JPH0283835A - Stamper for molding optical disk - Google Patents

Abstract

PURPOSE:To maintain the initial quality of the stamper necessary for producing an optical disk, i.e., to prolong the life thereof by forming a layer consisting of a corrosion resistant material on the surface of the stamper. CONSTITUTION:The layer consisting of the corrosion resistant material is formed on the surface of the stamper, by which the formation and growth of defects are drastically decreased. The corrosion resistant material is exemplified by noble metals as represented by Pt, Rh, Ir, and Au, nitrides as represented by BN, TiN, and AlN, and corrosion resistant alloys as represented by Ni-Mo-Fe-C, Ni-Mo-Fe-C-Cu-w, and Ti-Ag. Electroplating and electroless plating are both possible according to materials as the method for forming the corrosion resistant layer and above all, RF magnetron sputtering is more effectual. The thickness of the layer is preferably about the thickness at which the pattern shape on the nickel stamper does not change, more specifically about 0.03 to 0.07mum. The life of the stamper is thus greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a stamper used for molding a substrate of an optical disk.

[Prior art and problems]

A typical method for manufacturing a stamper for a conventional optical disc involves the following steps.

A silane coupling agent is applied as a primer on a polished glass disk, and a layer of photoresist (e.g., Sibley Co., Ltd. AZ-1350) as a latent image recording material is applied thereon, and then a focused Ar laser beam is applied. (Wavelength 45
79 people) selectively exposes the photoresist layer to write a signal or tracking groove, and develops, that is, elutes the exposed area, to form irregularities in the photoresist layer.

This is the glass master. A stamper is a replica of the glass master, and after forming a conductive layer on the surface of the glass master, a nickel plate with a thickness of 0.31 mm is formed by nickel electroforming, and a negative image of the pattern on the glass master is transferred. Manufactured by taking.

Using this stamper, a plastic substrate is molded by injection molding or compression molding, and the signal bits and tracking grooves of the master are reproduced. Any defects in the stamper will be transferred to the substrate, increasing the error rate of the final product. It is of course important that there are few defects immediately after stamper production, but it is clear that if the defects increase during use or storage of the stamper, the stamper will become unusable. The generation of defects determines the lifespan of the stamper. There are various causes for the generation of defects in stampers. A typical case is that foreign matter adheres to the front or back surface of the stamper during the molding operation, causing scratches. A multilayer stamper with increased surface hardness to prevent scratches is disclosed in Japanese Patent Laid-Open No. 59-193560. It has been known for a long time to improve the surface hardness of a nickel stamper in a stamper for manufacturing audio records by plating it with chrome.

However, the formation of scratches on the surface is caused by contact with a hard foreign object, and the contact between the molten resin and the stamper itself does not lead to the formation of scratches. Therefore, eliminating opportunities for contact with foreign substances is considered to be a more essential measure than improving surface hardness.

Corrosion on the surface of the stamper also becomes a defect. The mechanism of corrosion has not been fully elucidated, and is not always the same mechanism. The main reaction is an oxidation reaction, which includes trace amounts of NOx, which is contained in the air.

It is thought that acidic compounds such as SOx, H, S, and HCI are involved. Conventionally, in order to prevent corrosion of stampers, methods of coating the surface with an organic polymer film to protect the stamper during storage or storing it in an inert gas such as nitrogen have been used.

However, it is clearly not possible to apply these methods during molding operations that are exposed to high temperatures.

As a result of observing and examining the structure and growth of defects on the stamper using an optical microscope, SEM, etc., the present inventors found that under conditions of sufficiently controlled cleanliness, the frequency of scratches caused by contact with foreign objects is low, and that scratches are caused by corrosion. Defects, i.e. rust formation;
It has been found that growth is especially rapid under operating conditions of a molding machine exposed to high temperatures.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned current situation, and its purpose is to maintain the initial quality of the stamper necessary for manufacturing optical discs, that is, to extend the life of the stamper.

[Means to solve the problem]

The inventors have invented an effective means for this problem based on the observation of the phenomenon of two feet. That is, it has been found that formation and growth of defects can be significantly reduced by forming a layer made of a corrosion-resistant material on the surface of the stamper. Corrosion-resistant substances include PiSRh and Ir.

Noble metals represented by Au, nitrides represented by BNXTiN, 8IN, Ni-Mo-Fe-C, Ni-M
Corrosion-resistant alloys typified by o-FeC-Cu-W and Ti-Ag can be mentioned.

Corrosion-resistant layer formation methods include electrolytic plating,
Although electroless plating is also possible, a vacuum film forming method, especially RF magnetron sputtering, is effective in forming a dense thin film.

The thickness of the layer is such that the pattern on the nickel stamper, that is, the size and shape of pits corresponding to signals and groups for tracking, do not change significantly from before the formation of the corrosion-resistant layer, specifically 0.03 to 0.07 μm. degree is preferred.

〔Example〕

The present invention will be explained below with reference to Examples.

Example 1 First, a nickel stamper was produced by the most common electroforming method. A photoresist (Sibley's AZ 1350) was coated to a thickness of 800λ on a polished soda glass disk, and an Ar laser beam was scanned over the master on a rotating spindle, exposed and developed to form a 1.6μ pitch. Width 0.
A spiral groove with a diameter of 6μ and a depth of 700λ was formed. A nickel conductive layer with a thickness of 500A was formed on this master by electroless nickel plating, and a nickel replica was formed with a uniform thickness of 0.3+nm by nickel electroforming using a nickel sulfamate solution and a sulfur nickel electrode. , an inverted image of the original pattern was copied. A stamper was prepared by cutting the outer periphery and center hole to predetermined dimensions. A thin gold film layer of 500 layers was formed on the surface of this standby by a magnetron sputtering method using gold as a target.

The sputtering conditions were: evacuation time 10 minutes, sputtering Ar pressure 5 x 10-” Torr, and sputtering output R.
Using the thus obtained stamper, a polycarbonate optical disk substrate (outer diameter 130 mmφ, center diameter 15n++nφ, thickness 1.2 mm) was stamped at 4,000 W.
The stamper was injection molded at a mold temperature of 110°C and a cylinder temperature of 330°C. After molding, the stamper was washed and dried and stored in a nitrogen atmosphere. After 3 months, 4,000 stampers were molded. After another 3 months of storage, 4,000 stampers were molded. It was molded into a sheet. After molding a total of 12,000 sheets, no abnormalities were observed when the standby surface was observed using an optical microscope and visually, and the defect rate determined from changes in the intensity of reflected light by scanning the screen with a laser beam was less than 1 O-Il, which was lower than that before molding. No significant difference was observed compared to that.

Comparative Example 1 A stamper was produced in the same manner as in Example I, and molding was performed in the same manner as in Example 1 without forming a corrosion-resistant layer. Cleaning and storage after molding were performed in the same manner. After 6 months of molding, observation using an optical microscope and visual inspection revealed that fine rust was emerging around the inner and outer peripheries of the stanbar, and the defect rate was between 10-5 and 10-4, making the disc no longer suitable for practical use. It was clear that it was not possible to mold the substrate.

〔Effect of the invention〕

As is clear from the above examples, by applying a corrosion-resistant coating to the stamper surface, it is possible to greatly improve the life of the stamper.

Patent applicant Daicel Chemical Industry Co., Ltd.

Claims (1)

[Claims] A stamper for molding optical discs characterized by having a corrosion-resistant layer formed on its surface.