JPH11273145A - Optical recording medium and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability for heat resistance, wear resistance and information record preservable property by forming a rugged bit corresponding to recorded information on the surface of a substrate consisting of inorganic crystal material having light transmissivity. SOLUTION: A laser beam 10 is converged by a condenser lens 11, and is made incident from a surface opposite to the surface formed with the rugged pits 2 of the rotating substrate 1 to arrive at the rugged pits 2, and is abutted on a reflection film layer 3 to be reflected and to be returned. A protection film layer 4 is formed on the reflection film layer 3. A single crystal sapphire substrate having an optical axis in the direction perpendicular to the substrate 1 is used as the inorganic crystal material having light transmissivity, and the surface is optically ground to be made the substrate 1 for optical recording medium. Although the substrate 1 is inserted into a furnace in the air atmosphere to be heated to a maximum temp. 1000 deg.C, the rugged pits 2 are not changed, and when the recorded information is reproduced using a laser beam of wavelength 780 nm, a excellent reproducing signals without noise due to birefringence and with a small jitter component is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a disk type optical recording medium for recording information such as a compact disk (CD) and a digital video desk (DVD), and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the maturation of the information-oriented society, information recording by various electronic devices has been performed.
Various recording methods such as magnetism, light, and semiconductor are also used. Among them, the optical disk recording method using laser light is capable of large-capacity recording and is capable of non-contact high-speed access.

[0003] Optical disks can be classified into a read-only type known as a compact disk and a laser disk, a write-once type that can be recorded by the user himself, and a rewritable type that can be repeatedly recorded and erased by the user.

[0004] The write-once and rewritable optical disks are used as external memories of computers, documents, and image files. In a read-only optical disk, a data file typified by a CD-ROM has rapidly spread, and is used as a high-density recording medium in the personal field. Paying attention to the large capacity of the CD-ROM, application as a multimedia file including image data using an image compression technique such as MPEG2 is being studied.

[0005] In this application, the current storage capacity of 650 MB / disk is not sufficient, and is an issue to be studied at the research and development stage. On the other hand, high density is also an important theme for image files such as laser disks and DVDs.

At present, a read-only disc is made of polycarbonate or polymethyl methacrylate as an organic resin, and an aluminum alloy-based metal reflection is formed on a concave / convex pit previously formed by injection molding or press molding on a substrate. A film is formed and used for regeneration. The reflective film is formed by a film forming method such as a resistance heating vacuum evaporation method, an electron beam vacuum evaporation method, or a sputtering method, or a spin coating method.

Conventionally, in such an optical disk, 1.2
Irregular pits were formed in a transparent resin having a thickness of mm, and information was reproduced through the substrate.

The advantage of using the laser beam used for reproduction by making it incident from the substrate and condensing it on the uneven pit surface is as follows.
Even if there is some dirt or scratches on the substrate surface, the laser beam spreads and is large on the incident surface, so that the laser light is hardly affected by the dirt or scratches.

[0009]

As described above, the polycarbonate used in the conventional optical disk has excellent stability against hydrolysis, has a relatively high glass transition temperature of 150 to 160 ° C., and has a light transmission property. It has a transparency equivalent to water at about 90% in visible light, and has a remarkable height as an organic substance in terms of impact strength and ductility. However, since it is an organic substance, its resistance to high temperatures is low, and high heat such as combustion. Was a weak recording storage medium. Also, because it is organic,
Since the abrasion resistance is low and the pit surface is easily damaged, it is necessary to provide a protective layer.

As described above, for example, Japanese Patent Application Laid-Open No. 8-203126 proposes to use a rigid ceramic substrate to make up for the drawbacks of the organic resin. In this case, the ceramic substrate is an opaque rigid substrate. The laser light does not pass through the ceramic substrate and is used as a recording medium based only on surface reflection.

The recording pits formed on the ceramic substrate are formed by a photopolymer method (2P method, ie, PhotoPol method).
It is formed on the surface with resin by the ymarization method) and is not engraved on the ceramic substrate itself. Therefore, since the concave and convex pits for recording have no rigidity or heat resistance, no heat resistance is given to the recording retention.

Further, a transparent thin plate typified by a glass plate or a transparent resin plate is indispensable on the surface thereof, and since this transparent thin plate is bonded with a transparent adhesive, heat resistance, abrasion resistance, and heat resistance are improved. There was a problem in the impact properties, and the reliability for long-term record keeping could not be increased.

Further, in the future, when considering the improvement of the recording density of an optical disk with the aim of increasing the density, it is necessary to increase the numerical aperture (Numerical Aperture, hereinafter referred to as NA) of a lens used for laser focusing. There are two effective methods. In other words, the focused diameter W of the laser light focused by the lens is
Assuming that the wavelength of the laser is λ, W = 1.22λ / N. A
Can be described by N. A. Is larger, a smaller beam diameter can be realized.

However, N.I. A. Is increased, the distance between the condenser lens and the focal position is inevitably shortened. Therefore, when handling a substrate made of polycarbonate or the like having a thickness of about 1.2 mm, the N.D. A. There is a limit to how large it can be.

On the other hand, it is conceivable to cope with this problem by making the substrate thinner. However, in the case of an optical disk in which the birefringence of the substrate has a great influence on the reproduction signal characteristics, when the synthetic resin such as polycarbonate is molded thin, the birefringence is reduced. Therefore, there is a problem that it cannot be dealt with simply by making the substrate thinner.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an optical recording system which is excellent in heat resistance and abrasion resistance and has remarkably improved the reliability of information recording and storage performance. An object of the present invention is to provide a medium and a method for manufacturing the medium.

[0017]

Means for Solving the Problems In order to achieve the above object, a first aspect of the present invention is characterized in that a substrate made of an inorganic crystal material having translucency and a substrate formed on the surface of the substrate corresponding to recorded information. Pits.

A feature of the second invention is that a reflective film layer is formed on the concave and convex pits. A feature of the third invention is that the substrate is made of a cubic inorganic crystal material according to Brave lattice classification.

According to a fourth aspect of the present invention, when the substrate is formed of an inorganic single crystal material, the incident direction of light entering to read information from the uneven pits coincides with the C-axis direction of the single crystal. Is to be.

A fifth feature of the present invention resides in that the method includes a dry etching step of forming the concave and convex pits on the surface of the substrate.

According to a sixth aspect of the invention, there is provided a substrate made of glass, concave and convex pits formed on the surface of the substrate in accordance with recorded information, and a reflective film layer formed on the concave and convex pits. That is.

According to the present invention, loss of recorded information is prevented by using a transparent material such as sapphire as a transparent material forming a recording medium and utilizing its high melting point and high hardness. At that time, a light-transmitting oxide crystal material having high crystal symmetry is used so that incident light does not cause birefringence, and specifically, any of cubic, tetragonal, hexagonal, and rhombohedral crystals is used. A uniaxial (uniaxial) crystal consisting of In particular, in the case of polycrystal, it is desirable to use a crystalline material composed of a cubic crystal, and in the case of a single crystal, use a cubic crystal or process the light so that the incident direction of light coincides with the optical axis. Is desirable.

Here, the term "light-transmitting property" means that the material exhibits a light transmittance of 40% or more with respect to an inorganic crystal material having a thickness of 0.5 mm in a wavelength range of 100 nm to 8000 nm. Further, the melting point of the light-transmitting inorganic crystal material or the thermal decomposition temperature in air is 1000 ° C. or more.
Furthermore, the Mohs hardness of the light-transmitting inorganic crystal material is 5 or more. The light-transmissive inorganic crystal material has a thermal expansion coefficient of 1 × 10 ⁻⁴ / ° C. or less at room temperature.

Further, in consideration of the relationship between the wavelength of incident light and scattering / reflection or light absorption loss, the size of crystallites is particularly important in the case of a polycrystal. When the size of the crystallite is smaller than 0.1 μm, the wavelength becomes close to the wavelength of the laser light, scattering occurs, and light transmission is likely to be lost. Therefore,
The size of the crystallite needs to be larger than 0.1 μm.

By using an oxide crystal material among the inorganic crystal materials, stability during heating in air and retention of the material over time can be provided. For example, the sapphire single crystal is an oxide of aluminum and has a property of transmitting light with a wavelength of about 200 nm to 4000 nm. The crystal structure can be considered as a hexagonal system, and the C axis is the optical axis. Heat resistance temperature in air is 1600
Exceeding C, the hardness is 9 next to diamond in Mohs hardness. Vickers hardness is 2300. The coefficient of thermal expansion near normal temperature is also as small as 4 to 7 × 10 ⁻⁶ / ° C. Also, it has excellent mechanical properties and chemical corrosion resistance. Flexural strength is 6
It has a melting point of 90 MPa and a melting point of 2053 ° C., and can be said to be a light transmitting material excellent in high temperature resistance and abrasion resistance.

In addition, since it is a single crystal, the crystal orientation can be easily fixed, and the incident direction of the laser beam can be made coincident with the optical axis direction of the crystal. When the incident direction of the laser beam is made coincident with the optical axis direction in this manner, birefringence does not occur, and a noise component at the time of signal reading is easily removed. In particular, in the case of a tetragonal, rhombohedral, or hexagonal single crystal, it is desirable that the crystal orientation that matches the incident direction of the laser beam be a direction that matches the C axis of the crystal lattice.

Organic materials have a lower melting point than these inorganic crystal materials and are susceptible to heat. Since the abrasion resistance is low, a protective film layer is indispensable on the surface on which information is imprinted.
In addition, glass that is amorphous even with inorganic materials has higher heat resistance than organic materials, but has a considerably lower melting point than oxide crystal materials, and is easily deformed by heat. Low abrasion resistance and easily scratched.

In the current manufacturing process for an organic recording medium, a mask made of glass is masked according to the shape of the pits, then etched to form pits, and the pits are formed through a mold called a stamper. Generally, the image is transferred to an organic resin substrate.

On the other hand, when pits are formed directly on the surface of a recording medium made of an inorganic crystal material having excellent heat resistance and abrasion resistance, uniform pits are hardly formed by wet etching.
Dry etching is advantageous because it is inferior in mass productivity. Thereby, uniform pit formation can be realized in a short time.

The laser light reflecting film is also formed by thinning and attaching an inorganic crystal material having a significantly different refractive index from the light transmitting inorganic crystal material forming the substrate. In the case of using metal, it is conceivable that the metal portion is damaged by heating, but in that case, the information recording itself is not lost as long as only the metal portion can be repaired. Furthermore, when a platinum group metal or alloy is used as the metal, the high-temperature resistance is enhanced, and the metal part can be hardly damaged.

It is also possible to easily adopt a configuration in which two such recording media are laminated and adhered to form a single body, so that reading from both sides is possible.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first example of the optical recording medium of the present invention.
FIG. 3 is a cross-sectional view showing the embodiment. Asperity pits 2 are directly formed on a disc-shaped substrate 1 made of a translucent inorganic crystal material.
And a reflective film layer 3 is formed thereon.

Here, for the substrate 1 made of an inorganic crystal material, either a polycrystal or a single crystal can be used. The thickness of the board is
And the design value of the condenser lens 11,
For example, it is 1.2 mm. The uneven pits 2 engraved on the substrate 1 are formed by applying a photosensitive resin on the substrate 1 and exposing a signal by a laser beam in a pit shape to form a masking film from which only signal portions are removed. It is created by plasma etching the signal portion of the surface. Further, the reflective film layer 3 formed on the uneven pits 2 is formed by a method such as a sputtering method, a reactive evaporation method, an ion plating method, and a reactive cluster ion beam evaporation method.

Next, the information reproducing operation of this embodiment will be described. A laser beam 10 used for reproducing information emitted from a semiconductor laser element or the like constituting an optical pickup (not shown) is condensed by a condensing lens 11 and has a surface opposite to the surface of the rotating substrate 1 on which the uneven pits 2 are formed. Incident from the surface. The incident laser beam 10 reaches the concave and convex pits 2 formed on the opposite surface, is reflected by the reflective film layer 3 and is returned. Therefore, the reflected light contains information corresponding to the concave and convex pits 2. The information recorded by the concave / convex pits 2 is read out by demodulation.

FIG. 2 is a sectional view showing an optical recording medium according to a second embodiment of the present invention. In this example, a protective film layer 4 is formed on a reflective film layer 3, and the other configuration is the same as that of the first embodiment shown in FIG.

When the wear resistance of the reflective film layer 3 becomes a problem, a protective film layer 4 for protecting the reflective film layer 3 is required. The protective film layer 4 does not necessarily need to have heat resistance, and does not need to have translucency. Although it is conceivable that the recording information is lost at a high temperature, the recorded information is engraved on the transparent substrate 1 as uneven pits 2, and the laser light 10 is irradiated from the opposite surface of the surface on which the uneven pits 2 are formed. Since the light is incident and read, there is no problem even if the protective film layer 4 disappears. However, it is required that the abrasion resistance is stronger than that of the reflective film layer 3.

By the way, it is also possible to adopt a configuration in which the optical recording media shown in FIGS. 1 and 2 are prepared two by two and bonded together. However, when bonded with an organic resin-based adhesive, the adhesive disappears at a high temperature. At that time, the optical recording medium is divided into two pieces, but since the information recorded on each optical recording medium can be read,
There is no problem at all. Although the thickness is reduced by half, the light path length does not change, so that the reading device used for the optical recording medium before division can be used as it is. FIG. 3 is a sectional view showing an optical recording medium according to a third embodiment of the present invention. This example has the same configuration as the optical recording medium shown in FIG.
It has a configuration in which a plurality of optical recording media are bonded together on a surface having uneven pits, so that the amount of recorded information can be doubled.
The two substrates 1a and 1b having a light-transmitting property are bonded together by an adhesive 5 on the surfaces on which the concave and convex pits 2a and 2b are formed via the reflective film layer 3a and the reflective film layer 3b. It is configured as a recording medium.

The information of the concave / convex pits 2a on the substrate 1a side is read by inputting the laser beam 10 condensed by the condenser lens 11 from the surface opposite to the surface of the substrate 1a on which the concave / convex pits 2a exist. The information of the uneven pits 2b on the 1b side is obtained by using the laser 10 focused by the focusing lens 11 on the substrate 1b.
The light is read by entering from the surface on the side opposite to the surface on which the uneven pits 2b on the side are located.

FIG. 4 is a sectional view showing an optical recording medium according to a fourth embodiment of the present invention. This example has a configuration in which two optical recording media having the same configuration as the optical recording medium shown in FIG. 2 are bonded together on a surface having uneven pits, so that the amount of recorded information can be doubled. The protective film layer 4a and the protective film layer 4b are bonded together with an adhesive 5, and the two optical recording media are integrated.

In this embodiment, the reflective film layer 3 has poor abrasion resistance,
Even when there is a possibility that a flaw may occur in the bonding process, the protection effect of the protective film layers 4a and 4b prevents the reflective film layer 3 from being damaged.

FIG. 5 is a sectional view showing a fifth embodiment of the optical recording medium of the present invention. In this example, the surfaces of the optical recording medium having the same configuration as the optical recording medium shown in FIG. 1 and the optical recording medium having the same configuration as the optical recording medium shown in FIG. It has a laminated structure, and can double the amount of recorded information. In this case, the protective film layer 4 is composed of both reflective film layers 3a and 3 of the two optical recording media.
The protective film has an action of protecting the reflective film layer 3 from being damaged. The protective film layer 4 and the reflective film layer 3b are adhered by the adhesive 5, and the two optical recording media are bonded together to form one optical recording medium.

Next, this embodiment will be described in more detail with reference to examples.

Example 1 A translucent alumina polycrystal having an average crystallite size of 10 μm was prepared as a translucent inorganic crystalline material.
A disk having a thickness of 1.2 mm and a diameter of 80 mm was processed, a hole having a diameter of 15 mm was formed in the center, and the surface was optically polished to obtain a substrate 1 for an optical recording medium.

A photoresist was applied to this disk to a thickness of about 0.1 μm using a spinner. The disk coated with the photoresist was mounted on a laser oscillation device having a focus servo mechanism, irradiated with information by an argon laser, and developed to obtain a masked disk. The signal used was an EFM modulated signal used for a compact disk (CD).

This disk is placed in a dry etching apparatus for 1 hour.
Heating to 80 ° C., etching in plasma into which carbon tetrafluoride gas was introduced, and a track pitch of 0.8 μm
An uneven pit row having a minimum mark length of 0.25 μm and a depth of about 0.1 μm was formed by etching with a time control so as to have a depth of about 0.1 μm. The holding time was 160 minutes. The remaining masking agent was removed. By using a mixed gas of boron tetrafluoride gas and boron chloride, the etching rate can be increased, and the holding time can be reduced to 3 to 4 minutes.

On the pit formation surface, platinum was deposited to a thickness of 100 nm.
A thin film reflection plate (reflection film layer 3) was produced by sputtering deposition. Further, a protective film layer 4 made of an opaque hard resin film was formed thereon to protect the deposited platinum film.

When this disk was reproduced using a laser beam having a wavelength of 780 nm, a noise component presumably due to birefringence was slightly detected, but a good reproduced signal having a small jitter component was obtained as a whole.

Example 2 As a light-transmitting inorganic crystalline material, a single-crystal sapphire substrate having an optical axis perpendicular to the substrate surface was prepared, and processed into a disk having a thickness of 1.2 mm and a diameter of 80 mm. A hole having a diameter of 15 mm was made in the center, and the surface was optically polished to obtain a substrate 1 for an optical recording medium.

A photoresist was applied to this disc to a thickness of about 0.1 μm using a spinner. The disk coated with the photoresist was attached to a laser oscillation device having a focus servo mechanism, irradiated with information using an argon laser, and developed to obtain a masked disk. The signal used was an EFM modulated signal used for a compact disk (CD).

This disk is placed in a dry etching apparatus for 1 hour.
Heating to 80 ° C., etching in plasma into which the carbon tetrafluoride gas has flowed, and a track pitch of 1.6 μm
An uneven pit row having a minimum mark length of 0.25 μm and a depth of about 0.1 μm was formed by etching with a time control so as to have a depth of about 0.1 μm. The holding time was 160 minutes. The remaining masking agent was removed. By using a mixed gas of boron tetrafluoride gas and boron chloride, the etching rate can be increased, and the holding time can be reduced to 3 to 4 minutes.

On this pit forming surface, platinum was deposited to a thickness of 100 nm.
A thin film reflection plate (reflection film layer 3) was produced by sputtering deposition. Further, a protective film layer 4 made of an opaque hard resin film was formed thereon to protect the deposited platinum film.

When this disk was reproduced using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

The sapphire substrate has a refractive index of 1.78.
Since it is larger than 1.45 to 1.56 of polycarbonate, if the thickness of the disk is the same, N.I.
A. A condensing lens having a large diameter can be used, and the beam diameter of the reading laser beam can be reduced.

Example 3 As a light-transmitting inorganic crystalline material, a light-transmitting yttrium-aluminum-garnet polycrystalline substrate having a cubic crystal structure and an average crystallite size of about 10 μm was used. It was prepared and processed into a disk shape having a thickness of 1.2 mm and a diameter of 80 mm, a hole having a diameter of 15 mm was made in the center, and the surface was optically polished to obtain a recording medium substrate 1.

A photoresist was applied to this disk to a thickness of about 0.1 μm using a spinner. The disk coated with the photoresist was mounted on a laser oscillation device having a focus servo mechanism, irradiated with information by an argon laser, and developed to obtain a masked disk. The signal used was an EFM modulated signal used for a compact disk (CD).

This disk is placed in a dry etching apparatus for 1 hour.
Heating to 80 ° C., etching in plasma into which carbon tetrafluoride gas was introduced, and a track pitch of 0.8 μm
An uneven pit row having a minimum mark length of 0.25 μm and a depth of about 0.1 μm was formed by etching with a time control. The holding time was 160 minutes. The remaining masking agent was removed. By using a mixed gas of boron tetrafluoride gas and boron chloride, the etching rate can be increased, and the holding time can be reduced to 3 to 4 minutes.

On this pit formation surface, platinum was deposited to a thickness of 100 nm.
A thin film reflection plate (reflection film layer 3) was produced by sputtering deposition. Further, a protective film layer 4 made of an opaque hard resin film was formed thereon to protect the deposited platinum film.

When this disk was reproduced using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

Example 4 As a light-transmitting inorganic crystalline material, a single-crystal sapphire substrate having an optical axis perpendicular to the substrate surface was prepared and processed into a disk having a thickness of 1.2 mm and a diameter of 80 mm. A hole having a diameter of 15 mm was made in the center, and the surface was optically polished to obtain a recording medium substrate 1.

A photoresist was applied to this disk using a spinner so as to have a thickness of about 0.1 μm. The disk coated with the photoresist was attached to a laser oscillation device having a focus servo mechanism, irradiated with information using an argon laser, and developed to obtain a masked disk. The signal used was an EFM modulated signal used for a compact disk (CD).

This disk is placed in a dry etching apparatus for 1 hour.
Heating to 80 ° C., etching in plasma into which carbon tetrafluoride gas was introduced, and a track pitch of 1.6 μm
An uneven pit row having a minimum mark length of 0.25 μm and a depth of about 0.1 μm was formed by etching with a time control so as to have a depth of about 0.1 μm. The holding time was 160 minutes. The remaining masking agent was removed. By using a mixed gas of boron tetrafluoride gas and boron chloride, the etching rate can be increased, and the holding time can be reduced to 3 to 4 minutes.

A chromium oxide (Cr203) thin film having a thickness of 100 nm was formed on the pit formation surface by a reactive vapor deposition method to form a reflection plate (reflection film layer 3). Chromium oxide thin film
Metal chromium is used as an evaporation material in oxygen gas, and the degree of vacuum is 2 ×
It was prepared by holding at 10 ⁻⁴ Torr and a substrate temperature of 400 ° C. for 10 minutes.

When this disk was reproduced using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

Example 5 Two disks prepared in Example 4 were prepared, and the surfaces on which the concave and convex pits were formed were adhered to each other with an acrylic adhesive.
The configuration shown in FIG.

When this disk was reproduced on both sides by using a laser beam having a wavelength of 780 nm, good reproduced signals with no jitter component and small jitter components were obtained from both surfaces.

Example 6 Two disks prepared in Example 2 were prepared, and the surfaces on which the concave and convex pits were formed were adhered to each other with an acrylic adhesive.
The configuration shown in FIG.

When this disc was reproduced on both sides using a laser beam having a wavelength of 780 nm, good reproduced signals with no jitter component and small jitter components were obtained from both sides.

Example 7 A disk prepared in Example 2 and a disk prepared in Example 4 were prepared, and the pit-formed surface sides were adhered to each other with an acrylic adhesive to obtain the structure shown in FIG.

When this disc was reproduced on both sides by using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained from either side.

Comparative Example 1 As a comparative example, a track pitch of 1.6 μm, a minimum mark length of 0.2 mm having concave and convex pits of 0.25 μm,
A polycarbonate disk having a diameter of 80 mm and a center hole diameter of 15 mm was prepared.

A platinum thin film (reflective film layer 3) was formed to a thickness of 100 nm on the uneven pit surface of the disk by sputtering, and a protective film layer 4 made of hard resin was formed thereon.

When this disk was reproduced using a laser beam having a wavelength of 780 nm, a good reproduced signal having little noise due to birefringence and a small jitter component was obtained.

Comparative Example 2 As a comparative example, an optical glass substrate was prepared and had a thickness of 1.2 m.
m, processed into a disk shape with a diameter of 80 mm, with a diameter of 1
A hole of 5 mm was made, and the surface was optically polished to obtain a recording medium substrate 1.

A photoresist was applied to this disk to a thickness of about 0.1 μm using a spinner. The disk coated with the photoresist was attached to a laser oscillation device having a focus servo mechanism, irradiated with information using an argon laser, and developed to obtain a masked disk. The signal used was an EFM modulated signal used for a compact disk (CD).

This disk is placed in a dry etching apparatus for 1 hour.
Heating to 80 ° C., etching in plasma into which carbon tetrafluoride gas was introduced, and a track pitch of 1.6 μm
An uneven pit row having a minimum mark length of 0.25 μm and a depth of about 0.1 μm was formed by etching with a time control so as to have a depth of about 0.1 μm. The holding time was 160 minutes. The remaining masking agent was removed. By using a mixed gas of boron tetrafluoride gas and boron chloride, the etching rate can be increased, and the holding time can be reduced to 3 to 4 minutes.

On the pit formation surface, platinum was deposited to a thickness of 100 nm.
A thin film reflection plate (reflection film layer 3) was produced by sputtering deposition. Further, a protective film layer 4 made of an opaque hard resin film was formed thereon to protect the deposited platinum film.

When this disk was reproduced using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

Examples 1, 2, 3, 4, 5, 6, 7 and Comparative Examples 1 and 2 were inserted into a heating furnace in an air atmosphere,
After heating to 000 ° C., the heat resistance was examined.

Comparative Example 1 made from an organic resin was damaged by burning. For this reason, it was impossible to reproduce the information record.

In Comparative Example 2, the glass was softened and deformed, and a part of the glass was devitrified. For this reason, it was impossible to reproduce the information record.

In Example 1, only the organic layer formed as the reflective film layer 3 and the protective film layer 4 was lost, but no change occurred in the recording layer portion (two uneven pits). Reading of information recording can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduction signal was obtained.

Also in Example 2, only the organic layer formed as the reflective film layer 3 and the protective film layer 4 was lost, but no change occurred in the recording layer portion (two uneven pits). Reading of information recording can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

Also in Example 3, only the organic layer formed as the reflective film layer 3 and the protective film layer 4 was lost, but no change occurred in the recording layer portion (two uneven pits). Reading of information recording can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

In Example 4, the quality of the chromium oxide of the reflective film layer 3 was not changed, and no change occurred in the recording layer portion (two uneven pits). Reading information records
The test can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduction signal having no noise due to birefringence and a small jitter component was obtained.

In Example 5, the adhesive layer was lost and the film was divided into two pieces. However, no change occurred in the recording layer portion (two uneven pits) and the reflective film layer 3 portion. Reading of information recording was performed one by one, but the reading could be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, good reproduction without noise due to birefringence and a small jitter component was obtained. A signal was obtained.

In Example 6, the adhesive layer 5 and the protective film layer 4 were lost, and the recording medium was divided into two pieces.
Did not change. Reading of information recording was performed one by one, but the reading could be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, good reproduction without noise due to birefringence and a small jitter component was obtained. A signal was obtained.

Also in Example 7, five adhesive layers and the protective film layer 4 were lost, and the film was divided into two sheets. However, no change occurred in the recording layer portion (two uneven pits). Reading of information recording was performed one by one, but the reading could be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, good reproduction without noise due to birefringence and a small jitter component was obtained. A signal was obtained.

Glass beads were applied to Examples 1, 2, 3, 4, 5, 6, 7 and Comparative Examples 1 and 2 to evaluate the degree of damage due to abrasion.

Comparative Example 1 made from an organic resin was damaged by abrasion. For this reason, it has been impossible to reproduce information records.

In Comparative Example 2, the glass surface was scratched and partially devitrified. For this reason, it has been impossible to reproduce information records.

In Example 1, only the organic material layer formed as the reflective film layer 3 and the protective film layer 4 was damaged, but no change occurred in the recording layer portion (two uneven pits). Reading of information recording can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduction signal was obtained.

In Example 2, only the organic layer formed as the reflective film layer 3 and the protective film layer 4 was damaged, but no change occurred in the recording layer portion. Reading of the information record can be performed in the same manner as before the heat resistance test.
When reproduction was performed using a laser beam of 0 nm, a good reproduction signal having no noise due to birefringence and a small jitter component was obtained.

Also in Example 3, only the organic layer formed as the reflective film layer 3 and the protective film layer 4 was damaged, but no change occurred in the recording layer portion (two uneven pits). Reading of information recording can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduced signal having no noise due to birefringence and a small jitter component was obtained.

In Example 4, the chromium oxide of the reflective film layer 3 was not damaged, and no change occurred in the recording layer portion (two uneven pits). Reading information records
The test can be performed in the same manner as before the heat resistance test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduction signal having no noise due to birefringence and a small jitter component was obtained.

In Example 5, the light-transmitting crystalline material was not damaged, and the reflective film layer 3 and the recording layer portion (two concave and convex pits) were present inside, so that no damage was caused. Therefore, reading of the information record can be performed in the same manner as before the test, and the wavelength 7
When reproduction was performed using a laser beam of 80 nm, a good reproduction signal having no noise due to birefringence and a small jitter component was obtained.

Also in Example 6, no damage was caused to the translucent crystalline material, and the protective film layer 4, the reflective film layer 3, and the recording layer portion (two concave and convex pits) were present inside, and thus were not damaged. Therefore, reading of information recording could be performed in the same manner as before the test, and when reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduction signal with little noise component and no noise due to birefringence was obtained.

Also in Example 7, no damage was caused to the translucent crystalline material, and the protective film layer 3, the reflective film layer 4, and the recording layer portion (two concave and convex pits) were present inside, and thus were not damaged. . Therefore, reading of information recording could be performed in the same manner as before the test. When reproduction was performed using a laser beam having a wavelength of 780 nm, a good reproduction signal with no noise due to birefringence and a small jitter component was obtained.

In the above-described embodiment, the concave / convex pits 2 are formed by dry etching. However, a technique for forming the concave / convex pits 2 using a laser can also be used for the following reasons. It is clear that the inorganic crystalline material is a substance having excellent heat resistance and wear resistance. On the other hand, it is difficult to perform fine processing on the surface of such a material, and usually, fine processing using a laser has been common. Recent advances in laser processing technology have been remarkable,
Processing of about μm is becoming possible (for example, G.Me
adenetal et al “Excimer laser procession of chemi
cal vapor-deposited diamond fibers ”Journa1 0f Mat
erials Science32 (1997) 3801-3806). On the other hand, the size of the information recording pit of the optical recording medium is about 1 μm, so it is difficult at present to process the pit with a laser. It can be said that this technology can be used sufficiently.

[0099]

As described above in detail, according to the optical recording medium of the first invention, a disk substrate is made of a translucent inorganic crystal material, and information recording pits are formed directly on the substrate surface. Since it is engraved, it has heat resistance against high temperatures and high abrasion resistance, and can significantly improve the reliability of holding information records.

According to the second aspect of the present invention, since the reflective film layer is provided, information can be easily read out by a normal optical pickup.

According to the third aspect, since the substrate is a cubic crystal, there is no birefringence and reading without noise is possible.

According to the fourth aspect, since the incident direction of the information reading light coincides with the C axis, there is no birefringence,
Readout without noise becomes possible.

According to the fifth aspect, recording pits can be formed directly on a disk substrate using an inorganic crystal material.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the optical recording medium of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the optical recording medium of the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the optical recording medium of the present invention.

FIG. 5 is a sectional view showing a fifth embodiment of the optical recording medium of the present invention.

[Explanation of symbols]

 1, la, 1b substrate 2, 2a, 2b uneven pit 3, 3a, 3b reflective film layer 4, 4a, 4b protective film layer 5 adhesive

Claims (6)

[Claims] 1. An optical recording medium comprising: a substrate made of a translucent inorganic crystal material; and concave and convex pits formed on the surface of the substrate corresponding to recorded information. 2. The optical recording medium according to claim 1, wherein a reflection film layer is formed on the concave and convex pits. 3. The substrate according to claim 1, wherein the substrate is made of a cubic inorganic crystal material according to Brave lattice classification.
The optical recording medium according to the above. 4. When the substrate is formed of an inorganic single crystal material, an incident direction of light entering for reading information from the concave and convex pits coincides with a C-axis direction of the single crystal. The optical recording medium according to claim 1. 5. The method of manufacturing an optical recording medium according to claim 1, further comprising a dry etching step of forming the concave and convex pits on the surface of the substrate. 6. A substrate comprising: a glass substrate; concave and convex pits formed on the surface of the substrate corresponding to recorded information; and a reflective film layer formed on the concave and convex pits. Optical recording medium.