JP2003183034A - Synthetic quartz glass for optical member and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of stably manufacturing synthetic quartz glass excellent in homogeneity in fluorine contents, and to provide the synthetic quartz glass excellent in homogeneity in a refractive index, in light resistance, and in light transmittance. <P>SOLUTION: The synthetic quartz glass is characterized in that a mean bulk density of porous quartz glass in an OH group reducing process is ≤1.6 g/cm<SP>3</SP>, and in a sectional area perpendicular to a growing axis of the porous quartz glass, the difference between a maximum value and a minimum value in the bulk density is ≤0.6 g/cm<SP>3</SP>in a range excluding by 20 mm toward inside from the outer periphery of the sectional area. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to wavelengths of 155 to 25.
The present invention relates to a synthetic quartz glass for an optical member of an optical device using 0 nm light as a light source and a method for manufacturing the same. More specifically, A
rF excimer laser (wavelength 193 nm), Xe ₂ excimer lamp (wavelength 172 nm) and deuterium lamp (wavelength 17
0-400 nm), F ₂ laser (wavelength 157 nm), etc.
The present invention relates to a synthetic quartz glass for an optical member used as an optical component material such as a diffraction grating, a photomask, a pellicle (a pellicle material and a pellicle frame), a window material, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, in an optical lithography technique, an exposure apparatus for transferring a fine circuit pattern onto a wafer to manufacture an integrated circuit has been widely used. As integrated circuits have become highly integrated and highly functionalized, miniaturization of integrated circuits has progressed, and it is required for an exposure apparatus to form a high-resolution circuit pattern on a wafer surface with a deep depth of focus. Wavelength conversion is in progress. The exposure light source is advanced from the conventional g-line (wavelength 436 nm) or i-line (wavelength 365 nm), and the KrF excimer laser (wavelength 248 nm) or A
An rF excimer laser (wavelength 193 nm) is about to be used. Further, in order to cope with a next-generation integrated circuit having a circuit pattern of 100 nm or less, the use of an F ₂ laser (wavelength 157.6 nm) as an exposure light source is being studied.

In an optical system of an exposure apparatus having a light source having a wavelength of 155 to 400 nm as a light source, the optical system has excellent transparency over a wide range from the near infrared region to the ultraviolet region, has a very small coefficient of thermal expansion, and is relatively easy to process. For these reasons, synthetic quartz glass has been mainly used. As the synthetic quartz glass that has been conventionally used, for example, one disclosed in Japanese Patent Laid-Open No. 3-88742 is known.

That is, the synthetic quartz glass body is characterized by having an OH group content of 10 ppm or more and hydrogen of 5 × 10 ¹⁶ molecules / cm ³ or more.
However, even the synthetic quartz glass of the same invention has a problem that when it is irradiated with ultraviolet rays, damage such as increase in refractive index and decrease in transmittance occurs. KrF excimer laser,
Since the energy of photons increases as the wavelengths of ArF excimer laser and F ₂ laser become shorter, the light resistance to deep ultraviolet light to vacuum ultraviolet light having a wavelength of 200 nm or less has been a particular problem.

The cause of the increase in the refractive index and the decrease in the transmittance when irradiated with ultraviolet rays is not clear, but the defect precursors such as the distorted structure in the synthetic quartz glass, for example, the three-membered ring structure and the four-membered ring structure are ultraviolet rays. Cut by irradiation, E'center and NB
It is presumed that structural defects such as OHC are generated. Further, the OH group in the synthetic quartz glass not only affects the red fluorescence emission at the time of ultraviolet irradiation, but also reduces the light transmittance in the vacuum ultraviolet region having a wavelength of 180 nm or less. Therefore, it is preferable that the OH group content in the synthetic quartz glass is small.

Therefore, as a method for improving the light resistance and further the light transmission in the vacuum ultraviolet region, the present inventors have disclosed in JP-A No. 2001-19450 that fluorine is contained and the OH group content is less than 100 ppm. We have proposed a synthetic quartz glass for optical members, which is characterized by the following. By containing fluorine in the synthetic quartz glass in this manner, the distorted structure in the synthetic quartz glass is reduced, and damage caused by irradiation with ultraviolet rays is reduced. On the other hand, synthetic quartz glass for optical members is required to have a uniform refractive index (hereinafter referred to as “refractive index homogeneity”) in its usage region, but fluorine in synthetic quartz glass has an effect of lowering the refractive index. Therefore, it is desirable that the variation in fluorine content in the synthetic quartz glass is small.

Such a fluorine content is uniformly contained and O
As a method for producing synthetic quartz glass having a low H group content,
In Japanese Unexamined Patent Application Publication No. 2001-151531, by melting and stirring a synthetic quartz glass containing fluorine, the fluorine content distribution in the synthetic quartz glass is made uniform, and a synthetic quartz glass having an excellent fluorine content distribution is produced. A method has been proposed. However, as a result of detailed investigations by the present inventors on the method of producing the fluorine-containing synthetic quartz glass and the properties of the obtained synthetic quartz glass, it was found that a very high temperature was required for the melt rotary stirring treatment to make the fluorine content uniform. Therefore, impurities such as alkali metal may be mixed in, and heating with a propane gas flame may increase the OH group content in the synthetic quartz glass. Moreover, it was not possible to stably obtain a synthetic quartz glass having a low OH group content and a uniform fluorine content.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a method for stably producing a fluorine-containing synthetic quartz glass having an excellent fluorine content uniformity, and an excellent refractive index homogeneity, light resistance and light transmission. It is intended to provide a fluorine-containing synthetic quartz glass.

[0009]

Means for Solving the Problems The inventors of the present invention have made extensive studies as to the cause of the distribution of the fluorine content in synthetic quartz glass, and as a result, treat porous quartz glass in a prescribed atmosphere and conditions. As a result, after the OH group content of the porous quartz glass is reduced, the porous quartz glass is kept in a fluorine-containing atmosphere to dope the porous quartz glass with fluorine and simultaneously reduce the OH group content. In the process, it was found that the average bulk density of the porous quartz glass and its distribution have a great influence on the distribution of the fluorine content in the finally obtained synthetic quartz glass.

That is, the present invention has a wavelength of 155 to 250n.
In a method of manufacturing synthetic quartz glass for an optical member used as an optical member of an optical device using m light as a light source,
(A) a step of depositing and growing quartz glass fine particles obtained by flame hydrolysis of a glass forming raw material on a base material to form a porous quartz glass, and (b) OH of the porous quartz glass
A step of reducing the group content, (c) a step of holding the porous quartz glass in a fluorine compound-containing atmosphere and doping the porous quartz glass with fluorine, and (d) 1300 the porous quartz glass. A step of raising the temperature to ℃ or higher to obtain a transparent vitrified glass, and obtaining a transparent quartz glass body containing fluorine;
In the step (b), the average bulk density of the porous quartz glass in the step (b) is 1.6 g / cm ³ or less, and 20 mm from the outer periphery in a cross section perpendicular to the growth axis direction of the porous quartz glass.
The difference between the maximum and minimum bulk densities within the region excluding.
The present invention provides a method for producing synthetic quartz glass for optical members, which is 6 g / cm ³ or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Step (a) of the present invention is a step for producing porous quartz glass. In the manufacturing process of porous glass, the raw material for forming synthetic quartz glass is supplied to a multi-tube burner, fire-hydrolyzed, and the resulting quartz glass particles are deposited and grown on a substrate to form porous quartz glass. .

The raw material for forming the synthetic quartz glass is not particularly limited as long as it is a gasifiable raw material.
l ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , SiCH ₃ Cl
Chlorides such as ₃ , SiF ₄ , SiHF ₃ , SiH ₂ F ₂
Fluorides such _as, SiBr _4, SiHBr bromides such as _3, halogenated silicon compounds such as iodide such as SiI _4, or RnSi _{(OR) 4-n} (wherein R is an alkyl group having 1 to 4 carbon atoms, n represents alkoxysilane represented by an integer of 0 to 3) or _{(CH 3) 3 Si-O} -Si (CH
₃ ) Halogen-free silicon compounds such as ₃ are mentioned.

When a halogenated silicon compound is used as the glass forming raw material, the halogen in the glass forming raw material may remain in the synthetic quartz glass, and the residual content of the halogen varies to impair the homogeneity of the refractive index. there is a possibility. Therefore, a halogen-free organosilicon compound is preferable as the glass forming raw material. However, the halogen-free organosilicon compound is relatively expensive, and when it is used as a glass forming raw material, an increase in manufacturing cost cannot be avoided. Therefore, when a silicon halide compound is used as a glass forming raw material in order to suppress the production cost, it is preferable to use a silicon chloride compound which has the least influence on the refractive index.

The substrate on which the silica glass fine particles are deposited and grown is preferably rotated from the viewpoint of adjusting the bulk density distribution shape of the obtained porous silica glass and making it rotationally symmetric. The rotation speed is the deposition of quartz glass particles.
Although it depends on the growth rate, a range of 10 to 0.1 rotations per minute is preferable.

The step (b) of the present invention is a step of reducing the OH group content. Several methods are possible to reduce the content of OH groups contained in the porous quartz glass. Specifically, the following methods can be exemplified, but the present invention is not limited thereto. (Method 1) The porous quartz glass is kept in an atmosphere containing a fluorine compound. In this case, fluorine doping is simultaneously performed. (Method 2) The porous quartz glass is kept in an atmosphere containing a chlorine compound. (Method 3) The porous quartz glass is kept in an atmosphere containing carbon monoxide. (Method 4) The porous quartz glass is kept in an atmosphere containing hydrogen gas. In this case, the porous quartz glass is doped with hydrogen. Therefore, if necessary, a treatment for reducing the content of doped hydrogen is also used.

Of these four methods, Method 1 or Method 4 is preferable because the residual chlorine content in the finally obtained synthetic quartz glass is small and the safety is high. In the case of Method 1, the step of reducing the OH group content (step (b)) and the fluorine doping step (step (c)) can be combined.

The average bulk density of the porous quartz glass in the step of reducing the OH group content of the present invention is 1.6 g / cm.
^{It is set to 3} or less. By adjusting the average bulk density of the porous quartz glass in this way, it is possible to control the average fluorine concentration in the finally obtained synthetic quartz glass body. That is, in the range of average bulk density of 1.6 g / cm ³ or less, the smaller the average bulk density of the porous quartz glass, the higher the average fluorine concentration becomes. The higher the density, the finally obtained synthetic quartz glass bodies having a relatively low average fluorine concentration. When the average bulk density of the porous quartz glass exceeds 1.6 g / cm ³ , the OH group content cannot be sufficiently reduced even if the porous quartz glass is treated by the above four methods, It may be difficult to obtain porous quartz glass having a sufficiently reduced OH group content.

Further, in the OH group content reducing step of the present invention, the porous quartz glass has a bulk density variation amount (hereinafter referred to as bulk density distribution) of 0.6 g / cm ³ or less.
Specifically, in the cross section perpendicular to the growth axis direction of the porous quartz glass, the difference between the maximum and the minimum of the bulk density within the region excluding 20 mm from the outer periphery is 0.6 g / cm ³ or less. This bulk density distribution is particularly preferably 0.4 g / cm ³ or less. Bulk density distribution is 0.6 g / cm ³
If it exceeds, the distribution of the fluorine content in the finally obtained synthetic quartz glass body becomes large, and the homogeneity of the refractive index may be impaired.

The porous quartz glass having the average bulk density in the above range and the bulk density distribution in the above range can be controlled by adjusting the conditions for forming the porous quartz glass. That is, by controlling the input amounts of the glass forming raw material and oxygen gas, hydrogen gas, the temperature of the reaction field where the glass forming raw material undergoes a flame hydrolysis reaction to become silicon oxide is adjusted, and the bulk density of the porous quartz glass is adjusted. And its distribution can be controlled. Specifically, by relatively increasing the amounts of oxygen gas and hydrogen gas to be added to the glass forming raw material, the temperature of the reaction field can be increased and porous quartz glass having a high average bulk density can be obtained.

A bulk density adjusting step may be carried out between the step of producing the porous quartz glass and the step of reducing the OH group content (step (e)). That is, the average bulk density or bulk density distribution of the porous quartz glass can be adjusted by heating the obtained porous quartz glass in the range of 1000 to 1500 ° C. Specifically, by heating the porous quartz glass to a temperature of 1000 to 1500 ° C., it is possible to increase and adjust the average bulk density of the porous quartz glass as a whole.

When the porous quartz glass is heat-treated, the bulk density distribution of the porous quartz glass can be adjusted by intentionally providing a temperature gradient in the porous quartz glass.
For example, by subjecting porous quartz glass whose bulk density in the vicinity of the surface is lower than that in the interior to heat treatment so that the temperature in the vicinity of the surface is high and the temperature in the interior is low, the bulk density distribution of the porous quartz glass Can be reduced.

The step (c) of the present invention is a fluorine doping step.

In order to dope with fluorine, the porous quartz glass body is kept in a fluorine-containing atmosphere. The fluorine-containing atmosphere may be a fluorine-containing gas (eg, SiF ₄ , SF
₆ , CHF ₃ , CF ₄ , F _{2 and the} like) are preferably contained in an inert gas atmosphere of 0.1 to 50% by volume. The ambient temperature is preferably room temperature to 1300 ° C.

Atmospheric pressure of 100 Pa to 101 kP
a (101 kPa = atmospheric pressure) is preferable. Further, the holding time is preferably tens of minutes to tens of hours. In this case, since it is possible to uniformly dope the porous quartz glass body with fluorine in a short time, it is possible to reduce the pressure (100 Torr (13.3 kPa)).
It is particularly preferably 10 Torr (1.33 kPa) or less. It is preferable to introduce a fluorine-containing gas until the pressure reaches normal pressure while maintaining the condition in (1) to make a fluorine-containing atmosphere. Further, when fluorine is doped at a high temperature of 400 ° C. or higher, reduction type defects such as oxygen deficiency type defects are likely to be generated. Therefore, when fluorine doping is performed at a high temperature of 400 ° C. or higher, it is possible to prevent the generation of reduction-type defects by holding the porous quartz glass body in an inert gas atmosphere containing oxygen gas in addition to fluorine-containing gas. preferable.

The step (d) of the present invention is a transparent vitrification step. The transparent vitrification is performed by maintaining the porous quartz glass at a predetermined transparent vitrification temperature for a predetermined time. The transparent vitrification temperature is usually 1300 to 1600 ° C.
And particularly preferably 1350 to 1500 ° C. As the atmosphere at this time, an atmosphere containing 100% by volume of an inert gas such as helium or nitrogen, or an atmosphere containing an inert gas such as helium or nitrogen as a main component can be used. The pressure may be reduced pressure or normal pressure. Helium gas can be used especially under normal pressure. In the case of decompression, 100 Torr (13.
It is preferably 3 kPa) or less.

The synthetic quartz glass obtained by the method of the present invention has optical properties such as a homogeneity of refractive index and a low birefringence necessary for an optical member in order to be used as a lens for an exposure apparatus and other optical members. It is necessary to appropriately perform each heat treatment such as homogenization, forming, and annealing (hereinafter referred to as an optical heat treatment) for giving. The optical heat treatment can be performed after the transparent vitrification.

With respect to annealing, in particular, annealing can reduce distorted structures such as a three-membered ring structure and a four-membered ring structure in the synthetic quartz glass, and can improve light transmittance and light resistance in the vacuum ultraviolet region. , Is preferably carried out. Specific annealing conditions include synthetic quartz glass, an inert gas atmosphere such as nitrogen gas or argon gas,
Alternatively, in air or oxygen gas atmosphere, temperature 600 to 1100
It is preferable to maintain the temperature at a temperature of 101 kPa (atmospheric pressure) to 1 Pa for several tens to several hundreds of hours.

Next, the composition of the synthetic quartz glass for optical members of the present invention will be described. In the present invention, the OH group in the synthetic quartz glass not only increases the red fluorescence emission upon irradiation with ultraviolet rays but also impairs the light transmittance in the vacuum ultraviolet region, so that the content thereof is preferably small. Specifically, the OH group content in the synthetic quartz glass is less than 10 ppm, particularly preferably 5 ppm or less, and particularly, the wavelength of 155 to 180
1 when used as an optical member using a light of nm as a light source
ppm or less is preferable.

In the present invention, the chlorine content in the synthetic quartz glass deteriorates the light transmittance and the light resistance in the vacuum ultraviolet region, so it is preferable that the content of chlorine is small. Specifically, the chlorine content in the synthetic quartz glass is 10 ppm or less, particularly 5 ppm or less, and further preferably substantially no chlorine.

In the present invention, fluorine in the synthetic quartz glass has the effect of substituting with OH groups to reduce the content of OH groups, and also has the effect of reducing distorted structures such as a three-membered ring structure and a four-membered ring structure. There is. Specifically, the synthetic quartz glass of the present invention preferably contains 50 ppm or more of fluorine, and particularly preferably 200 ppm or more.

The distribution of the fluorine content is preferably 250 ppm or less, particularly 50 ppm or less, and more preferably 10 ppm or less in the range of use as an optical member, which is the difference between the maximum and the minimum of the fluorine content.

In the present invention, oxygen-deficient type defects (≡Si—Si≡ (≡ represents Si—O bond; hereinafter the same)) and oxygen excess type defects (≡Si—O—O—S) in synthetic quartz glass.
i≡), ≡SiH bond, dissolved oxygen molecule and the like adversely affect the vacuum ultraviolet light transmittance and the light resistance, and thus it is preferable that they are not substantially contained. In particular, the oxygen deficiency defect is OH
Since it is likely to be introduced when reducing the group content, it is preferable to carefully control so that it is not substantially contained.

In the present invention, alkali metals (Na, K, Li, etc.), alkaline earth metals (Mg, Ca, etc.), transition metals (Fe, Ni, Cr, C) in synthetic quartz glass are used.
Since metal impurities such as u, Mo, W, Al, Ti, and Ce) not only lower the transmittance in the ultraviolet region to the vacuum ultraviolet region but also reduce the ultraviolet resistance, their content is It is preferable that the number is as small as possible. Specifically, the total content of metal impurities is 100 ppb or less, especially 50
It is preferably ppb or less.

Further, the synthetic quartz glass obtained by the method of the present invention may be effective in containing hydrogen molecules in order to improve the ultraviolet resistance. Specifically, synthetic quartz glass is heat-treated in a hydrogen-containing atmosphere at a temperature of 500 ° C. or lower to diffuse and contain hydrogen molecules in the synthetic quartz glass.

The hydrogen molecule repairs paramagnetic defects such as E'center and NBOHC generated by ultraviolet irradiation and has a wavelength of 18
It has a function of suppressing the generation of an absorption band at 0 to 300 nm. When used as an optical member of an optical device that uses light having a wavelength of 180 to 250 nm as a light source, it is preferable that hydrogen molecules are contained in an amount of 1 × 10 ¹⁷ molecules / cm ³ or more.

However, hydrogen molecules in the synthetic quartz glass body are oxygen-deficient type defects (≡Si-Si) during ultraviolet irradiation.
≡) has the effect of promoting the generation, and the defect has a wavelength of 163n.
Since it has an absorber centering on m, it has a wavelength of 155 to 18
When used as an optical member of an optical device using 0 nm light as a light source, the hydrogen molecule content in the synthetic quartz glass is 1 ×.
It is preferably 10 ¹⁷ molecule / cm ³ or less. It should be noted that it may be preferable to set the content of hydrogen molecules in the synthetic quartz glass to 1 × 10 ¹⁷ molecules / cm ³ or less, depending on the use and the use conditions.

Further, the synthetic quartz glass for an optical member of the present invention has a wavelength of 157.
The internal light transmittance at 6 nm is preferably 80% / cm or more, particularly 90% / cm or more, and further 95% / cm or more.

The synthetic quartz glass for optical members of the present invention has a wavelength of 633n in the range of use as an optical member.
The refractive index homogeneity in m is preferably 100 ppm or less, more preferably 20 ppm or less, particularly 10 ppm or less, and further 2 ppm or less.

Further, the synthetic quartz glass for optical members of the present invention has a temperature of 100 ° C. in the usage region as an optical member.
The difference between the maximum and minimum thermal expansion coefficient in
It is preferably ⁻⁶ / K or less, and 40 × 10 ⁻⁶ /
It is more preferably K or less, and particularly 20 × 10
^{It is −6} / K or less, and further 4 × 10 ⁻⁶ / K or less.

[0040]

EXAMPLES Under the conditions shown in Table 1, a glass forming raw material of silicon tetrachloride or hexamethyldisiloxane (HMDS) was hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were formed on a rotating substrate. By depositing, a porous quartz glass having a diameter of 300 mm and a length of 600 mm was produced (step (a)).

Then, the porous quartz glass was fixed to the elevator through the substrate, and the porous quartz glass was placed in an electric furnace previously maintained at the temperature shown in Table 1 at a speed of 0.1 m / min. The average bulk density and bulk density distribution of the porous quartz glass were adjusted by raising and introducing and holding for the time shown in Table 1 (step (e)).

Here, a thickness of 100 mm was cut from the vicinity of the central portion in the longitudinal direction of the porous quartz glass, and the hardness of the cut surface was measured at 10 mm intervals in the diametrical direction at a total of 30 points with a hardness meter in a region excluding the outer circumference of 20 mm. By doing so, the bulk density of the porous quartz glass was evaluated. The average bulk density was the average value of the bulk density of 30 points in total, and the bulk density distribution was the difference between the maximum bulk density and the minimum bulk density of 30 points in total. Further, when obtaining the bulk density from the measured hardness, the relational expression between the hardness and the bulk density was previously obtained by using various porous quartz glasses having different bulk densities, and this relational expression was used. Figure 1
The measurement results of the bulk density distributions of Example 1, Example 4, Example 10, and Example 12 are shown in FIG.

Next, the porous quartz glass was taken out from the electric furnace, cooled to room temperature, and the prepared porous quartz glass was set in a furnace in which the atmosphere could be controlled under the conditions shown in Table 1. The OH group content reduction treatment and the fluorine doping treatment were carried out at (step (b) and step (c)).

After that, the porous quartz glass is pressured to 100 P.
While maintaining a reduced pressure of a or less, the temperature was raised to 1450 ° C. and maintained at this temperature for 10 hours to produce a transparent quartz glass body (step (d)).

The inner diameter of the transparent quartz glass body obtained in each example was 2
Set in a 40 mm carbon crucible, and place the crucible in an electric furnace with argon gas, 100 vol%, 1 atm.
The transparent quartz glass body was molded by raising the temperature to 1750 ° C. and holding at this temperature for 10 hours.

Then, an evaluation sample having a size of φ150 mm × 20 mm was cut out from approximately the center in the longitudinal direction of the obtained transparent quartz glass body, and ground with a # 1000 grinder so that the surface flatness was 5 μm or less. It carried out and evaluated the following.

(Evaluation of OH group content) Measurement was carried out by an infrared spectrophotometer in the vicinity of the center of the sample for evaluation to obtain a wavelength of 2.
The OH group content was determined from the absorption peak at 7 μm (JP Williams et al., Cerami.
c Bulletin, 55 (5), 524, 19
76). The detection limit of this method is 1 ppm.

(Evaluation of fluorine content and distribution thereof)
The fluorine content of 30 points in total in the diameter direction of the evaluation sample was analyzed by the fluorine ion electrode method at intervals of 10 mm. Here, the average value of the measured fluorine content of 30 points in total was defined as the average fluorine content, and the difference between the maximum fluorine content and the minimum fluorine content was defined as the fluorine content distribution. The method for analyzing the fluorine content is as follows. Journal of the Chemical Society of Japan, 1972 (2), 3
According to the method described in 50, the synthetic quartz glass was heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid (volume ratio 1: 1) were added to the obtained melt to prepare a sample liquid. The electromotive force of the sample liquid was changed to No. 9
45-220 and No. 45-220. 945-468 was used for each measurement with a radiometer, and the fluorine content was determined based on a calibration curve prepared in advance using a fluorine ion standard solution. The detection limit of this method is 10 ppm.

(Evaluation of Internal Light Transmittance at Wavelength 157.6 nm) 20 mm × 20 mm × 5 mm from the center of the sample for evaluation
And a sample of 20 mm × 20 mm × 30 mm are cut out, two 20 mm square surfaces are mirror-polished, and the wavelength is measured by a vacuum ultraviolet spectrophotometer (UV201M manufactured by Spectrometer Co., Ltd.) with the sample temperature kept at 25 ° C. 157.6n
The light transmittance at m was measured under a nitrogen atmosphere. 5m thickness
m and thickness of 30 mm for two types of samples having a wavelength of 157.6
The internal light transmittance T _157.6 at a wavelength of 163 nm was calculated from the nm light transmittances T ₁ and T ₂ according to the following formula (1).

[0050]

[Equation 1]

(Evaluation of homogeneity of refractive index) With a Fizeau interferometer,
With the oil-on-plate method, the helium neon laser light (wavelength 633 nm) was perpendicularly applied to the 240 mmφ surface of the evaluation sample, and the refractive index distribution in the center 200 mmφ surface was measured to find the difference between the maximum and minimum refractive indexes. Was defined as the refractive index homogeneity.

(Evaluation of Thermal Expansion Coefficient Distribution) The thermal expansion coefficient α at a temperature of 100 ° C. was measured with a laser thermal expansion meter (LIX-1 manufactured by Vacuum Riko) at 50 mm intervals in the diameter direction of the evaluation sample. The difference between the maximum and the minimum was defined as the thermal expansion coefficient distribution.

The results of each evaluation are shown in Table 2. Note that Examples 9, 12, 13 and 16 to 18 are comparative examples, and the others are examples. Also, for Examples 1, 4, 10, and 12,
FIG. 1 shows a graph of the bulk density distribution.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

EFFECTS OF THE INVENTION According to the present invention, the present invention provides a method for stably producing a fluorine-containing synthetic quartz glass excellent in the uniformity of the fluorine content, as well as the refractive index homogeneity, light resistance and light transmission. An excellent fluorine-containing synthetic quartz glass is obtained.

[Brief description of drawings]

Fig. 1 Graph of bulk density distribution

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Claims (9)

[Claims] 1. A method for producing synthetic quartz glass for an optical member used as an optical member of an optical device having a light source having a wavelength of 155 to 250 nm as a light source, wherein (a) a quartz glass obtained by flame hydrolysis of a glass forming raw material. A step of depositing and growing fine particles on a base material to form a porous quartz glass;
(B) a step of reducing the OH group content of the porous quartz glass, and (c) a step of holding the porous quartz glass in a fluorine compound-containing atmosphere and doping the porous quartz glass with fluorine. (D) a step of raising the temperature of the porous quartz glass to a temperature of 1300 ° C. or higher to obtain a transparent quartz glass body containing fluorine to obtain a transparent quartz glass body containing fluorine, and the average of the porous quartz glass in the step (b). In the cross section of the bulk silica glass having a bulk density of 1.6 g / cm ³ or less and perpendicular to the growth axis direction of the porous quartz glass, the difference between the maximum and minimum bulk densities within the region excluding 20 mm from the outer circumference is the maximum bulk density. A method for producing synthetic quartz glass for optical members, characterized in that the difference from the minimum is 0.6 g / cm ³ or less. 2. The steps (b) and (c) are carried out by keeping the porous quartz glass in a fluorine compound-containing atmosphere to dope the porous quartz glass with fluorine and at the same time reduce the OH group content. The method for producing synthetic quartz glass for an optical member according to claim 1, which is performed. 1. The method for producing the synthetic quartz glass for an optical member according to 1. 3. After the step (a), there is included (e) a step of heating the porous quartz glass in the range of 1000 ° C. to 1500 ° C. to adjust the average bulk density of the porous quartz glass. A method for producing the synthetic quartz glass for an optical member according to claim 1. 4. A synthetic quartz glass for an optical member used as an optical member of an optical device having a light source having a wavelength of 155 to 250 nm as a light source, wherein a fluorine content in an area used as the optical member is 50 ppm or more and an OH group content is 10p
Synthetic quartz glass for optical members, which is pm or less and has a difference between the maximum and minimum fluorine contents of 250 ppm or less. 5. A synthetic quartz glass for an optical member used as an optical member of an optical device having a light source having a wavelength of 155 to 180 nm as a light source, wherein a fluorine content in an area used as the optical member is 50 ppm or more and an OH group content is 1 pp
A synthetic quartz glass for an optical member, characterized in that it is m or less, and the difference between the maximum and minimum fluorine contents is 250 ppm or less. 6. A synthetic quartz glass for an optical member used as an optical member of an optical device having a light source having a wavelength of 155 to 180 nm as a light source, wherein a fluorine content in an area used as the optical member is 50 ppm or more, and an OH group content is 1 pp
The synthetic quartz glass for optical members is characterized in that it is m or less and the difference between the maximum and minimum fluorine contents is 50 ppm or less. 7. The synthetic quartz glass for an optical member according to claim 4, which has an internal light transmittance of 80% / cm or more at a wavelength of 157.6 nm in a region of use as an optical member. 8. The difference between the maximum and the minimum of the refractive index at a wavelength of 633 nm is 100 p in the usage area as an optical member.
The synthetic quartz glass for an optical member according to any one of claims 4 to 7, which has a pm or less. 9. A difference between the maximum and the minimum of the coefficient of thermal expansion at a temperature of 100 ° C. is 20 in the range of use as an optical member.
It is ^0x10 < ^-6 > / K or less, Claim 4 characterized by the above-mentioned.
8. A synthetic quartz glass for an optical member according to any one of items 8 to 8.