JPH0244546A - Production of master disk for optical disk - Google Patents

Abstract

PURPOSE:To stably produce even the master disk for an optical disk for high- density reproduction only of small crosstalks by forming a film under the pressure near a specific film forming part and removing a resist without executing post baking. CONSTITUTION:The film is formed under <=8X10<-4>Torr pressure near the film forming part by using a vapor deposition method or ion beam sputtering and the resist removal is executed without executing the post baking after resist coating, optical mastering and developing in the process for producing the master disk for the optical disk. Atoms do not receive the scattering by gaseous molecules and form the film by perpendicularly entering the substrate surface under the high vacuum of <=8X10<-4>Torr and, therefore, the easy perpendicular erection of the side surfaces of the formed bits to the disk surface is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing an optical disc master such as a high-density read-only optical disc master with low crosstalk.

Conventional Technology As the density of read-only optical discs increases, the track pitch becomes narrower and crosstalk between adjacent tracks becomes a problem. One possible solution to this problem is to change the pit shape, that is, to make the sides of the bit as perpendicular to the disk surface as possible.

Conventionally, a series of methods have been used: resist coating, optical mastering, development, post-bake, ion milling, and resist removal.Among these, the ion milling method uses an ion gun, which causes less side etching and makes it easier to create anisotropy. was adopted.

Problems to be Solved by the Invention In optical discs, the smallest bit is currently 0.471 m x 0.6 μm in terms of pit area and the bit depth is 1/4 wavelength =
It is very small, approximately 0.1 μm. Therefore, even in ion milling using an ion gun, it is not possible to obtain a clean bit with vertical sides as shown in Figure 2 (a).
Usually, the cross-sectional shape of the bit was rounded or triangular as shown in FIG. 2(b). That is, with the bit shape as shown in FIG. 2(b), reflected light from bits in adjacent tracks is scattered, resulting in increased crosstalk when the track pitch is narrowed to 1 μm or less.

An object of the present invention is to provide a method for manufacturing an optical disk master that solves the above-described conventional problems.

Means for Solving the Problems The present invention provides a method for manufacturing an optical disc master, in which a film is deposited on a film forming part by vapor deposition or ion beam sputtering without post-baking after resist coating, optical mastering, and development. The resist is formed and the resist is removed at a nearby pressure of 8×10 −' torr or less.

Under high vacuum such as action 8X 10-' torr or less,
Since the atoms are not scattered by gas molecules and are incident perpendicularly to the substrate surface to form a film, it is possible to easily make the sides of the resulting bit perpendicular to the disk surface.

In addition, post-bake, which is commonly carried out after resist development, is not performed in the present invention, so the resist profile becomes steep, resolution deteriorates due to resist shrinkage that occurs during post-bake, and resist step portions that occur when resist is removed. It is possible to prevent the bit pattern from being torn apart.

Example The present invention will be explained in detail below.

FIG. 1 is a partial sectional view of an optical disc master for explaining the method for manufacturing an optical disc master of the present invention. FIG. 1(a) shows the first step of applying resist 2 to the master surface l.
Figure (b) shows the optical mastering and development process, in which a bit pattern 3 is carved into the resist 2. FIG. 1C shows the process of forming the film 4 in a vacuum, and FIG. 1D shows the process of removing the resist, after which the bit pattern 5 remains on the master surface l.

Next, FIGS. 1(b'), (C'), and (d') show changes in the cross-sectional shape of the master when post-baking is performed after resist development, contrary to the present invention.

Comparing Figure 1 (b) and Figure 1 (b'), Figure 1 (
In b'), it can be seen that the resolution of resist 2 has decreased and the bit portion has become wider, and that the steepness of the resist profile has been lost. Figure 1 (C)
The biggest difference that can be seen by comparing and Figure 1 (C') is
In FIG. 1 (C9), the film 4 is also formed on the resist slope. Therefore, when we look at the finally obtained bit pattern 5 in FIG. Two things are obvious: the shape is jagged.

When a replica taken from this master disc was played back, crosstalk between adjacent tracks was degraded compared to that of the present invention, and was increased by +1.5 db.

Contrary to the present invention, FIGS. 1(c") and 1(d") show changes in the cross-sectional shape of the master when the pressure near the film forming part exceeds 8×10'' torr when forming the film 4. Due to the high pressure, atoms constituting the film 4 are scattered by gas molecules, making it impossible for them to be completely perpendicular to the surface of the master disk. Therefore, in FIG. 1(c''), atoms also adhere to the stepped portion of the resist 2 to form a film 4. Therefore, in FIG. 1(d'')
), looking at the bit pattern 5 finally obtained,
It can be seen that the shape of the side surface of the bit is jagged from the tearing of the film 4 itself at the resist step portion. When a replica taken from this master is played back, crosstalk between adjacent tracks is degraded compared to that of the present invention.
〇, it had increased by 5db.

The bit pattern 5 in FIG. 1(d) obtained by the present invention is as follows:
Compared to the one obtained by the conventional ion milling method shown in Figure 1(b), the unevenness is opposite, but it is clearly approaching the ideal bit pattern in Figure 2(a), indicating an improvement. It will be done. In fact, from a reproduction experiment of replicas taken from the master disc obtained by the present invention and the master disc obtained by the conventional ion milling method, it was found that the crosstalk between adjacent tracks was improved by 14 dB by the present invention.

Even if an ion gun is used to provide anisotropy, the (non-reactive) ion milling method cannot form minute bits in a good shape for the following two reasons. One is that the etching rate depends on the ion radiation angle.
That is, the etching rate is maximum at a certain angle close to horizontal incidence. For this reason, it is more stable if the side of the bit is at a certain angle rather than vertical.

The second is the reattachment effect of etched particles to the side surfaces of the resist. Because of this, the sides of the bit are not perpendicular to the master disk, but are curved.

Reactive etching using an ion gun is effective in eliminating these two effects. This is because in reactive etching, the etching rate does not depend on the ion radiation angle.
In addition, since the etched particles become gas molecules, they do not attach again. In conventional optical disc masters using glass substrates, reactive etching is performed using a fluorine-based gas that reacts with glass.

However, in an optical disk master having ■grooves for tracking, the material of the groove surface of the master disk is mainly composed of metals that are easy to cut into grooves, such as Cu or AI. There are no commonly used gas species that can vaporize . Therefore, the present invention is considered to be particularly useful for master discs having grooves.

Note that as the material for the V-groove surface of the master, Cu, which is the most suitable for micro-cutting, is usually used, but Cu is easily oxidized, and oxidized steel is likely to cause surface roughness. Therefore, even if the present invention is used as is, Cu will react with the developer during development and cause surface roughness, which will cause roughness on the bit surface, which in turn will lead to deterioration of the cross section during playback, and There will be large variations between the two. Therefore, as a countermeasure against this surface roughness, either: ① Form a metal thin film that is difficult to oxidize on the surface of the master disc in advance after cutting the grooves, or use a material whose main component is AI for the V-groove surface of the master disc. do,
There are two possibilities. In fact, no significant losstalk deterioration during playback was observed across all lots using either method.

Effects of the Invention In the present invention, the film is formed and the resist is removed at a pressure of 8X 10-'torr or less in the vicinity of the film forming part without post-baking, so even high-density reproduction-only optical disc masters with low crosstalk can be stably manufactured. .

[Brief explanation of the drawing]

FIGS. 1(a), (b), (c), and (d) are process diagrams showing the steps of the method for manufacturing an optical disc master of the present invention, and FIGS. 1(b'), (c'), and (d
') is a process diagram showing a comparative example, Figure 1 (C"'),
(d") is a process diagram showing a comparative example, FIG. 2(a),
(b) is a sectional view of the surface of a conventional optical disc master. l...Optical disc master surface, 2...Resist, 3
・ ・ ・Bit pattern, 4. ・ ・Membrane, 5.
...Bit pattern agent's name Patent attorney Shigetaka Awano Haka 1] Figure 1] Figure 2] Figure 2

Claims (5)

[Claims] (1) The method for manufacturing an optical disc master is characterized in that after resist coating, optical mastering, and development, a film is formed at a pressure of 8×10^-^4 torr or less near the film forming part and the resist is removed without post-baking. A method of manufacturing an optical disc master. (2) The method for manufacturing an optical disc master according to claim 1, wherein the film thickness is about 1/4 of the wavelength λ of the reproduction light in the reproduction optical disc material. (3) The method for manufacturing an optical disk master according to claim 2, characterized in that the optical disk master is previously machined with a V-groove for tracking. (4) The method for manufacturing an optical disk master according to claim 3, characterized in that a metal thin film that is resistant to oxidation is previously formed on the surface of the V-grooved optical disk master before applying the resist. (5) The method for manufacturing an optical disk master according to claim 3, wherein at least the surface on which the V-groove is cut is made of a material containing Al as a main component.