JPH0738259B2 - Optical disk manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] An optical disc in which a dead period is eliminated by adjusting a substrate heating condition and a heat treatment time of a recording medium formed on a transparent substrate to obtain a crystallized state equal to an erased state of information. Manufacturing method.

[Industrial application field]

The present invention relates to a method for manufacturing an optical disc that eliminates the dead period.

An optical disk is a memory that records information at a high density by using a laser beam, has a large recording capacity, can perform recording and reproducing in a non-contact manner, and is excellent in that it is not affected by dust.

Here, the optical disc uses a low melting point metal as a recording medium, and in addition to a read-only memory which records information by presence or absence of a hole, a difference in reflectance between crystal and crystal or crystal and amorphous (amorphous) is obtained. The rewritable memory (Erasable Memory) used is being developed.

The present invention relates to a method for manufacturing an optical recording medium utilizing crystal-crystal transition.

[Conventional technology]

Indium (In) is used as a recording medium of crystal-crystal transition type.
-An antimony (Sb) alloy or an In-Sb-selenium (Se) alloy is known.

The following is a description of the case where an In-Sb alloy is used as a recording medium for the mechanism of recording, reproducing and erasing information for an optical disc using such an alloy as a recording medium.

This device has a composition ratio of 1: 1 in atomic weight%, that is, a solid solution consisting of an Sb metal atom and an intermetallic compound having a composition of In ₅₀ Sb _{50 in} the phase diagram is composed of the Sb metal that constitutes the thermal energy This is because the dispersion state of atoms is different and the reflectance of laser light is different due to the difference in this state.

That is, according to the observation result by the electron microscope, in the recorded state, Sb atoms are aggregated at the irradiation position, and there is a fine In ₅₀ Sb ₅₀ intermetallic compound surrounding the Sb atom, and thus the state is high reflectance.

On the other hand, in the erased state, fine Sb atoms are uniformly dispersed in the fine In ₅₀ Sb ₅₀ intermetallic compound, and thus the state of low reflectance is obtained.

Such a state is explained, for example, with a recording medium in which the atomic weight% of In and Sb is 40:60 and the film thickness is 1000Å. Using a semiconductor laser, output 10 mW, pulse width 200 nS (high power, short time)
When the writing pulse of (1) is irradiated, the recording medium in the irradiation portion changes in state due to heating and melting for a short time, and the reflectance becomes approximately 40%. This is the information recording condition.

On the other hand, output 4mW, pulse width 400nS (medium power,
When the erase pulse is applied for a long period of time, the irradiated part changes in state due to heating, and the reflectance drops to about 30%.

This is a condition for deleting this information.

On the other hand, the output is about 0.5 mW at the information recording position (small power)
When irradiating the laser beam of No. 1, the state does not change.

This is the information reproduction condition.

Recording, reproducing and erasing of information on the optical disc are performed by utilizing the fact that the state of the recording medium changes due to the difference in the irradiation condition of the laser beam and the reflectance is different.

However, even when a recording medium with a composition ratio of In ₄₀ Sb ₆₀ was formed on a transparent substrate such as glass by a vacuum deposition method or the like, it did not show a high reflectance at the stage of immediately irradiating the writing pulse, and was stable. To obtain a high reflectance state, it is necessary to repeat the writing and erasing operations several times to bring the recording medium into a stable crystalline state.

FIG. 2 shows this state, in which the abscissa axis represents the number of times of recording and erasing in one cycle, and the ordinate axis represents the reflectance of the recording medium.

In the figure, the recording medium on which the film has been formed initially shows a reflectance of about 25% as shown in the initial state 1, but the irradiation of the writing pulse increases the reflectance to about 30% and the irradiation of the erase pulse. Then, the reflectivity gradually rises by repeating recording and erasing, and in the case of this example, it is stable after four times.

The period until reaching this stable state is the dead period (Incubation
It is said that, in order to use the optical disk as a memory, it has to be in a stable state after the dead period.

Therefore, in mass-producing optical discs, it was necessary to eliminate the dead period and shorten the process.

[Problems to be solved by the invention]

As described above, the rewritable optical disc has a dead period, and it is necessary to repeat the recording / erasing cycle to eliminate it, but this process is an obstacle to mass production.

Therefore, how to eliminate the dead period is an issue.

[Means for solving problems]

The above problem can be rewritten by recording and erasing information by utilizing the fact that the crystal state of the recording medium changes depending on the irradiation conditions of the recording medium formed on the transparent substrate and the reflectance is different. In another optical disc, the problem can be solved by eliminating the dead period by adjusting the substrate heating temperature and the heat treatment time in forming the film on the transparent substrate.

[Action]

The present invention has been made as a result of observing a crystalline state of a recording medium in a recorded state and an erased state.

That is, in the In-Sb-based recording medium, in the recorded state, Sb atoms having a grain size of about 20 nm and a composition ratio of In ₅₀ Sb ₅₀ intermetallic compound crystallites having a grain size of about 200 nm are aggregated. Is recognized.

Further, in the erased state, it can be seen that Sb atoms of almost the same particle size are uniformly dispersed in In ₅₀ Sb ₅₀ intermetallic compound microcrystals having a particle size of about 20 nm.

On the other hand, the InSb storage medium in an initial state in which a film is formed on a transparent substrate such as glass by a method such as a vacuum deposition method is amorphous.

Therefore, in order to eliminate the dead period, it is understood that the InSb storage medium in the initial state should be in the same crystalline state as the erased state.

By the way, heating the substrate during evaporation until now, or irradiating the recording medium after film formation with laser to crystallize it,
It has been attempted to eliminate the dead period by performing an initialization process such as heating the recording medium after the film formation.

However, as a result of observation with an electron microscope, the inventors have found that the grain size of the crystal obtained by such conventional initialization treatment is In ₅₀ Sb ₅₀
It was found that both the intermetallic compound and the Sb atom are about 10 nm, which is fine compared to the erased state.

Therefore, it became clear that more energy needs to be applied to eliminate the dead period.

Next, the inventors examined other crystal-to-crystal transition type recording media, and found that similar phenomena also exist in gallium-antimony (GaSb) -based and bismuth-tellurium (BiTe) -based recording media. .

For example, the composition ratio of GaSb is the same as InSb in terms of atomic weight%.
Since there is an intermetallic compound at the position of Ga ₅₀ Sb ₅₀ , the composition ratio of Sb is 60 to 70, that is, Ga ₄₀ Sb _{60 to} Ga ₃₀ Sb ₇₀
If a recording medium of this kind is used, a recording state in which Sb atoms are aggregated at the irradiation position can be created by high power, short time laser irradiation, and fine Sb atoms can be generated by medium power, long time laser irradiation. It is possible to create an erased state that is uniformly dispersed in the intermetallic compound, but in this case as well, the dead period is eliminated by heating the amorphous vapor-deposited film to a particle size in the erased state. be able to.

In the case of BiTe, the composition ratio of the intermetallic compound is atomic weight%.
Since it is at the position of Bi ₄₀ Te ₆₀ (Bi ₂ Te ₃ ), the alloy composition around Bi ₃₀ Te ₇₀ may be used for the recording medium. Particle size (about 20 nm)
The dead period can be eliminated by setting.

〔Example〕

Example 1: (Example of application to InSb alloy) When a recording medium having a composition ratio of In ₄₀ Sb ₆₀ was formed into a film having a thickness of 100 nm on a glass substrate by a binary vapor deposition method, the heating time of the substrate was changed. The temperature was fixed for 2 hours, the substrate temperature was changed to 150 to 240 ° C., and the condition that the crystal grain size was 20 nm was obtained.

Since the film formation is completed in a short time, most of the heat treatment is performed on the film-formed recording medium.

As a result, a particle size of 20 nm can be obtained when the substrate temperature is maintained at about 200 ° C. where recrystallization starts and heating is performed in an inert atmosphere (N ₂ ) for about 2 hours. understood.

In this case, the reflectance in the initial state 1 is about 1 as shown in FIG.
It shows a value of 30%, and even if the recording and erasing operations are repeated, the recording state 2 is about 40% and the erasing state is about 30%, which means that the dead period is eliminated.

Example 2: (Example of application to GaSb alloy) A recording medium having a composition ratio of Ga ₄₀ Sb ₆₀ was formed into a film having a thickness of 100 nm on a glass substrate by a binary vapor deposition method. It is crystalline.

When this Ga ₄₀ Sb ₆₀ is used as the recording medium, the recording state on the optical disc is 200n at the laser irradiation position as in the case of InSb.
Sb atoms of about m are aggregated, and a Ga ₅₀ Sb ₅₀ intermetallic compound having a particle size of about 20 nm is present surrounding this.

Further, in the erased state, the same amount of Sb atoms is dispersed in the Ga ₅₀ Sb ₅₀ intermetallic compound having a particle size of about 20 nm.

Therefore, recrystallization of this alloy (melting point 700 ° C) begins in order to make Ga ₄₀ Sb ₆₀ in the amorphous state into microcrystals in the erased state.
As a result of holding at 50 ° C. and heating in N ₂ atmosphere, it was possible to obtain the same crystal grain size as in the erased state by heating for about 2 hours.

For an optical disk that has undergone such processing, the reflectance is approximately 40% when writing with an output of 10 mW and pulse width of 200 nS (high power, short time) using a semiconductor laser, while output of 4 mW at this position Therefore, the reflectivity was about 30% when an erase pulse with a pulse width of 400 nS (medium power, long time) was irradiated, and the dead period could be eliminated by this treatment.

Example 3: (Application example to BiTe alloy) A recording medium having a composition ratio of Bi ₃₀ Te ₇₀ was formed into a film with a thickness of 100 nm on a glass substrate by a binary vapor deposition method. It is crystalline.

In the recorded state of this optical disk, Te atoms having a particle size of about 200 nm are aggregated at the laser irradiation position, and a Bi ₂ Te ₃ intermetallic compound having a particle size of about 20 nm is present surrounding the Te atoms.

In the erased state, Te atoms of the same size are dispersed in the Bi ₂ Te ₃ intermetallic compound having a particle size of about 20 nm.

Therefore, recrystallization of this alloy (melting point 560 ° C) begins in order to convert amorphous Bi ₃₀ Te ₇₀ into erased microcrystals.
As a result of holding at 50 ° C. and heating in N ₂ atmosphere, it was possible to obtain the same crystal grain size as in the erased state by heating for about 2 hours.

Next, regarding the optical disc that has been subjected to such a process, an output of 15 mW and a pulse width of 150 nS (large power,
The reflectance when writing for a short time) is about 25%, while the reflectance when an erase pulse with an output of 6 mW and a pulse width of 400 nS (medium power, long time) is applied to this position is about 25%.
This is 22%, and the dead period can be eliminated by this treatment.

〔The invention's effect〕

As described above, the dead period can be eliminated by implementing the present invention, and thus the cost can be reduced by shortening the manufacturing process.

[Brief description of drawings]

FIG. 1 is a reflectance change characteristic of an optical disc according to the present invention, and FIG. 2 is a reflectance change characteristic of a conventional optical disc. In the figure, 1 is an initial state, 2 is a recording state, and 3 is an erasing state.

Claims (2)

[Claims] 1. Rewriting for recording and erasing information by utilizing the fact that the crystalline state of the recording medium changes depending on the irradiation conditions of the recording medium formed on a transparent substrate and the reflectance is different. In a possible optical disc, the substrate heating temperature and the heat treatment time are adjusted in forming the film of the recording medium on the transparent substrate, and the crystal grain size of the recording medium is made equal to the crystal grain size in the erased state of the recorded information. Optical disc manufacturing method. 2. The method of manufacturing an optical disk according to claim 1, wherein the recording medium is made of an indium antimony alloy.