Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2000-11-22
2003-11-25
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S321000, C430S945000, C216S047000, C216S057000, C101S004000
Reexamination Certificate
active
06653057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stamper for forming a guiding groove of an optical disk substrate (or a magneto-optical recording medium substrate) and also to a method of manufacturing the same. The present invention is particularly useful for forming a land/groove recording optical disk of which both the land section and the groove section can be used for recording.
2. Related Background Art
FIG. 11
of the accompanying drawings schematically illustrates a magneto-optical recording medium prepared by forming films on a land/groove substrate. In
FIG. 11
, a recording track
8
located remotely as viewed from a light beam
125
incident to the recording medium is referred to as the land section, whereas a recording track
9
located closer as viewed from the light beam
125
is referred to as the groove section. In land/groove recording, the groove section operates as the guiding groove for tracking when the land track is used for signal recording/reproduction, whereas the land section operate as the guiding groove for tracking when the groove track is used for signal recording/reproduction. Thus, this recording medium can effectively be used for improving the recording density in the track direction because both the land section and the groove section that are located side by side can be used simultaneously for recording.
Since the domain wall displacement detection (DWDD) method (U.S. Pat. No. 6,027,825) is useful for improving the recording density along the linear direction, the areal recording density of a magneto-optical recording medium can be dramatically improved by combining this method and the land/groove recording compared with a conventional recording medium.
In the land/groove recording, the use of a so-called deep groove substrate (Japanese Patent Application Laid-Open No. 9-161321) having a sharply tapered land and groove as shown in
FIG. 11
is effective for facilitating the domain wall displacement. The tapered section (lateral walls between the land and the groove) are practically free from deposition of magnetic film if the magnetic films are formed by using a highly directional film forming method. Then, it is possible to produce magnetic domains whose lateral walls are practically free from magnetic domain walls for each of the land and groove sections so that the track can be magnetically segmented to facilitate the domain wall displacement. The mechanical distance between the land track
8
and the groove track
9
is preferably between about 100 nm and about 300 nm, which is at least greater than the total film thickness of the magnetic films (80 nm in the embodiment).
Additionally, the lateral walls that are free from deposition of magnetic film are effective for suppressing thermal interference of the adjacent tracks and improving the resistance against the cross erasure of the tracks. Additionally, such lateral walls may give rise to an effect of suppressing cross talks between the adjacent tracks during reproduction operation in the case of domain wall displacement detection method, because it is possible not to heat the neighboring tracks above the domain wall displacement triggering temperature Ts in the reproduction operation. Then, no domain wall displacement occurs in the magnetic domains of the neighboring tracks so that normal magneto-optical reproduction operation proceeds. Significant cross talks do not take place when the length of the recording mark is made smaller than the resolution of a light spot used for the reproduction operation.
Then, due to the synergetic effect of the magnetic segmentation of tracks and the improvement in the resistance against cross erasures and the suppression of cross talks, it is possible to dramatically improve the areal recording density by combining a deep groove substrate and the domain wall displacement detection method (see, inter alia, Shiratori: “Realization of a High Density Magneto-optical Disk by Using the Domain Wall Displacement Detection Method”, Bulletin of Japan Applied Magnetism, Vol. 23, No. 2, 1999, pp. 764-769).
Meanwhile, the technique of anisotropic etching is generally used for preparing a deep groove substrate that is required to have a nearly rectangular cross section. For example, Japanese Patent Application Laid-Open No. 7-161080 describes a method of manufacturing and processing a stamper for forming a land/groove substrate by reactive ion etching (RIE).
The known method of manufacturing and processing a stamper for forming a land/groove substrate will be described by referring to
FIGS. 13A through 13H
and
FIGS. 14A and 14B
of the accompanying drawings. Firstly, a synthetic quartz master substrate
1
having an outer diameter of 350 mm, an inner diameter of 70 mm and a thickness of 6 mm that has been polished to have a surface roughness of less than 1 nm is thoroughly rinsed (FIG.
13
A). (1) Then, a primer and a positive photoresist
2
are sequentially applied to the surface of the synthetic quartz master substrate
1
by spin coating. Subsequently, the master substrate is pre-baked in a clean oven. The resist has a thickness of about 200 nm (FIG.
13
B). (2) Thereafter, a predetermined area of the master substrate is exposed to a laser beam emitted from a cutting machine having an Ar ion laser having a wavelength of 458 nm as a light source with a constant track pitch. In
FIG. 13C
, reference numeral
3
denotes the laser beam emitted from the cutting machine and reference numeral
4
denotes the exposed area, while reference number
5
denotes the unexposed area. The master substrate is continuously exposed to the laser beam typically by selecting the intensity of the laser beam so as to have a track pitch of 1.6 &mgr;m and a land (or groove) width of about 0.8 &mgr;m after the development process. During the exposure, the synthetic quartz master substrate is driven to rotate at a rate of 450 rpm and the laser beam spot has a diameter of 1.3 &mgr;m (FIG.
13
C). (3) Thereafter, the exposed areas are removed by spin development, using an inorganic alkali developing solution. Then, the master substrate is washed by means of a pure water shower, spin-dried and post-baked in a clean oven for post processing (FIG.
13
D). (4) Thereafter, the master substrate is placed in a chamber of a reactive ion etching system, and after evacuating the chamber to a degree of vacuum of 1×10
−4
Pa, the master substrate is subjected to a reactive ion etching process by introducing CHF
3
gas with a gas flow rate of 6 sccm, a gas pressure of 0.3 Pa, an RF power supply rate of 300 W, a self bias voltage of −300V and a gap of 100 mm separating the electrodes. The etching process is conducted until a predetermined groove depth (e.g., 85 nm) is obtained by regulating the etching time (FIG.
13
E). (5) Then, the master substrate
7
is immersed in aremover solution prepared by mixing concentrated sulfuric acid and hydrogen peroxide to remove the remaining resist. In
FIG. 13F
, reference numeral
8
denotes a land section and reference numeral
9
denotes a groove section (FIG.
13
F). (6) After rinsing, the surface of the master substrate
7
is turned electroconductive by forming a Ni film
10
on the surface by sputtering (FIG.
13
G). (7) Then, the master substrate
7
is subjected to an electroforming process, using Ni. In
FIG. 13H
, reference numeral
11
denotes an electroformed Ni layer (FIG.
13
H). (8) After polishing the electroformed Ni surface, the electroformed Ni layer
11
is removed from the master substrate
7
(FIG.
14
A). (9) Now, a finished stamper
12
is finally produced (FIG.
14
B). The same land/groove pattern can be copied to the surfaces of a number of glass substrates typically by means of a photopolymer (2P) method, using the finished stamper.
Japanese Patent Application Laid-Open No. 6-258510 discloses a mold for reproducing a diffraction grating by using a reactive ion etching technique and a method of manufacturing such a mold.
FIG. 19
of the accompanying drawings is a schematic perspective
Angebranndt Martin
Canon Kabushiki Kaisha
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