U.S. patent application number 10/748193 was filed with the patent office on 2004-08-05 for synthesized silica glass optical member and method for manufacturing the same.
This patent application is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Abe, Jun, Ejima, Seiki, Makikawa, Shinji, Mantoku, Nonuyasu.
Application Number | 20040148968 10/748193 |
Document ID | / |
Family ID | 18579349 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040148968 |
Kind Code |
A1 |
Abe, Jun ; et al. |
August 5, 2004 |
Synthesized silica glass optical member and method for
manufacturing the same
Abstract
A method for manufacturing a synthesized silica glass optical
member, the method comprising: providing a porous silica glass
body; heating the porous silica glass body in an atmosphere
containing hydrogen or oxygen, and sintering the porous silica
glass body in an atmosphere containing fluorine compound.
Furthermore, a synthesized silica glass optical member manufactured
by the method.
Inventors: |
Abe, Jun; (Annaka-Shi,
JP) ; Mantoku, Nonuyasu; (Annaka-Shi, JP) ;
Makikawa, Shinji; (Annaka-Shi, JP) ; Ejima,
Seiki; (Kita-gun, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
Shin-Etsu Chemical Co.,
Ltd.
Tokyo
JP
|
Family ID: |
18579349 |
Appl. No.: |
10/748193 |
Filed: |
December 31, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10748193 |
Dec 31, 2003 |
|
|
|
09797857 |
Mar 5, 2001 |
|
|
|
6701752 |
|
|
|
|
Current U.S.
Class: |
65/111 ;
65/397 |
Current CPC
Class: |
C03C 4/0085 20130101;
C03C 2203/44 20130101; C03C 2201/12 20130101; C03C 4/0071 20130101;
C03C 2201/21 20130101; C03C 3/06 20130101; C03B 2201/21 20130101;
C03C 23/007 20130101; C03B 19/1453 20130101; C03B 2201/12
20130101 |
Class at
Publication: |
065/111 ;
065/397 |
International
Class: |
C03B 037/075 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2000 |
JP |
2000-058810 |
Claims
What is claimed is:
1. A method for manufacturing a synthesized silica glass optical
member, said method comprising: providing a porous silica glass
body; heating the porous silica glass body in an atmosphere
containing hydrogen; and sintering the porous silica glass body in
an atmosphere containing a fluorine compound.
2. The method according to claim 1, wherein a temperature of said
heating is within a range from 500.degree. C. to a critical
temperature below which the porous silica glass body does not
shrink.
3. The method according to claim 2, wherein a temperature of said
heating is 1250.degree. C. or below.
4. The method according to claim 1, wherein said heating precedes
said sintering.
5. The method according to claim 1, wherein said providing the
glass body includes forming glass particles by flame hydrolysis of
a raw material.
6. A method for manufacturing a synthesized silica glass optical
member, said method comprising: providing a porous silica glass
body; heating the porous silica glass body in an atmosphere
containing oxygen; and sintering the porous silica glass body in an
atmosphere containing a fluorine compound.
7. The method according to claim 6, wherein a temperature of said
heating is within a range from 500.degree. C. to a critical
temperature below which the porous silica glass body does not
shrink.
8. The method according to claim 7, wherein a temperature of said
heating is 1250.degree. C. or below.
9. The method according to claim 6, wherein said heating precedes
said sintering.
10. The method according to claim 6, wherein said providing the
glass body includes forming glass particles by flame hydrolysis of
a raw material.
11. The method according to any one of claims 1-10, wherein the
fluorine compound comprises SiF.sub.4.
12. A synthesized silica glass optical member manufactured by a
method according to any one of claims 1-11.
13. A method for a lithography using a photo mask, in which the
photo mask utilizes a glass optical member, said method comprising:
providing a porous silica glass body for the glass optical member;
heating the porous silica glass body in an atmosphere containing
hydrogen; and sintering the porous silica glass body in an
atmosphere containing a fluorine compound.
14. The method according to claim 13, further comprises providing a
light source of the lithography having a wavelength of 400 nm or
less.
15. The method according to claim 14, wherein the light source
includes an F.sub.2 excimer laser a light source.
16. A method for a lithography using a photo mask, in which the
photo mask utilizes a glass optical member, said method comprising:
providing a porous silica glass body for the glass optical member;
heating the porous silica glass body in an atmosphere containing
oxygen; and sintering the porous silica glass body in an atmosphere
containing a fluorine compound.
17. The method according to claim 16, further comprises providing a
light source of the lithography having a wavelength of 400 nm or
less.
18. The method according to, claim 17, wherein the light source
includes an F.sub.2 excimer laser a light source.
Description
[0001] This patent application claims priority based on a Japanese
patent application No. 2000-58810 filed on Mar. 3, 2000, the
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical member to be
used in an apparatus using a light source of an ultraviolet laser
having a wavelength of 400 nm or less, especially F.sub.2 excimer
laser. The present invention particularly relates to a synthesized
silica glass optical member suitable for a lens, a window member, a
mirror, a prism, a filter, and the like, and a method for
manufacturing it.
[0004] 2. Description of the Related Art
[0005] Because synthesized silica glass contains a quite small
amount of metal impurities that absorb light, and has high purity,
the synthesized silica glass has high transparency over a wide
wavelength range from a near-infrared region to a vacuum
ultraviolet region to be transparent. In addition, the synthesized
silica glass has a very small thermal expansion coefficient to be
excellent in the stability of size. Accordingly, the synthesized
silica glass has mainly been used as optical members of optical
apparatus using the g-ray (436 nm) and the i-ray (365 nm) as their
light sources conventionally.
[0006] Recently, as LSI's (Large Scale. Integrated circuits) have
highly been integrated, a fine drawing technique capable of drawing
lines narrower in width is required for an optical lithography
technique for drawing integrated circuit patterns on wafers.
Accordingly, the wavelengths of exposure light sources have been
being shortened. As a result, KrF excimer lasers (248 nm) and ArF
excimer lasers (193 nm), both having wavelengths shorter than the
conventional g-ray (436 nm) and the i-ray (365 nm), have come to be
used as light sources of steppers for lithography. Moreover, the
examination about F.sub.2 excimer lasers (157 nm) having a shorter
wavelength also has begun. On the other hand, photomask substrates
for optical members to be used in the steppers are required to have
characteristics such as optical transparency in the wavelength
ranges to be used, stability and durability.
[0007] Conventional synthesized silica glass to be used in these
optical systems produces new absorption bands in an ultraviolet
region when it is irradiated by a high energy ray of, for example,
a KrF excimer laser (248 nm) or an ArF excimer laser (193 nm) for a
long time. The synthesized silica glass produces an absorption band
of about 215 nm in wavelength, the so-called E' center, and an
absorption band of about 260 nm in wavelength, the so-called NBOHC
(Non-Bridging Oxygen Hole Center). These absorption bands produce
such undesirable phenomena in these optical systems as the decrease
of their transmittancy, the increase of their absolute refractive
indices, the changes of their distributions of the refractive
indices, the generation of fluorescence, and the like.
Consequently, the conventional synthesized silica glass has the
aforesaid problems for being used as an optical member of optical
systems having a light source of an excimer laser.
[0008] The mechanism of the generation of these absorption bands
has not fully investigated, however the mechanism can be considered
that the new absorption bands are produced owing to paramagnetic
defects that are produced in the synthesized silica glass owing to
the optical reactions that are expressed by the following formulae
(1) and (2) and generated by the irradiation of a laser beam on
such peculiar defects of the synthesized silica glass as an oxygen
lacking type defect expressed by a chemical formula
.ident.Si--Si.ident.and an oxygen excessive type defect expressed
by a chemical formula .ident.Si--O--O--Si.ident..
.ident.Si--Si.ident.+h.nu..fwdarw.2.ident.Si. (1)
.ident.Si--O--O--Si.ident.+h.nu..fwdarw.2.ident.Si--O. (2)
[0009] Accordingly, for the improvement of the transparency in the
wavelength band of F.sub.2 excimer lasers, there have been made
attempts to obtain the durability to the irradiation of the
ultraviolet rays by making silica glass obtained by the vapor-phase
axial deposition (VAD) method contain fluorine, or by making silica
glass obtained by the flame hydrolysis method called as the direct
method contain hydroxyl groups or hydrogen molecules.
[0010] For example, Japanese Laid-Open Patent Publication HEI
10-67521 discloses a method for adding a fluorine gas to a porous
silica glass by making a raw material gas contain the fluorine gas
at the time of forming the porous silica glass body by generating
the flame hydrolysis of the raw material with a burner. Japanese
Laid-Open Patent Publication HEI 11-240728 discloses a method for
making a porous silica glass body transparent glass by heating the
porous silica glass body in an atmosphere including a hydrogen gas
and a water vapor at 1400.degree. C. or more. Moreover, Japanese
Laid-Open Patent Publications HEI 8-67530 and HEI 8-75901 disclose
a method of the heat treatment of a porous silica glass body in a
hydrogen gas atmosphere after the vitrification of the porous
silica glass body in an atmosphere of a SiF.sub.4/He gas.
[0011] However, even in the thus manufactured high purified
synthesized silica glass, absorption bands owing to structural
defects called as the E' centers and the NBOHC's appear to decrease
the transmittancy thereof in an ultraviolet region extremely when
the synthesized silica glass is irradiated by an excimer laser beam
for a long time.
SUMMARY OF THE INVENTION
[0012] Therefore, it is an object of the present invention to
provide a synthesized silica glass optical member and method
therefor which overcome the above issues in the related art. This
object is achieved by combinations described in the independent
claims. The dependent claims define further advantageous and
exemplary combinations of the present invention.
[0013] Another object of the present invention is to improve the
transmittancy of a synthesized silica glass, aforementioned, to
which fluorine compound is added in the ultraviolet region and to
suppress the generation of absorption and fluorescence emission by
the irradiation of an excimer laser beam. Further object of the
present invention is, therefore, to provide a synthesized silica
glass optical member excellent in laser light durability
characteristics as an optical glass member for transmitting
ultraviolet rays, and to provide a method for manufacturing it.
[0014] According to a first aspect of the present invention, there
is provided a method for manufacturing a synthesized silica glass
optical member, said method comprising: providing a porous silica
glass body; heating the porous silica glass body in an atmosphere
containing hydrogen or oxygen, and sintering the porous silica
glass body in an atmosphere containing fluorine compound.
[0015] According to a second aspect of the present invention, there
is provided a synthesized silica glass optical member manufactured
by the method above.
[0016] According to a third aspect of the present invention, there
is provided a method for a lithography using a photo mask, in which
the photo mask utilizes a glass optical member, said method
comprising: providing a porous silica glass body for the glass
optical member; heating the porous silica glass body in an
atmosphere containing hydrogen or oxygen; and sintering the porous
silica glass body in an atmosphere containing a fluorine
compound.
[0017] This summary of the invention does not necessarily describe
all necessary features of the present invention. The present
invention may also be a sub-combination of the above described
features. The above and other features and advantages of the
present invention will become more apparent from the following
description of embodiments taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of the presently preferred exemplary embodiments of the
invention taken in conjunction with the accompanying drawings.
[0019] FIG. 1 shows an apparatus for a VAD method for manufacturing
a porous silica glass, body, according to an embodiment of the
present invention.
[0020] FIG. 2 shows an apparatus for a high temperature treatment
and vitrification process for manufacturing an synthesized silica
glass, according to the embodiment of the present invention.
[0021] FIG. 3 is a graph showing the characteristics of the
transmittancy of synthesized silica glass obtained in Example 1
according to an embodiment of the present invention and Comparative
examples 1-3.
[0022] FIG. 4 is a graph showing the characteristics of the
transmittancy of synthesized silica glass obtained in Example 2
according to the embodiment of the invention and Comparative
examples 4-6.
[0023] FIG. 5 is a table showing the conditions of the processing
of Example 1 and Comparative examples 1-3.
[0024] FIG. 6 is a table showing the conditions of the processing
of Example 2 and Comparative examples 4-6.
DETAILED DESCRIPTION OF EMBODIMENTS
[0025] The invention will now be described based on the
embodiments, which do not intend to limit the scope of the present
invention, but exemplify the invention. All of the features and the
combinations thereof described in the embodiment are not
necessarily essential to the invention.
[0026] The inventors of the present invention performed studies in
detail about a sintering atmosphere at the time of the
vitrification of a porous silica glass body. As a result, the
inventors found the following fact and resolved the aforesaid
problem. That is, when the porous silica glass body is heated at a
high temperature at which the porous silica glass body does not
shrink in an atmosphere containing hydrogen or oxygen at first, and
then the porous silica glass body is sintered by being further
heated to be transparent glass, the transmittancy of the porous
silica glass body is improved by about 5% or more than that of the
conventional one.
[0027] In an embodiment of the present invention, a porous silica
glass body for a synthesized silica glass optical member is
obtained by a VAD method. The VAD method may be achieved by using,
for instance, an apparatus as shown in FIG. 1. An initial material
not shown is attached with a support shaft 16, which is rotatable
around its axis and movable in the axial direction. A raw material,
SiCl.sub.4, oxygen and hydrogen with an argon gas as a carrier gas
are supplied to a burner 14. Glass particle are formed by flame
hydrolysis reactions caused in the flame by the burner. The glass
particles thus formed are deposited on a growing portion 12 of a
porous silica glass body 10 which is growing on the initial
material while the silica glass body 10 is rotating around the axis
of the support shaft 16 and being moved along with the support
shaft 16 in the axial direction.
[0028] The porous silica glass 10 thus obtained is subjected to
heat treatments, using an apparatus as shown in FIG. 2. The porous
silica glass body 10 which is supported by the support shaft 22 is
heated with an atmosphere containing hydrogen or oxygen by a heater
18 in a container 20. Then, the porous silica glass body 10 is
sintered with an atmosphere containing fluorine compound within the
container 20 by the heater 18 it to be transparent glass. In this
embodiment, these two processes are carried out with the same
apparatus. However, it is not limited to the embodiment, and
different equipments may be used for the respective processes.
[0029] The step of heating the porous silica glass body is
preferably performed within a temperature range from 500.degree. C.
to a critical temperature below which the porous silica glass body
does not shrink, especially below a temperature of 1250.degree.
C.
[0030] A synthesized silica glass optical member according to the
embodiment of the present invention is manufactured by the method
described above.
[0031] The optical member thus formed is applied to a photo mask of
a lithography. For the lithography, a light source of an
ultraviolet laser having a wavelength of 400 nm or less, especially
F.sub.2 excimer laser is used.
EXAMPLES
Example 1
[0032] A porous silica glass body was obtained by a VAD method,
using an apparatus as shown in FIG. 1 in which the flame hydrolysis
reactions of a raw material, SiCl.sub.4, were caused in the flames
of oxygen and hydrogen with an argon gas as a carrier gas. The
density of the obtained porous silica glass body was 0.22
g/cm.sup.3. The obtained porous silica glass body was processed by
the first processing in which the porous silica glass body was
passed through in a hydrogen and helium atmosphere at a temperature
of 1,000.degree. C. at a passing speed of 3 mm/min. in the high
temperature section at first. Then, the porous silica glass body
was processed by the second processing (sintering) in which the
porous silica glass body was passed through in a SiF.sub.4
atmosphere at a temperature of 1,380.degree. C. at a passing speed
of 3 mm/min. in the high temperature section. Thereby, a
transparent glass body was obtained. The obtained transparent glass
body was sliced and polished into the thickness of 10 mm, and the
transmittancy thereof in an ultraviolet region was measured. The
processing conditions are shown in FIG. 5, and the results of the
measurements are shown in FIG. 3.
Comparative Examples 1-3
[0033] Porous silica glass bodies as comparative examples were made
similarly to Example 1 of the embodiment of the present invention.
The porous silica glass bodies of Comparative Examples 1-3 were
sintered under the conditions shown in FIG. 5, and transparent
glass bodies were obtained.
[0034] More specifically, the porous silica glass body for
Comparative Example 1 was subjected to only one heating process
such that the porous silica glass body was passed through in a
SiF.sub.4 atmosphere at a temperature of 1,380.degree. C. at a
passing speed of 3 mm/min without any pre-heating process.
[0035] The porous silica body for Comparative Example 2 was also
subjected to only one heating process such that the porous silica
glass body was passed through in an SiF.sub.4 and H.sub.2
atmosphere at a temperature of 1,380.degree. C. at a passing speed
of 3 mm/min without any pre-heating process.
[0036] The porous silica body for Comparative Example 3 was
processed by the first processing in which the porous silica glass
body was passed through in a helium and Cl.sub.2 atmosphere at a
temperature of 1,000.degree. C. at a passing speed of 3 mm/min. in
the high temperature section at first, for dehydration. Then, the
porous silica glass body was processed by the second processing for
sintering in which the porous silica glass body was passed through
in a SiF.sub.4 and H.sub.2 atmosphere at a temperature of
1,380.degree. C. at a passing speed of 3 mm/min. in the high
temperature section.
[0037] The obtained transparent glass bodies were sliced and
polished into the thickness of 10 mm, respectively, and the
transmittancy of them was measured in an ultraviolet region. The
results of the measurements are shown in FIG. 3.
[0038] As apparent from FIG. 3, it is recognized that the
transmittancy of the curved line 1 indicating the results of
Example 1 according to the embodiment of the invention in the
ultraviolet region, especially at the wavelength of 157 nm of the
F.sub.2 excimer laser beam is 75.0% that is improved by 6.6% in
comparison with the 68.4% of the curved line 2 (Comparative example
1). Incidentally, the transmittancy of the curved line 3
(Comparative example 2) and the curved line 4 (Comparative example
3) is zero at the wavelength of 157 nm, and the comparative
examples 2 and 3 are not fitted as an optical member of an
apparatus using the F.sub.2 excimer laser as its light source.
[0039] By the performance of the first processing in a hydrogen
atmosphere according to the embodiment of the invention, it can be
recognized that the transmittancy in the ultraviolet region is
remarkably improved.
Example 2
[0040] A porous silica glass body was obtained by the VAD method,
using the apparatus as shown in FIG. 1 in which the flame
hydrolysis reactions of a raw material, SiCl.sub.4, were caused in
the flames of oxygen and hydrogen with an argon gas as a carrier
gas. The density of the obtained porous silica glass body was 0.22
g/cm.sup.3. The obtained porous silica glass body was processed by
the first processing in which the porous silica glass body was
passed through in a oxygen and helium atmosphere at a temperature
of 1,000.degree. C. at a passing speed of 3 mm/min. in the high
temperature section. Then, the porous silica glass body was
processed by the similar second processing for sintering in a
SiF.sub.4 atmosphere at a temperature of 1,380.degree. C. Thereby,
a transparent glass body was obtained. The obtained transparent
glass body was sliced and polished into the thickness of 10 mm, and
the transmittancy thereof in an ultraviolet region was measured.
The processing conditions are shown in FIG. 6, and the results of
the measurements are shown in FIG. 4.
Comparative Examples 4-6
[0041] Porous silica glass bodies were made similarly to Example
according to the embodiment of the present invention. The porous
silica glass bodies were sintered under the conditions shown in
FIG. 6, and transparent glass bodies were obtained.
[0042] More specifically, the porous silica glass body for
Comparative Example 4 was subjected to only one heating process
such that the porous silica glass body was passed through in a
SiF.sub.4 atmosphere at a temperature of 1,380.degree. C. at a
passing speed of 3 mm/min without any pre-heating process.
[0043] The porous silica body for Comparative Example 5 was also
subjected to only one heating process such that the porous silica
glass body was passed through in an SiF.sub.4 and O.sub.2
atmosphere at a temperature of 1,380.degree. C. at a passing speed
of 3 mm/min without any pre-heating process.
[0044] The porous silica body for Comparative Example 6 was
processed by the first processing in which the porous silica glass
body was passed through in a helium and Cl.sub.2 atmosphere at a
temperature of 1,000.degree. C. at a passing speed of 3 mm/min. in
the high temperature section at first, for dehydration. Then, the
porous silica glass body was processed by the second processing for
sintering in which the porous silica glass body was passed through
in a SiF.sub.4 and O.sub.2 atmosphere at a temperature of
1,380.degree. C. at a passing speed of 3 mm/min. in the high
temperature section.
[0045] The obtained transparent glass bodies were sliced and
polished into the thickness of 10 mm, respectively, and the
transmittancy of them was measured in an ultraviolet region. The
results of the measurements are shown in FIG. 4.
[0046] As apparent from FIG. 4, it is recognized that the
transmittancy of the curved line 1 indicating the results of
Example 2 according to the embodiment of the present invention in
the ultraviolet region, especially at the wavelength of 157 nm of
the F.sub.2 excimer laser beam is 72.2% that is improved by 5.2% in
comparison with the 67.0% of the curved line 2 (Comparative example
4). Moreover, it is also recognized that the transmittancy of the
curved line 1 is far higher than the transmittancy, 24.7%, of the
curved line 3 (Comparative example 5) and that, 26.6%, of the
curved line 4 (Comparative example 6).
[0047] By the performance of the first processing in an oxygen
atmosphere, it is recognized that the transmittancy in the
ultraviolet region is remarkably improved.
[0048] The synthesized silica glass optical member obtained by the
method according to the embodiment of the present invention can
suppress the generation of absorption and fluorescence emissions
when it is irradiated by an excimer laser beam, and has high
transmittancy in an ultraviolet region, especially at the
wavelength of 157 nm of a F.sub.2 excimer laser beam. Consequently,
the synthesized silica glass optical member is excellent in a laser
beam resistance characteristic.
[0049] Although the present invention has been described by way of
exemplary embodiments, it should be understood that many changes
and substitutions may be made by those skilled in the art without
departing from the spirit and the scope of the present invention
which is defined only by the appended claims.
* * * * *