Optical: systems and elements – Lens – With support
Reexamination Certificate
2002-09-30
2004-09-14
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Lens
With support
C359S819000, C353S100000, C396S526000, C362S455000
Reexamination Certificate
active
06791766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for holding an optical member, an optical device, an exposure apparatus, and a device manufacturing method, and more particularly, it relates to a method and a device for holding an optical member that holds an optical member such as a lens having a flange portion on the periphery portion, an optical device having a plurality of the optical members within its barrel, an exposure apparatus comprising the optical device as its optical system, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, various exposure apparatus have been used in a lithographic process for producing devices such as semiconductor devices. In recent years, for example, projection exposure apparatus such as reduction projection exposure apparatus (so-called steppers) that reduce and transfer a pattern formed on a mask (also referred to as a reticle) proportionally enlarged around four to five times onto a substrate subject to exposure such as a wafer via a projection optical system based on a step-and-repeat method, or scanning projection exposure apparatus (so-called scanning steppers) that are an improvement of the steppers based on a step-and-scan method, are mainly used for producing semiconductor devices.
With these exposure apparatus, exposure wavelength has shifted to a shorter range in order to cope with finer integrated circuits and to achieve high resolution. Recently, the exposure apparatus using the ArF excimer laser which wavelength is 193 nm is in practical use, and exposure apparatus that use shorter wavelength such as the F
2
laser beam (wavelength: 157 nm) or the Ar2 laser beam (wavelength: 126 nm) are also being developed.
Beams in the wavelength range called the vacuum ultraviolet that belong to the band 200 nm-120 nm, such as the ArF excimer laser beam, the F
2
laser beam, or the Ar
2
laser beam, have low transmittance to optical glass. Therefore, glass materials that can be used are limited to fluorite, magnesium fluoride, or fluoride crystal such as lithium fluoride. In addition, since these beams are greatly absorbed by gases such as oxygen, water vapor, and hydrocarbon gas (hereinafter referred to as “adsorptive gas”), it is necessary to replace gases existing on optical paths of exposure beams with gases which absorption of vacuum ultraviolet beams is low, that is, inert gas such as nitrogen or helium (hereinafter referred to as “low absorptive gas” as appropriate), so as to lower the concentration of the absorptive gases existing on the optical paths so that it does not exceed several ppm.
Therefore, for example, in an exposure apparatus that uses an ArF excimer laser beam as the exposure beam, in an optical system that has a relatively long optical system such as a projection optical system the interior is divided into a plurality of spaces, and each space is either filled with the low absorptive gas referred to above or a flow of the low absorptive gas is created in the space at all times.
FIG. 18
shows an example of a projection optical system used in a conventional exposure apparatus. A projection optical system PL′ shown in
FIG. 18
comprises a double-structured barrel
350
consisting of an outer barrel
351
A and inner barrels
351
B
1
-
351
B
4
, and optical member cells C
1
′, C
2
′, C
3
′, and C
4
′ arranged within the barrel
350
at a predetermined interval along the AX direction of an optical axis. The optical member cells C
1
′, C
2
′, C
3
′, and C
4
′ are fixed on the inner circumference surface of the inner barrels
351
B
1
,
351
B
2
,
351
B
3
, and
351
B
4
, respectively.
The optical member cells C
1
′, C
2
′, C
3
′, and C
4
′ comprise lenses L
1
′, L
2
′, L
3
′, and L
4
′ serving as optical members, and lens holding devices for holding the lenses L
1
′, L
2
′, L
3
′, and L
4
′. In the space between the adjacent optical member cells, sealed chambers S
1
′, S
2
′, and S
3
′ are formed, respectively. And to each of the sealed chambers S
1
′, S
2
′, and S
3
′, gas supplying routes
330
A,
330
B, and
330
C, and gas exhausting routes
330
D,
330
E, and
330
F are connected, respectively, for example, so as to create a flow of the low absorptive gas at all times inside the sealed chambers S
1
′, S
2
′, and S
3
′.
FIG. 19A
shows an enlarged view of an optical member cell C
3
′ in
FIG. 18
, while
FIG. 19B
shows a disassembled perspective view. As is shown in these drawings, a flange portion is provided on an outer periphery of a lens L
3
′ on its lower half portion. The lens L
3
′ is inserted from above into a hollow cylindrical lens holding metallic part
325
, and the flange portion is supported from below at three points with supporting members
322
a
,
322
b
, and
322
c
(supporting member
322
c
is not shown in the drawings) which are arranged projecting from the inner circumference surface of the lens holding metallic part
325
spaced at an angle of approximately 120°. In addition, clamps
352
a
,
352
b
, and
352
c
(clamp
352
b
located in the depth of field of the drawing is not shown) are fixed to the lens holding metallic part
325
with bolts
354
a
,
354
b
, and
354
c
, respectively, on an upper surface of the flange portion at positions corresponding to the supporting members
322
a
,
322
b
, and
322
c
. So the upper surface of the flange portion is pushed downward with the clamps
352
a
,
352
b
, and
352
c.
That is, the lens L
3
′ is fixed with respect to the lens holding metallic part
325
by the flange portion provided on its outer periphery being clamped with the supporting members
322
a
,
322
b
, and
322
c
and the clamps
352
a
,
352
b
, and
352
c
. In this case, the movement of the lens L
3
′ is restricted in three degrees of freedom in the optical axis direction by the clamping force of the clamps
352
a
,
352
b
, and
352
c
, and the movement in the directions of the remaining three degrees of freedom is restricted by the friction between the flange portion and the supporting members and the friction between the flange portion and the clamps.
Further, the reason for employing the structure referred to above that require support at three points is because the lens, which is the object of support, can easily be attached to the lens holding metallic part and stresses due to vibration, temperature change, posture change, and the like on the lens and the lens holding metallic part can be reduced most effectively after the lens is attached, as is with the kinematic support mount which is a typical three point structure.
Incidentally, reference number
356
in
FIG. 19A
is a filler in order to prevent gases from flowing between the sealed chambers S
2
′ and S
3
′ arranged above and below the lens L
3
′ and to also prevent the position of the lens L
3
from shifting.
The other optical member cells C
1
′, C
2
′, and C
4
′ are identically configured with the optical member cell C
3
′.
With the conventional lens holding structure described above, however, since the flange portion of the lens L
3
′ is supported at three points by the supporting members
322
a
,
322
b
, and
322
c
, in other words, the lens L
3
′ is not supported at points other than the three points, the periphery portion of the lens L
3
′ bends slightly in a trefoil shape (the portion not supported sags) with its own weight making the lens L
3
′ deform asymmetrically with respect to the optical axis. Furthermore, the clamping force acting on the flange portion deforms the optical surface of the lens L
3
′ via the flange portion.
So far, such deformation of the lens or the deformation of the optical surface and deterioration in the optical performance of the projection optical system caused by them has been a triv
Dang Hung Xuan
Martinez Joseph
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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