Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
2001-03-05
2004-08-03
Griffin, Steven P. (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S413000, C065S421000, C501S905000
Reexamination Certificate
active
06769273
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a silica glass member and a silica glass member obtained by the method and, more particularly, to a method of manufacturing a silica glass member suitably used for an imaging optical system such as an illumination optical system or projection optical system in a projection exposure apparatus for transferring a predetermined mask pattern onto a substrate, and a silica glass member obtained by the method.
BACKGROUND ART
As a projection exposure apparatus, an apparatus having a structure as shown in
FIGS. 18A and 18B
is conventionally used.
More specifically, in the projection exposure apparatus shown in
FIG. 18A
, a light beam from a light source
501
such as a mercury arc lamp is condensed by an elliptical mirror
502
and then converted into a parallel light beam by a collimator lens
503
. This parallel light beam passes through a fly-eye lens
504
comprised of a set of optical elements
504
a each having a rectangular section as shown in
FIG. 18
, so a plurality of light source images are formed on the exit side of the fly-eye lens. An aperture stop
505
having a circular aperture portion is placed at the light source image position. Light beams from the plurality of light source images are condensed by a condenser lens
506
so a reticle R as a target illumination object is uniformly illuminated in a superposed manner.
A pattern on the reticle R thus uniformly illuminated with the illumination optical system is projected/exposed to a wafer W with a resist coated thereon, by a projection optical system
507
constituted by a plurality of lenses. This wafer W is placed on a wafer stage WS that two-dimensionally moves. In the projection exposure apparatus shown in
FIG. 18A
, exposure of so-called step-and-repeat scheme is performed so that when exposure in one shot region on the wafer is ended, the wafer stage is sequentially two-dimensionally moved for exposure to the next shot region.
In recent years, a scanning exposure scheme has been proposed in which the pattern on the reticle R can be transferred onto the wafer W at high throughput by irradiating the reticle R with a rectangular or arc light beam and scanning the reticle R and wafer W, which are conjugate with respect to the projection optical system
507
, in predetermined directions.
In either projection exposure apparatus, an optical member used in its optical system is required to have a high transmittance for exposure light used. This is because the optical system of the projection exposure apparatus is formed by combining a number of optical members, and if optical losses of the number of optical members used are integrated, the influence of total decrease in transmittance becomes large althrough the optical loss per lens is small. When an optical member having a low transmittance is used, it absorbs exposure light and increases the temperature of the optical member, resulting in uneven refractive index. Additionally, the polished surface deforms due to local thermal expansion of the optical member. This degrades the optical performance.
In the projection optical system, the optical member is required to have a highly uniform refractive index in order to obtain a finer and clearer projected/exposed pattern. The reason for this is that a propagation delay of light occurs due to an unenen refractive index, greatly affecting the imaging performance of the projection optical system.
As a material of an optical member used in the optical system of a projection exposure apparatus using UV light (wavelength: 400 nm or less), silica glass or calcium fluoride crystal, which has a high transmittance for UV light and is excellent in uniformity, is generally used.
Furthermore, a technique has been recently proposed in which the wavelength of the light source is shortened to transfer a finer mask pattern image onto a wafer surface, i.e., improve the resolution. For example, the wavelength is shortened from conventional g line (wavelength: 436 nm) or i line (wavelength: 365 nm) to KrF (wavelength: 248 nm) or ArF (wavelength: 193 nm) excimer laser.
In projection exposure using such a short-wavelength excimer laser, since it aims at obtaining a finer mask pattern, a material having more excellent characteristics for the transmittance or uniformity of refractive index is used.
However, even a material having high and uniform transmittance and refractive index does not always present a desired resolution when a plurality of materials are combined to form an optical system.
DISCLOSURE OF THE INVENTION
The present invention has been made in consideration of the above problems of the prior art, and has as its object to provide a method of manufacturing a silica glass member, which makes it possible to efficiently and properly obtain a silica glass member necessary for obtaining a sufficiently high resolution in the imaging optical system of a projection exposure apparatus, and a silica glass member obtained by the manufacturing method.
As a result of extensive studies aiming at achieving the above object, the present inventors have found that the imaging performance of a projection optical system and the resolution of a projection exposure apparatus are affected by the birefringence of an optical member, and when the magnitude of the birefringence, i.e., the birefringence value (absolute value) of an optical member is 2 nm/cm or less, and the distribution of birefringence values in the optical member has a central symmetry, imaging performance close to the designed performance of the projection optical system and a resolution close to the designed performance of the projection exposure apparatus are obtained, and have disclosed it in Japanese Patent Laid-Open No. 8-107060.
However, when the required resolution of a projection exposure apparatus further rises, and light having a shorter wavelength is used as exposure light, or an optical member having a large diameter and thickness is used, no satisfactory imaging performance of the projection optical system and no satisfactory resolution of the projection exposure apparatus can be obtained even by employing the conventional design concept.
As a result of more extensive studies, the present inventors have found, as a reason why a projection optical system and projection exposure apparatus having desired optical performance cannot be obtained even by using an optical member having a satisfactory transmittance or satisfactorily uniform refractive index, that since the optical members have birefringence value distributions, respectively, and the birefringence value distributions are integrated in the entire optical system when a plurality of optical members are combined as a projection optical system, the light wavefront of the entire optical system is disturbed, adversely affecting the imaging performance of the projection optical system or resolution of the projection exposure apparatus.
More specifically, the conventional evaluation of the birefringence value of an optical member is done only on the basis of its magnitude (absolute value), and there is no concept of the birefringence value distribution of an optical member. For example, to measure the birefringence value of a silica glass member, birefringence values are measured at several points near 95% of the diameter of the member, and the maximum value is used as the birefringence value of the member, as recognized by those who skilled in the art. However, the present inventors measured the distribution of birefringence values of a silica glass member in detail and found that the birefringence values actually have an uneven distribution.
Hence, even for a silica glass member having a highly uniform refractive index, the influence of birefringence in the member cannot be sufficiently evaluated only by managing the maximum value of the birefringence values in the member. Especially, it is very hard to obtain an optical system having desired performance by combining a plurality of members.
As described above, since the evaluation of birefringence in
Hiraiwa Hiroyuki
Nakagawa Kazuhiro
Griffin Steven P.
Lopez Carlos
Nikon Corporation
LandOfFree
Method of manufacturing silica glass member and silica glass... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing silica glass member and silica glass..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing silica glass member and silica glass... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3280360