Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2000-04-11
2001-08-28
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S320000, C430S326000
Reexamination Certificate
active
06280910
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a photoresist for an optical disc particularly capable of being preferably utilized for manufacturing an optical disc having high recording density and also relates to a method of preparing an optical disc by utilizing the photoresist.
In a conventional art, an optical disc is generally manufactured in accordance with the following steps.
First, a positive-type photoresist is coated with uniform thickness on a glass substrate which was ground finely to thereby form a photoresist layer. In the next step, a laser beam is irradiated to a portion of the photoresist layer at which a pit is formed. A portion of the photoresist layer irradiated to the laser beam is easily dissolved in an alkali liquid developer in comparison with another portion not irradiated. Accordingly, when the development is performed by coating the alkali liquid developer on the photoresist layer, a recess corresponding to a pit is formed to the portion irradiated to the laser beam. Thereafter, a metallic film is formed on the photoresist layer to which an electro conductivity is imparted, and in this step, for example, silver (Ag) or nickel (Ni) may be utilized as a metal for forming the metallic film. In the next step, an electrocasting treatment is performed to form an electrocast product, Ni electrocast, for example, on the metallic film. The nickel electrocast is then peeled off from the glass substrate and the photoresist layer together with the metallic film, the thus peeled off nickel electrocast and metallic film being called a metallic original, i.e. stamper.
In such optical disc original manufacturing steps, a photoresist for manufacturing a semiconductor is utilized as it is in the conventional art.
However, in recent studies and experiments of the inventors of the subject application for achieving high density of an optical disc, it was found that the conventional photoresist for manufacturing a semiconductor is not suitable for the manufacturing of the optical disc having high recording density.
Namely, in a case where an optical disc original having high density with small pit size is manufactured by utilizing a conventional photoresist for manufacturing a semiconductor and the optical disc is formed from this optical disc original, a noise level increases at a reproduction time in accordance with the reduction of the pit size and, hence, a sufficient CN ratio (carrier-wave
oise ratio), this providing a significant problem.
SUMMARY OF THE INVENTION
An object of this invention is to substantially eliminate the defects or drawbacks encountered in the prior art described above and to provide a photoresist for an optical disc and a method of preparing an optical disc utilizing the photoresist, capable of obtaining an optical disc having improved high recording density in which pit shapes are not uneven in making small the pit size, and hence, with the low noise level at a reproduction time and the improved CN ratio.
This and other objects can be achieved according to this invention by providing a positive-type photoresist adapted for manufacture of an optical disc original comprising a photosensitive material and a base resin, in which a value A in a formula A=(a
1
−a
3
)m
10
, wherein a
1
represents a molar absorption coefficient of the photosensitive material with respect to a light utilized for an actual recording, a
3
represents a molar absorption coefficient of a decomposed product derived from the photosensitive material with respect to a light utilized for an actual recording and m
10
represents an original density of the photosensitive material, is in a range of 1.2≦A value ≦2.0, and in which a value of B in a formula B=(a
2
m
20
+a
3
m
10
), wherein a
2
represents a molar absorption coefficient of the base resin with respect to a light utilized for an actual recording, a
3
represents a molar absorption coefficient of a decomposed product with respect to a light utilized for an actual recording, m
10
represents an original density of the photosensitive material and m
20
represents a density of the base resin, being constant, is in a range of B value ≦0.3.
According to this invention, there is also provided a method of preparing an optical disc comprising the steps of:
Preparing a positive-type photoresist composed of a base resin and a photosensitive material and also preparing a glass substrate;
coating the photoresist on the glass substrate to form a resist film;
forming a pit pattern through a light exposure to the resist film;
developing the resist film after the light exposure to form a resist original;
effecting a plating treatment to the resist original to form a stamper;
forming a replica disc through an injection molding process by utilizing the stamper;
forming a reflection film on the replica disc; and
forming an overcoat layer on the reflection film,
wherein the positive-type photoresist satisfies a condition that a value of A in a formula A=(a
1
−a
3
) m
10
, wherein a
1
represents a molar absorption coefficient of the photosensitive material with respect to a light utilized for an actual recording, a
3
represents a molar absorption coefficient of a decomposed product derived from the photosensitive material with respect to light utilized for actual recording. and m
10
represents an original density of the photosensitive material, is in a range of 1.2≦A value ≦2.0, and in which a value of B in a formula B=(a
2
m
20
+a
3
m
10
), wherein a
2
represents a molar absorption coefficient of the base resin with respect to a light utilized for an actual recording, a
3
represents a molor absorption coefficient of a decomposed product with respect to a light utilized for an actual recording, m
10
represents an original density of the photosensitive material and m
20
represents a density of the base resin, being constant, is in a range of B value ≦0.3.
The stamper may be formed by an electrocasting method.
According to the photoresist of the character described above, a resolving power of the exposure development, i.e. gradiation displaying ability, can be improved without damaging the resolution. Accordingly, when an optical disc with high density having small pit size is manufactured by utilizing this photoresist, the product optical disc has less shape unevenness even in the small pit size, whereby the noise level can be lowered during the reproduction and the improved CN ratio can be achieved.
The component of the photoresist of the optical disc of the character described above will be mentioned hereunder.
The photoresist includes a base resin and a photosensitive agent. An alkali fusible novolak resin is preferably utilized as the base resin, for example, and it is desired for this base resin to have a small molecular weight distribution (weight average molecular weight M
w
umber average molecular weight M
n
), and preferably, the molecular weight distribution M
w
/M
n
is a value less than 5.8. On the other hand, o-quinonediazido or naphtho-quinonediazido may be utilized as the photosensitive agent utilized together with the base resin.
This photoresist for the optical disc is a light fusible (positive type) photosensitive resin which becomes alkali fusible by the irradiation of light, which satisfy the condition that the value A in the formula (1) is within a range of 1.2≦A value ≦2.0 and the value B in the formula (2) is within a range of B value ≦0.3.
The A value denotes a rate of change of transmittance per unit depth of a resist film and the B value denotes an optical density of the base resin and the decomposed material per unit depth of the resist film. With reference to the photoresist in which these A and B values are within the ranges described above, a resolving power of the exposure development, i.e. gradiation displaying ability, can be improved without damaging the resolution. Accordingly, when an optical disc with high density having small pit size is manufactured by utilizing such photo-resist, the product optical disc ha
Higuchi Takanobu
Iida Tetsuya
Ogoshi Kunizo
Sasaki Hironao
Chu John S.
Pioneer Electronic Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Photoresist for optical disc and method of preparing optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoresist for optical disc and method of preparing optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoresist for optical disc and method of preparing optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2495126