JP2774321B2 - Optical recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an optical recording medium for use in an optical disk, an optical card, or the like capable of recording large-capacity, high-density information.
More specifically, the present invention relates to an optical recording medium suitable for recording information by irradiating a laser beam and causing an irradiating portion to cause an optical change, and a method of manufacturing the same.

(Prior art) In recent years, with the development of small and high-performance lasers, research on so-called optical-related technologies, such as optical communication, optical measurement, and optical recording, has been rapidly progressing. Some are in practical use. Above all, optical recording, which irradiates a thin-film medium on a substrate with a focused laser beam and causes a structural change such as perforation or amorphous-crystal transition in the thin film to record information, has a higher density than magnetic recording. , Which is attracting attention as a new technology capable of recording a large amount of information. Here, the method of performing recording by perforating a thin film is characterized in that once information is written, erasing is impossible and information can be retained permanently, and is called a write-once recording medium.

On the other hand, a method of performing recording based on an amorphous-crystal transition is called a rewritable recording medium because writing and erasing can be performed many times by making the transition between two states reversible. ing. This rewritable recording medium usually contains Te
A thin film of a chalcogenide-based glass is used, and the Te in the film is made amorphous by rapid heating and quenching of the thin film with a laser beam, and writing is performed, and the amorphous Te is crystallized by slow cooling with a laser beam To erase. However, when writing and erasing are repeated many times, the film undergoes irreversible changes such as deformation, perforation, etc., which causes a problem that information remains unerased. For preventing multiple deformation of the recording film by the laser heating and to prevent mechanical damage due to an external force, typically added, SiO ₂ film, a hard over-coat layer and the under-coat layer such as ZnS film, mechanical For example, a method of suppressing deformation is adopted. In this case, writing above ¹⁰⁶ times, it is possible to repeatedly erase operations. However, inorganic dielectric films such as SiO ₂ and ZnS generally have high thermal conductivity, and energy loss occurs due to thermal diffusion from the recording film to the dielectric film during laser heating. For this reason, a recording medium using an inorganic dielectric film as a protective layer is excellent in repeatability, but requires a large laser power for writing and erasing.
That is, there is a problem that the recording sensitivity is reduced.

To solve this problem, a dielectric film having a low thermal conductivity may be used as a protective film. However, generally, a material having a low thermal conductivity is an organic substance, and is often inferior in heat resistance. For example, an acrylic resin or a polycarbonate resin has a thermal conductivity one order of magnitude lower than that of an inorganic material such as SiO _2, but is deformed when heated to 150 ° C. or more. Therefore, a recording medium in which the organic film as the protective layer, although excellent in recording sensitivity, decreased repeatability is significantly, 10 ^twice about writing, there is a problem that not work at erasing.

Under such circumstances, a so-called phase-change optical recording medium utilizing a rewritable crystal-amorphous transition has a recording sensitivity and a repeatability that are mutually related, and it is not possible to simultaneously improve the performance of both. It has been considered extremely difficult.

(Problems to be Solved by the Invention) The present invention provides an optical recording medium capable of simultaneously improving the recording sensitivity and the repeatability of writing / erasing in the above-mentioned conventional optical recording medium, and a manufacturing technique for manufacturing the same. Is to do.

(Means for Solving the Problems) In the present invention, as the dielectric protective layer in contact with the recording layer, a material having low thermal conductivity and excellent heat resistance, that is, a Si—N film, a Si—C A film, a Si—O film containing carbon and hydrogen, or the like is used. An electron cycloton (ECR) plasma CVD method is adopted as an optimal technique with good controllability for producing these films. Generally CV
Method D is a method in which a reactive gas is decomposed and reacted on a substrate to form a thin film.Even if the target film itself is mainly composed of an inorganic substance, C and H contained in gas components are contained in the film. Many are taken in. Depending on the amounts of C and H, the CVD film may have low thermal conductivity and excellent heat resistance.However, in the CVD method, the substrate needs to be heated to a high temperature of several hundred degrees or more. It is not suitable for application to optical disks that often use plastic as a substrate. In order to solve such a manufacturing problem, a plasma CVD method, particularly an ECR plasma CVD method, has recently attracted attention as a method for obtaining the aforementioned CVD film at a low temperature.

In the ECR plasma CVD (hereinafter abbreviated as ECR) method, high-density plasma is generated by electron cyclotron resonance in an ion source, the plasma is guided onto a substrate in a sample chamber, and reacted on the substrate to deposit a film. . This method is excellent in controllability and productivity, the substrate temperature may be room temperature, and the temperature rise during film deposition is said to be at most about 60 ° C., and is suitable as a technique for manufacturing a dielectric protective film of an optical disk. Also, C, H in the film
Can be easily controlled by the gas flow rate supplied to the apparatus or the high-frequency power.

In the present invention, the film production by the ECR method, which has been recently established as a thin film production technique, is applied to a dielectric protective film of an optical disk, particularly a phase change rewritable optical disk. The dielectric protective film obtained by the present invention provides optimum characteristics for a rewritable optical disk medium that is required to have both low thermal conductivity, excellent heat resistance, and simultaneously satisfy both recording sensitivity and repeatability. Things.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Example 1 An experiment of manufacturing a phase change rewritable optical disk and measuring characteristics was performed. First, using a 5 inch φ grooved polycarbonate resin disk as a substrate, a substrate / dielectric protective layer (undercoat) / recording layer / dielectric protective layer (overcoat) / metal reflective layer / epoxy resin layer for sealing An optical disk was manufactured with the configuration described above. (See Japanese Patent Application No. 61-64496)
For coats and overcoats, Si
An -NH film was produced. The reactive gases used were SiH ₄ and N ₂ . The film thickness is about 100 nm for the undercoat and about 200 nm for the overcoat. The H content in the film is controlled by changing the high frequency power supplied to the ion source of the ECR device from 100 W to 600 W, and the H content is 2 at.%, 5 at.%, 10 at.%, And 20 at.
Seed discs were made. An Sb-Tb-based alloy film (40 nm thick) is used for the recording layer, and Au (30 nm thick) is used for the metal reflective layer.
Each was produced by the RF sputtering method. The hydrogen content in the undercoat and the overcoat is a value estimated from measurement of infrared absorption. The sealing epoxy resin layer is formed by spinner coating and has a thickness of about 10 μm. For these disks, recording sensitivity and repetition of recording / erasing were measured by an optical disk dynamic characteristic evaluation apparatus.

The results for the recording sensitivity are shown in FIG. In FIG. 1, R is the reflectance. The measurement conditions are a linear velocity of 10 m / s, a recording frequency of 5 MHz, and a duty of 30%, which corresponds to a recording pulse width of 60 ns. The disk was recorded by initializing the recording layer and changing it into a crystalline state to make it amorphous. Looking at the change in the signal contrast with respect to the recording power, the higher the H content in the dielectric protective film, the lower the recording power, the higher the recording sensitivity. This is because as the H content increases,
This suggests that the thermal conductivity of the dielectric protection layer is reduced, and therefore energy loss due to thermal diffusion can be reduced.

Next, the measurement results of the repeatability are shown in FIG. The recording and erasing conditions were set to the optimum conditions for each disk based on the measurement results shown in FIG. Now, as the repeatability reducing the H content in the protective layer is excellent, H:. 2at In percent of the disk was found to sufficiently withstand ¹⁰⁷ or more repetitions operation. This suggests that the lower the H content, the more an inorganic film having excellent heat resistance can be obtained.

Generally, the limit of repeatability is represented by an increase in noise level.

Combining the characteristics of FIG. 1 and FIG. 2, the H content is 5 at.
% As in the of the following recording threshold 15 mW, and the repeatability 10 ⁶ or more times, meets sufficiently high recording sensitivity and repeatability of the characteristics required of the rewritable optical disc. Therefore, by the ECR method, it was possible to realize an optical disk having a dielectric protective layer having excellent low heat conductivity and heat resistance. Here, compared with the optical disk medium manufactured by other manufacturing methods, RF
Overcoat Si-N film produced by sputtering,
In a medium with an undercoat, the recording threshold is 20 mWW or more, and there is a problem in recording sensitivity. Further, a medium in which an overcoat and an undercoat are formed as an organic resin film has a repetition rate of at most about 10 times, and cannot be a practical medium.

On the other hand, in a Si—N—H film produced by the ECR method, for example, H
With a content of 5 at.%, The thermal conductivity was measured to be 3.8
× 10 ^-3 cal / cm · sec · deg (actual measured value of Si-N 2.24 × 10 ^-2 ca
l / cm · sec · deg, measured value of epoxy resin approx. 5 × 10 ^-4 cal /
cm · sec · deg) and heat resistance measured by thermogravimetric analysis, the thermal decomposition temperature is 700 ° C or higher (actual measured value of Si-N is 1200 ° C or more, epoxy resin measured value is 170 ° C). Suitable for.

Example 2 The same experiment as in Example 1 was performed, except that the dielectric protection layer was an Si—C—H film by the ECR method. The reactive gases used for ECR are SiH ₄ and C ₂ H ₄ . When a disk was manufactured by changing the H content and the characteristics thereof were evaluated, when the H content was 10 at.%, A high-performance optical disk having both excellent recording sensitivity and repeatability was realized. Here, too, the effectiveness of the ECR method was demonstrated.

Example 3 The same experiment as in Example 1 was performed by using a Si—O—C—H film as a dielectric protective film by an ECR method. The reactive gases used for ECR are SiH ₄ and CO ₂ . A disk was prepared by changing the contents of C and H, and the characteristics were evaluated. When the C content was 5 at.% And the H content was 5 at.%, Both the recording sensitivity and the repetitiveness were excellent.
A high-performance optical disk was realized. Here again, the ECR method was proved to be suitable for producing a protective layer of an optical disc.

Further, as an extension of the present invention, during film formation by the ECR method,
By changing the gas flow rate or the high frequency power, the composition (for example, H content) can be changed in the film deposition direction.
In this case, for the portion that becomes high heat in contact with the recording layer,
H content is reduced to increase heat resistance, and several tens nm from recording layer
In the portions separated as described above, the H content can be increased to reduce the energy loss due to thermal diffusion. As described above, by modulating the composition in the dielectric protection layer, a high-performance optical disc having further excellent recording sensitivity and repeatability can be realized.

Although the present invention has been described mainly with respect to a phase-change type optical disk, the effect of using a film formed by the ECR method as a dielectric protection layer is similarly effective for other types of disks such as a magneto-optical type optical disk.

In the present invention, the heat resistance is mainly described as a factor that determines the repeatability, but it is also an important factor that the protective layer is a mechanically strong hard film. It is a matter of course that the protective film of the high-performance optical disk described in the embodiment of the present invention is sufficiently hard to be mechanically strong, and this was also confirmed from an experiment using a hardness tester. That is, the ECR plasma CVD method used in the present invention is also promising as a technique for producing a hard film.

(Effects of the Invention) As described above, a phase-change rewritable optical disk having a protective layer manufactured by the ECR method is a high-performance optical disk having excellent recording sensitivity and repeatability, and is manufactured by another technology. It shows excellent characteristics that cannot be realized by the above. Especially in the ECR method, the film can be formed even at the substrate temperature of room temperature, the film deposition rate is several tens of mm / min, and the productivity is excellent, and the film composition can be easily controlled. It should be a breakthrough in this field as an optical disk medium manufacturing technology.

In the present invention, an ECR device to produce a dielectric protective layer,
An experiment was performed using two manufacturing apparatuses, an RF sputtering apparatus for forming a recording layer and a metal reflection layer. However, it is sufficiently possible to produce a recording medium consistently in-line by combining an ECR device and at least one of an RF sputtering device and a vapor deposition device, and to manufacture a recording medium. But no problem. On the contrary, since the film deposition rate of the ECR method is high, the manufacturing cost per disk is considered to be low.

The optical recording medium of the present invention, called recording sensitivity and repeatability,
It solves the biggest problem facing rewritable optical disks, and its impact on the industry is extremely large.

[Brief description of the drawings]

FIG. 1 is a view showing a silicon nitride film formed by ECR plasma CVD according to a first embodiment of the present invention.
FIG. 2 shows the recording sensitivity characteristics of an optical disk having an N—H film as a dielectric protective layer, with the H content in the dielectric protective film as a parameter. FIG. 2 shows an ECR plasma CVD method of Example 1 of the present invention. By Si
FIG. 9 is a diagram showing the repetition characteristics of recording / erasing of an optical disk having an -N-H film as a dielectric protection layer, using the H content in the dielectric protection film as a parameter.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Iwao Hatakeyama, Inventor 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Yuki Yamazaki 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Nippon Telegraph and Telephone Corporation (72) Inventor Ikuo Yagi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Kasumi Morita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-62-92250 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/24

Claims (3)

(57) [Claims] 1. An optical recording medium having a recording layer that absorbs light and deteriorates, and a dielectric layer disposed adjacent to the recording layer, wherein the dielectric layer is formed by electron cyclotron plasma CVD.
With a H content of 2 at% to 20 at%
-An optical recording medium comprising an H film. 2. An optical recording medium comprising: a recording layer that absorbs light and deteriorates; and a dielectric layer disposed close to the recording layer, wherein the dielectric layer is formed by electron cyclotron plasma CVD.
Si-C with H content of 2 at% to 20 at% formed by
-An optical recording medium comprising an H film. 3. An optical recording medium having a recording layer that undergoes deterioration by absorbing light and a dielectric layer disposed close to the recording layer, wherein the dielectric layer is formed by electron cyclotron plasma CVD.
The content of C is 5at% and the content of H is 2at%
An optical recording medium comprising a Si—O—C—H film of from 1 to 20 at%.