Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-10-25
2002-01-22
Rutledge, D. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C250S492100, C438S946000, C438S625000
Reexamination Certificate
active
06341006
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a projection exposure apparatus and, more particularly, to a projection exposure apparatus that uses far ultraviolet light for pattern formation in the process of producing semiconductor devices (IC, CCD, etc.), liquid crystal display devices, thin-film magnetic heads, and so forth.
The demand for larger-scale integration of semiconductor devices has been increasing year by year, and the pattern rule (i.e., a line width of a pattern) of the required circuit patterns has been correspondingly decreasing. It is known that the line width that can be resolved by a projection optical system reduces in proportion to the wavelength. Therefore, in order to form a circuit pattern of smaller pattern rule by photo-lithography process, it is only necessary to shorten the wavelength of light used for exposure. At the present, an exposure apparatus in which a KrF excimer laser having a wavelength of 248 nm is used as a light source has already been developed. Further, a mercury lamp having a wavelength of about 220 nm or 184 nm, an ArF excimer laser having a wave length of 193 nm and the like have been noted as a short wavelength light source.
In conventional exposure apparatuses in which g-ray (having a wavelength of 436 nm), i-ray (having a wavelength of 365 nm), a KrF excimer laser or a mercury lamp emitting light having a wave length of about 250 nm is used as a light source, since the wavelengths of these light beams are not overlapped with an absorption spectrum zone of oxygen, there is no inconvenience such as reduction in light available rate caused when light is absorbed by oxygen molecules in a light path and/or generation of ozone due to light absorption of the oxygen molecules.
However, in the light source such as the ArF excimer laser, since light emitting spectrum is overlapped with the absorption spectrum zone of oxygen, the above-mentioned reduction in light available rate and/or generation of ozone due to light absorption of the oxygen molecules will occur. For example, if it is assumed that transmittance of the ArF excimer laser beam in the vacuum or in inert gas such as nitrogen or helium is 100%/m, in a free-run condition (natural light emitting condition). i.e., in an ArF wide range laser, the transmittance becomes about 90%/m, and, even when an ArF narrow band laser is used for reducing a spectrum width to avoid absorbing lines of oxygen, the transmittance is decreased to about 98%/m.
It is considered that the reduction in transmittance is caused by influences of absorption of light caused by the oxygen molecules as well as generation of ozone. The generation of ozone not only affects a bad influence upon the transmittance (light available rate) but also worsens performance of the apparatus due to reaction to a surface of optical material or other components of parts.
In such exposure apparatuses, in order to prevent the reduction in transmittance and/or generation of ozone by reducing oxygen density in the light path, it is well known that a space including the entire light path must be filled with inert gas such as nitrogen (for example, refer to Japanese Patent Laid-open No. 6-260385 corresponding to U.S. Ser. No. 206,618 filed on Mar. 7, 1994).
FIG. 15
schematically shows a construction of an exposure apparatus (optical systems associated with illumination and image focusing are mainly illustrated and other parts are omitted from illustration). A light beam from an ArF excimer laser light source
201
is changed to a predetermined form by a beam shaping lens
202
and then is reflected by a mirror
203
to be incident on a beam expander lens
204
. The light flux incident to the beam expander lens
204
is expanded or enlarged to a predetermined magnitude and then is reflected by a mirror
205
to be directed to a fly-eye lens
206
as an optical integrator, where illuminance is made uniform and an illuminating range is determined. Light from the fly-eye lens
206
is focused on a reticle conjugate surface by a first relay lens
207
. The reticle conjugate surface is provided with a reticle blind
208
for regulating or limiting an exposure range. Light passed through the reticle blind
208
is illuminated onto a reticle
212
through a second relay lens
209
, a mirror
210
and a main condenser lens
211
. Light having passed through the reticle
212
is illuminated onto a wafer
214
through a projection lens
213
, thereby focusing an image of the reticle
212
on the wafer
214
.
FIG. 16
is a sectional view of an illumination optical system of the exposure apparatus, showing a light path from the ArF excimer laser light source
201
to the main condenser lens
211
. A frame
221
contains optical parts such as the beam shaping lens
202
constituting the illumination optical system and is attached to the ArF excimer laser light source
201
via a bellows
223
. Nitrogen gas from a nitrogen gas supply source
224
is supplied from one side of the frame
221
(i.e., a side to which the laser light source
201
is attached in
FIG. 16
) through a piping L
201
a
and is discharged to a discharge device
225
from the other side of the frame
221
.
In
FIG. 16
, while various optical parts were shown with simplification, actually, as shown in
FIG. 17
(fully described later), each of the optical parts is constituted by a plurality of lenses which are integrally secured to the frame
221
by a support blocks
237
. In
FIG. 16
, the reflection mirror
210
and the main condenser lens
211
are secured to the frame
221
by using a same support block
237
h
, and the other optical parts are secured to respective support blocks
237
a
-
237
g.
Each of the optical parts secured to the frame
221
forms respective optical block at each of the support blocks
237
a
-
237
h
, and maintenance (such as replacement) is effected for independent block. Lids
222
a
,
222
b
,
222
c
serves to close openings (through which the optical blocks are inserted and removed when the optical blocks are mounted and dismounted with respect to the frame
221
) formed in the frame
221
, so that the interior of the frame
221
is sealed by the lids
222
a
,
222
b
,
222
c
. Incidentally, although not shown, O-rings or packings are disposed between the frame
221
and the lids
222
a
,
222
b
,
222
c
to improve sealing ability.
FIG. 17
shows an example of the optical parts. Lenses
232
a
,
232
b
,
232
c
are successively inserted into a lens barrel
231
and are secured by a hold-down ring
234
. Incidentally, there are provided separation rings
233
a
,
233
b
for maintaining predetermined distances between the lenses. Vent holes
235
a
,
235
b
,
236
a
,
236
b
formed in the lens barrel
231
and the separation rings
233
a
,
233
b
serve to introduce inert gas between the lenses. When the nitrogen gas is supplied into the frame
221
, the nitrogen gas also flows into the lens barrel
231
through the vent holes
235
a
,
235
b
,
236
a
,
236
b
to replace the air between the lenses by the nitrogen gas. The lens barrel
231
is secured to the support block by set screws
238
.
However, in the illumination optical system of the exposure apparatus shown in
FIG. 16
, even when maintenance regarding at least one of the parts disposed in the frame
221
is effected, the entire interior of the frame
221
is exposed to atmosphere. Thus, a large amount of nitrogen gas contained within the frame
221
escapes or leaks outside, with the result that it takes a long time to re-fill the nitrogen gas in the frame
221
after the maintenance. Further, it is very difficult to judge whether the frame
221
is filled with the nitrogen gas sufficient to not affect an influence upon the exposure.
To solve the problem, it is conceivable to increase the number of hermetic blocks to thereby reduce the volumetric capacity of each block. However, merely increasing the number of blocks causes an increase in the number of transparent windows defining the boundary between each pair of adjacent blocks. Further, each transparent window also h
Murayama Masayuki
Ozawa Haruo
Armstrong, Westerman, Hattori, Mcleland & Naughton, LLP
Nikon Corporation
Rutledge D.
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