JPH02158936A - Production of information recording medium - Google Patents

Abstract

PURPOSE:To suppress the deterioration in characteristics by repetition and to improve corrosion resistance by forming films by using a gas consisting of He or Ne and by sputtering in the case of producing the recording medium provided with a recording film and the protective films on a substrate. CONSTITUTION:The protective films 2, 4 and the recording film 3 are provided on the substrate 1 to form the recording medium. The gas consisting of the He or Ne is used and the sputtering is executed to form the films in the production of this medium. The holes in the films are removed and the density of the films are improved if the gaseous mixture composed of the He and Ne is used. The change in the thermal properties by repetition is, therefore, lessened and the deterioration in the characteristics is drastically suppressed. Since the dense films are formed, the infiltration of moisture and oxygen into the films is prevented and the corrosion resistance is improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an information recording medium that can record, reproduce, and erase information by optical means. The present invention relates to a method for manufacturing an information recording medium with excellent repeatability.

(Prior Art) In recent years, as the amount of information has increased, optical discs that can record and reproduce high-density information using laser beams have been widely used. There are two types of optical discs: a write-once type, which allows recording only once, and a rewritable type, which allows recorded information to be erased and used many times. Write-once optical discs are already used primarily as permanent storage files for ancient literature and images.

However, for applications other than those that require permanent storage, there is a demand for a rewritable optical disc that allows information to be rewritten. In such an information recording medium, the number of repetitions that can be rewritten varies depending on the application, but is at least 10 times.
Zero or more times are required. In particular, when used as an external memory for a computer, a repetition rate of 10h is required.

Rewritable optical discs use the magneto-optical method, which uses the difference in the polarization plane of reflected light depending on the magnetization direction to reproduce information, and the magneto-optical method, which uses the fact that reflectance and transmittance differ depending on the crystal structure. There is a phase change method for reproducing information.

All of the above methods have the following two points in common. The first point is that information is recorded and erased by heating the recording film with laser light, which is so-called heat mode recording. In the case of the magneto-optical method, information is recorded and erased by heating the recording film and applying an external magnetic field to change the magnetization direction of the recording film. On the other hand, in the case of the phase change method, information is recorded and erased by changing the crystal structure depending on the maximum temperature reached during heating and the cooling rate during cooling. In either case, it is still heat mode recording in which recording and erasing is performed by heating the recording film. The second common point relates to the structure of the recording medium used. That is, the recording medium used in each method is made of different materials, but it is composed of at least a substrate, a recording film, and a protective film made of a dielectric material, and the protective film is provided in contact with the recording film. In some cases, a reflective layer may be provided. As shown in FIG. 1, a typical layer structure includes a protective film 2 and a recording film 3 on a substrate 1.
, protective films 4 are sequentially laminated.

Here, the protective film serves to prevent thermal deformation of the substrate and deformation of the recording film during repeated recording and erasing, as well as to prevent oxidation of the recording film. In particular, in the case of a phase change method, a heat-resistant protective film is required in order to heat the recording film to a high temperature above its melting point during recording or erasing.

From the above two common points, the protective film used in either method is required to have at least the following characteristics.

■ Heat resistance: No heat damage occurs during heating during recording and erasing ■ Low thermal conductivity: Low thermal conductivity to a certain extent so that generated heat is dissipated and high laser power is not required for heating ■ Heat resistance: Recording and erasing Changes in thermal properties, mechanical properties, etc. should be as small as possible during repeated erasing ■ Low moisture permeability Low moisture permeability to prevent corrosion of the recording film Particularly in the case of a phase change method, depending on the cooling rate after heating the recording film The resulting crystal structures are different, and since the recording film is once heated to a high temperature above its melting point during recording or erasing, a protective film with excellent heat resistance and heat cycle resistance is required.

Among the above characteristics, (1) and (2) mainly depend on the material used, while (2) and (2) depend largely on the film forming method as well as the material.

Furthermore, if the recording film is once heated above its melting point and melted during recording or erasing, heat cycle resistance of the recording film itself is also required.

(Problems to be Solved by the Invention) - Recording films and protective films for boat fishing can be formed by vapor deposition, sputtering, etc., but sputtering is suitable for mass production. As the discharge gas used in the sputtering method, Ar gas is most preferred in terms of sputtering rate and cost.

However, when using a protective film formed by the conventional sputtering method using Ar gas, there is a problem that the characteristics deteriorate when recording and erasing are repeated many times, making it impossible to put it into practical use. Particularly in phase change type recording media, characteristic deterioration due to repetition has been a serious problem. Specifically, as recording and erasing are repeated, erasing becomes insufficient, and previously recorded signals remain largely unerased, or bubbles or holes form.

The inventors investigated the cause of this problem and found that as recording and erasing is repeated, the protective film becomes denser due to a kind of sintering effect and its thermophysical properties change. It is thought that the thermal conductivity increases with increasing densification, which shortens the time the recording film is held above the temperature required for its crystallization, resulting in insufficient erasing.

In addition to the characteristic deterioration due to the repetition of the above process, the protective film formed by the conventional sputtering method becomes a film with many pores due to gases such as Ar and oxygen being taken into the film during film formation, resulting in recording problems. It was also not completely satisfactory from the viewpoint of preventing corrosion of the membrane.

Furthermore, if there are minute holes in the recording film, as recording and erasing are repeated, the holes may coalesce and become larger.
It is thought that the particles migrate to the interface between the recording film and the substrate or the protective film, causing phenomena such as bubble generation and pore formation.

(Means for Solving the Problems) The present invention relates to a method for manufacturing an information recording medium that solves these problems, and in a method for manufacturing an information recording medium in which a recording film and a protective film are provided on a substrate, This method of manufacturing an information recording medium is characterized in that film formation is performed by a sputtering method using a sputtering gas made of He or Ne.

The sputtering gas may be only Ile gas, only Ne gas, or a mixed gas with Ar.

Further, when performing reactive sputtering, oxygen or nitrogen can be further added. That is, when forming a protective film of oxide or nitride using a metal or semimetal target, reactive sputtering with addition of oxygen or nitrogen results in a faster film formation rate and is suitable for mass production. Film formation by the above method may be applied only to the recording film or only to the protective film.

There are no particular restrictions on the material that can be used for the protective film, and metal or semimetal oxides, nitrides, sulfides, fluorides, or mixtures thereof, such as 5iOz, 5s3Na, and ZnS 1Mgh, are widely used.

There are no particular limitations on the recording film either (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, etc. are used).

(Function) When a sputtering gas made of He or Ne is used, pores in the film are removed and the density of the film is improved, so that changes in thermal properties due to repetition are small, and property deterioration can be greatly suppressed. Furthermore, the dense film prevents moisture and oxygen from entering the recording film, and has a great effect on preventing corrosion of the recording film. Furthermore, the internal stress of the film is also reduced and its adhesion to the substrate is improved.

A polycarbonate substrate with a diameter of 130 mm and a thickness of 1.2 mm was set in a sputtering tank and heated at 5 x 10-7 Tor.
After evacuation to r, 5iOz (100nm)
, Ge-Te-Sb recording film (80 nm), 5i
Films were sequentially formed by sputtering in the order of Oz (100 nm). The sputtering conditions for each layer are as shown in Table 1.

Table 1 As a comparative example, a sample was prepared which was exactly the same as the example except that all the sputtering was performed using static gas only.

These disks were rotated at 1800 rpm+, and semiconductor laser light was focused and irradiated through the polycarbonate substrate, and the following evaluations were performed.

First, initial crystallization was performed by continuously emitting a laser beam at a location with a diameter of 60 mm on the disk for the circumference of the disk. Next, after recording a 2 MHz pulse signal, the C/N ratio was measured. Thereafter, an erasing operation was performed by continuously emitting a laser beam corresponding to the circumference of the disk, and then the C/N ratio was measured.

The results of repeating the above recording and erasing are shown in FIGS. 2 and 3. The C/N ratio after erasing was taken as the remaining eraser.

From FIG. 2, in the comparative example, the number of unerased items increases after 100 repetitions, but from FIG. 3, in the example, C
It can be seen that both the /N ratio and the unerased area have not changed at all from the initial stage.

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

Further, although a mixed gas of Ar and IIe was used as the sputtering gas, the same effect can be obtained by using a mixed gas of Ar and Ne.

(Effects of the Invention) As described above, according to the present invention, it is possible to form a dense and precise protective film, and (1) there is little deterioration of characteristics due to repetition (2) there is high reliability with high corrosion resistance. It is possible to provide an information recording medium with high quality.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one aspect of the structure of the information recording medium according to the present invention, and FIGS. 2 and 3 are graphs showing the recording/erasing repetition characteristics of the disks of the comparative example and the example, respectively. . 1...Substrate 2.4...Protective film 3...Recording film Patent applicant Asahi Kasei Industries, Ltd. First factor

Claims (1)

[Claims] 1. A method for manufacturing an information recording medium in which a recording film and a protective film are provided on a substrate, characterized in that the film is formed by sputtering using a gas consisting of He or Ne.