Exposure apparatus and exposure method

Photocopying – Projection printing and copying cameras – Illumination systems or details

Reexamination Certificate

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Details

C369S044380, C369S099000, C369S121000

Reexamination Certificate

active

06704096

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method which can be applied, for example, to an exposure apparatus for a disc master to be used to form an optical disc. An SHG exposure laser beam having a wavelength of 300 nm or less is modulated by a modulation means, and applied to a disc master by proximity effect using an objective lens of a numerical aperture of 1.0 or more, whereby an optical disc having a substantially higher recording density as compared to that of conventional discs is obtained. According to the present invention, it is possible to perform exposure on the disc master of such an optical disc.
2. Description of the Related Art
Conventionally, in the production of an optical disc, exposure is performed on a disc master by an exposure apparatus, and then the disc master is developed to prepare a mother disc, and a stamper is prepared from the mother disc for mass production of optical discs.
FIG. 6
is a plan view of an exposure apparatus of this type seen from above. In this exposure apparatus
1
, exposure is effected on a disc master
2
by an exposure laser beam, whereby a latent image corresponding to the pits and grooves is formed on the disc master
2
.
To prepare the disc master
2
, precision polishing is performed on a glass disc having a diameter of approximately 200 mm and a thickness of several mm, and a resist layer having a thickness of approximately 0.1 &mgr;m is formed thereon by spin coating of photoresist. As the photoresist, a photosensitive material exhibiting a sufficient sensitivity to the exposure laser beam is applied. The disc master
2
is attached to an air spindle through chucking and held by this exposure apparatus
1
to be rotated at a predetermined speed.
As the laser light source
3
, a Kr ion laser, for example, is used, which emits a laser beam having a wavelength of 413 nm as an exposure laser beam L
1
. Mirrors
4
and
5
bends the optical path of the exposure laser beam L
1
emitted from the laser light source
3
and leads it to an EOM (electro optic modulator)
6
. The EOM
6
rotates the plane of polarization of the exposure laser beam L
1
in response to a drive signal and emits the beam. Subsequently, a polarization beam splitter
7
selectively allows a predetermined polarization plane component of the exposure laser beam L
1
to be transmitted.
A half mirror
8
divides the exposure laser beam L
1
emitted from the polarization beam splitter
7
into two beams, and a photoreceptor
9
receives the beam transmitted through the half mirror
8
and outputs the light quantity detection result. In the exposure apparatus
1
, the drive signal of the EOM
6
is corrected based on the light quantity detection result to thereby form an automatic light quantity control circuit, effecting control such that the light quantity of the exposure laser beam L
1
is kept constant.
A lens
10
condenses the exposure laser beam L
1
reflected by the half mirror
8
and inputs it to an AOM (acousto optic modulator)
11
, which ON/OFF-modulates the exposure laser beam L
1
by a modulation signal corresponding to a pit row. Subsequently, a lens
12
converts the beam output from the acousto optic modulator
11
to a parallel beam and outputs it. A half mirror
13
divides the beam output from the lens
12
into two beams. A photoreceptor
14
receives one of the two beams and outputs the reception result, whereby in the exposure apparatus
1
, the result of modulation of the exposure laser beam L
1
by the acousto optic modulator
11
can be monitored.
On the other hand, a concave lens
15
outputs the other one of the two beams obtained through division by the half mirror
13
as a diverging ray. Subsequently, a convex lens
16
converts the diverging ray to a parallel beam. Thus, the concave lens
15
and the convex lens
16
constitute a beam expander, and outputs the exposure laser beam L
1
after setting the beam diameter to a predetermined value.
A mirror
17
receives the exposure laser beam L
1
from the beam expander through beam splitter
18
, and emits this exposure laser beam L
1
toward the disc master
2
. An objective lens
19
is formed by a lens similar to the objective lens of a microscope. As shown in
FIG. 7
, the exposure laser beam L
1
whose optical path has been bent by the mirror
17
is condensed on the resist layer of the disc master
2
to thereby form a pit latent image.
When thus performing exposure on the disc master
2
by the exposure apparatus
1
, the exposure laser beam L
1
is reflected by the resist layer of the disc master
2
, and the resulting return beam L
2
travels in the opposite direction through the optical path of the exposure laser beam L
1
to impinge upon the half mirror
13
. Mirrors
22
,
23
and
24
sequentially bend the optical path of the return beam transmitted through the half mirror
13
, and a lens
25
guides the return beam reflected by the mirror
23
to an imaging device
26
consisting of a CCD camera. The imaging device
26
receives this return light to thereby detect the beam configuration of the exposure laser beam L
1
on the resist layer of the disc master
2
. Due to this arrangement, the exposure apparatus
1
can monitor to check as to whether the focus control is correctly effected or not through the observation of the beam configuration. Further, it is possible to set the control target in the focus control.
In the exposure apparatus
1
, the optical system from the laser light source
3
to the half mirror
13
, which processes the exposure laser beam L
1
, and the optical system from the half mirror
13
to the imaging device
26
, which receives the return beam, are secured to an optical base plate which is the base of this exposure apparatus. In contrast, the optical system from the concave lens
15
to the objective lens
19
is arranged on a movable optical table
29
, which can move in the radial direction of the disc master
2
by means of a predetermined drive mechanism. Due to this arrangement, in the exposure apparatus
1
, the movable optical table
29
is gradually moved in the peripheral direction of the disc master
2
, with the disc master
2
rotating, whereby the scanning trail of the exposure laser beam is spirally formed on the disc master
2
, and a pit row latent image according to the modulation by the acousto optic modulator
11
is formed on this scanning track.
In the exposure apparatus
1
, there is further formed an auto focus optical system on the movable optical table
29
. In the auto focus optical system, a laser diode
30
emits a laser beam LF having a wavelength of, for example, 680 nm, and a polarization beam splitter
31
reflects this laser beam LF and emits it to a dichroic mirror
17
. A ¼ wavelength plate
32
imparts a phase difference to the laser beam LF emitted from the polarization beam splitter
31
before emitting it, and a beam splitter
18
synthesizes the laser beam LF with the exposure laser beam LR before emitting it to the mirror
17
. Thus, in the auto focus optical system, the laser beam LF is applied to the disc master
2
together with the exposure laser beam LR.
The laser beam LF, which has a beam diameter much smaller than that of the exposure laser beam LR, is synthesized with the exposure laser beam LR. Further, the synthesis is effected such that the optical axis of the laser beam LF is spaced apart from the optical axis of the exposure laser beam LR, the optical axis of which substantially coincides with the optical axis of the optical system including the objective lens
19
, etc.
Due to this arrangement, in the auto focus optical system, regarding the return beam, which is obtained through specular reflection at the resist layer of the disc master
2
of the laser beam LF obliquely impinging upon the disc master
2
, the position of the optical axis varies according to the distance between the objective lens
19
and the resist layer. Regarding the return beam thus obtained, the auto focus optical system im

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