JPH0248990A - Optical recording medium and production thereof - Google Patents

Abstract

PURPOSE:To enhance oxidation resistance of a recording film by providing on a base a recording film comprising a thin film containing Te as a main constituent and containing specified amounts of Cr, C and H, and setting the Cr content of the recording film at a given point to be lower as the point is farther from the surface of the base. CONSTITUTION:A recording film 12 comprising a thin Te-Cr alloy film containing C and H is formed on a base 11 by magnetron sputtering method using Te and Cr as separate targets in a mixed gas of a hydrocarbon gas, e.g. CH4 or C2H2, with an inert gas, e.g. Ar, to produce an optical recoding medium 10. The contents of C and H in the recording film 12 can be freely controlled by regulating the mixing ratio of CH4 and Ar and an applied high-frequency power. The optical recording medium thus obtained has the recording film enhanced in oxidation resistance or durability, and can be expected to have a prolonged useful life.

Description

Detailed Description of the Invention Technical Field of the Invention The present invention relates to an optical recording medium in which information is recorded by forming pits in a recording film on a substrate by irradiation with an energy beam such as light or heat, and a method for manufacturing the same. Regarding.

Technical Background of the Invention and Problems There are two types of optical recording media: those that form physical changes such as holes or recesses in a part of the recording film by irradiation with an energy beam, and those that form physically changed parts such as holes or recesses in a part of the recording film. There is a method of forming an optical characteristic changing section in which optical characteristics (refractive index, reflectance, etc.) are changed.

As a recording film in any type of optical recording medium, a recording film mainly composed of a low melting point metal such as tellurium (To) has been known (Japanese Patent Application Laid-Open No. 71/1958, Publication No. 58-9234). A Te film, which is a typical low-melting point metal film, can produce desired physical changes or optical property changes (hereinafter collectively referred to as
It is extremely promising as a high-sensitivity material. Sensitivity here is defined as the energy (mJ/c4) required to form pits per unit area.

However, when To is left in the atmosphere, it is oxidized by oxygen or moisture, increasing its light transmittance and becoming transparent. When such a Te film is used as a recording film, the film thickness is extremely thin, on the order of several hundred films, so that if the light transmittance increases due to oxidation of the film, the sensitivity will drop significantly. That is, when the film is oxidized, the melting temperature and evaporation temperature rise, and absorption of energy such as light decreases due to transparency, which increases the energy required to form pits, resulting in a significant decrease in sensitivity.

For example, when a Te film is left in an atmosphere with a temperature of 70° C. and a relative humidity of 85%, the sensitivity decreases by about 20% in about 5 hours and by about 50% in about 15 hours.

In order to solve these problems, various measures have been taken to prevent oxidation of the Te film. One known method is to coat the Te film with a stable inorganic substance. Although this method is effective in preventing oxidation of the Te film, it reduces sensitivity and is expensive. Not put into practical use. On the other hand, a method of coating Te film with plastic is also known;
Since the thermal conductivity of the Te film is low, it is advantageous in that the degree of deterioration of the sensitivity is small, but since it allows oxygen and water to permeate relatively easily, it is not very useful in preventing oxidation of the Te film.

In addition, C and H are included in the Te film (Japanese Patent Publication No. 1983-
33320), a technique has been proposed to prevent oxidation of the Te film as a recording layer.
With this technology, the oxidation resistance is still insufficient when the C content is low, and in order to improve the oxidation resistance, C
If the content is increased, it has the disadvantage that the C/N ratio during information reproduction decreases.

In addition, in order to solve the above-mentioned problems,
No. 63,038 discloses an optical recording medium having a recording film containing To as a main component and Cr.

As disclosed in this publication, when Cr is contained in a recording film whose main component is Te, the oxidation resistance of the recording film improves in proportion to the content, extending the life of the optical recording medium. It is known that this can be achieved.

However, an optical recording medium having a recording film containing Te as a main component and Cr has the disadvantage that recording sensitivity decreases if a large amount of Cr is contained. Therefore, Cr contained in the recording film whose main component is Te.
From the viewpoint of improving oxidation resistance and recording sensitivity, the content is set such that Cr is 5 to 15% by weight relative to Te in the recording film, as shown in JP-A-59-63,038. It was generally determined that

However, the present inventors have found that the recording sensitivity of an optical recording medium equipped with a Te-based recording film containing 5 to 15% by weight of Cr is still lower than that of a recording film containing only a Te film. Served. The inventors of the present invention have conducted intensive studies on optical recording media having a recording film containing Te as a main component and Cr, and have found that the Cr content is extremely low and the Te main component is Te containing C and H. According to an optical recording medium having a recording film as a component in which the content of C in the recording film is lower on the surface side than on the substrate side, oxidation resistance can be improved. Regardless, it has been found that the recording sensitivity is significantly improved and the recording margin is widened. In addition, the present inventors have thus discovered that Cr,
It has been found that if a heat treatment is performed after forming a recording film containing C and H and mainly composed of Te on a substrate, the recording sensitivity can be further improved and the recording margin can be widened.

Purpose of the Invention The present invention was made based on these new findings, and aims to improve the oxidation resistance of the recording film, extend the life of the optical recording film, and record information with less energy. It is an object of the present invention to provide an optical recording medium with high sensitivity and a wide recording margin, and a method for manufacturing the same.

Summary of the Invention In order to achieve the above object, an optical recording medium according to the present invention includes a substrate and a recording film formed on the substrate, and by irradiating the recording film with an energy beam, In an optical recording medium in which information is recorded by forming pits in the recording film, the recording film is a thin film containing Te as a main component and Cr, C, and H, and the recording film contains Cr. The content ratio is in the range of 0.1 to 40 atomic % based on the total number of atoms constituting the recording film, and the content of C in the recording film decreases in the direction away from the substrate surface. It is said that

According to the optical recording medium according to the present invention, Cr, C, and H are contained in the recording film mainly composed of To, and the C content in the recording film is lower on the surface side than on the substrate side. As a result, the oxidation resistance of the recording film is significantly improved, and it is expected that the life of the optical recording medium will be extended. In addition, in the present invention, the content of Cr in the recording film is 0.1 to 40.
When it is set to a value lower than conventional values, such as atomic percent, particularly 0.1 to 10 atom percent, it has superior recording sensitivity compared to conventional Te recording films with a high Cr content. Furthermore, in the present invention, since the C content for improving oxidation resistance can be reduced by including Cr, the recording margin is narrowed and the C/N is reduced due to an increase in the C content. A decrease in the ratio can be effectively prevented.

Further, in order to achieve the above object, the method for manufacturing an optical recording medium according to the present invention comprises a substrate and a recording film formed on the substrate, and by irradiating the recording film with an energy beam, In the method for manufacturing an optical recording medium in which information is recorded by forming pits in this recording film, when forming a recording film consisting of a thin film containing Te as a main component and Cr, C, and H on the substrate, , the recording film is deposited with a lower hydrocarbon gas concentration in the deposition atmosphere in the later stages of deposition than at the start of deposition, and after such deposition,
A feature of this method is that this recording film is heat-treated.

The heat treatment is preferably performed at a temperature of 70 to 300°C for 5 seconds or more.

According to the method for manufacturing an optical recording medium according to the present invention, since the formed recording film is heat-treated, the shape of the pits formed in the recording film can be made uniform even by minute fluctuations in the recording energy output. The recording margin is widened, the C/N ratio is improved, and the recording sensitivity of the resulting optical recording medium is improved.

In the present invention, a narrow recording margin means that the C/N ratio changes in accordance with fluctuations in the recording energy output (hereinafter used with the same meaning).

In other words, a narrow recording margin means that when the recording energy output is varied, the C/N ratio decreases, so the range of recording energy output that exhibits a C/N ratio above a certain amount is narrow. . Further, the C/N ratio indicates the amount of noise during information reproduction, and the higher the C/N ratio, the better.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a schematic cross-sectional view of an optical recording medium according to an embodiment of the present invention.

As shown in FIG. 1, the optical recording medium 10 according to the present invention includes:
It consists of a substrate 11 and a recording film 12 formed on the surface of this substrate.

In addition to inorganic materials such as glass or aluminum, the substrate 11 may also be made of polymethyl methacrylate, polycarbonate, a polymer alloy of polycarbonate and polystyrene, such as ethylene and 1,4,5,8-dimethanol-1,2,3,4. , 4a, 5,8,8a-copolymer with octahydronaphthalene (tetracyclododecene), ethylene and 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a, 5. Copolymer with 8,8a-octahydronaphthalene (methyltetracyclododecene), ethylene and 2-ethyl-1,4,5,8-dimethano-1°2.3,4.4a,5, U.S. Pat. No. 4,614,77 for copolymers with 8,8a-octahydronaphthalene, etc.
Organic materials such as amorphous polyolefin, poly4-methyl-1-pentene, epoxy resin, polyethersulfone, polysulfone, polyetherimide, etc. as shown in the specification of No. 8 can be used. The thickness of this substrate 11 may be any thickness sufficient to impart appropriate rigidity to the entire recording medium 10, and is preferably 0.5 to 2.5 mm.
, particularly preferably 1 to 1, . 5! It is about I11.

The recording film 12 according to the present invention has To as a main component, Cr,
It is a thin film containing at least C and H, and may also contain a low melting point metal other than Te or other components. Elements other than Te that can be included in the recording film 12 include TI and Mn SNi.

Zr, Nb, Ta, Aff,, Pt5Ss, BIIn,
Se, Pb, Co, SI Pds Sn.

Zn etc. are exemplified.

The content ratio of Cr contained in such a recording film 12 is 0.1 to 40 atomic %, preferably 0.5 to 10 atomic %, particularly preferably 1 atomic %, based on the total number of atoms contained in the recording film.
The content is preferably in the range of 4 atomic %. By including Cr in such a range, although the oxidation resistance of the recording film 12 is improved, the recording sensitivity does not decrease.
This is because recording sensitivity can be improved in some cases. Note that in the present invention in which heat treatment is performed after the recording film is formed, the Cr content is not limited to the above range.

Further, the content of C in the recording film 12 should be 1 to 40 at%, preferably 1 to 10 at%, based on the number of atoms in the entire recording layer, from the viewpoint of improving the life of the recording film and recording sensitivity. is desirable. In particular, in the present invention, the C content in the recording film is
It changes so that it decreases in the direction away from the substrate surface. That is, the C content on the substrate side of the recording film is increased continuously or stepwise, for example, by forming a two-layer film or a multilayer film of two or more layers, compared to the C content near the outer surface of the recording film. In an extreme case, the C content near the outer surface of the recording film may be O.

Further, the content of H in Record III 12 is desirably 1 to 40 atomic %, preferably 1 to 25 atomic %, based on the whole, from the viewpoint of lifespan and the like. Note that the content of each element contained in the recording film 12 is, for example, I for metal elements.
C and H are measured by CP emission spectrometry (inductively coupled plasma emission spectrometry), and organic elemental analysis.

To write information on the recording film 12 having the above composition, the recording film 12 is irradiated with an energy beam such as a laser beam that is modulated (on-off) depending on the information to be recorded. A bit may be formed in the irradiated portion. This bit may be a physically changed part such as a hole or a recess, or it may be an optical property changed part that changes optical properties such as refractive index or reflectance.

The thickness of the recording film 12 is 8, which is required to be thick enough to obtain sufficient light reflectance and thin enough not to impair sensitivity. Specifically, when forming a physically changed part such as a hole in the recording film 12, the thickness of the recording film is 100 mm or more.
1 μm, preferably about 100 to 5000 people, more preferably about 150 to 500 people. Further, when forming an optical characteristic changing portion such as reflectance or refractive index on the recording film 12, the thickness of the recording film is 100 μm to 1 μm, preferably 100 μm.
~5000 people, preferably 200~2000 people.

In order to form such a recording film 12 on the surface of the substrate 11, it can be performed, for example, as follows.

First, using Te and Cr as separate targets or a Te-Cr alloy as a target, an organic gas containing C and H, such as a hydrocarbon gas such as CH or C2H2, and an inert gas such as A gas are combined. A recording film 12 made of a Te-Cr alloy thin film containing C and H is formed on the substrate 11 by magnetron sputtering in a mixed gas. It is also possible to form the recording film 12 made of a Te-Cr alloy thin film containing C and H on the substrate by using the vapor of It is possible to form the recording film 12. Furthermore, as another method, some or all of the To, Cr, and C1H atoms may be ionized and deposited in the form of a beam on the substrate.

The contents of C and H in the recording film 12 made of the Te-Cr alloy thin film containing C and H are as follows: CH4 and A'
can be freely controlled by adjusting the mixing ratio with In this case, the H content at which the film is most chemically stable is determined by the C content. Here, hydrogen gas (
The H content can be arbitrarily selected as long as it is not so large as to generate H2). Furthermore, since the film thickness is proportional to the sputtering time, it can be freely controlled.

In the present invention, in order to reduce the C content in the recording film in the direction away from the substrate surface, the concentration of hydrocarbon gas in the film formation atmosphere is lowered in the latter stage of film formation than at the start of film formation of the recording film 12. ing. At this time, the concentration of hydrocarbon gas may be lowered continuously, but it may be lowered stepwise (for example, by stacking two or more layers of recording films with decreasing C content from the substrate side). ) can also be done. In this way, by lowering the hydrocarbon gas concentration in the film-forming atmosphere in the later stages of film-forming than at the start of film-forming, it is possible to achieve durability or recording with a lower C content on the outer surface of the recording film than on the substrate-side surface. A recording film 12 with excellent properties can be obtained on the substrate 11.

Te-containing C and H formed in this way
The optical properties such as reflectance or attenuation coefficient of the recording film 12 made of a Cr alloy thin film vary depending on the content of C and H, and in order to use it for information recording, the film thickness should be adjusted depending on the optical properties as described above. is determined.

Note that methane, ethane, acetylene, etc. are used as the hydrocarbon introduced into the vapor deposition apparatus when forming the recording film. Such hydrocarbons are usually introduced into a vapor deposition apparatus together with an inert gas, and examples of the inert gas used at this time include helium, neon, argon, krypton, and nitrogen. Argon is preferred.

The recording film 12 formed under the above conditions is amorphous and has significantly improved oxidation resistance and recording sensitivity compared to a film formed from a single low melting point metal such as Te.

For example, in a Te recording film containing Cr5C and H, the change in reflectance after 100 hours in an environment of 70°C and 85% RH (relative to humidity) is smaller as the Cr content increases; It was confirmed through experiments that the oxidation resistance of the recording film according to the present invention is improved compared to the recording film of the present invention.

Furthermore, it has been confirmed through experiments that, for example, the recording film according to the present invention has a relatively small recording energy output and improved recording sensitivity.

Furthermore, as shown in FIG. 2, the optical recording medium according to the present invention (curve A in the figure) is superior to the conventional optical recording medium having a Te film containing C and H (curve B in the figure). Therefore, the C/N ratio hardly changes with respect to minute fluctuations V in the recording energy output. It was confirmed that the recording margin was wide.

Furthermore, as shown in FIG. 3, the optical recording medium according to the present invention (curve A in the figure) is different from the conventional Te
It was also confirmed that, compared to an optical recording medium having a film (curve B in the figure), there was almost no change in reflectance over time and the durability was improved.

Further, in the present invention, as described above, the recording film 1 is placed on the substrate 11.
After forming the recording film 2, the recording film 12 can be heat-treated in an inert gas, reducing gas, or gas atmosphere containing oxygen, if necessary. The heat treatment temperature needs to be below the melting point of Te contained in the recording film, preferably in the range of 70 to 300°C, especially 90 to 150'C. The heat treatment time is preferably 5 seconds or more,
Particularly preferably from 5 seconds to 10 hours, most preferably from 5 minutes
It is 2 hours.

In this way, by heat-treating the recording film 12 after forming the recording film 12 on the substrate 11, the recording sensitivity of the recording film is improved and the recording margin is widened.

Effects of the Invention In the present invention, a recording film containing Te as a main component contains Cr, C, and H, and the content of C in the recording film is reduced on the outer surface side of the recording film. The oxidation resistance and durability of the recording film are improved, and it is expected that the life of the optical recording medium will be extended. In particular, the content of Cr in the recording film is reduced to 0.
．． If the value is set to 1 to 10 atomic %, which is lower than the conventional value, excellent recording sensitivity will be obtained.

Further, according to the method for manufacturing an optical recording medium according to the present invention, since the heat treatment is performed after the recording film is formed, the pit shape formed in the recording film can be made uniform and small, and the recording film can be made uniform and small. This has excellent effects such as widening the range of energy output (widening the recording margin) and improving the recording sensitivity of the resulting optical recording medium.

[Examples] The present invention will be described below based on more specific examples, but the present invention is not limited to these examples.

Example 1 After evacuating the vacuum container, Ar gas and CH4 gas were introduced, and the internal pressure was set to 6 x 10-3 Torr (A
r/CH4=2/8: gas flow rate ratio). Next, simultaneous sputtering was performed using Te and Cr as targets. At that time, by controlling the voltage applied to each target, Te53 was deposited on the amorphous polyolefin substrate.
A film of Cr2 C15H30 was formed to a thickness of 60. Furthermore, the gas flow rate ratio is set on this film as A r / CH4=
Te81Cr2C1o in the same way as 8/2
A second film H1 was formed to obtain a recording film with a total thickness of 260 people.

Example 2 In the same manner as in Example 1, a film of Te53Cr2C15H3o was formed to a thickness of 100 on an amorphous polyolefin substrate. Next, on this film, T858cr2c15H
A second film having a thickness of 3o was formed to obtain a recording film with a total thickness of 260.

Example 3 T was deposited on an amorphous polyolefin substrate in the same manner as in Example 1.
A film of e53Cr2CI5H3o was formed to a thickness of 100 people. Next, a film of Te87Cr2C4H7 was formed as Ar/CH-9/1 on this film, with a total film thickness of 3
Twenty Te-Cr-C-H recording films were obtained.

Example 4 T was deposited on an amorphous polyolefin substrate in the same manner as in Example 1.
A film of e53Cr2C15H3o was formed to a thickness of 100 people. Next, a second film having T89B"4 with only A" was formed on this film to obtain a recording film with a total film thickness of 250 people.

Example 5 The recording film obtained in Example 4 was heat-treated at a temperature of 100° C. for 20 minutes in a nitrogen gas atmosphere.

Comparative Example 1 The gas flow rate ratio is A r / CH4 = 9 / 1,
A recording film of Te CH with a film thickness of 250 mm was obtained on an amorphous polyolefin substrate using a Te target.

Reference Example 1 Using only Ar as the introduced gas, simultaneous sputtering of Te and Cr was performed to deposit TeCr on an amorphous polyolefin substrate.
A recording film with a film thickness of 250 mm was obtained.

[Test results] (1) Rotate the disk at 1800rpa+, 3.7
A laser beam was irradiated at a frequency of MIIz, and the recording characteristics were examined. Here, C/Nmax indicates the maximum value of the C/N ratio when the laser power is changed. Recording sensitivity is C/N>C/
N maxXo, the minimum value of the laser power that is 9,
The margin represents the range of laser power where C/N>C/N aaxXo, 9. The results are shown in Table 1.

Table 1 Table (2) Table 2 shows the test results when the reflectance R after being left for 500 hours in an environment with a temperature of 70° C. and a relative humidity of 85% was compared with the initial reflectance Ro.

[Brief Description of the Drawings] Figure 1 is a schematic sectional view of an optical recording medium according to an embodiment of the present invention, and Figures 2 and 3 are effects of the optical recording medium according to the present invention and a conventional optical recording medium. This is a graph showing the above differences. 10... Optical recording medium 11... Substrate 12...
・Recording film

Claims (1)

[Scope of Claims] 1) Consisting of a substrate and a recording film formed on the substrate, the recording film is irradiated with an energy beam to form pits in the recording film and record information. In the optical recording medium made of The content of C in the recording film is in the range of 0.1 to 40 atomic %, and the content of C in the recording film decreases in a direction away from the surface of the substrate. 2) An optical recording medium consisting of a substrate and a recording film formed on the substrate, in which information is recorded by forming pits in the recording film by irradiating the recording film with an energy beam. In the manufacturing method, when a recording film consisting of a thin film containing Te as a main component and Cr, C, and H is formed on the substrate, the temperature in the film formation atmosphere in the latter stage of film formation is higher than that at the start of film formation. The film is formed with a low hydrocarbon gas concentration, and after such film formation,
A method for manufacturing an optical recording medium, which comprises heat-treating the recording film. 3) The content ratio of Cr contained in the recording film is in the range of 0.1 to 40 atomic % with respect to the total number of atoms constituting the recording film. A method for manufacturing an optical recording medium. 4) The method for manufacturing an optical recording medium according to claim 2 or 3, wherein the heat treatment is performed at a temperature of 70 to 300°C for 5 seconds or more.