure of the medium is such that a recording film, a dielectric film, a reflective film, and a protective film are laminated on a substrate. Since the heat sink layer is not formed on the recording film, it has the same problems as those in the above-mentioned known example.

Further, Japanese Patent Application Laid-Open No. 4-177625 discloses a configuration of an optical recording medium in which a heat diffusion layer, a protective film, a recording film, a protective film, and a metal reflective film are laminated from the substrate side. Since a reflective film is used, the above-described problem exists, and a thermal diffusion layer is provided between the substrate and the recording film in order to eliminate temperature unevenness on both the front and back surfaces of the recording film. However, since the energy of light incident on the recording layer is restricted, there is a problem that its design is difficult.

On the other hand, Japanese Patent Laid-Open No. 5-120728 discloses that in an optical recording medium comprising a recording layer and a reflective layer, a reflective layer made of a dielectric is formed on a surface of the reflective layer opposite to the recording layer. Although a structure in which a prevention layer is provided is disclosed, it has the same problem as described above in that the heat sink layer is not provided and the reflection layer is laminated on the recording layer.

Japanese Patent Application Laid-Open No. 8-96413 also discloses an optical phase change type information recording medium in which a recording film is provided with a metal reflective film having a plurality of layers via a dielectric protection layer. However, as described above, there is no heat sink layer, and the same problem as described above is involved in that the reflective layer is laminated on the recording layer.

Accordingly, an object of the present invention is to provide an optical disk which improves the above-mentioned drawbacks of the prior art, is easy in optical design, has good repetition resistance, and can execute information recording / reproduction even at a low linear velocity. Is the purpose.

[0018]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention employs the following technical configuration. That is, a first aspect according to the present invention is an optical disc in which at least a recording film, a protective film, a heat sink layer, and a dielectric reflection film are laminated in this order on a substrate substrate. Is an optical disc having a configuration in which at least a protective film, a recording film, a protective film, a heat sink layer, and a dielectric reflection film are laminated in this order on a substrate substrate.

On the other hand, as a third aspect according to the present invention,
It comprises at least a first step of forming a recording film on a substrate substrate, a second step of forming a protective film on the recording film, and a third step of forming a heat sink layer on the protective film. That is the manufacturing method of the optical disk.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical disk and the method for manufacturing the optical disk according to the present invention employ the above-mentioned technical configuration.
A metal reflective film is used by providing a metal film having a thickness of about m and a multilayer film in which two or more, preferably three or more dielectric layers are alternately laminated with a center wavelength at the wavelength used. Instead of using a reflective film composed of a dielectric layer and using a thin-film heat sink layer together, the optical design is easy, and a wide operating linear velocity region and high repetition resistance can be secured. An effect can be obtained.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an optical disk and a method of manufacturing the optical disk according to the present invention.

FIG. 1 is a sectional view showing the structure of a first specific example of an optical disk according to the present invention. In FIG. 1, at least a recording film 3, a protective film 4, and a heat sink layer 5 are formed on a substrate 1. The optical disk 10 is formed by laminating dielectric reflection films 6 in this order.

As is apparent from FIG. 1, as a second specific example of the optical disk according to the present invention, at least a protective film (lower protective film) 2, a recording film 3, and a protective film ( An optical disk 10 is shown in which an upper protective film 4, a heat sink layer 5, and a dielectric reflection film 6 are laminated in this order.

That is, the inventor of the present invention has made intensive studies to form an optical film that can meet various purposes on the recording film 3 on the optical disk substrate 1 to form a reflective film 6. As described later, for example, the heat sink film layer 5 having a thickness of about several tens of nm on the recording film 3 is provided with, for example, three or more dielectric layer alternating films with the center wavelength being the wavelength used. It has been found that the optical design is easy and a wide linear velocity region and high repetition resistance can be secured.

If the structure of the optical disk 10 according to the present invention is described in more detail, it is desirable that the heat sink layer 5 according to the present invention is formed of a metal film, and that the thickness thereof is particularly small. Therefore, it is preferable that the metal film is formed of a metal film having an extremely thin film thickness.

The thickness of the heat sink layer 5 used in the optical disk 10 according to the present invention is, for example, a thermal diffusivity such that the heat applied to the heat sink layer 5 can quickly diffuse. It is preferable that the layer has a thickness sufficient to maintain light transmittance while maintaining the above.

In other words, the heat sink layer 5 according to the present invention has a function of effectively diffusing the heat accumulated in the recording layer 3 to the outside, and the light transmitted through the recording layer is incident on the dielectric film which also serves as a reflection film. It is desirable to have such a function.

More specifically, the thickness of the heat sink layer 5 is preferably 10 nm or more and 50 nm or less. The reason is that if the thickness of the heat sink layer 5 is too thick, light absorption cannot be ignored, and if it is too thin, it becomes difficult to control the film thickness.

The material of the heat sink layer used in the present invention is, for example, Cu, A having high thermal conductivity.
u, Ag, Al and alloys mainly composed of these are preferred.

Considering that Cu is inexpensive, it is most preferable. It is needless to say that the material of the heat sink layer is not particularly limited because other metals or alloys can be used depending on the application.

The operation of the heat sink layer 5 is as follows.

When the temperature of the recording film 3 is increased by the laser light, heat propagates to the heat sink layer 5 via the upper protective film 4.

Since the metal film constituting the heat sink layer 5 has a high thermal conductivity, heat is quickly transferred to the heat sink layer 5.
It diffuses inside and cools down.

Therefore, the recording film 3 can be used at a low linear velocity for slowly raising the temperature, and the repetition resistance can be secured. Light passes through the heat sink layer 5 and passes through the dielectric multilayer film 6.
The light is reflected by and enters the reproduction system.

On the other hand, the dielectric reflection film 6 used in the present invention is preferably composed of a dielectric multilayer reflection film, and the dielectric multilayer reflection film 6 is composed of at least two kinds of different dielectric films. It is also desirable that the dielectric layer is formed by laminating dielectric layers made of a material.

That is, in the present invention, it is desirable that the dielectric multilayer reflective film 6 is a multilayered film formed by laminating at least two types, preferably three or more types of dielectrics. .

The different dielectric materials constituting the dielectric multilayer reflective film 6 are preferably, for example, a combination of a high refractive index dielectric and a low refractive index dielectric.

More specifically, the dielectric multilayer reflective film 6
The physical thickness (d) of each dielectric film constituting
With respect to the laser light wavelength (λ ₀ ) and the refractive index (n), nd = 1 / 4λ ₀ ... [I] It is realized by doing.

That is, in the present invention, the thickness of the dielectric multilayer reflective film 6 is set to １ ／ of the wavelength of the laser beam used.
Preferably has a film thickness value equal to the product of the film thickness and the refractive index, or a film thickness value near the film thickness.

By using this method, the dielectric multilayer reflective film 6 having a high reflectance can be easily obtained without depending on the wavelength of light.

Among the dielectrics used in the dielectric multilayer film used in the present invention, high refractive index dielectrics having a relatively high refractive index include, for example, CeO ₂ (n = 2.4),
TiO ₂ (n = 2.3) is preferred.

As the low refractive index dielectric, for example,
MgF ₂ (n = 1.4) and SiO ₂ (n = 1.5) are preferred.

The reason for selecting such a dielectric multilayer is that it is excellent in light resistance and heat resistance.

The dielectric film layer in the dielectric multilayer reflection film 6 must be composed of at least two layers, and is preferably composed of three layers or a laminate of three or more layers. It is desirable to have.

The number of the dielectric layers constituting the dielectric multilayer reflective film 6 may be three or more.

Further, the number of layers of each dielectric constituting the dielectric multilayer reflective film 6 may be increased according to the required reflectance, but is preferably about 3 to 6 layers.

The reason is as follows. That is, if the reflectivity of the crystal part is about 20% or more and the reflectivity of the amorphous part is about 5% or less, the reflectivity is practical, but three layers are the minimum number of layers for that purpose. Further, even if a multilayer film having six or more layers is formed, the reflectivity hardly increases. Therefore, considering man-hours, three to six layers are appropriate.

In the present invention, as is apparent from FIG. 1, it is preferable that the dielectric reflection film 6 is further covered with a protection film 7 made of a UV protection film or the like.

Therefore, the optical disk 10 according to the present invention
First, when the optical disk 10 is irradiated with a laser, heat generated in the recording film 3 propagates through the protective film 4 and is diffused in the heat sink layer 5. The cooling rate of the recording film 3 can be controlled by adjusting the thickness of the protective film 4.

Further, according to the present invention, when the thickness of the heat sink layer 5 is optically in the range of 10 to 50 nm, the laser light transmitted through the heat sink layer 5 is reflected by the dielectric multilayer reflective film 6. You will enter the playback system.

Next, a more specific example of the optical disk 10 of the present invention will be described in detail in the form of an embodiment with reference to FIGS.

First, as shown in FIG. 6, an optical disk 10 used in this example was formed on a molded polycarbonate (PC) disk substrate 1 with a layer configuration as shown. In any of such film forming methods, the film is formed using a sputtering method after evacuation to a degree of vacuum.

The layer structure of the specific example shown in FIG. 6 is described as follows (the thickness in parentheses is a film thickness in nm).

1. PC board / 2. ZnS-SiO ₂ (1
40) / 3. Ge ₂ Sb ₂ Te ₅ (20) / 4. ZnS-Si
O ₂ (80) / 5. Cu (20) / 6. CeO ₂ (40) / Mg
An alternating multilayer film of F ₂ (68) / CeO ₂ (40) / MgF ₂ (68).

Next, the film was taken out of the film forming apparatus, and the UV protective film 7 was coated on the dielectric multilayer reflective film 6.

In these embodiments, the Cu film corresponds to the heat sink layer, and the film above the Cu film corresponds to the dielectric multilayer reflective film.

In addition, as a comparative example, C:
An optical disk 10 having the following configuration without a u film was evacuated to the same degree of vacuum using the same film forming apparatus, and then a film formed by sputtering was prepared.

1. PC board / 2. ZnS-SiO ₂ (1
40) / 3. Ge ₂ Sb ₂ Te ₅ (12) / 4. ZnS-Si
O ₂ (20) / 6. CeO ₂ (40) / MgF ₂ (68) / C
An alternate multilayer film of eO ₂ (40) / MgF ₂ (68).

The thickness of each of the dielectric multilayer films 6 in the above two specific examples is adjusted for a laser wavelength of 380 nm.

At 380 nm, as shown in the graph of FIG. 5, since the reflectance is lowered, Al cannot be used for the metal reflection film.

On the other hand, the optical disk 1 shown in the specific example of FIG.
The reflectance of 0 is 25.7% in the crystal part and 3.4% in the amorphous part, indicating practical values. Therefore, it can be seen that by using this design method, the reflection film 6 can be designed regardless of the wavelength, even when the metal reflection film cannot be used.

FIG. 7 shows the linear velocity dependence of the signal amplitude measured for the above specific example and the comparative example having no heat sink layer.

That is, at the time of the measurement, the linear velocity measurement was performed at a linear velocity of 6 m / s to 9 m / s, and then the measurement was performed using a signal waveform tester.

In FIG. 7, the vertical axis is normalized based on the amplitude at a linear velocity of 9 m / s. As shown in FIG. 7, in the optical disk 10 according to the present invention, as shown by the black circle graph, the signal amplitude is high even when the linear velocity is low, and the usable linear velocity is lower on the lower linear velocity side. Can be seen spreading.

On the other hand, in the comparative example in which the heat sink layer 5 was not provided, as shown by the white circle graph, it was shown that as the linear velocity was lowered, the signal amplitude was greatly reduced. It turns out that it lacks practicality.

On the other hand, FIG. 8 shows that the laser beam has a linear velocity of 6 m /
A result obtained by calculating the maximum temperature distribution in the direction in which the optical disk 10 is swept by s by simulation is shown.

As can be understood from FIG. 8, the solid line graph showing the measurement results of the optical disk 10 according to the present invention shows that the maximum temperature in the mark length region is kept low while the heat sink layer 5 is provided. In the dotted line graph showing the measurement result of the comparative example that does not have, the maximum temperature in the mark length region,
It is understood that it becomes considerably high.

As is apparent from the above results, the optical disk 10 of the present invention has a lower maximum temperature, indicating that the optical disk 10 of the present invention has improved repetition resistance.

The material of the dielectric multilayer reflective film 6 in the present invention is not limited to the above.

That is, in the present invention, the larger the refractive index difference between the high refractive index dielectric and the low refractive index dielectric, the more the dielectric multilayer film functions as a band stop filter having a wider band width. the if narrow ZnS-SiO ₂ as a high refractive index dielectric, it is possible to use AlN as a low refractive index dielectric.

On the other hand, as is clear from the above description, the method for manufacturing an optical disk according to the present invention is, as a specific method for manufacturing the optical disk, for example, at least forming a recording film on a substrate substrate. A first step, a second step of forming a protective film on the recording film, a third step of forming a heat sink layer on the protective film, and a fourth step of forming a dielectric reflection film on the heat sink layer This is a method for manufacturing an optical disk comprising the steps of:

Further, in the method of manufacturing an optical disk according to the present invention, a step of forming a protective film on the substrate in advance may be added before the first step. desirable.

In the method for manufacturing an optical disk according to the present invention, when the heat sink layer 5 is formed in the third step, the thickness of the heat sink layer 5 is maintained while maintaining the heat diffusion property. However, it is also preferable to form the film so as to have a thickness sufficient to maintain the light transmittance.

On the other hand, in the method for manufacturing an optical disk according to the present invention, the thickness of the heat sink layer 5 is set to 10
It is also desirable to form a film by setting the thickness to 50 nm.

Further, in the method for manufacturing an optical disk according to the present invention, the dielectric reflection film in the fourth step is obtained by laminating at least two dielectric layers made of different dielectric materials. It is also desirable that the dielectric multilayer reflective film has a film thickness such that 1/4 of the wavelength of the laser beam used is equal to the product of the film thickness and the refractive index. It is also preferable to form a film while controlling the film thickness to a value near the film thickness.

In the method of manufacturing an optical disk according to the present invention, preferably, after the fourth step, a fifth step of further covering the dielectric reflection film with a protective film is provided. .

[0077]

As described above, according to the present invention, it is possible to produce an optical disk which is easy in optical design, has good repetition resistance, and can be used at a low linear velocity.

Accordingly, it is an object of the present invention to provide an optical disk which improves the above-mentioned drawbacks of the prior art, is easy in optical design, has good repetition resistance, and can execute information recording / reproduction even at a low linear velocity. Is the purpose.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a specific configuration of an optical disk according to the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a configuration of a conventional optical disc.

FIG. 3 is a graph showing an example of a heating curve during a writing operation on an optical disc.

FIG. 4 is a graph showing an example of a temperature distribution in a recording layer along a line direction of a laser at the time of writing on an optical disk.

FIG. 5 is a graph showing an example of a reflectance spectrum of aluminum Al.

FIG. 6 is a cross-sectional view showing a more detailed configuration of one specific example of the optical disc according to the present invention.

FIG. 7 is a graph showing the linear velocity dependence of the signal amplitude of the optical disk according to the present invention and the optical disk of the comparative example.

FIG. 8 is a graph showing the maximum linear temperature distribution obtained from simulations of the specific example of the optical disk according to the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate base material 2 ... Protective film (lower protective film) 3 ... Recording film 4 ... Protective film 5 ... Heat sink layer 6 ... Dielectric reflective film 7 ... UV protective film 10 ... Optical disk

Claims (17)

[Claims] 1. An optical disk, wherein at least a recording film, a protective film, a heat sink layer, and a dielectric reflection film are laminated on a substrate in this order. 2. An optical disk characterized in that at least a protective film, a recording film, a protective film, a heat sink layer, and a dielectric reflection film are laminated in this order on a substrate. 3. The optical disc according to claim 1, wherein the heat sink layer is made of a metal film having an extremely thin film thickness. 4. The optical disc according to claim 3, wherein the thickness of the heat sink layer is sufficient to maintain light diffusivity while maintaining thermal diffusivity. 5. The heat sink layer has a thickness of 10-5.
The optical disc according to any one of claims 1 to 4, wherein the optical disc has a thickness of 0 nm. 6. The optical disk according to claim 1, wherein the dielectric reflection film is a dielectric multilayer reflection film. 7. The dielectric multilayer reflective film according to claim 1, wherein at least two types of dielectric layers composed of different dielectric materials are laminated.
7. The optical disk according to any one of claims 1 to 6, 8. The optical disk according to claim 7, wherein the different dielectric materials are a combination of a high refractive index dielectric and a low refractive index dielectric. 9. The film thickness of the dielectric multilayer reflective film is such that 1/4 of the wavelength of the laser beam used is equal to the product of the film thickness and the refractive index, or a film near the film thickness. 9. The optical disc according to claim 1, wherein the optical disc has a thickness. 10. At least a first step of forming a recording film on a substrate substrate, a second step of forming a protective film on the recording film, and a third step of forming a heat sink layer on the protective film. And a method for manufacturing an optical disk. 11. The method for manufacturing an optical disk according to claim 10, wherein a first step of forming a protective film on the substrate in advance is added before the first step. . 12. When forming the heat sink layer in the third step, the thickness of the heat sink layer is set to a thickness sufficient to maintain light transmission while maintaining heat diffusion. 12. The method for manufacturing an optical disk according to claim 10, wherein the film is formed in a manner as described above. 13. The heat sink layer may have a thickness of 10 to 10.
13. The film is formed by setting the thickness to 50 nm.
The manufacturing method of the optical disc according to the above. 14. The optical disk according to claim 10, further comprising a fourth step of forming a dielectric reflection film on the heat sink layer after the third step. Production method. 15. The method according to claim 1, wherein the dielectric reflection film in the fourth step is formed by laminating at least two dielectric layers made of different dielectric materials.
5. The method for manufacturing an optical disk according to item 4. 16. The dielectric multilayer reflective film having a thickness of:
It is characterized in that the film is formed while controlling so that a quarter of the wavelength of the laser beam used is equal to the product of the film thickness and the refractive index or a film thickness value near the film thickness. The method for manufacturing an optical disk according to claim 15, wherein 17. The method according to claim 14, further comprising, after the fourth step, a fifth step of covering the dielectric reflection film with a protective film. An optical disc manufacturing method.