JPS6224455A - Production of optical disk - Google Patents

Abstract

PURPOSE:To improve the adhesiveness between a resin substrate and substrate protective film by stripping the substrate coated with a resin curable by UV rays from a stamper in the half cured state then irradiating UV rays thereto while depositing a material for forming the substrate protective film by evaporation thereon to cure the resin. CONSTITUTION:The resin 2 curable by UV rays is coated on the substrate 1 by a spin coating method; thereafter the stamper 3 on which pregrooves are die-molded is brought into press contact therewith and the UV rays 4 are uniformly irradiated to the resin from the substrate 1 side, then the stamper 3 is detached from the substrate 1. Although the lower side of the resin 2 is thoroughly cured, the part adhered to the stamper 3 is imperfectly cured. The substrate 1 is then set to an electron beam vapor deposition machine and SiO2 is deposited thereon by electron beam evaporation; at the same time, UV rays are irradiated thereto from an IR lamp. The curing is thereby executed in the state of incorporating the SiO2 into the resin and the substrate protective film 5 is formed without making a distinct boundary between the substrate and the protective film, by which the generation of exfoliation and crack is obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [1 Already Required] A method for manufacturing an optical disk, in which an optical disk substrate coated with a semi-cured ultraviolet curable resin is cured by irradiating ultraviolet rays while depositing a substrate protective film.

[Industrial application field]

The present invention relates to a method for manufacturing an optical disc with improved adhesion between a substrate and a substrate protective film.

An optical disk is a memory that records high-density information using laser light, and has excellent features such as a large recording capacity, non-contact recording and reproduction, and being unaffected by dust.

In other words, the laser beam can be narrowed down to a small diameter of about 1 μm by the lens, and therefore 1 μm in diameter.
The area required for recording bit information is only about 1 μm2.

Therefore, compared to the magnetic disk or magnetic tape, which requires an area of several tens to several hundreds of micrometers to record one bit of information, the area is much smaller than that of a magnetic disk or magnetic tape, and therefore, large-capacity recording is possible.

The present invention relates to a method of manufacturing an optical disc using a 't3-mei resin substrate.

[Traditional technique (nei)]

Optical discs are made of transparent resin such as polymethyl methacrylate (abbreviated as PMM8) or polycarbonate-1 (abbreviated as 1) C), or glass, and are coated with a transparent material such as silicon dioxide (SiO2). A recording layer is formed through a substrate protective film, and a protective film is further coated on top of the recording layer.

Information is recorded and reproduced using a laser beam that projects the recording layer through the substrate, taking advantage of the fact that the reflectance varies depending on the presence or absence of recorded information.

As mentioned earlier, there are two types of disk substrates: resin and glass, but the latter is fragile and expensive, so resin is generally used except for those for special purposes. ing.

Now, recording and reproducing information is performed by projecting a laser beam onto a pregroove (guide groove) with a width of about 0.6 μm provided on the disk substrate, but this pregroove is provided directly on the disk substrate. There are two types: one type, and another type in which a resin is coated on a disk substrate and the resin is formed.

In other words, the former is formed by casting resin onto a stamper on which pre-grooves are pre-formed, while the latter is formed by coating a flat resin substrate with ultraviolet curing resin using a method such as a spin cord method. The stamper is then pressure-bonded, and in this state, ultraviolet rays are irradiated from the substrate side to cure the stamper, and the stamper is peeled off from the stamper.

Comparing these two pregroove substrates, the latter has fewer defects and is superior.

Optical discs are produced by coating such a pregroove substrate with a substrate protective film made of silicon dioxide (SiOz) to a thickness of 200 to 500 layers using a method such as electron beam evaporation, and then coating a recording layer on top of this to a thickness of 300 to 500 layers. It is made by forming a protective film on top of the protective film.

Here, the reason why the recording layer is provided on the pregroove substrate through the substrate protective film made of Si02 is that the recording layer is composed of tellurium selenium (Te-5e) + tellurium germanium (Te-Ge), etc. Regarding read only memory (Read Only Memory), if a recording layer is formed directly on a resin substrate (for example, a P?ll'lA substrate), the laser spot will be generated on the recording layer due to the low softening temperature of PMMA. When drilling holes using irradiation, it is not possible to make a clean hole.

Therefore, a glassy Si02 layer is provided on the PMMA to thermally insulate it from the recording layer.

However, since the resin substrate such as PMMA and the SiO2 layer have different coefficients of thermal expansion, there is a problem that the adhesion is poor and peeling easily occurs.

In other words, the coefficient of thermal expansion of resin such as PMMA is 2 to 10X.
The coefficient of thermal expansion of Si02 is 0.5 Xl0-6/'C, which is about two orders of magnitude smaller than that of IO-5/'C.

Therefore, an optical disk in which a recording layer is formed on a SiOz layer has a problem in that it is likely to peel off from the resin substrate due to temperature fluctuations during use.

One possible way to improve adhesion is to perform vapor deposition while heating the substrate, but this is difficult because resins such as PMMA have a low softening temperature, and ion blating is a method to obtain sufficient adhesion. However, there is a problem that the vapor deposited film formed by this method is highly distorted and cracks appear after the film is formed.

[Problems to be solved by the invention] As described above, the resin substrate on which the optical disc is formed and the S
The substrate protective film made of iO□ does not have sufficient adhesion, which impairs the reliability of the optical disc.

Therefore, the problem is how to improve the adhesion between the resin substrate and the substrate protective film.

[Means for solving problems]

Is the above problem about emotion? ) For optical discs in which the pre-groove for recording in step 3 is formed using an ultraviolet curable resin, the substrate coated with the ultraviolet curable resin is peeled off from the stamper in a semi-cured state, and then the substrate is irradiated with ultraviolet rays while depositing the substrate protective film forming material. This problem can be solved by a method for manufacturing an optical disc, which is characterized in that it is cured by drying.

[Effect]

The present invention provides a method for forming a substrate protective film with good adhesion between a resin substrate having different coefficients of thermal expansion, by forming a substrate protective film in a state in which a resin layer with pregrooves is incompletely cured, and this substrate protective film is Adhesion is improved by curing the resin layer during the rotor formation process and continuously changing it without creating a clear boundary between the substrate and the protective film.

A method for implementing this is to form the resin layer that forms the pregroove using an ultraviolet curing resin, and when performing electron beam evaporation of SiO□, the resin and SiO2 are mixed by irradiation with ultraviolet light in parallel. This creates a hardened layer that improves adhesion.

Further, such a mixed layer acts as a buffer layer against strain caused by differences in thermal expansion coefficients, thereby suppressing the occurrence of cranks in the SiO2 layer.

〔Example〕

FIGS. 1A to 1C show a method for manufacturing an optical disc according to the present invention.

That is, as shown in the same figure (A), an ultraviolet curing resin 2 prepared by mixing diacrylate of 4,8-bishydroxymethyltricyclodecane with a polymerization initiator, butyl ether, was deposited on a PMMA substrate 1 by a spin cord method. After applying the coating to a thickness of about 30 μm, a stamper 3 with a pregroove formed therein is pressed onto it, and in this state, PH is applied.
Ultraviolet light 4 was uniformly irradiated from the side of the MA substrate 1 at an intensity of 160 W/cm 2 for 60 seconds.

Then, the stamper 3 is separated from the PMMAi plate 1.

Figure (B) shows this state.

In this case, since the ultraviolet rays are irradiated from the side of the PHMA substrate 1, the lower side of the ultraviolet curing resin 2 is sufficiently cured, but the portion that was adhered to the stamper 3 is in an incompletely cured state.

Since the ultraviolet curing resin 2 is anaerobic, it will not harden even if left in the atmosphere.

Next, the PMMA substrate 1 is placed in an electron beam evaporator equipped with a rotating mechanism with the surface to which the ultraviolet curing resin 2 is attached facing downward, and the chamber is evacuated to 5 x 10-' Torr and SiO□ is applied from below. was evaporated with an electron beam and irradiated with ultraviolet light from an ultraviolet lamp.

FIG. 5C shows the state of the substrate protective film 5 formed in this manner.

Here, the deposition rate of Si02 was 1 person/second, and the ultraviolet irradiation intensity was 160 W/cm2, and the irradiation was repeated for 60 seconds.

In this case, the incompletely cured ultraviolet curable resin becomes curable by evacuation, and is cured with SiOz mixed in by ultraviolet irradiation that is performed simultaneously with vapor deposition.

Incidentally, the SiO2 vapor deposition was continued even after the end of the ultraviolet irradiation, and a substrate protective film 5 made of about 200 SiO2 was formed.

The optical disk substrate on which the substrate protective film 5 was formed in this manner was subjected to a temperature cycle test of 0 to 80°C 500 times, but no peeling occurred and no cracks were observed. .

〔Effect of the invention〕

As described above, by carrying out the present invention, there is no separation between the pregroove substrate and the SiO2 substrate protective film despite the difference in thermal expansion coefficients, thereby making it possible to improve the reliability of the optical disk.

[Brief explanation of the drawing]

FIGS. 1A to 1C are cross-sectional views of the manufacturing process of the optical disc according to the present invention. In the figure, 1 is a PMMA substrate, 2 is an ultraviolet curing resin,
3 is a stamper, 4 is an ultraviolet ray, and 5 is a substrate protective film.

Claims (1)

[Claims] For optical discs in which a pregroove for recording information is formed using an ultraviolet curable resin, the substrate coated with the ultraviolet curable resin is peeled off from a stamper in a semi-cured state, and then UV irradiation is applied while a substrate protective film forming material is evaporated. 1. A method for manufacturing an optical disc, which comprises curing the optical disc.