JPH0253239A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To manufacture the medium simply with high accuracy by forming a recording layer on a substrate by sputtering an alloy target having uniform crystalline orientation. CONSTITUTION:The recording layer 3 is formed by sputtering the alloy target 1 having crystalline orientation comprising anisotropic crystal such as AS2Te3, Bi2Te3 and Sb2Te3. The film as formed is amorphous, but by heat treatment, it crystalizes to have the same crystalline orientation as that of the target. Namely, when the target 1 has a c-axis orientation parallel to its sputtering surface, the obtained film on the substrate 2 is c-axis oriented parallel to the surface of the film. When the target is c-axis oriented perpendicular to the sputtering surface, the obtained film is also c-axis oriented perpendicular to the film surface. Thereby, such an optical recording medium excellent in repeatability of recording/erasing, long-term stability of recorded state and fast erasability can be manufactured efficiently with high accuracy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing an optical recording medium that records information using the heat mode or photon mode of light such as a laser beam. It is possible to record and erase information at high speed by reversibly causing amorphization and crystallization in an optical recording medium, and the long-term preservation of recorded information is excellent, h) 1) The present invention relates to a method for manufacturing an optical recording medium that has excellent repeatability of recording and erasing and also excellent reproducibility of these characteristics.

(Blank below) [Prior art] Recently, with the development of compact and high-performance lasers, research in the field of technology that uses laser beams, that is, so-called optical-related technologies such as optical communication and optical recording, has progressed rapidly. Some of them have been put into practical use. In particular, optical recording, in which information is recorded and erased by irradiating a thin film-like medium on a substrate with a focused laser beam to cause structural changes such as perforation or amorphous-crystalline transition in the thin film, is capable of recording and erasing information at high density. - It is attracting attention as a new technology that enables large-capacity recording. The material of the thin film medium used for these recordings is usually Te or Se.
Chalcogen such as Bi, Sn.

Multi-component materials containing metals such as Pb, Sb, and In and semiconductors such as Ge are used, and these are deposited onto a substrate with a film thickness of 10 to 1100 nm by sputtering or vacuum evaporation.
It is formed as a thin film of n.

Furthermore, among the above-mentioned technologies, optical recording based on structural changes such as amorphous-crystalline transitions is capable of recording and erasing information many times in principle, and is suitable as a so-called rewritable optical recording medium. It is expected to have a wide range of uses. In this optical recording, recording is performed by heating a thin film recording medium with a laser beam above its melting point and rapidly cooling it to make the laser irradiated area amorphous. The laser irradiation conditions for recording and erasing, which are heated to a temperature higher than the crystallization temperature and annealed to restore the crystalline state and perform erasing, and the stability against repetition of the recording and erasing.
The long-term stability of the recording state strongly depends on conditions such as the composition and structure of the recording film.
New proposals and research regarding recording films, as seen in Japanese Patent Application Laid-Open No. 62-222443, are being actively conducted. In this way, various recording film materials and methods for producing them have been studied, but the goal is to maintain the stability of the signal level in the recorded state and erased state against repeated recording and erasing. is the largest one.

[Problems to be Solved by the Invention] However, in the past, there were the following problems.

A rewritable optical recording medium must operate stably even after many repeated recording and erasing operations.
For repetitions of 106 times or more, the levels of the recording signal and the erasing signal are arbitrarily defined, and the levels of the two signals are reversibly reproducible and the information is 0N-OF.
F must be done. However, the level of the erase signal is generally unstable, and as recording and erasing are repeated, the value of the erase signal gradually changes, resulting in a problem in that the S/N ratio decreases significantly.

This is because the amorphous state in the recorded state is a state in which the atomic arrangement is completely randomized, and it is easy to obtain a uniform state by quenching by rapid heating and cooling with a laser pulse, whereas in the erased state As a crystal, various states occur due to slight fluctuations in the laser irradiation conditions.
-It is thought that this is because it is difficult to define it intentionally.

To address these problems, various studies have been conducted on the composition of recording films, particularly on the composition of Te or Se-based alloy films, but the recent trend is to simply control the composition of the alloy. There is a growing consensus that this is insufficient and that further performance improvements cannot be expected unless other conditions are considered. Also, along with this,
There is also a need for more precise control in the manufacturing method of recording media. Research and development competition in these fields among domestic and foreign research institutions is becoming more intense every day.

Under these circumstances, the present inventors have developed a thin film material called MORP.
Focusing on hology, the inventors discovered that the crystal orientation of the recording film is deeply involved in the characteristics of the medium, as described in Japanese Patent Application No. Sho [i2-171284]. That is, IIlo of the recording film
This study shows that by controlling the rhology, especially the crystal orientation, it is possible to improve not only the stability of repeated recording/erasing characteristics but also the recording life, high-speed erasing performance, etc. However, accurately and easily controlling crystal orientation in terms of manufacturing technology is a fairly advanced technology and is an important issue that requires further study.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an optical recording medium that can be manufactured with higher precision and in a simpler manner by solving the problems related to the method of manufacturing a recording medium as described above.

[0! To achieve the above object, the present invention provides a method for manufacturing an optical recording medium in which a recording layer whose state changes due to a temperature increase due to previous absorption or absorption of light is provided. Specifically, the method includes a step of sputtering an alloy target having a different crystal orientation to form a recording layer on a substrate.

In general, a thin film produced by sputtering an alloy target has an amorphous or microcrystalline aggregate structure;
The orientation of each crystal grain is random and not uniform.

A film obtained by heat-treating an amorphous thin film to crystallize it is also generally an aggregate of microcrystals in which crystal grains are randomly oriented. However, recent basic research into the thin film formation mechanism has revealed that in sputtering, the crystal structure of the sputtered target itself may be incorporated into the structure of the film deposited on the substrate.

That is, a film produced by sprinkling a target with a certain crystal structure has a certain degree of relationship with the structure of the optical target, and may have the same crystal structure. Even if the newly produced film is amorphous, the film that is crystallized by heat treatment often has the same crystal structure as the original target. The reason for this is not yet clear, but one hypothesis is that during sputtering, the target evaporates not as a single atom but as a cluster, or that in the case of a material with a highly directional atomic arrangement, the directionality is caused by a film forming from within the target. For example, it may be transplanted directly into the plant.

Now, for optical recording media, especially rewritable optical recording media, it is desired that the crystallized state be uniform and have a structure with good reproducibility. This crystalline state is not an aggregation of random microcrystals, but one with good crystal orientation is excellent as an optical recording medium, as described in Japanese Patent Application No. 62-171284. As described in the same specification, one way to obtain a thin film with good crystal orientation is to manufacture it as a multilayer film, but as a simpler and more productive method, It is conceivable to utilize the crystal structure and crystal orientation of the target itself.The present inventors focused on this point, and used an alloy target with good crystal orientation as a base material and sputtered it to form an optical recording medium. When the recording layer was formed and the characteristics of the recording medium were evaluated, it was found that it exhibited extremely excellent characteristics.

In the present invention, As2Te, , Bi2Te3. Sb2T
A recording layer was fabricated by sputtering using an alloy target having such crystal orientation as a base material for a material having crystal anisotropy such as e.g. Although the obtained thin films were amorphous in the as-prepared state, it was found that the crystal orientation of the films that were crystallized by heat treatment was the same as that of the base material. In other words, from a target whose C-axis is oriented parallel to the sputtering surface of the target, a film whose C-axis is oriented parallel to the film attachment surface of the substrate, and a target whose C-axis is oriented perpendicular to the sputtering surface of the target. A film with the C-axis oriented perpendicular to the film adhesion surface of the substrate could be produced. This situation is schematically shown in FIG.

Fig. 1(A) shows a case where a recording layer 3 is formed on a substrate 2 by sputtering an alloy target 1 with the C-axis oriented perpendicular to the sputtering surface, and Fig. 1(B) shows a case where the C-axis is oriented parallel to the sputtering surface. This figure shows a case where a film is formed using an oriented alloy target 1.

These clothes also have excellent characteristics as recording media, and it was confirmed that they operate extremely stably when recording and erasing data is repeated. This is either recording or erasure,
This is based on the fact that the crystalline state corresponding to deafness is defined as a homogeneous state with good orientation and good reproducibility.

In addition, among the above two types of orientation, the one with C@ orientation parallel to the substrate surface has the stability of the amorphous state obtained by making it amorphous (corresponding to recording in recording erasing). On the other hand, when the C-axis is oriented perpendicular to the crystal plate surface, laser heating crystallization of the amorphous state (usually equivalent to erasing of recorded data) occurs extremely quickly, resulting in the so-called high-speed erasing property. It was found to be superior in terms of

[Example] This will be explained below using specific examples.

A recording medium having a 5b-Te alloy film as a recording layer was produced by cross-sectional RF sputtering. 1.2mm thick as a substrate
Glass substrate and 5 inch diameter grooved polycarbonate.
A disk substrate was used. The configuration of the medium is ZnS7:/Darcoat II! (thickness 10100n/5b-Te alloy film (
Thickness 10100n/znS overcoat @ (thickness 101
00n, and is further tightly sealed with an ultraviolet curing resin. As a sputtering target for forming a 5b-Te alloy film, a target with the C-axis oriented perpendicular to the target layer (A) as shown in Figure 1(A) was used.
rGas pressure 9 x 10-'Pa, RF power 100
Sputtering was performed under W(7) conditions. Although the produced film was amorphous in the as-prepared state, it was subjected to heat treatment for 200'C11o to crystallize it, and then evaluated by X-ray diffraction.

Figure 2 shows the X-ray diffraction results. As shown in the figure, this film has a C-axis orientation perpendicular to the substrate surface. We conducted an experiment on erasing records in a stationary system using a focused laser beam on this sample. As a laser, an Al1 GaAs laser diode (wavelength: 830 nm) converged to a diameter of 1.2 .mu.- was used. As a result, the recording medium of this example has 1
Recording with 8 mW, 30 ns laser light (amorphous), 1
It was found that it can be erased (crystallized) with a laser beam of 0 mW and 50 nS. In addition, it operates extremely stably even with repeated recording and erasing, and the recording (amorphous) state and erasing (crystalline) state are extremely stable.
Excellent reproducibility of reflected signal level in both conditions, 1
It was found that 0' or more repetitions are possible.

For media on polycarbonate disks, disk characteristics were also evaluated using a rotating measuring device. As a result, in the stationary system evaluation described above, the erasure time was 50n.
Reflecting the short length of s, it was confirmed that high-speed erasing is possible in terms of disk characteristics, that is, at a linear speed of 20i/
At high speed rotation of s, the C (carrier) level decreases by 4 with one erase beam irradiation for recording C/N of 53 dB.
We were able to achieve over 0dB. The signal changes during repeated recording and erasing are stable, and as shown in Figure 3, both the C level during recording, the residual C level during erasing, and the N (noise) level are stable against repetitions of 10' or more. I found that it works.

Example 2 A recording medium was produced by RF sputtering under the same conditions as in Example 1. However, in this example, the sputtering target for forming the 5b-Te alloy film was used as shown in Fig. 1(B).
The C-axis was oriented parallel to the target plane as shown in FIG. The obtained film was still amorphous in the as-prepared state, but after crystallization by heat treatment at 300°C for 10 minutes, it was evaluated by X-ray diffraction.
As shown in FIG. 4, it was found that the C-axis was oriented parallel to the substrate surface.

A stationary recording/erasing experiment was conducted on this sample using a convergent laser beam as in Example 1, and it was found that the recording medium of this example was capable of recording (recording) using a 18 mW, 30 ns laser beam.
It was found that it was possible to erase (crystallize) with a laser beam of 10 mW and 100 ns. Furthermore, it operated stably even when recording and erasing was repeated, and it was possible to repeat recording and erasing more than 10' times.

In the rotation system evaluation for polycarbonate disk media, the reduction in C level by one erasing beam irradiation was more than 30 dB for a recording C/N of 51 dB in high-speed rotation at a linear velocity of 20 m/s. High-speed erasing was possible. Regarding the repeatability of recording and erasing, as shown in Figure 5, it operated extremely stably, and the C level, residual C level, and N level remained stable with almost no fluctuation after 10' repetitions. .

For comparison, the disk characteristics of a medium on a polycarbonate disk manufactured in the same manner as in Example 1 using a non-oriented alloy target were measured using a rotating measuring device. The results are shown in Figure 6. The recording layer formed by sputtering a non-oriented target is non-oriented, so the crystallization state is not determined uniquely, and the level of residual carriers after erasing varies. . Furthermore, since the erased state is not unique, the noise level increases as recording and erasing are repeated.

As mentioned above, the alloy films obtained from the 5b-Te alloy targets whose C-axes are oriented perpendicularly or parallel to the target surface to be sputtered have their C-axes oriented perpendicularly or parallel to the substrate surface, and the structure of the base material It was a reflection of the Since the recording medium in which each alloy film is used as a recording layer has a constant reflected light level during crystallization, the signal level during erasing is constant, and therefore, the repeatability of recording and erasing is excellent. Samples with crystal orientation generally have a crystallization rate higher when heated to a high temperature by laser heating than samples whose recording layer is a collection of random microcrystals without crystal orientation; therefore, this is shown in Examples. It was possible to erase it at high speed.

Comparing the performance between samples with two types of orientation, the one with the C-axis oriented perpendicular to the substrate surface (Figure 1 (A)) has a higher crystallization rate, whereas the one with the C-axis oriented parallel to the substrate surface has a higher crystallization rate. The one shown in FIG. 1 (B) had a higher crystallization temperature and was stable in an amorphous state. The cause of this is not clear, but it is probably c! Within the (ab1 plane perpendicular to This is presumed to be due to a phenomenon based on crystal anisotropy.

Incidentally, the same study as in the above two examples was also conducted on Bi2Te5°8s and Te, which have the same type of structure as Sb and Te. As a result, it was verified that an alloy film with crystal orientation was formed from an alloy target with crystal orientation, and the performance as a recording medium was excellent in repeated recording and erasing properties.

The difference between each material is the crystallization rate of Bi2
Te, > Sb2Te, > As2Te3, and in terms of amorphous lifetime, As2Te, > Sb, Te3 > B
A difference of 12Te= was observed. These are crystal bonds,
Alternatively, this may be due to differences in the strength of bonds between atoms.

Furthermore, Bi2Te3. Sb2Te3. As2Te
Ge, Sn, and P are added as a third element to each of the three materials in 3.
A similar study was conducted on a material to which 20 atk of at least one element selected from the group consisting of Sb, As, Sb, Bi, and In was added. As a result, even in material systems to which these elements are added, the basic crystal orientation of the two base materials remains unchanged in the alloy film obtained by sputtering the alloy target. This was confirmed. Also, the performance as a recording medium is excellent in the repeatability of recording and erasing.
It has been found that the medium performance is the same as the two base elements, and that depending on the type of added element, the media performance, such as an improvement in the amorphous lifetime and an improvement in the erasure (crystallization) speed, can be further improved.

That is, when elements with strong covalent bonding properties such as As, Ge, and Sb are added, the crystallization temperature is significantly improved and the amorphous life is lengthened (for example, in the case of Ge-added Sb2Te:+, the crystallization temperature is 350 ℃, and the lifetime of amorphous X at room temperature is estimated to be more than 30 years), whereas Sn, Pb, and B
Adding elements with strong metal bonding properties such as i and In improves high-speed erasure (high-speed crystallization) (for example, in the case of Pb-added Sb2Te3, laser heating crystallization of amorphous marks is possible at 12 mW and 40 ns). In terms of disk characteristics, C
It was found that a level reduction of 40 dB was achieved.
Note that the concentration of the additive element is not limited to that in this example, and it is possible to add up to about 30 at.0 within a range where the alloy can be used as an optical recording layer.

[Effects of the Invention] As described above in detail with reference to Examples, the present invention provides optical recording with excellent media performance such as repeatability of recording/erasing, long-term stability of recorded state, and high-speed erasing performance. A medium can be manufactured efficiently and with good reproducibility. The present invention has further investigated the manufacturing method of high-performance optical recording media having crystal orientation, and obtained extremely good results when an oriented alloy target was used as a sputtering alloy target. This method is low cost and suitable for mass production, and considering the recent situation where research and development of optical recording media is significant and commercialization is long-awaited, it is an effective method for achieving high performance of optical disks and optical cards. Its impact is extremely large as it provides a technological breakthrough.

In addition, although the above explanation has been given regarding a device that utilizes an amorphous-crystal transition, the effect of manufacturing a recording layer using a crystal-oriented alloy target is similar to that of a medium that utilizes a crystal-crystal transition (2 The same holds true for those that utilize phase changes between crystal structures of seeds or more.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the relationship between the crystal orientation of the base metal target and the film obtained by sputtering it, which is heat-treated and crystallized. Figures 2 and 4 are perpendicular to the sputtering surface and Figures 3 and 5 show the X-ray diffraction peak intensity diagram after crystallization of a recording layer obtained by sputtering a C-axis oriented alloy target, respectively. ζ in optical discs with layers, C level, N level due to repeated recording and erasing,
Figure 6 shows changes in residual C level. Figure 6 is a diagram showing changes in C level, N level, and residual C level due to repeated recording and erasing in an optical disc having a non-oriented recording layer. DESCRIPTION OF SYMBOLS 1... Alloy target, 2... Substrate, 3... Alloy film.

Claims (1)

[Claims] 1) In a method for manufacturing an optical recording medium having a recording layer whose state changes due to absorption of light or temperature rise due to absorption of light, the recording layer is formed on a substrate by sputtering an alloy target having a uniform crystal orientation. 1. A method of manufacturing an optical recording medium, comprising the step of forming.