JP2724183B2 - Manufacturing method of information recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an information recording medium on which information can be recorded / reproduced / erased by optical means. More specifically, the present invention relates to a method for recording / erasing information. The present invention relates to a method for producing an information recording medium having excellent repetition characteristics.

(Prior Art) In recent years, an optical disk capable of recording and reproducing high-density information by using a laser beam accompanying an increase in the amount of information has been actively used. Optical discs include a write-once type, which can be written only once, and a rewritable type, which can erase recorded information and can be used many times. The write-once optical disk is already used mainly as a permanent storage file for documents and images.

However, there is a demand for a rewritable optical disk capable of rewriting information except for applications requiring permanent storage. In such an information recording medium, the number of rewritable repetitions depends on the application, but at least 10
Zero or more times are required. Especially when used in an external memory computer it is needed number of repetitions of ¹⁰⁶ times.

As a rewritable optical disk, the difference in reflectivity and transmittance due to the difference in crystal structure and the magneto-optical method in which information is reproduced using the difference in the polarization plane of reflected light depending on the magnetization direction is used. There is a phase change method for reproducing information by using a phase change method.

Both of the above methods have the following two common points. The first point is that the recording and erasing of information are performed by heating a recording film with a laser beam, that is, a so-called heat mode recording. In the case of the magneto-optical method, information is recorded and erased by changing the magnetization direction of the recording film by applying an external magnetic field while heating the recording film. On the other hand, in the case of the phase change method, recording and erasing of information are performed by changing the crystal structure according to the maximum temperature reached during heating and the cooling rate during cooling. In any case, there is no change to the heat mode recording in which recording / erasing is performed by heating the recording film. The second common point relates to the configuration of the recording medium used. In other words, the recording medium used in any of the methods is made of a different material, but is composed of at least a substrate, a recording film, and a protective film made of a dielectric, and the protective film is provided in contact with the recording film. In some cases, a reflective layer may be provided. As a typical layer structure, there can be mentioned a structure in which a protective film 2, a recording film 3, and a protective film 4 are sequentially laminated on a substrate 1 as shown in FIG. Here, the protective film serves to prevent thermal deformation of the substrate and deformation of the recording film at the time of repeated recording / erasing, and also to prevent oxidation of the recording film. In particular, in the case of the phase change method, a heat-resistant protective film is required in order to temporarily heat the recording film to a high temperature equal to or higher than the melting point during recording or erasing.

From the above two common points, at least the following characteristics are required for the protective film used in any of the methods.

Heat resistance No thermal damage during heating during recording and erasing Low thermal conductivity Low heat conductivity to some extent so that heat generated is dissipated much and high laser power is not required for heating Heat cycle property In repeated recording and erasing Changes in thermal, mechanical, mechanical properties, etc. are as small as possible Low moisture permeability Low moisture permeability to prevent corrosion of the recording film Especially in the case of the phase change method, the crystal structure that can be formed depends on the cooling rate after heating the recording film In addition, since the recording film is once heated to a temperature higher than the melting point at the time of recording or erasing, a protective film having excellent heat resistance and heat cycle resistance is required.

Of the above characteristics, and depends mainly on the material used, and greatly depends on the film formation method together with the material.

(Problems to be Solved by the Invention) Generally, a protective film can be formed by a vapor deposition method, a sputtering method, or the like, but the sputtering method is suitable for mass production. As a discharge gas used for the sputtering method, Ar gas is most often used in terms of sputtering rate and cost.

However, in the case of using a protective film formed by a conventional sputtering method using Ar gas, there is a problem that if recording and erasing are repeated many times, the characteristics are deteriorated and cannot be put to practical use. In particular, in a phase change type recording medium, the characteristic deterioration due to repetition was a serious problem. More specifically, when recording and erasing are repeated, erasure becomes insufficient, and a phenomenon occurs in which a previously recorded signal has a large unerased residue.

The present inventors have investigated the cause, and inferred that as recording and erasing are repeated, the protective film becomes dense due to a kind of sintering action, and the thermal properties change. In particular, it is considered that the thermal conductivity increases with densification as the number of repetitions increases, thereby shortening the time that the recording film is kept at a temperature higher than the temperature required for its crystallization, resulting in insufficient erasing. .

Also, along with the characteristic deterioration due to the repetition of the above, the protective film formed by the conventional sputtering method becomes a film with many holes because a gas such as Ar or oxygen is taken into the film at the time of film formation,
As a result, it was not satisfactory in terms of preventing corrosion of the recording film.

(Means for Solving the Problems) The present invention relates to a method for manufacturing an information recording medium which has solved the above problems, and a method for manufacturing an information recording medium having a recording film and a protective film provided on a substrate. Ar and the protective film
This is a method for producing an information recording medium, wherein a film is formed by a sputtering method using a mixed gas of H ₂ .

50 volume% to 5% by volume as the amount of H ₂ is mixed in Ar gas is preferable.

When performing reactive sputtering as a sputtering gas,
It can further adding oxygen or nitrogen to Ar and H _2. That is, in the case of forming an oxide or nitride protective film using a metal or metalloid target, reactive sputtering with addition of oxygen or nitrogen is faster and more suitable for mass production.

The material that can be used for the protective film is not particularly limited, and includes oxides, nitrides, sulfides, and fluorides of metals and metalloids such as SiO ₂ , Si ₃ N ₄ , ZnS, and MgF ₂ or a mixture thereof. Are widely used.

The recording film is not particularly limited, and a magneto-optical recording film made of a transition metal and a rare earth element, a phase change recording film made of an alloy of Te or Se, a recording film made of an organic dye, and the like are used. The recording film is formed by a vapor deposition method, a sputtering method, a coating method, or the like, and is preferably formed in the same vacuum chamber as the protective film.

(Operation) When a mixed gas of Ar and H ₂ is used, vacancies in the film are removed and the density of the film is improved, so that the change in thermophysical properties due to repetition is small, and the characteristic deterioration can be largely suppressed. Further, since the film is dense, it is possible to prevent moisture and oxygen from entering the inside, and the effect of preventing corrosion of the recording film is great. Furthermore, the internal stress of the film can be reduced as a secondary effect, and the adhesion to the base can be improved.

EXAMPLE A polycarbonate substrate having an outer diameter of 130 mm and a thickness of 1.2 mm was set in a sputtering tank, and after evacuating to 5 × 10 ⁻⁷ Torr, SiO ₂ (100 nm), Ge-Te-Sb recording film (80 nm) , SiO ₂ (1
(00 nm) in that order by sputtering. The sputtering conditions for each layer are as shown in Table 1.

As a comparative example, a sample exactly the same as the example was prepared except that SiO ₂ was sputtered only with Ar gas.

These disks were rotated at 1800 rpm, and the light of a semiconductor laser was condensed and irradiated over a polycarbonate substrate, and the following evaluation was performed.

First, a laser beam was continuously emitted at a position of 60 mm in diameter on the disk for one round of the disk to perform initial crystallization. next
After recording a 2 MHz pulse signal, the C / N ratio was measured. Thereafter, the C / N ratio was measured after an erasing operation was performed by continuously emitting laser light for one round of the disk. FIGS. 2 and 3 show the results of repeating the above recording and erasing. The C / N ratio after the erasure was left unerased.

From Figure 2, but unerased 100 iterations after the comparative example increases after 10 ^four times in the embodiment of Figure 3 also C / N
It can be seen that both the ratio and the rest remain unchanged from the initial stage.

Further, these disks were left under an environment of a temperature of 80 ° C. and a humidity of 80% for 500 hours. In the comparative example, a large number of pinholes were generated and an increase in noise was observed, but in the example, no pinhole was generated and no increase in the noise was observed.

(Effects of the Invention) As described above, according to the present invention, a dense protective film having a high density can be formed, and (1) the characteristic deterioration due to repetition is small (2) the corrosion resistance is high A high information recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the structure of an information recording medium according to the present invention, and FIGS. 2 and 3 are graphs showing the recording / erasing repetition characteristics of a disk of a comparative example and an example, respectively. . 1 ... substrate 2, 4 ... protective film 3 ... recording film

Claims (2)

(57) [Claims] 1. A method for manufacturing an information recording medium having a recording film and a protective film provided on a substrate, wherein the protective film is formed by a sputtering method using a mixed gas of Ar and H _2. Manufacturing method of information recording medium _2. A mixed gas of Ar and H ₂ containing 5% by volume of Ar gas.
_{2. The} method for producing an information recording medium according to claim 1, wherein the mixture is a mixture of 50% by volume of H ₂ gas.