JP2003201126A - Synthetic quartz glass for optical member and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain synthetic quartz glass for optical members which excels stably in light transmittance and light resistance in UV to vacuum UV rays. <P>SOLUTION: This method includes (a) a process step of forming porous quartz glass by depositing and growing quartz glass particulates obtained by flame hydrolyzing glass-forming raw materials on a base material, (b) a process step of reducing the OH group content in the porous quartz glass by holding the porous quartz glass under a hydrogen-containing atmosphere, (c) a process step of doping fluorine to the porous quartz glass by holding the porous quartz glass under a fluorine compound-containing atmosphere, and (d) a process step of obtaining a transparent quartz glass body containing the fluorine by heating the porous quartz glass up to a temperature above 1,300°C thereby forming the transparent glass. <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 optical lithography technology,
An exposure apparatus for transferring a fine circuit pattern onto a wafer to manufacture an integrated circuit is 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) to KrF excimer laser (wavelength 248 nm) or ArF.
An excimer laser (wavelength 193 nm) is about to be used. In addition, in order to support next-generation integrated circuits with circuit patterns of 100 nm or less, the exposure light source F
_{The use of two} lasers (wavelength 157.6 nm) is being investigated.

An optical member of an exposure apparatus using a light source having a wavelength of 155 to 400 nm as a light source 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, the one disclosed in Japanese Patent Laid-Open No. 3-88742 is known. That is, it is characterized in that the synthetic quartz glass body has an OH group content of 10 ppm or more and contains 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. Since the energy of photons increases as the wavelength of light becomes shorter with KrF excimer laser, ArF excimer laser, and further with F ₂ laser, light resistance to deep ultraviolet light to vacuum ultraviolet light having a wavelength of 200 nm or less has been a particular problem. Although the cause of the increase in the refractive index and the decrease in the transmittance when irradiated with ultraviolet rays is not clear,
It is presumed that the distorted structure in the synthetic quartz glass, for example, a defect precursor such as a three-membered ring structure or a four-membered ring structure is cut by the irradiation of ultraviolet rays to generate structural defects such as E ′ center and NBOHC. 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 reducing the damage caused by the irradiation of ultraviolet rays, the inventors of the present invention disclosed in Japanese Patent Laid-Open No. 2001-1.
9450 discloses a wavelength of 400n containing fluorine and having an OH group content of less than 100 ppm.
A synthetic quartz glass for an optical member has been proposed which uses ultraviolet rays of m or less to vacuum ultraviolet rays as a light source. By containing fluorine in the synthetic quartz glass, the distorted structure in the synthetic quartz glass is reduced, and the damage caused by ultraviolet irradiation is reduced. In addition, the OH group content in synthetic quartz glass is 100 p
Since it is as small as less than pm, the red fluorescence emission intensity at the time of ultraviolet irradiation is also small and the light resistance is excellent.

As a method for producing such synthetic quartz glass containing fluorine and having a small OH group content, Japanese Patent Application Laid-Open No. 20-58200
No. 01-199735 and Japanese Patent Laid-Open No. 8-75901 are proposed. In these proposals, silica glass fine particles obtained by flame hydrolysis of a glass forming raw material are deposited and grown on a substrate to form a porous silica glass, and then the porous silica glass is first heated in a chlorine compound atmosphere. The method includes a step of reducing the OH group content in the porous quartz glass by treatment, and then performing heat treatment in a fluorine compound atmosphere to dope fluorine into the porous quartz glass, and then making it transparent glass. It is a method for producing synthetic quartz glass, which is characterized by the above. However, since this manufacturing method includes the step of treating the porous quartz glass in a chlorine compound-containing atmosphere, chlorine may remain in the finally obtained synthetic quartz glass. Since chlorine in the synthetic quartz glass becomes paramagnetic defects such as E'center due to the irradiation of ultraviolet rays, if a large amount of chlorine is contained in the synthetic quartz glass, the light resistance is insufficient, which is a problem.

In addition to the above proposal, silica glass fine particles obtained by flame hydrolysis of a glass forming raw material are deposited and grown on a substrate to form a porous silica glass, and the obtained porous silica glass is converted into fluorine. There is also a proposal to reduce the OH group content in the porous quartz glass by treating it in a compound-containing atmosphere and to make it transparent glass after doping with fluorine. However, in this method, as compared with the case of using a chlorine compound, when the porous quartz glass is treated in a fluorine compound atmosphere, the OH group content in the porous quartz glass cannot be stably reduced, Further, depending on the conditions, oxygen deficiency type defects (≡Si-Si≡) may be generated during the same treatment. Oxygen-deficient defects have an absorption band centered at 163 nm and not only impair the light transmittance in the vacuum ultraviolet region of wavelength 155 to 180 nm, but also adversely affect the light resistance, so oxygen-deficient defects are substantially contained. Not preferably. Further, this oxygen deficiency type defect is more likely to be generated as the OH group content remaining in the porous quartz glass after the same treatment is smaller, which is a problem.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a synthetic quartz glass for optical members, which is stable and excellent in light transmittance and light resistance in ultraviolet rays to vacuum ultraviolet rays, and a method for producing the same.

[0009]

Means for Solving the Problems As a result of intensive studies on the cause of chlorine remaining in synthetic quartz glass, the inventors of the present invention firstly treated porous quartz glass in an atmosphere containing hydrogen gas. If the OH group content in the porous quartz glass is reduced and then the porous quartz glass is treated in a fluorine compound-containing atmosphere and then made into a transparent vitreous material, the chlorine content is low and the fluorine dope is stable and excellent in light resistance. It has been found that synthetic quartz glass can be produced.

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 fine quartz glass particles obtained by flame hydrolysis of a glass forming raw material on a base material to form porous quartz glass; and (b) exposing the porous quartz glass to a hydrogen-containing atmosphere. Holding and reducing the OH group content in the porous quartz glass; (c) 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. A manufacturing method is provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Step (a) of the present invention is a step for producing 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, but SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , Si
Chlorides such as CH ₃ Cl ₃ , SiF ₄ , SiHF ₃ , S
Fluoride such as iH ₂ F ₂ , SiBr ₄ , SiHBr ₃
Bromides such as, alkoxy represented by 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 an integer of 0 to 3) silane and _{(CH 3) 3 Si-O} -S
A halogen-free silicon compound such as i (CH ₃ ) ₃ may be mentioned.

The step (b) of the present invention is a step of reducing the OH group content with hydrogen. In the step of reducing the OH group content by hydrogen, the porous quartz glass is treated in an atmosphere containing hydrogen gas, so that the OH of the porous quartz glass is reacted by the reactions shown in Formulas (1) and (2).
Reduce the group content.

[0013]

[Equation 1]

The hydrogen gas-containing atmosphere in the step of reducing the OH group content is preferably an inert gas atmosphere containing 0.1 to 100% by volume of hydrogen gas, and particularly hydrogen gas 10
An atmosphere of 0% by volume is preferred. Processing temperature is 500-13
00 ° C. is preferable, and 800 to 1200 ° C. is particularly preferable. If it is lower than 500 ° C, the reaction rates of the above (1) and (2) become extremely slow, and the OH group content in the porous quartz glass may not be sufficiently reduced. Since the densification of the fine quartz glass progresses, the OH group concentration in the porous quartz glass may not be reduced. Processing pressure is from 101 (atmospheric pressure)
1500 kPa is preferable. The treatment time depends on the size of the porous quartz glass to be treated and the treatment conditions, but is from several hours to
Hundreds of hours are preferred.

The step (c) of the present invention is a fluorine doping step. In the fluorine doping step, by holding the porous quartz glass in a fluorine-containing atmosphere, oxygen-deficient defects generated in the OH group reducing step by the reaction shown in the formula (3) are replaced with ≡SF bonds. Then, a fluorine-doped porous quartz glass that does not substantially contain oxygen-deficient defects is obtained.

[0016]

[Equation 2]

Therefore, the concentration of fluorine in the finally obtained synthetic quartz glass body is determined by the concentration of oxygen-deficient defects generated in the OH group reduction step, and the higher the concentration of oxygen-deficient defects, the more the fluorine concentration. A synthetic quartz glass body containing fluorine is obtained.

The fluorine compound-containing atmosphere may be a fluorine-containing gas (eg, SiF ₄ , SF ₆ , CHF ₃ , CF ₄ ,
An inert gas atmosphere containing 0.1 to 100% by volume of (F ₂ etc.) is preferable. The ambient temperature is 500 to 1300 ° C,
Especially 800-1200 degreeC is preferable. Further, the atmospheric pressure is preferably 10 to 101 kPa (101 kPa = atmospheric pressure). Furthermore, the holding time depends on the size of the porous quartz glass,
Although it depends on the treatment conditions and the concentration of oxygen-deficient defects generated in the step of reducing the OH group content, several tens of minutes to several tens of hours are preferable. In this case, since the porous quartz glass can be uniformly doped with fluorine in a short time, under reduced pressure (100 Pa or less,
Particularly, 10 Pa or less is preferable. It is preferable to introduce a fluorine-containing gas until it reaches a normal pressure while keeping it in (1) to make a fluorine compound-containing atmosphere. Further, when the porous base material is treated at a high temperature of 1000 ° C. or higher in a fluorine compound-containing atmosphere, reduction type defects are easily generated. Therefore, in an atmosphere containing oxygen gas in addition to fluorine-containing gas and inert gas. It is preferable to prevent the generation of reduction-type defects by treating with.

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.

In the present invention, the hydrogen content reducing step (e) for reducing the hydrogen molecule content in the porous quartz glass may be carried out after the OH group content reducing step by hydrogen. When hydrogen molecules are dissolved in the porous quartz glass, when a heat treatment is performed at a high temperature of 1000 to 1500 ° C. in the subsequent fluorine doping step or transparent vitrification step, generation of oxygen deficiency type defects is newly generated. May invite. In order to prevent this, a treatment to reduce the hydrogen molecule content in the porous quartz glass is performed between the OH group content reduction step and the fluorine doping step, or the hydrogen content reduction step is performed in combination with the fluorine doping step. Preferably.

The step of reducing the hydrogen content is performed by treating the porous quartz glass in an atmosphere containing substantially no hydrogen. Further, the hydrogen content reducing step can also serve as the fluorine doping step, but only when the maximum processing temperature of the fluorine doping step is higher than the maximum processing temperature of the OH group content reducing step. The atmosphere containing substantially no hydrogen is not particularly limited as long as the hydrogen gas is 0.1 vol% or less, and an atmosphere containing an inert gas as a main component is preferable. The pressure may be normal pressure, but it is preferably reduced pressure in order to shorten the treatment time. In the case of reducing the pressure, it is particularly preferable that the pressure is 100 Pa or less. 500 to 1400 ° C under these atmospheres
It is preferable that the treatment is performed for several tens of hours.

Further, in the present invention, the average bulk density of the porous quartz glass when carrying out the step of reducing the OH group content is 1.6 g / cm ³ or less, and the bulk density distribution (that is, the growth axis of the porous quartz glass is In the cross section perpendicular to the direction, the difference between the maximum and minimum bulk densities in the region excluding 20 mm from the outer circumference) is preferably 0.6 g / cm ³ or less. This is because the conditions for forming the porous quartz glass are adjusted, or the amount of the porous quartz glass is reduced to 1000 between the step of manufacturing the porous quartz glass and the step of reducing the OH group content.
It can be performed by heating in the range of ℃ to 1500 ℃.

By setting the average bulk density of the porous quartz glass within the above range in the step of reducing the OH group content, the OH group content in the porous quartz glass can be sufficiently reduced, and In the fluorine doping step, oxygen deficiency type defects in the porous quartz glass can be repaired and fluorine doping can be sufficiently performed, and problems such as residual oxygen deficiency type defects hardly occur. Further, by setting the bulk density distribution within the above range, distribution is unlikely to occur in the OH group content and the fluorine content in the finally obtained synthetic quartz glass body, and the uniformity of the refractive index and the light transmittance is improved. To do.

The synthetic quartz glass obtained by the method of the present invention has optical characteristics such as a refractive index homogeneity 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, more preferably 1 ppm or less.

In the present invention, the chlorine content in the synthetic quartz glass deteriorates the light transmittance and light resistance in the vacuum ultraviolet region, so that 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.

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 600 ° 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, the hydrogen molecules in the synthetic quartz glass body have an action of promoting the generation of oxygen-deficient type defects (≡Si-Si≡) during irradiation of ultraviolet rays, and since the defects have an absorber centered at a wavelength of 163 nm, When used as an optical member of an optical device having a light source of 155 to 180 nm as the light source, the hydrogen molecule content in the synthetic quartz glass is 1 × 10 ^17.
The number of molecules / cm ³ or less is preferable. In addition,
Depending on the conditions of use, it may be preferable to set the hydrogen molecule content in the synthetic quartz glass to 1 × 10 ¹⁷ molecules / cm ³ or less.

[0033]

EXAMPLES (Examples 1 to 11) Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were deposited on a substrate to form a porous quartz glass having a diameter of 350 mm and a length of 600 mm. It was produced (step (a)).

Next, the porous quartz glass was placed in an electric furnace capable of controlling the atmosphere, and the treatments described below were sequentially carried out. Treated under a hydrogen-containing atmosphere under the conditions shown in Table 1,
The OH group content in the porous quartz glass was reduced (step (b)).

Subsequently, the porous quartz glass was treated under the conditions shown in Table 1 to reduce the residual hydrogen in the porous quartz glass,
After the removal (step (e)), it was treated under a fluorine compound-containing atmosphere under the conditions shown in Table 1 to obtain a fluorine-doped porous quartz glass (step (c)).

Finally, the transparent quartz glass body (diameter 180 mm, length 350) was heated to 1450 ° C. while maintaining a reduced pressure of 150 Pa or less and kept at this temperature for 10 hours.
mm) was produced.

(Example 12) Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were deposited on a substrate to prepare a porous quartz glass having a diameter of 350 mm and a length of 600 mm. Next, the porous quartz glass was placed in an electric furnace capable of controlling the atmosphere, and the treatments described below were sequentially performed. First, chlorine / helium = 10/90 vol%, 10
The treatment was performed at 1 kPa and 1200 ° C. for 10 hours to reduce the OH group content in the porous quartz glass. Then, silicon tetrafluoride / oxygen / helium = 10/10/80 vol%,
It was treated at 101 kPa and 1200 ° C. for 5 hours to obtain a fluorine-doped porous quartz glass. Finally, the temperature was raised to 1450 ° C. while the pressure was reduced to 150 Pa or less, and the transparent quartz glass body (diameter 180
mm, length 350 mm).

(Example 13) Silicon tetrachloride was hydrolyzed in an oxyhydrogen flame and the formed SiO ₂ fine particles were deposited on a substrate to prepare a porous quartz glass having a diameter of 350 mm and a length of 600 mm. Next, the porous quartz glass was placed in an electric furnace capable of controlling the atmosphere, and first, silicon tetrafluoride / oxygen =
10 / 90vol%, 101kPa, 1 at 1000 ° C
The treatment was carried out for 0 hours to obtain a fluorine-doped porous quartz glass.
Then, with the pressure maintained at 150 Pa or less,
The temperature was raised to 50 ° C., and this temperature was maintained for 10 hours to prepare a transparent quartz glass body (diameter 180 mm, length 350 mm).

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, a sample for evaluation 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) The fluorine content near the center of the sample for evaluation was analyzed by the fluorine ion electrode method.
The method for analyzing the fluorine content is as follows. According to the method described in The Chemical Society of Japan, 1972 (2), 350, 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. A sample solution was prepared. The electromotive force of the sample liquid was changed to No. 945-220 and No. 945-4
68 was used to measure 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 chlorine content) The chlorine content was analyzed by fluorescent X-ray analysis in the vicinity of the center of the sample for evaluation. The detection limit of this method is 10 ppm or less.

(Evaluation of Presence / Absence of Oxygen Deficiency Type Defects) Evaluation Samples
20mm x 20mm x 5mm sample from near the center, and
And cut a sample of 20 mm × 20 mm × 30 mm and
Mirror-polish two surfaces of 20 mm square each and increase the sample temperature to 2
Vacuum ultraviolet spectrophotometer (Spectrometer Co., Ltd.)
Made by "UV201M", same below) wavelength 163nm
From the formula (4) by measuring the light transmittance in
Internal transmittance T at 163 nm₁₆₃Calculate the quartz
OH group concentration C in glass_OH(Ppm) to formula (5)
Value calculated by T _idBy comparing with
The presence or absence of the depression was evaluated.

[0045]

[Equation 3]

[0046]

[Equation 4]

When there is an oxygen deficiency type defect, since it has an absorption band centered at 163 nm, it becomes lower than the value calculated by the above equation (5).

(Evaluation of initial light transmittance of 157.6 nm) A sample of 20 mm × 20 mm × 10 mm was cut out from the vicinity of the center of the sample for evaluation, two 20 mm square surfaces were mirror-polished, and a vacuum ultraviolet spectrophotometer (manufactured by Spectrometer Co., Ltd.) was used. "UV201M") was used to evaluate the light transmittance (%) at a wavelength of 157.6 nm.

(Evaluation of light resistance) An F ₂ laser was irradiated in the direction perpendicular to the surface of 20 mm square from the vicinity of the center of the sample for evaluation at an energy density of 5 mJ / cm ² / pulse and a frequency of 200 Hz for a total of 5 × 10 ⁶ pulses, 157.6n before and after irradiation
The light transmittance reduction amount (difference in light transmittance) (%) at m was measured with a vacuum ultraviolet spectrophotometer (“UV201M” manufactured by Spectrometer Co., Ltd.) to evaluate the light resistance. It means that the smaller the decrease in transmittance is, the more excellent the light resistance is. The light resistance evaluation was performed on the evaluation samples of Examples 1 to 8 and 12.

The results of each evaluation are shown in Table 2. Examples 1 to 8 are examples, and others are comparative examples.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

EFFECTS OF THE INVENTION According to the present invention, a synthetic quartz glass for optical members, which is stable and excellent in light transmittance and light resistance from ultraviolet rays to vacuum ultraviolet rays, and a method for producing the same can be obtained.

Claims (3)

[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 keeping the porous quartz glass in a hydrogen-containing atmosphere to reduce the content of OH groups in the porous quartz glass, and (c) keeping the porous quartz glass in a fluorine compound-containing atmosphere. A step of doping the porous quartz glass with fluorine, and (d) a step of raising the temperature of the porous quartz glass to a temperature of 1300 ° C. or higher to obtain a transparent vitreous material to obtain a transparent quartz glass body containing fluorine. A method of manufacturing synthetic quartz glass for optical members, comprising: 2. 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 the fluorine content is 50 ppm or more, O
H group content is 10ppm or less, chlorine content is 50ppm
The synthetic quartz glass for optical members is as follows, which is substantially free of oxygen-deficient defects. 3. 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 the fluorine content is 50 ppm or more, O
A synthetic quartz glass for an optical member, which has an H group content of 1 ppm or less, a chlorine content of 50 ppm or less, and is substantially free of oxygen-deficient defects.