U.S. patent application number 09/921137 was filed with the patent office on 2002-03-28 for fluorine-containing glass.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Enomoto, Tadashi, Ohga, Yuichi.
Application Number | 20020037797 09/921137 |
Document ID | / |
Family ID | 26597418 |
Filed Date | 2002-03-28 |
United States Patent
Application |
20020037797 |
Kind Code |
A1 |
Ohga, Yuichi ; et
al. |
March 28, 2002 |
Fluorine-containing glass
Abstract
Fluorine-containing glass which comprises silica and contains,
in said silica, not more than 10 ppm of OH group, not more than 10
ppm of Cl and not less than 1000 ppm of F, said fluorine-containing
glass having a concentration ratio of F/Cl of 100 or more. Also
disclosed is fluorine-containing glass which contains not more than
10 ppm of OH group, not more than 10 ppm of Cl and not less than
1000 ppm of F, and has a concentration ratio of F/Cl of 1000 or
more.
Inventors: |
Ohga, Yuichi; (Kanagawa,
JP) ; Enomoto, Tadashi; (Kanagawa, JP) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Sumitomo Electric Industries,
Ltd.
|
Family ID: |
26597418 |
Appl. No.: |
09/921137 |
Filed: |
August 3, 2001 |
Current U.S.
Class: |
501/54 |
Current CPC
Class: |
C03B 19/1453 20130101;
C03B 19/1423 20130101; C03B 2207/36 20130101; C03B 2207/70
20130101; C03C 3/06 20130101; C03B 2201/07 20130101; C03C 23/0025
20130101; C03B 2201/12 20130101; C03B 2201/075 20130101; C03C
2201/23 20130101; C03B 2207/30 20130101; C03C 2203/54 20130101;
C03C 2201/11 20130101; C03C 2201/12 20130101; C03B 2207/32
20130101 |
Class at
Publication: |
501/54 |
International
Class: |
C03C 003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2000 |
JP |
P. 2000-237361 |
Jun 22, 2001 |
JP |
P. 2001-189837 |
Claims
What is claimed is:
1. Fluorine-containing glass which comprises silica and contains,
in said silica, not more than 10 ppm of OH group, not more than 10
ppm of Cl and not less than 1000 ppm of F, said fluorine-containing
glass having a concentration ratio of F/Cl of 100 or more.
2. Fluorine-containing glass which contains not more than 10 ppm of
OH group, not more than 10 ppm of Cl and not less than 1000 ppm of
F, and has a concentration ratio of F/Cl of 1000 or more.
3. Fluorine-containing glass which contains not more than 10 ppm of
OH group, not more than 1 ppm of Cl and not less than 1000 ppm of
F, and has a concentration ratio of F/Cl of 10000 or more.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to fluorine-containing glass
and, more particularly, is to provide a glass composition having
improved transmittance in the UV region.
BACKGROUND OF THE INVENTION
[0002] Synthetic silica glass articles have widely been used as
optical parts and materials for optical transmission media such as
optical fibers and optical wave guides, devices using various
optical sources and working machines based on their excellent
properties that they are transparent for radiation of a wide
wavelength range covering UV region and vacuum UV region as well as
near infrared region and visible region (which means they suffer
less transmission loss), that they have enough resistance against
change in temperature, and that they have a smaller linear
expansion coefficient and an enough corrosion resistance. However,
pure silica glass has a problem that they generate a new absorption
band upon being irradiated with high energy UV rays, resulting in
reduction in transmittance, change in refractive index and
generation of fluorescent light.
[0003] In addition, in the use of semiconductor-manufacturing
apparatus, LCD substrates and substrates for photomask, a much more
improved heat resistance is being required for silica glass. For
example, JP-A-5-97466 (Literature 1) (The term "JP-A" as used
herein means an "unexamined published Japanese patent application")
proposes, as glass containing less contents of water and halogen
and having a high heat resistance, dehydrated glass containing 90%
by weight or more of silica, 1 ppm or less of aluminum, 100 ppm or
less of water and 100 ppm or less of chlorine and having an
annealing point of 1150.degree. C. or higher, and a process for
producing the dehydrated glass utilizing microwave heating.
[0004] There has been fluorine-containing glass having a refractive
index and a viscosity decreased by adding fluorine to pure quartz
(synthetic silica glass), and it is known that the above-described
problem with respect to UV transmittance can be solved by the
addition of fluorine.
[0005] For example, JP-A-11-305419 (Literature 2) proposes
synthetic silica glass containing 1000 ppm or more of OH group, 50
ppm or less of chlorine and 300 ppm or more of fluorine, and
synthetic silica glass containing 100 ppm or less of OH group and
100 to 30000 ppm of fluorine, as glasses showing a high
transmittance for radiation of a short wavelength region and a good
UV ray resistance.
[0006] As one use of the synthetic silica glass under irradiation
with UV rays, there is a use as a material for photomask substrate
to be subjected to a photo-lithography process wherein an
integrated circuit pattern is formed on a wafer upon manufacturing
LSI. In recent years, with an increase in degree of integration and
performance of LSIs, a technology of forming patterns with a finer
line width of 0.2 .mu.m or less has been required, and thus light
sources for exposure to be used in steppers for lithography, which
are capable of emitting shorter wavelength radiation, having been
intended to develop.
[0007] That is, it has been demanded that the light source be
changed so as to provide shorter wavelength radiation, from
conventional g-line emitted from a mercury lamp (436 nm in
wavelength) to i-line (365 nm), KrF excimer laser (248 nm) and ArF
excimer laser (193 nm), and further to a low-pressure mercury lamp
(185 nm), ArCl excimer laser, ArCl excimer lamp (175 nm), Xe.sub.2
excimer laser and Xe.sub.2 excimer lamp (172 nm) and F.sub.2 laser
(157.6 nm).
[0008] However, pure silica glass (SiO.sub.2) per se scarcely
transmits F.sub.2 laser (157.6 nm in wavelength), though it can be
used to the level of ArF excimer laser (193 nm). Even the synthetic
silica glasses having an adjusted composition as described in the
foregoing Literatures 1 and 2 are still insufficient as to UV ray
transmittance and laser resistance in the vacuum UV ray region of
200 nm or less such as the wavelength of F.sub.2 laser radiation.
Hence, it has been urged to develop synthetic silica glass having
sufficient transmittance for UV rays with a much higher energy and
UV ray resistance.
SUMMARY OF THE INVENTION
[0009] The present invention has been made in view of the foregoing
problems.
[0010] Accordingly, an object of the present invention is to
provide fluorine-containing silica glass which has a high UV
ray-transmitting characteristic in a UV region of 200 nm or less in
wavelength (vacuum UV region) such as a F.sub.2 laser radiation and
has sufficient UV ray resistance.
[0011] Other objects and effects of the present invention will
become apparent from the following description.
[0012] According to a recent report, "Dry & F doped Fused
Silica", so-called "OH group-free, F-doped silica glass", is
believed to be the best material as a material adapted for F.sub.2
laser radiation ("Concerning photomasks adapted for F.sub.2 laser"
by Hiroki Jinbo, Optical Alliance, vol. 11, No. 4, pp. 20 to 25,
published by Nikkan Kogyo Shuppan in year 2000: Literature 3).
However, investigation of the present inventors revealed that, even
the concentration of OH group is at a low level the glass fails to
have sufficient transmittance and laser resistance when the
concentration of fluorine is at a low level.
[0013] As a result of extensive investigation on glass
compositions, the inventors found that transmittance properties in
a vacuum UV region of 200 nm or less and laser resistance can be
improved by adjusting contents and content ratio to such specific
ranges that OH group content is 10 ppm or less, Cl content is 10
ppm or less, and F content is 1000 ppm or more, with F/Cl ratio
being 100 or more. The present invention is based on this
finding.
[0014] That is, the above-described objects of the present
invention have been achieved by providing the following
fluorine-containing glasses.
[0015] (1) Fluorine-containing glass which comprises silica and
contains, in said silica, not more than 10 ppm of OH group, not
more than 10 ppm of Cl and not less than 1000 ppm of F, said
fluorine-containing glass having a concentration ratio of F/Cl of
100 or more.
[0016] (2) Fluorine-containing glass which contains not more than
10 ppm of OH group, not more than 10 ppm of Cl and not less than
1000 ppm of F, and has a concentration ratio of F/Cl of 1000 or
more.
[0017] (3) Fluorine-containing glass which contains not more than
10 ppm of OH group, not more than 1 ppm of Cl and not less than
1000 ppm of F, and has a concentration ratio of F/Cl of 10000 or
more.
[0018] The reasons why transmittance properties in the vacuum UV
region and laser resistance can be improved by the constitution of
the invention may be considered as follows.
[0019] It is considered that the structure of the
fluorine-containing glass is fundamentally based on SiO.sub.1.5F
structure (3SiO.sub.2+SiF.sub.4.fwdarw.4SiO.sub.1.5F). That is, the
fluorine-containing glass is considered to have the structure
wherein Si is partly ended with F.
[0020] In order to ensure 80% or more transmittance at wavelengths
in the vacuum UV region, particularly at 157 nm which is the
wavelength of excimer laser and to obtain enough resistance against
a F.sub.2 laser, it is considered to be necessary to sufficiently
replace the bonds such as Si--OH, Si--Cl and Si--Si by Si--F bond
having a higher bond energy.
[0021] In the invention, portions of glass ended with F (Si--F) are
increased by decreasing the Cl content, increasing the F content,
and adjusting the concentration ratio of F/Cl to 100 or higher,
thus transmittance in the UV region and laser resistance being
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a graph showing the relation between the F/Cl
concentration ratios of the glass samples obtained in Examples 1
and 2 and Comparative Examples 1 and 2, and the degrees of
deterioration in transmittance (%) after irradiation with a F.sub.2
excimer laser (157 nm in wavelength)
[0023] FIG. 2 is a schematic diagram showing conditions of
dehydration step, F-adding step and vitrifying step employed in
Examples 1 and 2 and Comparative Example 1 of the invention.
[0024] FIG. 3 is a schematic diagram showing conditions of
dehydration step, F-adding step and vitrifying step employed in
Comparative Examples 2 and 3 and Examples 3 and 4 of the
invention.
[0025] FIG. 4 is a schematic diagram showing conditions of
dehydration step, F-adding step and vitrifying step employed in
Example 5 of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The OH group concentration in the glass of the invention is
adjusted to be 10 ppm or less. If it exceeds 10 ppm, there results
a serious absorption loss in the UV region, thus transmittance
being decreased.
[0027] The concentration of OH group is preferably minimized.
However, glass is generally produced by depositing glass fine
particles which are generated by hydrolysis reaction or oxidation
reaction of glass-forming gases in a flame (so-called VAD method or
OVD method), and hence OH group is unavoidably formed in the glass
during the glass-synthesizing step. As a step for removing the OH
groups (dehydration), the glass is heat-treated in a Cl-containing
inert gas atmosphere and, as a result, Si--Cl bond is formed in the
glass. However, it is not desirable that the concentration of Cl
increases too much in order for removing the OH group. Thus, the
upper limit of acceptable OH group concentration is 10 ppm.
[0028] In the invention, the concentration of Cl in the glass is
adjusted to be 10 ppm or less. As is described above, if the Cl
concentration exceeds 10 ppm, a sufficiently high UV ray
transmittance and high laser resistance cannot be obtained. On the
other hand, dehydration conditions that make the glass free from Cl
leave too much amount of OH group. Thus, the acceptable upper limit
of the Cl concentration is 10 ppm. Adjusting the Cl concentration
in the glass to less than 10 ppm can be achieved by, for example,
keeping at a low level the Cl concentration of the atmosphere in
which the glass is heat-treated to dehydrate. However, it is also
necessary at the same time that the amount of residual OH groups is
controlled to 10 ppm or less.
[0029] In the invention, the F concentration in the glass is
adjusted to be 1000 ppm or more, with F/C ratio (by concentration)
being 100 or more, more preferably 1000 or more.
[0030] By introducing F in such a large amount, the bonds of Si--OH
and Si--Cl formed in the synthesizing step and the dehydrating step
can be converted into Si--F bond having a higher bond energy, which
serves to obtain a high UV ray transmittance and enough laser
resistance. The upper limit of the F concentration is about 30,000
ppm, because this level is the maximum value obtainable by a
fluorine-consolidating method at ordinary temperature (sooting
-consolidating in an atmosphere of 100% F).
[0031] As is shown in Examples and Comparative Examples described
below, a degree of deterioration in transmittance after irradiation
with a F.sub.2 laser is represented as follows.
[0032] Degree of deterioration of transmittance
(%)=(T.sub.0-T.sub.1)/T.su- b.0.times.100 wherein
[0033] T.sub.0 represents a transmittance before irradiation with
the F.sub.2 laser and is taken as 100%, and
[0034] T.sub.1 represents a transmittance after irradiation.
[0035] In order to control the degree of transmittance
deterioration after irradiation with radiation of a wavelength of
157 nm to a level of <5%, it is necessary to adjust the F/Cl
concentration ratio to be >100, the OH concentration to be
.ltoreq.10 ppm, the Cl concentration to be .ltoreq.10 ppm and the F
concentration to be .gtoreq.1000 ppm.
[0036] Further, to adjust the degree of transmittance deterioration
to 1%, it is necessary to control the F/Cl concentration ratio to
be .gtoreq.1000, the OH concentration to be .ltoreq.10 ppm, the Cl
concentration to be .ltoreq.10 ppm and the F concentration to be
.gtoreq.1000 ppm.
[0037] In producing the fluorine-containing glass of the invention,
raw materials of glass such as SiCl.sub.4, HSiCl.sub.3,
CH.sub.3SiCl.sub.3, (CH.sub.3).sub.2SiCl.sub.2,
CH.sub.3Si(CH.sub.3O).sub.3 and Si (OCH.sub.3).sub.4 and, if
necessary, an inert gas are introduced into a flame comprising a
fuel gas such as hydrogen (H.sub.2) or a hydrocarbon such as
CH.sub.4 and a combustion-aiding gas such as oxygen to cause flame
hydrolysis reaction of the raw materials in the flame, and glass
fine particles (SiO.sub.2) thus produced are deposited to obtain a
glass fine particle deposit body.
[0038] In order to attain the OH group amount according to the
invention, conditions in the steps of synthesizing and depositing
glass fine particles are adjusted so that OH group is difficultly
introduced into the glass. For this purpose, the synthesis of the
glass fine particles is carried out by controlling the-flow rate of
the fuel gas such as hydrogen and the combustion-aiding gas such as
oxygen fed to a burner for synthesis so as to minimize the amount
of OH group in the resultant glass or, as described below, by
introducing a halogen-containing gas into the burner together with
the glass raw material gases upon the glass synthesis to synthesize
glass fine particles while conducting dehydration.
[0039] In addition, in the subsequent dehydrating step, the
concentration of a dehydrating gas, heating temperature and heating
time are adjusted so as to attain sufficient dehydration.
[0040] On the other hand, the Cl amount according to the invention
can be attained by, for example, decreasing the Cl amount in the
atmosphere in the case where a Cl-containing gas such as a chlorine
gas (Cl.sub.2) is used as a dehydrating gas, or by adding a large
amount of F in the F-adding step to convert Si--Cl bond into Si--F
bond.
[0041] As for conditions in the dehydration step, heat treatment is
conducted at a temperature of 800 to 1200.degree. C. in a
halogen-containing atmosphere. As the halogen, halogen compounds
such as CF.sub.4, C.sub.2F.sub.6, SiF.sub.4 and Si.sub.2F.sub.6 may
be used as well as the Cl compounds such as Cl.sub.2, SOCl.sub.2
and SiCl.sub.4. As other atmospheric gas, it is preferred to use,
for example, a He gas.
[0042] In order for adding F to the glass of the invention, the
glass fine particle deposit body is subjected to dehydration
treatment, then heat treated in a F-containing atmosphere at a
temperature of 1000 to 1500.degree. C., followed by vitrification,
alternatively, the glass is consolidated to vitrify while adding F.
Examples of the F compound for use in the atmosphere in the
F-adding step include, for example, SiF.sub.6, SF.sub.6, CF.sub.4
and C.sub.2F.sub.6. As other atmospheric gases, those illustrated
with respect to the dehydrating step may be used.
[0043] In the glass-vitrifying step, the glass may be heated to
1400 to 1500.degree. C. in the F-containing atmosphere, as in the
F-adding step, to vitrify, or alternatively, vitrification may be
conducted in a F-free atmosphere (for example, atmosphere of He gas
alone). In view of characteristic properties, it is preferred to
vitrify in the F-containing atmosphere.
[0044] In the invention, another preferred embodiment of the
process is that in which a gas of a F-containing compound is
introduced together with the gas of raw materials of glass into the
flame upon synthesis of a glass fine particle deposit body to
thereby previously produce a glass fine particle deposit body
having less content of OH group, then the deposit body is subjected
to dehydration step under the condition of a decreased Cl amount,
followed by addition of F and glass vitrification. As the
F-containing compound, the same compounds as illustrated with
respect to the F-adding step may be used.
[0045] The present invention will be illustrated in greater detail
with reference to the following Examples, but the invention should
not be construed as being limited thereto.
EXAMPLE 1
[0046] 9 slm (liter/min) of a glass raw material gas of SiCl.sub.4,
180 liters/min of H.sub.2, 180 liters/min of O.sub.2 and 20
liters/min of Ar were introduced into a concentric 12-fold pipe
burner, and an SiO.sub.2 soot (porous matrix) having a diameter of
150 mm and a length of 600 mm was synthesized according to flame
hydrolysis method. This soot was retained in a uniformly heating
furnace, and heated in an atmosphere comprising a He gas and a
Cl.sub.2 gas and having a Cl concentration of 0.5 mol at a rate of
3.degree. C./min from 800 to 1100.degree. C. to conduct dehydration
treatment and, at 1100.degree. C., the atmosphere was changed to a
helium atmosphere containing 5 mol % of SiF.sub.4 to thereby
initiate the fluorine-adding treatment. After retaining for 60
minutes at the temperature, the temperature was raised at a rate of
3.degree. C./min up to 1450.degree. C. and, and then retained for
30 minutes at 1450.degree. C. to vitrify (condition 1). The steps
employed in Condition 1 are schematically shown in FIG. 2.
[0047] The thus obtained fluorine-containing glass of the invention
(Example 1) was a transparent glass body. The OH group content was
measured with a sample having a diameter of 25 mm and a thickness
of 50 mm worked out from the transparent glass body. In addition,
the degree of deterioration in transmittance after irradiation with
F.sub.2 laser (taking initial transmittance as 100%; hereinafter
merely referred to as "degree of transmittance deterioration") was
determined by measuring transmittance of a sample having a diameter
of 25 mm and a thickness of 6.35 mm worked out from the transparent
glass body, before and after irradiation with a F.sub.2 laser,
using VUV-200 (trade name) made by Nippon Densi K.K. Irradiation
was conducted using a F.sub.2 laser (wavelength: 157 nm) at an
output power of 25 .mu.J/cm.sup.2 and 1.5.times.10.sup.9 pulses.
The results thus obtained are shown in Table 3 below.
[0048] Additionally, analysis of the composition of the transparent
glass body was conducted as follows.
[0049] Measurement of OH Concentration
[0050] Conducted according to the method described in D. M. Dood
and D. B. Fraser, "Optical determination of OH in fused silica",
Journal of Applied Physics, vol. 37 (1996), p.3911 (Literature
4).
[0051] Measurement of Cl Concentration
[0052] A sample was dissolved in a HF aqueous solution, and the HF
solution containing dissolved therein the sample was dropped on a
Si wafer using a pipet and, after drying, quantitative analysis of
Cl was conducted according to the whole reflection fluorescent
X-ray analyzing method (measuring device: TREX610 (trade name) made
by Technos).
[0053] Measurement of F Concentration
[0054] Conducted according to ion chromatography. First, 0.1 g of a
sample silica glass and 1 g of sodium carbonate were pulverized and
mixed, then heated to melt and, after cooling, ultra-pure water was
added thereto to prepare an aqueous solution. This aqueous solution
was passed through a cation exchange resin to separate away sodium
ion, and fluoride ion in the passed solution was quantitatively
measured according to ion chromatography.
EXAMPLES 2 AND COMPARATIVE EXAMPLE 1
[0055] Transparent glass bodies (Examples 2 and Comparative Example
1), obtained by subjecting the porous matrix prepared in the same
manner as in Example 1 to condition 2 or 3 wherein the atmosphere
of dehydrating step and the atmosphere of fluorine-adding and
consolidating steps were changed as shown in Table 1, were measured
with respect to concentrations of respective ingredients and degree
of transmittance deterioration in the same manner as in Example 1.
The results thus obtained are also shown in Table 3 and FIG. 1
below.
1 TABLE 1 Dehydrating Dehydrating F-Adding Vitrifying Vitrifying
Atmosphere Temperature Atmosphere F-adding Temperature Atmosphere
Temperature Example Condition 1 0.5% Cl.sub.2/He 1100.degree. C. 5%
SiF.sub.4/He 1100-1400.degree. C. 5% SiF.sub.4/He 1450.degree. C.
Example 1 Condition 2 2% Cl.sub.2/He " " " " " Example 2 Condition
3 10% Cl.sub.2/He " " " " " Comparative Example 1
[0056] As is apparent from Tables 1 and 3 and FIG. 1, when the Cl
concentration in the dehydrating atmosphere becomes lower, the Cl
concentration in the resultant glass becomes lower and the F/Cl
ratio becomes larger, so that the degree of transmittance
deterioration becomes smaller.
COMPARATIVE EXAMPLES 2 AND 3
[0057] Transparent glass bodies were obtained by subjecting the
porous matrix prepared in the same manner as in Example 1 to
condition 4 or 5 shown in Table 2 in place of condition 1. These
transparent glass bodies thus obtained under the conditions of 4
and 5 (Comparative Examples 2 and 3, respectively) were measured
with respect to concentrations of respective ingredients and degree
(%) of transmittance deterioration in the same manner as in Example
1. The results thus obtained are also shown in the following Table
3 and FIG. 1.
2 TABLE 2 Dehydrating Dehydrating Vitrifying Vitrifying Atmosphere
Temperature F-Adding Atmosphere F-adding Temperature Atmosphere
Temperature Example Condition 4 10% Cl.sub.2/He 1100.degree. C.
0.3% SiF.sub.4/He 1100-1400.degree. C. 0.3% SiF.sub.4/He
1500.degree. C. Comparative Ex. 2 Condition 5 0.5% Cl.sub.2/He " "
" " " Comparative Ex. 3
[0058] As is apparent from Tables 2 and 3, the glass of Comparative
Example 2 had a less F content and a less F/Cl ratio, since
condition 4 was employed wherein the concentration of the
F-containing gas in the F-adding step is lower than that in
condition 3, and suffered 2-fold or more deterioration of
transmittance in comparison with the glass of Comparative Example
1.
[0059] In addition, according to condition 5, since the
concentration of the F-containing gas in the F-adding step was
lower than that in condition 1, conversion of Si--Cl bond into
Si--F bond in the vitrifying step does not proceed sufficiently,
thus smaller F/Cl ratio and inferior degree of transmittance
deterioration being obtained.
[0060] In conditions 3 and 4, treatment was conducted employing a
higher Cl concentration (10%). It is seen that, when a large amount
of Cl remains in the glass soot, treatment in an atmosphere of a
higher F concentration is necessary for sufficiently replacing Cl
with F in the vitrifying step.
[0061] In conditions 1 and 5, treatment was conducted employing a
lower Cl concentration (0.5%). It is seen that when the Cl
concentration is at such a low level, replacement by F can be
attained by treatment employing a lower F concentration, but the
conversion into Si--F less proceeds at a F concentration of 0.3%
(condition 5) than at a F concentration of 5% (condition 1),
depending on which the amount of residual Cl increases.
EXAMPLE 3
[0062] 3 slm of C.sub.2F.sub.6 was introduced into a burner
together with a SiCl.sub.4 gas of a glass raw material, and an
F-containing SiO.sub.2 porous matrix having a diameter of 150 mm
and a length of 600 mm was synthesized according to flame
hydrolysis method. Subsequent steps were conducted under the same
conditions as condition 5 (employed in Comparative Example 3) to
conduct dehydration, addition of fluorine and vitrification
(condition 6). Atmosphere and temperature conditions in each step
are schematically shown in FIG. 3. The transparent glass body
(Example 3) thus obtained was measured with respect to
concentrations of respective ingredients and degree (%) of
deterioration of transmittance in the same manner as in Example 1.
The results thus obtained are also shown in the following Table
3.
EXAMPLE 4
[0063] 3 slm of C.sub.2F.sub.6 was introduced into a burner
together with a SiCl.sub.4 gas of a glass raw material, and an
F-containing SiO.sub.2 porous matrix having a diameter of 150 mm
and a length of 600 mm was synthesized according to flame
hydrolysis method. Subsequent steps were conducted under the same
conditions as condition 5 (employed in Comparative Example 3) to
obtain a transparent glass body (the same one as obtained in
Example 3). This transparent glass body was exposed to a H.sub.2
atmosphere at 500.degree. C. and 200 atmospheric pressures for 2
weeks to thereby add H.sub.2 to the glass body (condition 7). This
treatment of adding H.sub.2 converted Si--F bond into Si--OH bond.
The transparent glass body (Example 4) to which H.sub.2 had been
added was measured with respect to concentrations of respective
ingredients and degree (%) of deterioration of transmittance in the
same manner as in Example 1. The results thus obtained are also
shown in the following Table 3.
COMPARATIVE EXAMPLE 4
[0064] 3 slm of C.sub.2F.sub.6 was introduced into a burner
together with a SiCl.sub.4 gas of a glass raw material, and an
F-containing SiO.sub.2 porous matrix having a diameter of 150 mm
and a length of 600 mm was synthesized according to flame
hydrolysis method. The resultant porous matrix was heated at
1600.degree. C. in a He atmosphere to vitrify with omitting
dehydration treatment and F-adding treatment (condition 8). The
transparent glass body (Comparative Example 4) thus obtained was
measured with respect to concentrations of respective ingredients
and degree (%) of deterioration of transmittance in the same manner
as in Example 1. The results thus obtained are also shown in the
following Table 3.
[0065] Since the F compound gas was introduced into the burner upon
synthesis of glass in Example 3, Cl concentration in the glass in
Example 3 was lower than in Comparative Example 3, F concentration
was higher than in Comparative Example 3, and the F/Cl ratio was
three times as much as that in Comparative Example 3. Example 3
provided considerably good results with the degree of deterioration
of transmittance being as low as 2%.
[0066] In Example 4, the transparent glass body obtained in the
same manner as in Example 3 was treated with H.sub.2, and hence OH
concentration in the glass became as high as 10% which was the
upper limit in the invention, whereas F concentration decreased,
and F/Cl was 100. In spite of the F/Cl ratio, the result in the
degree of transmittance deterioration obtained in Example 4 was as
good as that in Example 3.
[0067] In Comparative Example 4, both dehydration step and the
fluorine-adding treatment were omitted, and the concentration of OH
group exceeded the scope of the invention, with the degree of
deterioration of transmittance being as large as 8%.
3 TABLE 3 Concentration of Ingredients in Glass (SiO.sub.2) F/Cl
Degree of Deterioration in Producing OH Concentration Cl
Concentration F Concentration Concentration Transmittance (%) at
157 nm after Example Condition (ppm) (ppm) (ppm) Ratio Irradiation
with F.sub.2 Laser Ex. 1 Condition 1 <1 1 10000 10000 0.5 Ex. 2
Condition 2 <1 10 10000 1000 1.0 Com. Ex. 1 Condition 3 <1
100 10000 100 4.0 Com. Ex. 2 Condition 4 <1 100 2000 20 10.0
Com. Ex. 3 Condition 5 <1 20 2000 100 6.0 Ex. 3 Condition 6
<1 10 3000 300 2.0 Ex. 4 Condition 7 10 10 1000 100 2.0 Com. Ex.
4 Condition 8 100 10 1000 100 8.0 Ex. 5 Condition 9 <1 0.1 1000
10000 0.3 (0.5*) *Degree of transmittance deterioration when
irradiated at an output power of 1 mJ/cm.sup.2 and 5.2 .times.
10.sup.6 pulses.
[0068] It is seen from the results of Examples 1 to 4 and
Comparative Examples 1 to 4 that in order to control the degree of
transmittance deterioration at a wavelength of 157 nm to be less
than 4%, it is necessary to adjust the F/Cl (concentration ratio)
to be not lower than 100, the OH concentration to be not higher
than 10 ppm, the Cl concentration to be not higher than 10 ppm and
the F concentration to be not lower than 1000 ppm. Moreover, in
order to control the degree of transmittance deterioration at a
wavelength of 157 nm to be less than 1%, it is necessary to adjust
the F/Cl (concentration ratio) to be not lower than 1000, the OH
concentration to be not higher than 10 ppm, the Cl concentration to
be not higher than 10 ppm and the F concentration to be not lower
than 1000 ppm.
EXAMPLE 5
[0069] An SiO.sub.2 soot (porous matrix) having a diameter of 150
mm and a length of 600 mm was synthesized in the same manner as in
Example 1. This soot was retained in a uniformly heating furnace,
and heated in a He atmosphere having a SiF.sub.4 molar
concentration of 5% at a rate of 3.degree. C./min from 800 to
1100.degree. C. After retaining for 60 minutes at the temperature,
the temperature was raised at a rate of 3.degree. C./min up to
1450.degree. C. and, and then retained for 30 minutes at the
temperature to vitrify. The conditions as to the atmosphere and
temperature used in the above-described steps (condition 9) are
schematically shown in FIG. 4.
[0070] The transparent glass body thus obtained was measured with
respect to concentrations of respective ingredients and degree (%)
of transmittance deterioration in the same manner as in Example 1.
The results thus obtained are also shown in the foregoing Table
3.
[0071] Additionally, the transmittance deterioration characteristic
was also evaluated by changing the conditions such that irradiation
was conducted using a F.sub.2 laser (wavelength: 157 nm) at an
output power of 1 mJ/cm.sup.2 and 5.2.times.10.sup.6 pulses. The
results thus obtained are also shown in Table 3.
[0072] As can be seen from Table 3, the degree of the transmittance
deterioration was sufficiently suppressed at a low level with
respect to both of the above irradiation conditions.
[0073] Furthermore, it can be understood from the results of
Example 5 that the effect of suppressing the transmittance
deterioration becomes greater with a less Cl concentration.
[0074] As has been described hereinbefore, glass molecules can be
ended with F (terminated with Si--F) by adjusting the amount of OH
group, the amounts of F and Cl and the F/Cl ratio to specific
ranges, thereby transmittance properties in UV region and vacuum UV
region and laser resistance of the resultant glass being markedly
improved.
[0075] Since the silica glass articles of the invention have
improved resistance against radiation of UV region, vacuum UV
region and, in particular, against a F.sub.2 excimer laser of 157
nm in wavelength, they are extremely advantageous in the field of
optical devices, parts, working machines and photolithography
substrates utilizing this radiation.
[0076] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made without departing from the spirit and scope thereof.
* * * * *