Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
1999-05-07
2001-05-29
Kelly, C. H. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S321000
Reexamination Certificate
active
06238846
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a stamper for producing optical discs, which method comprises the application of a photoresist film to a substrate and the subsequent structuring of said photoresist film by exposing and developing said photoresist film. The present invention furthermore relates to a stamper thus obtained and to an optical disc obtained by means of such a stamper.
2. Description of Related Art
A method of this kind is known from Dutch patent application no. 9400225. According to the method of manufacturing a stamper disclosed therein, a stamper plate is subjected to a pre-treatment consisting of a cleaning step and the possible application of a primer for the photoresist to be applied. Then a negative-effect photoresist is coated onto the pre-treated stamper plate, which photoresist is then dried so as to obtain a photoresist film. In a subsequent step, the photoresist film that has been coated onto the stamper plate is selectively exposed to laser light. By selectively exposing the negative-effect photoresist, an acid is formed in the exposed areas, after which a heating step is carried out, as a result of which the photoresist in the exposed areas will be crosslinked whilst catalysis of the acid takes place. Then the selectively exposed, coated photoresist is integrally exposed, as a result of which an acid is formed in the non-exposed areas as well, which acid causes the areas which have not been selectively exposed, and which are not crosslinked, therefore, to dissolve more quickly during the developing step. After said selective exposure, the integrally exposed, coated photoresist film is developed for the purpose of obtaining the structured photoresist film. The exposed areas of a negative photoresist film thus remain after the developing step, whilst non-exposed areas are removed by means of a developing process. Then an additional exposure step in the deep UV range and a heating step at a high temperature (hard bake) are carried out in order to strengthen the exposed and thus crosslinked areas additionally by further crosslinking of polymer chains. A stamper obtained by using such a method comprises a nickel shell provided with photoresist posts. Due to dimensional stability deficiencies of the photoresist posts, stamper thus formed, which is used in the mould of an injection moulding machine for mass-producing CD replicas, has a limited life. Signal measurements in combination with transmission order measurements on the CD replicas thus produced indicate that the post geometries on the stamper had deteriorated to an unacceptable degree after about 5,000 replicas, which has an adverse effect on the signal quality.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to develop a method of manufacturing a stamper which eliminates the above problems.
According to the present invention, the method as referred to in the introduction is characterized in that an electrically conducting substrate is used, wherein the photoresist film that has been structured onto the substrate is subjected to a passivation treatment, after which the thus passivated substrate, which is provided with a structured photoresist film, is subjected to a galvanic treatment for the purpose of forming a nickel layer thereon, after which the nickel layer thus formed is separated from the substrate so as to obtain the stamper.
Although European patent application No. 0 738 573 discloses a method wherein nickel or nickel alloys are coated onto the structured photoresist layer, it should be understood that such a metallisation layer is necessary in order to be able to use the master in a subsequent galvanic process. Such a metallisation layer enables electrical contact with the master. The master disclosed in said European patent application consists of a non-electrically conducting organic material on glass, which requires an electrically conducting layer, in particular the metallisation layer, for growing the nickel layer in a galvanic process for the purpose of obtaining the mould (a master consisting of nickel). According to the method of the present invention, the application of such a metallisation layer is not necessary and the galvanic treatment can be started directly after a passivation treatment has been carried out, by connecting the present substrate cathodically, wherein the electrical conduction takes place via the nickel.
According to the method of the present invention, it is preferred to use nickel as the electrically conducting substrate. Nickel is the standard stamper material in the injection moulding process. Moreover, nickel possesses good mechanical properties, in particular as regards hardness and dimensional stability, whilst the galvanic process is a quick process.
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Patent Abstracts of Japan, vol. 017, No. 278 (C-1065), 28 Mei 1993 & JP 05 009775 A (Canon Inc.) 19 Januari 1993.
Patent Abstracts of Japan, vol. 012, No. 104 (P-685), Apr. 6, 1988 & JP 62 236156 A (Seiko Epson Corp), 16 Oktober 1987.
Kelly C. H.
Odme International B.V.
Pillsbury & Winthrop LLP
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