JPH03171428A - Method for initial crystallization of phase-transition type information recording medium - Google Patents

Abstract

PURPOSE:To obtain a uniform crystal phase over the whole recording layer by irradiating the area to be crystallized in a recording layer with higher energy than the required energy for information recording. CONSTITUTION:Laser light from a semiconductor laser source 13 is changed into a parallel beam by a collimator lens 14, directed to enter an objective lens 16 by a beam splitter 15, and condensed on a recording layer of a disk substrate 10. The condensed beam on the recording layer is controlled so that its energy density exceeds the power required for recording in the recording layer. By this method, all the area irradiated with the beam is heated over the melting point of the constituents of the recording layer and then cooled. Since this process is effected independently of the position in the recording layer, the whole recording layer can be uniformly crystallized initially.

Description

Detailed Description of the Invention [Objective of the Invention 1] (Industrial Application yf) The present invention provides a method for changing the phase between different phases in a recording layer by illuminating a light beam such as a laser beam or an electron beam. The present invention relates to an initial crystallization method for a phase change information recording medium that records and erases information by causing

(Prior Art) So-called phase change type information recording media that can record and erase information have been developed. Recording is performed on this phase change type information recording medium as follows. First, the entire information recording medium is irradiated with a light beam to bring the recording layer into a highly crystalline state (a state in which atoms are relatively correctly arranged, hereinafter referred to as a crystalline state). By irradiating this recording layer with short pulsed light, that portion is applied and rapidly cooled, resulting in a state where the crystallinity is reduced (a state where the atomic arrangement is disordered, hereinafter referred to as a non-quality state). Since each part has a different atomic arrangement structure, the optical properties such as reflectance and light transmittance are different, and information is recorded in the recording layer.

Further, recorded information can be erased by irradiating the information recording portion of the recording layer with long pulsed light and slowly cooling it.

In this way, information can be recorded and erased using phase change, and information can be reproduced by detecting the optical characteristics accompanying this change.

In addition, the so-called overwrite method, which uses a light beam consisting of continuous light and short pulsed light to erase information recorded in the recording layer and record new information at the same time, has been attracting attention recently. The above-mentioned phase change can also be realized in this method.

Incidentally, the recording layer of such a phase change information recording medium is formed by a vacuum process such as a sputtering method or a vacuum evaporation method.
Immediately after film formation, the constituent atoms are in a completely random state, that is, in an amorphous state, and this non-quality state is stable. In order to initially crystallize such a recording layer in a poor quality state, it is necessary to irradiate the recording layer with light having a power higher than the power used when erasing information (hereinafter referred to as erasing power). Normally, the method of initial crystallization of the recording layer is to irradiate the track forming part of the recording layer with continuous light at the erasing power level while rotating the disk, scan it multiple times, and gradually crystallize that part. Some operations are performed on the entire disk.

(Problem to be Solved by the Invention) However, in such a method, when the number of rotations of the disk is constant, the four-way rotation speed of the disk gradually decreases from the outer circumference toward the center of the disk.
When a light beam is scanned over the recording layer multiple times with constant energy, the degree of crystallization differs between the outer peripheral portion and the central portion of the recording layer, resulting in uneven crystallization. Therefore, optical properties such as reflectance of the recording layer differ between the outer circumferential portion and the central portion of the disk, resulting in a difference in initial crystallization level. As a result, when information is recorded or erased, information is left unerased or recorded incorrectly.

The present invention has been made in view of these points, and an object of the present invention is to provide a method for initial crystallization of an information recording medium that can uniformly and easily initialize the entire recording layer.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a film that contains a non-quality phase in the as-formed state, and changes in phase with different phases when irradiated with a light beam, thereby recording and erasing information. A method for initial crystallization of an information recording medium, the method comprising: irradiating a phase change information recording medium with a recording layer with a light beam to crystallize the recording layer, the light beam imparting information to the recording layer; It is characterized by having a power that exceeds the power of a light beam during recording.

(Function) According to the initial crystallization method for a phase change information recording medium of the present invention, the irradiation of the light beam onto the information recording medium is performed using power (hereinafter referred to as recording power) when recording information corresponding to the recording layer. This is done by scanning a light beam with a power exceeding 1.

That is, when crystallizing the recording layer, energy exceeding the energy required for information recording is applied to the crystallized portion of the recording layer. This makes it possible to determine whether the materials that make up the recording layer are related to the location of the recording layer. ．． It reaches a temperature exceeding the melting point and enters a molten state.

By cooling the recording layer from a molten state, a uniform crystalline phase can be obtained throughout the recording layer. Therefore, the optical properties such as the reflectance of the recording layer 5 are constant over the entire recording layer.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view of an information recording medium used in the method according to the present invention. 1 in the figure is a disk substrate. The disk substrate 1 is made of a transparent material that does not change much over time, such as glass or a plastic material such as polymethyl methacrylate resin or polycarbonate resin.

A recording layer 2 is provided on the surface of a disk substrate 1.

Materials for forming the recording layer 2 include Te, Se, Ge,
Metals such as Sb, In, semimetals, or GeTe
Examples include alloys such as Sb and InSbTe. These metals, alloys, etc. can undergo a phase change between a crystalline phase and an amorphous phase by being irradiated with a light beam under different conditions. Further, a recording layer formed of these materials has characteristics such as a large reproduced signal, high recording sensitivity, and high stability of the non-quality state 6 as a recording state. Furthermore, since these recording layers have a high crystallization rate, their initial crystallization rate is high. Such a recording layer is formed by a sputtering method, a vacuum evaporation method, or the like.

An organic protection layer 3 is provided on the surface of the recording layer 2. This protective layer 3 is provided to protect the surface of the recording layer 2 during nodding of the information recording medium. Usually, the protective layer 3 is made of ultraviolet curing resin.

Furthermore, as shown in FIG. 3, inorganic protective layers 4 and 5 may be provided between the substrate 1 and the recording layer 2 and between the recording layer 2 and the protective layer 3 so as to support the recording layer 2, respectively. . Examples of the material for the inorganic protective layers 4 and 5 include metal or semimetal oxides, fluorides, sulfides, and nitrides. The inorganic protective layers 4 and 5 are provided to prevent the recording layer 2 from deteriorating over time.

Furthermore, as shown in FIG. 4, a structure in which a reflective layer 6 is provided between the inorganic protective layer 4 and the organic protective layer 3 may be used.

Next, an example of the initial crystallization method for the information recording medium of the present invention will be explained with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of an apparatus used in an embodiment of the method of the present invention. In the figure, 10 is a disk substrate. Disk board 10
is rotatably attached to a motor 11 that rotates the disk substrate 10. An optical device 12 for condensing laser light onto the disk substrate 10 is installed above the disk substrate 0.

The optical device 12 includes a semiconductor laser source 13, a collimator lens 14, a beam splitter 15, and an objective lens 16.
It is equipped with The collimator lens l4 is located on the side of the semiconductor laser source 13, and the beam splitter 15 is located on the side of the collimator lens 14 so as to receive the light emitted from the semiconductor laser source 13 through the collimator lens 14. Further, the objective lens 16 is located below the beam splitter 15.

The optical device 12 is also connected to a control means 17 that controls the scanning of the optical device 12 as a whole.

In such an apparatus, initial crystallization is performed as follows.

First, laser light is emitted from the semiconductor laser source 13.

This laser light becomes parallel light by passing through a collimator lens]4. The direction of this parallel light is changed by the beam splitter 15, reaches the objective lens 16, and is thereby focused onto the recording layer of the disk board 10. At this time, the energy density of the light focused on the recording layer is set to exceed the recording power of the recording layer.

In this way, the beam light is irradiated at any location on the recording layer of the disk substrate with an energy density exceeding the recording power. Therefore, all parts irradiated with the beam light reach a temperature exceeding the melting point of the material forming the recording layer and are cooled.

This is independent of the location of the recording layer, so that the entire recording layer is initially crystallized uniformly.

Recording of information on the initial recording layer is performed by irradiating the recording layer with a light beam having a short pulse width and heating and rapidly cooling the irradiated area to change it to a non-quality state9. Furthermore, information is erased by illuminating the recording layer with a light beam of lower power than that used during information recording, for example, a light beam with a longer pulse width fA=t. In addition, when reproducing recorded information, the recording layer is irradiated with a light beam with a lower power than when erasing information, and the optical characteristics between the information recording part and the non-information recording part, such as the difference in the foul rate, are detected. Do by doing.

Test Example Initial crystallization of an information recording medium was actually carried out using the apparatus shown in FIG.

First, an InSb alloy film was formed to a thickness of 1000 mm on the surface of a polycarbonate resin substrate having an outer diameter of 5.25 inches by sputtering. Next, an ultraviolet curing resin was coated on the InSb alloy layer and cured with ultraviolet light to form an organic protection layer. In this way, a disk substrate was produced.

The obtained disk substrate was placed in the apparatus shown in FIG.

Disc board]. It was rotated at 800 rpm. Co-rotating disk Jl (optical power 16mW on the plate)
0? Initial crystallization was performed by irradiating a certain beam of light over a distance of 30 mm to 60 m from the center of the disk substrate while scanning with an optical device. Note that the recording power when an InSb alloy is used for the recording layer is 15IIlwte.

The relationship between the distance from the center of the disk substrate and the reflectance of the recording layer at this time is shown by characteristic line 20 in FIG. For comparison, the relationship between the distance from the center of the disk substrate and the reflectance of the recording layer is also shown in Figure 5 as a characteristic line 21 for initial crystallization using a beam with an optical power of 12 mW. do.

As is clear from FIG. 5, the reflectance of the recording layer initially crystallized by the method of the present invention is constant in any part of the recording layer, and the entire recording layer is initially crystallized uniformly. Ta. On the other hand, when initial crystallization is performed using a beam whose optical power is less than the recording power, the anti-11 ratio differs depending on the location of the recording layer, and the initial crystallization rate differs depending on the location of the recording layer. There were differences in level.

11. Effects of the Invention As explained above, the method for initial crystallization of an information recording medium of the present invention enables initial crystallization of the entire recording layer uniformly and easily.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic structure of an apparatus used in an embodiment of the method of the present invention, and FIGS. 2 to 4 are cross-sectional views of an information recording medium used in the method of the present invention. FIG. 5 is a graph showing the relationship between reflectance and distance from the center of the disk plate. 1, 10... Disc substrate, 2... Recording layer, 3...
・Organic substance protective layer, 4, 5... Inorganic substance protective layer, 6...
Reflection required, 11...Motor 12...Optical device, 1
3... Semiconductor laser source, 14... Collimator lens, 15... Beam splitter, 16... Objective lens, 17... Control means.

Claims (1)

[Claims] A light beam is applied to a phase-change information recording medium that has a recording layer that contains an amorphous phase in the as-formed state and that changes phase between different phases when irradiated with a light beam to record and erase information. A method for initial crystallization of an information recording medium, in which the recording layer is crystallized by irradiation, wherein the light beam has a power exceeding the power of the light beam when recording information on the recording layer. An initial crystallization method for a phase change information recording medium.