JPS61208648A - Production of optical recording medium - Google Patents

Abstract

PURPOSE:To decrease a noise level in optical recording by passing electric current to a recording film in the stage of subjecting a recording film to a heat treatment for the purpose of crystallization after film formation. CONSTITUTION:SnO2 or ITO is deposited by evaporation as a transparent electrode film 2 on a disk-shaped glass substrate 1. Since the film 2 plays the role of a protective film on the lower side of the recording film 3, there is no particular need for a protective film. A Te-Sn alloy film is formed as the recording film 3 on the film 2. The alloy film 3 having 8:2 atomic ratio of Te:Sn is deposited on the substrate by depositing respectively Te and Sn by evaporation from two vapor deposition sources which permit independent temp. control while the substrate mounted in a vacuum deposition device is rotated. The recording films of all the disks are in the polycrystalline state after the end of heating when these disks are put into a thermostatic chamber and are heated. The size of the crystal grains is smaller and is uniform on the side where the current is passed. The noise level of the optical recording is thereby decreased and the optical recording medium having high reliability is provided.

Description

[Detailed Description of the Invention] [Summary] In an optical recording medium, when crystallizing the recording film before writing, heat treatment is performed while passing a current through the recording film, thereby achieving the optimum crystalline state for the recording film. It is possible to achieve this.

[Industrial application field]

The present invention relates to a method of manufacturing an optical recording medium, and particularly to a method of manufacturing an optical recording medium in which a signal is recorded by irradiating a recording film with light to selectively change reflectance or transmittance.

Optical recording media that perform signals and recording using changes in reflectance or transmittance generally perform recording between amorphous and crystalline materials or between crystalline materials by selectively irradiating light. Recording can be performed by changing the state of the film.

[Conventional technology]

Conventionally, optical discs that utilize changes in reflectance and transmittance are
A recording material such as a chalcogenide alloy, m-v group compound, or other semiconductor is deposited on an acrylic substrate or a glass substrate by vapor deposition or sputtering. However, the recording film deposited in this manner is generally in an unstable state with a disordered crystal structure, and is not in a state suitable for use as is for writing. Therefore, in order to optimize this, we have adopted a method in which the recording film is heat-treated in a constant temperature bath to crystallize it.

[Problem that the invention seeks to solve]

However, when the recording film is heat-treated in a constant temperature bath, crystal grains grow large and crystallization becomes uneven, resulting in an increase in the noise level in optical recording.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention supplies a current to the recording film during heat treatment for crystallization after the recording film is formed.

[For production]

When a current is applied to a recording material such as a chalcogenide alloy during crystallization, the bonds between the atoms that form the crystal are broken by the electric charge, which suppresses grain growth during crystallization of the recording film, making it a good choice for optical recording films. It becomes possible to obtain microcrystals with a desired uniform particle size. This effect of energization on crystal growth is well known in the field of thin film technology. In this way, a desired crystalline state can be achieved by appropriately adjusting the applied current, voltage, temperature and time of heat treatment.

[Example] Example 1 This will be explained with reference to FIG. 1. Snug or IT is applied as a transparent electrode film 2 on a disk-shaped glass substrate 1 with an outer diameter of 30 mm.
O (indium-tin-oxide) was deposited. Film thickness is 5
A range of 0 to 500 na+ is appropriate.

In conventional optical discs, etc., SiO is placed between the substrate 1 and the recording film 3.
A protective film such as □ was formed, but in this example, since the transparent electrode film 2 also plays the role of a protective film under the recording film 3, there is no need to add a special protective film.

A Te--Sn alloy film was formed as a recording film 3 on the transparent electrode film 2. The alloy film 3 with a Te:Sn atomic ratio of 8=2 is deposited on the substrate ( transparent electrode film). The film thickness was 150ns. Such a deposited alloy film is in an irregular state (non-crystalline state) with a disordered crystal structure.

SnO□ or ITO was deposited as a protective film 4 on the alloy film 3 to a thickness of 150 na+. Prepare two such discs, one of which has Protection II! Chromium was further vapor-deposited as a metal electrode film 5 to a thickness of 200 nm.

These disks were placed in a constant temperature bath and heated at 150° C. for 1 hour. However, during that time, the disk having the metal electrode film 5 is
As shown in the figure, between the metal electrode film 5 and the transparent electrode film 2,
A voltage of 0V was applied and a current was caused to flow.

After the heating was completed, a small piece of the recording film 3 was peeled off from each disc and observed under a transmission electron microscope, and it was found that the recording film of both discs was in a polycrystalline state. The grain size of the crystal grains of the disk in which no current was passed was within the range of approximately several 100 nI11 to 2 μm, and that of the disk in which current was passed was approximately 5 on 1 m to 100 nm.
It was within the range of s. In other words, when a current is applied, the crystal grains are smaller and more uniform in size.

When the C/N ratio (carrier-to-noise ratio) was measured (bandwidth 30 kHz) by recording a 1 MHz signal at a rotation speed of 600 rpa+ on these discs (recording media), it was found that the discs that did not conduct current The current was 43 dB, and the current was 47 dB. That is, an increase in C/N of 4 dB was observed by flowing current during heat treatment. □lu The procedure of Example 1 was repeated. However, in Example 1, a DC voltage was applied to cause current to flow, but in this example, 100V, 50Hz
An alternating current voltage was applied to cause a current to flow.

The C/N ratio of the disk with no current flowing through it was 43 dB, and the C/N ratio of the disk with current flowing through it was 48 dB.

Example 3 In the same manner as in Example 1, two disc-shaped optical recording media were prepared using a Te-Sn alloy as the recording material. However, in this example, a Sin film was created instead of the transparent electrode film 2, and the atomic ratio of Te:Sn in the recording film was 85:15, and the film thickness was 10 on.
−. Further, only a SiO□ protective film was formed on the alloy film, and no metal electrode film was formed.

Next, with reference to FIG. 2, which is a cross-sectional view passing through the center of the disk, a method of passing current through one disk will be explained.

A recording film is formed on the glass substrate 11 (this recording film 12 is made of Te-
It consists of three layers with a five-layer alloy film sandwiched between upper and lower sides of a protective film of Sin. ) is formed. That is, this recording medium has the same structure as the conventional one. An inner ring 13 and an outer ring 14 made of copper are placed on the inner and outer peripheries of this recording film 12, respectively, and are pressed with a presser plate 15 to ensure contact between the rings 13 and 14 and the recording film 12. . Then, by applying a voltage of 100 V between the inner ring 13 and the outer ring 14, a current was caused to flow through the recording film 12.

Also in this example, during the heat treatment, one disk was energized as described above, and the other disk was not energized. The heat treatment was performed at 150° C. for 10 minutes in a constant temperature bath.

The optical recording medium (disc) thus obtained was examined under an optical microscope (1
When observed at a magnification of 0.000 times), the surface of the sample to which no current was applied appeared rough, whereas the surface of the sample to which an electric current was applied was uniform and smooth.

When the C/N ratio was measured in the same manner as in Example 1,
The one with no current flowing was 43 dB, but the one with current flowing was 47 dB.

Note that each of the optical recording media of Examples 1 to 3 was rewritable and exhibited good rewritability.

〔Effect of the invention〕

According to the method of the present invention, the recording film of an optical recording medium for recording signals can be uniformly crystallized to a desired grain size by changing the reflectance and transmittance, thereby reducing the noise level of optical recording. , it is possible to provide a highly reliable optical recording medium.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an optical disc according to a first embodiment of the present invention;
FIG. 2 is a sectional view showing the state of heat treatment of an optical disk in a second embodiment of the present invention. 1--Substrate, 2---Transparent electrode film, 3-
・Recording film, 4-track protective film, 5-metal electrode film, 11--substrate, 12-recording film, 13--copper inner ring, 14--
-・Copper outer ring, 15-... Pressing plate.

Claims (1)

[Claims] 1. In manufacturing an optical recording medium in which a signal is recorded by selectively changing the reflectance or transmittance of the recording film by irradiating the recording film with light, after forming the recording film on the substrate, A method for manufacturing an optical recording medium, which comprises heat-treating and crystallizing the recording film while passing an electric current through it.