JP2003201124A - Synthetic quartz glass for optical member and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably manufacturing synthetic quartz glass which is excellent in light resistance and light transmissivity and which contains high concentration of fluorine. <P>SOLUTION: The method incorporates a process for controlling OH group content in the porous quartz glass by holding the porous quartz glass in a steam-containing atmosphere, a process for doping the porous quartz glass with fluorine and simultaneously reducing the OH group content by holding the porous quartz glass in a fluorine compound-containing atmosphere and a process for obtaining a transparent quartz glass body by heating the porous quartz glass at ≥1,300°C and converting the porous quartz glass to 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.

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, 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.

Hydrogen molecules in the synthetic quartz glass are E'centers (≡Si.) And NBOHC generated by ultraviolet irradiation.
According to the following formula, a paramagnetic defect such as (≡SiO.) Is converted into a structure having an absorption band in the ultraviolet region into a structure having no absorption band in the ultraviolet region such as ≡SiH or ≡SiOH. Therefore, the same invention provides a synthetic quartz glass that is less likely to be reduced in transmittance due to ultraviolet irradiation.

[0005]

[Equation 1]

However, the hydrogen molecules in the synthetic quartz glass only have a function of repairing defects caused by irradiation with ultraviolet rays, and the invention of the same publication does not fundamentally improve the light resistance. Even with synthetic quartz glass, there is a problem that damage such as increase in refractive index occurs when it is irradiated with ultraviolet rays. These problems are caused by increasing the energy of photons as the wavelength of light becomes shorter with KrF excimer laser, ArF excimer laser, and further with F ₂ laser. Therefore, when used as an optical member for deep ultraviolet light to vacuum ultraviolet light having a wavelength of 200 nm or less. Was especially serious.

Although the cause of the increase in the refractive index and the decrease in the transmittance when irradiated with ultraviolet rays is not clear, 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. It is considered that the reduction of the distorted structure in the synthetic quartz glass is indispensable for the fundamental improvement of the light resistance.

Further, the OH group in the synthetic quartz glass not only affects the red fluorescence emission upon irradiation with ultraviolet rays, 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 the light transmittance in the vacuum ultraviolet region, the inventors of the present invention described in JP-A-2001-19450 disclose that they contain fluorine and O.
We have proposed a synthetic quartz glass for optical members, which has an H group content of less than 100 ppm. 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.

The inventors of the present invention have proposed the following method in Japanese Patent Laid-Open No. 2001-19450 as a method for producing synthetic quartz glass containing fluorine and having a small OH group content.
That is, silica glass fine particles obtained by flame hydrolysis of a glass forming raw material are deposited and grown on a base material to form a porous silica glass, and the obtained porous silica glass is heated to 600 ° C. or less in a fluorine compound-containing atmosphere. The OH group content in the porous quartz glass is reduced by the treatment at the temperature of 1, and the glass is transparentized after being doped with fluorine. However, this method may not be sufficient when a large amount of fluorine dope is required.

Further, as a method for producing a synthetic quartz glass having a high fluorine content, for example, Japanese Patent Laid-Open No. 2001-89170.
In gazettes and the like, a method for producing a synthetic quartz glass containing a high concentration of 1000 ppm or more of fluorine is proposed by treating porous quartz glass in a fluorine compound atmosphere at a temperature of 600 to 1450 ° C. However, oxygen-deficient defects (≡Si—Si≡) may be generated when the porous quartz glass is treated in a fluorine compound atmosphere. 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, in Japanese Patent Laid-Open No. 2001-19450, the porous quartz glass is reduced in the OH group content, and after the fluorine doping treatment or when the treatment is carried out, the porous quartz is contained in an atmosphere containing oxygen gas. A method of repairing oxygen-deficient defects by treating glass has been proposed. However, in this case, there is a possibility that another different defect, that is, an oxygen-excessive defect is newly generated.

Further, in order to repair the oxygen-deficient type defects generated in the steps before the transparent vitrification step, a method of heat-treating a transparent synthetic quartz glass block in an atmosphere containing oxygen gas is disclosed in Japanese Patent Laid-Open No. 8-75901. However, there are problems that the treatment requires a very long time, oxygen-excessive defects are generated, and oxygen molecules may be contained in the synthetic quartz glass. Oxygen-rich defects and oxygen molecules in synthetic quartz glass have wavelengths of 155 to 155.
Since it has a light absorption band in a wide range of 180 nm, impairs the light transmittance in the same wavelength range, and further emits red fluorescence upon irradiation with ultraviolet rays, NBOHC is generated to reduce the light transmittance in the vacuum ultraviolet to ultraviolet range. It is preferable not to contain it.

[0014]

DISCLOSURE OF THE INVENTION The present invention provides a method for stably producing a synthetic quartz glass containing a high concentration of fluorine, which is excellent in light resistance and light transmittance, and excellent in light resistance and light transmittance. It is intended to provide a fluorine-containing synthetic quartz glass.

[0015]

The present inventors have found that the content of oxygen-deficient defects and oxygen-excessive defects in synthetic quartz glass,
Further, the influence of the conditions when treating the porous quartz glass in the fluorine compound-containing atmosphere on the fluorine content in the synthetic quartz glass was investigated in detail. As a result, in order to suppress the generation of oxygen-deficient defects, the temperature at which the porous quartz glass is treated in a fluorine compound-containing atmosphere is important. It was found that only the substitution reaction between the OH group and the fluorine in the quartz glass can proceed, and the generation of oxygen-deficient defects can be prevented.

In this case, since it is not necessary to treat the porous quartz glass or the synthetic quartz glass body in an oxygen-containing atmosphere for the purpose of repairing oxygen-deficient defects,
A synthetic quartz glass containing no oxygen-rich defects or oxygen molecules can be obtained. Furthermore, in this case, the fluorine content in the finally obtained synthetic quartz glass depends on the OH group content in the porous quartz glass, and the higher the OH group content in the porous quartz glass, the more the fluorine content. A high amount of synthetic quartz glass can be obtained.

That is, the present invention has a wavelength of 155 to 250 nm.
In the method for producing a synthetic quartz glass for an optical member used as an optical member of an optical device which uses the light of (1) as a light source, (a) silica glass fine particles obtained by flame hydrolysis of a glass forming raw material are deposited and grown on a substrate. O in the porous quartz glass by the step of forming the porous quartz glass, and (b) maintaining the porous quartz glass in an atmosphere containing water vapor.
Controlling the H group content, (c) maintaining the porous quartz glass in a fluorine compound-containing atmosphere, doping the porous quartz glass with fluorine, and simultaneously reducing the OH content; ) 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. It is provided.

[0018]

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.

When a silicon halide 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, an organosilicon compound containing no halogen is relatively expensive, and when this 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 manufacturing 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 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 controlling the OH group content in the porous quartz glass. In the step of controlling the porous quartz glass, the porous quartz glass was
Hold at a temperature of 50 ° C. in an atmosphere containing water vapor. The water vapor-containing atmosphere is preferably an inert gas atmosphere containing 0.1 to 100% by volume of water vapor. The atmospheric pressure is preferably 100 Pa to 101 kPa (that is, atmospheric pressure). Furthermore, the holding time is preferably several hours to several tens of hours. In this case, in order to uniformly dope OH groups into the porous quartz glass in a short time, a reduced pressure (13.3 kPa) is used.
It is particularly preferably 1.3 kPa or less. It is preferable to introduce a water vapor-containing gas to a normal pressure in the state of being held in (1) to make a water vapor-containing atmosphere.

In the present invention, the average bulk density of the porous quartz glass at the time of carrying out the OH group content control step is 1.6 g / cm ³ or less, and the bulk density distribution (that is, the growth axis direction of the porous quartz glass is In a cross section perpendicular to, the difference between the maximum and minimum bulk densities within a 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 in the OH group content controlling step within the above range, the OH group content in the porous quartz glass can be sufficiently controlled, and this Fluorine doping in the subsequent fluorine doping step can be sufficiently performed. 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 step (c) of the present invention is a fluorine doping step. To dope with fluorine, the porous quartz glass is kept in a fluorine-containing atmosphere. The fluorine-containing atmosphere may be a fluorine-containing gas (for example, SiF ₄ , SF ₆ , C
An inert gas atmosphere containing 0.1 to 50% by volume of HF ₃ , CF ₄ , F _{2 and the} like) is preferable. Ambient temperature is room temperature ~
800 ° C is preferred. Also, the atmospheric pressure is 100 Pa to 1
01 kPa (101 kPa = atmospheric pressure) is preferable. Furthermore, the holding time is preferably several hours to several tens of hours. In this case, since the porous quartz glass can be uniformly doped with fluorine in a short time, the fluorine-containing gas is kept under a reduced pressure (13.3 kPa or less, particularly preferably 1.3 kPa or less) until the atmospheric pressure is reached. It is preferable to introduce it and make it a fluorine-containing atmosphere. When fluorine doping is performed at a high temperature exceeding 800 ° C., reduction type defects such as oxygen deficiency defects are likely to be generated.

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. Under an inert gas atmosphere such as nitrogen gas or argon gas, the temperature is 500 to 1200 ° C and the pressure is 10
By holding at 1 kPa (atmospheric pressure) to 1 Pa for several tens to several hundreds of hours and performing annealing, a distorted structure such as a three-membered ring structure or a four-membered ring structure in the synthetic quartz glass can be reduced. However, the higher the fluorine content in the synthetic quartz glass, the shorter the annealing treatment can reduce the distorted structure in the synthetic quartz glass. The optical heat treatment can be performed after the transparent vitrification.

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 10 ppm or less, particularly 5 ppm or less, and further 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 fluorine in an amount of 500 ppm or more, particularly 1000 ppm or more.

Further, the fluorine content distribution is preferably 400 ppm or less, particularly 5 in terms of the difference between the maximum and the minimum fluorine content in the usage region as an optical member.
It is preferably 0 ppm or less, more preferably 10 ppm or less.

In the present invention, oxygen-deficient type defects (≡Si—Si≡, (≡ represents Si—O bond; hereinafter the same)) and excess oxygen type defects (≡Si—O—O—) in synthetic quartz glass.
Si≡), ≡SiH bonds, dissolved oxygen molecules 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 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.

Hydrogen molecules repair the paramagnetic defects such as the E'center and NBOHC, which are generated by ultraviolet irradiation, and have 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 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 should be 1 × 10 ¹⁷ molecules / cm ³ or less, depending on the application and use conditions. It may be preferable.

[0036]

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. Porous quartz glass with a diameter of 350 mm and a length of 600 mm (average bulk density 0.7 g)
/ Cm ³ and bulk density distribution 0.1 g / cm ³ ) were prepared.
(Step (a)).

Then, the porous quartz glass was set in a furnace capable of controlling the atmosphere, the temperature was maintained at a reduced pressure of 150 Pa or less, the temperature was raised to the temperature shown in Table 1, and a predetermined gas was introduced at this temperature. Then, the OH group content was controlled (step (b)). Subsequently, the porous quartz glass was set in a furnace capable of controlling the atmosphere, and the temperature was raised to the temperature shown in Table 1 while maintaining a reduced pressure of 150 Pa or less, and a predetermined gas was introduced at this temperature, The content of OH groups in the porous quartz glass was reduced and, at the same time, fluorine doping was performed (step (c)).

Then, the porous quartz glass is pressed at a pressure of 150 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 prepare a transparent quartz glass body (diameter φ230 mm, length 450 mm) (step (d)).

The inner diameter of the transparent quartz glass body obtained in each example was 2
Set in a 50 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.

An evaluation sample of size 150 mm × 20 mm in thickness was cut out from the center of the obtained transparent quartz glass body in the longitudinal direction, and the following evaluations were performed.

(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 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 157.6 nm was calculated from the nm light transmittances T ₁ and T ₂ according to the following formula (1).

[0044]

[Equation 2]

(Evaluation of content of three-membered ring structure and four-membered ring structure) Raman spectroscopic measurement (Ramonor manufactured by Jobin Ybon)
T64000 excitation light source: Argon ion laser (wavelength 514.5 nm)) was performed, and the scattering peak intensities I ₁ and 60 at 495 cm ⁻¹ in the laser Raman spectrum.
The scattering peak intensity _{I 2} of 5 cm ^-1, the intensity of the scattering peak intensity _{I 0} of 440 cm ^-1 ratio _I 1 / _{I 0} and _I 2 /
I ₀ was determined. The smaller the intensity ratio I ₁ / I ₀ and the intensity ratio I ₂ / I ₀ , the better.

The intensity of each scattering peak I₁, I_Two, I₀
The method of obtaining is as follows. 495 cm^-1Scattering of
Peak and 605 cm^-1For the scattering peak of
Curve fitting by one Lorenz function
To minimize the least squares error from the real spectrum.
Then, the coefficient of each function was determined. 440 cm
^-1For the scattering peak of
From 495 cm ^-1Scattering peak and 605 cm
^-1Scattering peak and 440 cm^-1And the scattering peak of
For the residual (baseline) that has been
Perform curve fitting for each and
Approximate the least-squares error of
The coefficient was determined. Using the function obtained above,
The intensity of the scattering peak was determined.

(Evaluation of Presence or Absence of Oxygen-Deficient 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
Measure the light transmittance under a nitrogen atmosphere and calculate from equation (2)
Internal transmittance T at 163 nm₁₆₃Calculate the quartz
OH group concentration C in glass_OH(Ppm) to formula (3)
Value calculated by T _idOxygen deficiency by comparing with
The presence or absence of mold defects was evaluated.

[0048]

[Equation 3]

[0049]

[Equation 4]

When there is an oxygen deficiency type defect, there is an absorption band centered at 163 nm, which is lower than the value calculated by the above equation (3).

(Evaluation of Presence or Absence of Oxygen Excess Defects) A synthetic quartz glass sample of 20 mm square × 10 mm thickness is prepared from the vicinity of the center of the evaluation sample, and the OH group content in the sample is measured by an infrared spectrophotometer. Next, the same sample was used for hydrogen gas 100%, 10
After holding at 1 kPa and 1000 ° C. for 30 hours and cooling to room temperature, the OH group content in the sample is measured again by the same method. The amount of change in the OH group content in the sample before and after the heat treatment was calculated, and if the amount of change was 1 ppm or less, it was determined that the sample did not contain oxygen-excessive defects.

(Evaluation of light resistance) F ₂ laser (center wavelength: 15
7.6 nm, LPX240 made by Lambda Physik Ltd. 1
Produced in Evaluation 3 under the condition of mJ / cm ² / pulse,
2 × in total for the 5 mm thick and 30 mm thick samples used
Irradiation was performed for 10 ⁷ pulses. Before irradiation for two samples, 2
The transmittance at 157.6 nm after irradiation with × 10 ⁷ pulses was measured by a vacuum ultraviolet spectrophotometer and was determined to be 157.6 according to the formula (2).
nm internal transmittance was calculated, and the change ΔT ₁₅₇ in the 157.6 nm internal transmittance before and after irradiation was calculated by the formula (4). The smaller ΔT ₁₅₇ is, the more stable the vacuum ultraviolet ray transmittance is and the more excellent it is. ND indicates that the change in transmittance was less than the measurement accuracy (± 0.1% or less).

[0053]

[Equation 5]

The results of each evaluation are shown in Table 2. Examples 1, 2, 14, and 15 are comparative examples, and the others are examples.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

INDUSTRIAL APPLICABILITY The present invention provides a method for stably producing a synthetic quartz glass containing a high concentration of fluorine, and a fluorine-containing synthetic quartz glass which is excellent in light resistance and light transmission. is there.

Claims (3)

[Claims] 1. A method of 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) silica glass fine particles obtained by flame hydrolysis of a glass forming raw material. Deposited on the base material
Growing to form a porous quartz glass, (b)
A step of controlling the OH group content in the porous quartz glass by maintaining the porous quartz glass in an atmosphere containing water vapor; and (c) maintaining the porous quartz glass in an atmosphere containing a fluorine compound. , A step of doping the porous quartz glass with fluorine and simultaneously reducing the OH content,
(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. Manufacturing method. 2. The synthesis for optical members according to claim 1, wherein the step (c) is carried out by holding the porous quartz glass at a temperature of 800 ° C. or lower in an atmosphere containing a fluorine compound and an inert gas. Quartz glass manufacturing method. 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 250 nm as a light source, which has an OH group content of less than 10 ppm and a fluorine content of 500 ppm or more and is substantially oxygen. Synthetic quartz glass for optical members, which is characterized by not containing excessive defects, oxygen-deficient defects, and oxygen molecules.