Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2000-04-17
2001-10-09
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S945000, C369S275400, C369S275300
Reexamination Certificate
active
06300041
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to an optical recording medium, particularly to one aiming for improvement and the like of recording density of a write-once or a rewritable type optical recording medium also having a reproduction-only recording area.
2. Background of the Invention
An optical disk which is one kind of the optical recording medium generally has a spiral shaped track at a predetermined pitch p (for example, p=0.7 to 1.6 &mgr;m ) in a signal recording area
2
on one surface (a signal surface)
4
of a substrate
3
made of optically transparent plastic as shown in FIG.
1
A. The track consists of either continuous groove shaped concaves and convexes (groove
5
as a concave portion and land
6
as a convex portion) as shown in
FIG. 1B
or a pit row formed of continuous pits
8
as shown in FIG.
1
C.
Of the optical disks, in an optical disk which makes it possible for a user to write in information (hereafter, referred to as a recordable optical disk) such as a write-once type and a rewritable type employing a phase change recording method or a magneto-optical recording method, what constitutes the main current is one which employs either the groove
5
or the land
6
in
FIG. 1B
as a recording area while employing the remaining one as a tracking light reflection area.
On the other hand, in the reproduction-only optical disk, what constitutes the main current is one in which the pit row where the pit
8
is continuous in
FIG. 1C
is employed simultaneously as a recording area and a tracking diffraction grating.
When information is to be recorded and reproduced, a laser light is irradiated from an optical pick-up (not shown) upon an opposite surface (read-out surface)
7
of the signal surface
4
while an optical disk
1
is rotated by the driving of a spindle motor (not shown).
Then, in a recordable optical disk, at a time of recording, information is written by its irradiating light in, for example, a record area on the land
6
as a mark which is equivalent to a pit in the reproduction-only disk, and at a time of reproducing, the written information is read out by a reflection light. Also, in order that the laser light for the recording and the reproduction is always irradiated on a predetermined track, tracking is carried out by detecting, for example, a reflecting light from the grooves
5
and the lands
6
.
On the other hand, in the reproduction-only optical disk, read-out of the information and the tracking are respectively carried out by detecting a reflecting light and a diffraction light from the signal surface
4
on which the pit row
8
is formed.
Since the shape of such the track affects performance as a recording medium, it is demanded that the substrate
3
is most precisely manufactured.
FIG. 2
illustrates a generally practiced manufacturing process of the substrate of an optical disk.
(1) Manufacture of a Master
Glass as a material for a master is worked to become a plate shape, its surface is ground sufficiently flat, washed and dried whereby a glass master
23
is manufactured.
(2) Painting of Photoresist
Photoresist, e.g., positive type resist which becomes soluble in alkali by exposure treatment
20
is painted about as thick as about 0.1 &mgr;m on the glass master
23
and the photoresist
20
is dried by carrying out heat treatment on the glass master
23
.
(3) Recording by a Laser Beam (Cutting)
The photoresist
20
is exposed to light by condensing a recording laser light
31
by an objective lens
32
and irradiating it on the photoresist
20
on the glass master
23
. In a case of the recordable optical disk, the irradiation is carried out continuously and in a case of the reproduction-only optical disk, the irradiation is carried out intermittently. Concurrently, an exposure spot is fed in a radius direction of the master
23
at a constant feeding pitch, i.e., at an equal distance per one rotation while rotating the glass master
23
in a circumferential direction. As a result, in the case of the recordable optical disk, a latent image for a track consisting of a groove in a spiral shape at a constant interval is generated in the photoresist
20
whereas in the case of the reproduction-only optical disk, a latent image for a track consisting of spiral shaped pit rows at a constant interval is generated in the photoresist
20
.
(4) Development
By developing the photoresist
20
in an alkaline developing solution, its exposure portion is removed. As a result, in the case of the recordable optical disk, a track pattern consisting of an alternation of a groove
25
and a land
26
in a spiral shape at a predetermined pitch is formed on the glass master
23
. Also, in the reproduction-only optical disk, a track pattern consisting of continuous spiral shape pit rows
28
at a predetermined pitch is formed.
(5) Manufacture of a Stamper
By electroforming nickel on the glass master
23
and peeling off a formed nickel layer, a nickel master (stamper)
34
onto which the pattern on the glass master
23
is transferred is manufactured.
(6) Plastic Molding
By molding plastic as a material for the substrate of the optical disk through an injection molding method or the like using the stamper
34
, an optical disk substrate
3
having the track consisting of the groove and the land or the pit row as shown in
FIGS. 1A
to
1
C is manufactured. This substrate
3
is a replica of the glass master
23
.
After the replica is manufactured, a recording film, a reflection film and the like (not shown) are formed on the signal surface
4
of the substrate
3
in the recordable optical disk, while in the reproduction-only optical disk, a reflecting film, a protection film and the like (not shown) are formed on the signal surface
4
of the substrate
3
.
FIG. 3
shows a schema of whole the structure of an apparatus (a cutting machine) used for carrying out the cutting in the process in
FIG. 2
, and
FIG. 4
shows detailed structure of its optical system. The cutting machine is formed of the following parts.
(1) Laser Apparatus
41
as a Light Source
As one example, a Kr ion laser apparatus with a wavelength of 413 nm is used.
(2) Recording Light Intensity Control Unit
42
An apparatus for eliminating instability of output from the light source to control the final recording light intensity for which a servo system employing an electro-optical crystal element (EO)
42
a
, an analyzer
42
b
, a photo-diode
42
c
, a recording light intensity control circuit
42
d
is used.
(3) Light Modulating Unit
43
This is an optical system provided with a light modulator
43
a on an optical path formed of beam splitters BS
1
, BS
2
, and convex lenses L
1
and L
2
. The light modulator
43
a is used to form a pit of a length corresponding to a voltage level of an electric record signal, and to convert the voltage level of the record signal to a light intensity. For example, when the voltage level of the record signal consists of 2 values such as “0” and “1”, a passing light is made on and off. As the light modulator is required to have performance capable of being used in a band of several tens of MHz, usually, an EOM (electro-optic crystal element modulator) and an AOM (acousto-optic crystal element modulator) are used.
(4) Beam Expander Unit
44
This is an optical system to expand a diameter of a beam of a recording laser light and a spot diameter of a condensed light is adjusted by its enlargement factor (magnification).
(5) Objective Lens
45
This is an optical system which condenses and irradiates the recording laser beam upon the photoresist
20
on the glass master
23
.
(6) A Turntable
46
for Holding and Rotating the Glass Master
23
in a circumferential direction.
(7) Feeding Mechanism (not shown)
This is a mechanism for feeding an exposure spot of the record laser beam in a radius direction of the glass master
23
by holding the beam expander unit
44
and the objective lens
45
on a shifting stationary plate and shifting the shifting stationary plate by a motor and the like in a radius direction of the
Kanno Masayoshi
Masuhara Shin
Suzuki Akitoshi
Angebranndt Martin
Frommer William S.
Frommer Lawrence & Haug LLP.
Simon Darren M.
Sony Corporation
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