JPH04286683A - Optical recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To develop a new recording medium of which a recording and erasing cycle is extremely enlarged though said cycle is limited to one hundred thousand times since for a traditional optical recording medium using, as a recording layer, a thin film of GeSbTe alloy or InSbTe alloy formed by using a target material of 3N-4N in purity by a sputtering method, impurities are concentrated to form nuclei, and coarse crystal grains are generated. CONSTITUTION:For an optical recording medium wherein Ge2 Sb3 Te4 of 99.999wt% in purity is used as a target material, and a thin film of Ge2 Sb3 Te4 in composition ratio is formed to 30nm in film thickness on a glass substrate to form a recording layer, even after one million recording and erasing cycles, a variation rate of a reflectance ratio is almost as same as initially and deterioration in characteristics is hardly recognized.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical recording medium that utilizes phase change between crystalline and amorphous materials, and more specifically,
The present invention relates to a rewritable optical disc recording medium and a method of manufacturing the same.

0002

2. Description of the Related Art Conventionally, rewritable optical recording media are known that utilize reversible optical change between an amorphous state and a crystalline state.

Among these, JP-A No. 63-100632 ``Optical Recording Medium'' discloses the use of a GeSbTe alloy thin film as a recording layer, and JP-A No. 62-145547 ``Optical Recording Medium'' and JP-A No. 63-1982 disclose the use of a GeSbTe alloy thin film as a recording layer. No. 237990 "Optical Recording Medium" similarly discloses the use of an InSbTe alloy thin film as a recording layer. In this case, when recording is performed using these optical recording media, the recording layer is irradiated with light for a short period of time to melt the irradiated portion of the recording layer, and then, after the light irradiation, it is rapidly cooled by thermal diffusion. , an amorphous spot is formed and recording is performed.

Conversely, in order to erase a record, the amorphous portion is irradiated with light and heated in a range below the melting point and above the crystallization temperature to crystallize the recording layer, thereby erasing the record.

[0005] Furthermore, GeSb forming these recording layers
Te-based alloy thin films and InSbTe-based alloy thin films are usually formed by sputtering, but the purity of the GeSbTe-based alloy target material or InSbTe-based alloy target material is nominally 99.9 (3N) to 99.99 (4N).
Since it is as low as wt %, it also contains several atomic % of the impurity oxygen element, and therefore the formed recording film usually contains a large amount of impurities such as oxygen, silicon, and tungsten.

Furthermore, as the number of rewrites increases, that is, the number of phase changes between the liquid phase and the solid phase increases, impurities contained in the recording medium segregate and concentrate near the interface between the recording area and the non-recording area. This leads to the generation of coarse crystal grains around the recording point, which causes a decrease in the erasing rate.

The present inventors believe that this cause can be explained by the principles of the natural solidification method and band purification method (zone purification method) in metal refining technology. That is, in general, in the band purification method, when the base material begins to solidify, impurities are expelled from the solid phase to the liquid phase according to the segregation coefficient of the impurities with respect to the base material, and the impurities gather at the solid-liquid interface. If this operation is repeated several times, the impurity concentration at the solid-liquid interface will increase.

Similarly, in an optical disk, when recording points are formed on the optical disk, impurities gather at the interface between the liquid phase melted by light irradiation and the solid phase which is the non-recording portion. In addition, since the recording points of optical discs are made amorphous by rapid cooling and solidification, the distance that impurities expelled into the liquid phase diffuse through the liquid phase is extremely short, and the amorphous material formed by rapid cooling and solidification is The impurity concentration at the interface between the recording point and the non-recording point becomes high. Furthermore, optical discs are normally subjected to repeated recording and erasing operations tens of thousands to millions of times, and impurities at the interface between amorphous recording points and non-recording points become further concentrated and become nuclei for generating coarse crystal grains. considered to be a thing.

[0009]

[Problems to be Solved by the Invention] As mentioned above, since the conventional recording film for optical discs is formed by sputtering using a target material with a purity of 3N to 4N, there are many impurities in the recording film. As the number of rewrites increases, impurities become concentrated at the interface between the recorded point and the non-recorded area, becoming crystal growth nuclei and generating coarse crystal grains, resulting in a decrease in the number of rewrites and erasure rate.

[0010]Therefore, it has been desired to develop an optical disc recording film containing less impurities, but the conventional target manufacturing technology has a limit of 99.99 wt% (4N).

[0011]

[Means for Solving the Problems] In order to solve the problems, the present inventors conducted intensive research and found that a GeSbTe-based or InSbTe-based target with a purity of 99.999wt% (5N) or more for use in sputtering film formation was used. The present invention has been made possible by discovering that a recording film with good rewriting characteristics can be formed by similarly increasing the purity of the recording film itself to 99.999 wt % or higher.

[0012] That is, the first object of the present invention is to provide a substrate with the formula Gex Sby Tez (where 1≦x≦55
, 3≦y≦80, 20≦z≦65, and x,
y and z each represent atomic percent), and the purity of these compositions is 99.
The second object is to provide an optical recording medium characterized in that it consists of 999 wt% (5N) or more;
0, 10≦y≦80, 20≦z≦75, and x
, y, and z each represent atomic percent), and the purity of these compositions is 99%.
．． The third purpose is to provide an optical recording medium with a purity of 999 wt% or more (5N); the third purpose is to form a heat insulating layer on a substrate in advance, and then use a target material with a purity of 99.999% or more to form a Gex Sby Tez (However, 1≦x≦
55, 3≦y≦80, 20≦z≦65) or In
x Sby Tez (However, 1≦x≦80, 10≦
y≦80, 20≦z≦75) An optical recording medium characterized in that a recording layer is formed, and then a heat insulating layer and a cooling layer are formed on the recording layer, and then an annealing treatment is performed. An object of the present invention is to provide a manufacturing method.

[0013]

[Function] In general, as the number of rewrites increases in the recording film of a phase change optical disk, impurities in the recording film segregate at the interface between the recording point and the non-recording area, become concentrated, and cause the generation of coarse crystal grains. This is causing the rate to decline.

As mentioned above, in order to prevent as much as possible the deterioration of rewrite characteristics due to the increase in the number of rewrites, the method of the present invention uses a GeSbTe alloy target material used when forming a recording film on an optical disk substrate by sputtering. Or, the purity of the InSbTe alloy target material is 99.99.
The content is 9wt% (5N) or more.

The recording layer formed using this target material contains almost no impurities such as oxygen atoms, silicon, or tungsten compared to those using conventional materials, and the purity of the obtained recording layer itself is 99%. Since it is .999wt% or more, the segregation and concentration of impurities at the interface between the recording point and the non-recording area due to the increase in the number of rewrites is prevented as much as possible, and the generation of coarse crystal grains around the recording point is reduced, resulting in an increase in the number of rewrites. It was confirmed that the optical disc recording medium had an excellent erasing rate.

It has been confirmed through experiments by the inventor that the target material used in the method of the present invention has the following purity of 99.999 wt % or more. That is, as a Gex Sby Tez alloy target material, 1≦x≦55, 3≦y≦80, 2
Alloys in the range 0≦z≦65 are preferred, while In
x Sby Tez alloy target material:
Alloys in the ranges of 1≦x≦80, 10≦y≦80, and 20≦z≦75 are preferable.

[0017] Hereinafter, the present invention will be explained in detail using examples.

[0018]

[Example 1] First, a 110 nm Z film was formed on a 76 mm x 26 mm x 1.2 t glass substrate under an Ar pressure of 1 Pa.
An nS-SiO2 mixed heat insulating layer is formed by sputtering, and then Ge2S with a purity of 99.999 wt% is formed on the heat insulating layer.
b3 Te4 Composition ratio Ge2 Sb3 from target material
A recording layer made of Te4 was formed to a thickness of 30 nm. Next, 190 nm of ZnS-SiO was deposited on the recording layer.
2. An optical recording medium was obtained by forming a mixed heat insulating layer and a 30 nm Au cooling layer thereon in the same manner.

When the obtained optical recording medium was annealed at 200° C., the recording layer was crystallized and the reflectance increased to twice its initial value. In addition, thermal rapid annealing is used to form shallow diffusion layers in the manufacturing process of semiconductor integrated circuits.
When applied to crystallization), the recording layer was crystallized over the entire surface of the substrate, and the reflectance increased to twice its initial value.

Next, a static tester (wavelength 83
A recording/erasing test was conducted using a lens with a diameter of 0 nm and a numerical aperture of 0.5). In this case, the recording pulse was 15 mW, 100 ns
ec, the erase pulse was 6 mW, 100 nsec, and the reproduction was performed under the conditions of 0.7 mW. 10
00,000 recording/erasing cycles were possible. The rate of change of the reflectance signal after 1 million cycles was almost the same as that at the initial stage, with no characteristic deterioration, and the occurrence of coarse crystal grains around the recording points was extremely small. In addition, this optical recording medium was subjected to high temperature and high humidity conditions of 80° C. and 85% RH.
After being left for 1,000 hours, the reflectance remained unchanged from the initial state.

[0021]

[Example 2] First, reactive sputtering was performed on a 76 mm x 26 mm x 1.2 t glass substrate in N2 gas at 1 Pa using an aluminum target material.
A 00 nm thick AlN heat insulating layer was formed. Next, purity 99
．． A recording layer having a composition ratio of In33Sb34Te33 and a thickness of 300 nm was formed using a 999 wt % In33Sb34Te33 target material. Further, an AlN heat insulating layer with a thickness of 100 nm was formed on this recording layer, and an Au cooling layer was similarly formed on this heat insulating layer to obtain an optical recording medium.

Using the obtained optical recording medium, a recording/erasing test was conducted using a static tester (wavelength: 830 nm, numerical aperture: 0.5) under the conditions shown in Example 1. - Erasing cycles are possible, and the change rate of the reflectance signal after 1 million cycles was almost the same as the initial one, and there was no characteristic deterioration.

Furthermore, the occurrence of coarse crystal grains around the recording point was extremely small, and even though this optical recording medium was left under high temperature and high humidity conditions of 80° C. and 85% RH for 2,000 hours, the reflectance did not change from the initial state. There wasn't.

[0024]

[Example 3] The target material shown in Example 1 was
An optical recording medium was produced under the same conditions except that Sb60Te28 material (5N) was used.

[0025] When the obtained optical recording medium was evaluated in the same manner as in Example 1, it was found that 1 million recording/erasing cycles were possible, and the rate of change in the reflectance signal after 1 million cycles was the same as that at the initial stage. There was no characteristic deterioration, and the occurrence of coarse crystal grains around the recording points was extremely small. Similarly, high temperature
The reflectance after the high humidity test was unchanged from the initial value.

[0026]

[Example 4] The target material shown in Example 2 was
An optical recording medium was produced under the same conditions as in Example 2 except that Sb60Te35 material (5N) was used.

[0027] When the obtained optical recording medium was evaluated in the same manner as in Example 2, it was found that 1 million recording/erasing cycles were possible, and the rate of change of the reflectance signal after 1 million cycles was the same as that at the initial stage. There was no characteristic deterioration, and the occurrence of coarse crystal grains around the recording points was extremely small. Similarly, the reflectance after the high temperature/high humidity test was unchanged from the initial value.

[0028]

[Comparative Example 1] The target material shown in Example 1 was
Sb3 Te4 composition with purity of 99.9wt% (3N)
An optical recording medium was produced under the same conditions except that the same conditions were used.

When the obtained optical recording medium was evaluated in the same manner as in Example 1, the reflectance signal began to fluctuate after 100,000 recording/erasing cycles, and there were many coarse crystals that caused noise near the recording point. It was confirmed that particles were generated. Furthermore, the reflectance after the high temperature/high humidity test was reduced by 15% compared to the initial value.

[0030]

[Comparative Example 2] The target material of Example 2 was In33Sb
An optical recording medium was produced under all the same conditions except that the 34Te33 composition was replaced with one having a purity of 99.9 wt% (3N).

When the obtained optical recording medium was evaluated in the same manner as in Example 2, the reflectance signal began to fluctuate after 150,000 recording/erasing cycles, and many coarse crystals that caused noise were found near the recording point. It was confirmed that particles were generated. Furthermore, the reflectance after the high temperature/high humidity test was reduced by 20% compared to the initial value.

[0032]

[Comparative Example 3] The target material of Example 1 was changed to Ge12Sb.
An optical recording medium was produced under all the same conditions as in Example 1, except that the composition was replaced with one having a 60Te28 composition and a purity of 99.9 wt% (3N).

When the obtained optical recording medium was evaluated in the same manner as in Example 1, it was found that the reflectance signal began to fluctuate after 100,000 recording/erasing cycles, and there were many coarse crystals that caused noise near the recording point. It was confirmed that particles were generated. Furthermore, the reflectance after the high temperature/high humidity test was reduced by 20% compared to the initial value.

[0034]

[Comparative Example 4] The target material of Example 2 was changed to In5Sb
An optical recording medium was produced under all the same conditions as in Example 2, except that the composition was replaced with one having a 60Te35 composition and a purity of 99.9 wt% (3N).

When the obtained optical recording medium was evaluated in the same manner as in Example 2, it was found that the reflectance signal began to fluctuate after 100,000 recording/erasing cycles, and there were many coarse crystals that caused noise near the recording point. It was confirmed that particles were generated. Furthermore, the reflectance after the high temperature/high humidity test was reduced by 30% compared to the initial value.

[0036]

Effect of the invention: According to the method of the present invention, 99.999wt%
By producing an optical recording medium in which a recording layer is formed by a sputtering method using a GeSbTe alloy target material or an InSbTe alloy target material of (5N) or more, (1) the erasing rate is high and there is little unerased material; 2)
Even if recording and erasing is repeated many times, recording sensitivity may decrease.
(3) There is no decrease in playback signal strength or increase in signal noise, and extremely excellent recording, playback, and erasing characteristics; and (3)
Optical recording media with excellent properties such as improved weather resistance against high temperatures and high humidity can now be obtained by a simple method.

Claims (3)

[Claims] Claim 1: On the substrate, the formula Gex Sby Tez
(However, 1≦x≦55, 3≦y≦80, 20≦z
≦65, and x, y, and z each represent atomic %), and the purity of these compositions is 99.999 wt% (5N) or more. optical recording medium. 2. On the substrate, a compound having the formula Inx Sby Tez
(However, 1≦x≦80, 10≦y≦80, 20≦z
≦75, and x, y, and z each represent atomic percent), and the purity of these compositions is 99.999 wt% (5N) or more. optical recording medium. [Claim 3] A heat insulating property is formed on the substrate in advance, and then a target material with a purity of 99.999wt% (5N) or higher is used to conduct Gex Sby Tez (where 1≦x≦
55, 3≦y≦80, 20≦z≦65) or In
x Sby Tez (however, 1≦x≦80, 10≦y
≦80, 20≦z≦75), and then a heat insulating layer and a cooling layer are further formed on the recording layer, and then thermal rapid annealing treatment is performed. Method of manufacturing media.