JP2019069883A - Silica glass member - Google Patents

Abstract

To provide a silica glass member having excellent refractive index homogeneity, and a method for producing the silica glass member that can easily produce the silica glass member having excellent refractive index homogeneity.SOLUTION: A silica glass member is used for a light lithography step using vacuum ultraviolet light as a light source. A content of fluorine is 1 wt.% or more and 5 wt.% or less, and a range from the maximum to the minimum of fluorine concentrations is 100 ppm or less, and an OH group concentration is 10 ppm or less.SELECTED DRAWING: None

Description

  The present invention relates to a silica glass member, for example, to a silica glass member for a photomask used for photolithography in a vacuum ultraviolet wavelength region.

In recent years, photolithography in the vacuum ultraviolet wavelength region has a tendency toward further miniaturization, and a slight difference in refractive index that can be ignored conventionally is not acceptable, and refractive index homogeneity higher than before is required. There is.
The homogeneity of the refractive index is one of the important optical properties of silica glass, and it appears as striae if the inhomogeneity of the refractive index in the surface of the silica glass is significant. Moreover, although it can not be said that it is a cord, what has a fairly heterogeneous refractive index distribution appears as cord-like heterogeneity.
When silica glass having this striae and striae-like heterogeneity is used as a photomask material in a lithography process, the light intensity distribution on the semiconductor wafer deviates from the design value, and the abnormal light intensity distribution remains unchanged. It is pointed out that the pattern is transferred to a semiconductor wafer (Patent Document 1).

In Patent Document 2, it is shown that the homogeneity of the refractive index in silica glass can be obtained by controlling the fluorine concentration, the OH group concentration, the chlorine concentration, and the distribution thereof in silica glass. In particular, it is shown that the fluorine content distribution needs to be precisely controlled since fluorine has a large influence on the refractive index.
In addition, in this patent document 2, when producing silica glass using the soot method, the distribution of the content of fluorine in the silica glass is OH in the porous silica base material immediately before the treatment with the fluorine compound-containing gas. It becomes almost equal to the distribution of the basic concentration.
Therefore, control of the concentration distribution of fluorine in silica glass is controlled by adjusting the synthesis conditions (ratio of oxygen to hydrogen gas to the raw material) or by synthesizing the synthesized porous silica glass body, for example, with an inert gas of 10 ^-4 Pa or less It has been shown that this is done by adjusting the heat treatment at a temperature of 1100 ° C. or less under reduced pressure.

By the way, as a method for producing fluorine-containing silica glass, for example, as shown in Patent Document 3, a raw material gas for producing silica and a fluorine compound gas are introduced into a flame by a combustion supporting gas and a combustible gas to react There is a so-called direct method of depositing silica glass fine particles on a target and simultaneously vitrifying them.
Further, as shown in Patent Document 2 as well as Patent Document 2, the combustion supporting gas, the flammable gas and the raw material gas for producing silica are supplied from the burner to the reaction zone, and flame hydrolysis of the raw material gas for producing silica is carried out in this reaction zone. There is a so-called soot method in which silica fine particles are generated to prepare a porous silica matrix, and the matrix is heated, melted and vitrified in an atmosphere containing a fluorine compound gas.
Furthermore, as disclosed in Patent Document 5, a method of producing a fluorinated silica glass by making a porous body of dry gel or sintered gel by a sol-gel method, immersing in a fluorine compound solution, drying and sintering is also disclosed. There is.

JP 2005-31689 A JP 2001-180956 A Unexamined-Japanese-Patent No. 2000-143252 Japanese Patent Application Laid-Open No. 2002-60227 Japanese Patent Application Laid-Open No. 62-100443

In any of the direct method and the soot method described above, the distribution of the content of fluorine is controlled by adjusting the ratio of the combustion supporting gas, the flammable gas, the fluorine raw material, etc. among the manufacturing conditions of silica glass It is considered possible.
However, when silica glass is produced by the direct method, silica glass synthesized using a fluoride of silicon as a raw material has a problem that it is difficult to obtain high homogeneity.
Since the refractive index decreases as the region having a high fluorine content in silica glass, the distribution of the fluorine content in silica glass needs to be uniform, but the diffusion coefficient of fluorine in silica glass is small, It is considered that the cause is that the non-uniformity of the content distribution of fluorine generated when depositing the silica glass fine particles on the target is hardly relieved by the end of the synthesis.

  On the other hand, when silica glass is produced by the soot method, the content distribution of fluorine in the silica glass is mainly determined by the density distribution of the soot body and the concentration of the fluorine-containing gas during atmosphere treatment and vitrification. The content distribution of fluorine can be designed by appropriately adjusting these conditions.

However, it is industrially difficult to achieve a uniform distribution of the fluorine content distribution in the entire region including the central portion and the outer peripheral portion of silica glass.
In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 2001-342034, a refractive index fluctuation distribution based on a virtual temperature is formed in the direction to cancel the refractive index fluctuation distribution based on the content distribution of fluorine A method of controlling the distribution is shown (In addition, in JP 2001-342034, as described in paragraph (0051), the viscosity is lowered by raising the temperature of silica glass, and forced (physical) stirring is performed. Improve the uniformity).

As described above, the method of controlling in consideration of the influence of another characteristic value such as the fictive temperature is fluorine as heat treatment such as annealing performed as an additional process after producing silica glass as a means of modifying silica glass. It is difficult to use because the concentration may change.
In addition, when the above method is adopted, a certain degree of refractive index homogeneity can be obtained, but there has been a problem that it is difficult to obtain silica glass having a very small refractive index distribution, which is required in recent years.

In order to solve the above problems, the present inventors have intensively studied on the premise of producing silica glass by the soot method, and have conceived a silica glass member having more excellent refractive index homogeneity, and a method for producing the same. We came to complete the invention. In addition, it was conceived that fluorine doping to the porous body of the soot method can be applied to doping to the porous body by sol-gel method.
An object of the present invention is to provide a silica glass member excellent in refractive index homogeneity, and a method of manufacturing a silica glass member capable of easily manufacturing a silica glass member excellent in refractive index homogeneity. .

  The silica glass member according to the present invention made to achieve the above object is a silica glass member used in a photolithographic process using vacuum ultraviolet light as a light source, and the fluorine content is 1 wt% or more and 5 wt% or less And, the range between the maximum value and the minimum value of the fluorine concentration is 100 ppm or less, and the OH group concentration is 10 ppm or less.

As described above, since the content of fluorine is 1 wt% or more and 5 wt% or less, and the width between the maximum value and the minimum value of the fluorine concentration is 100 ppm or less, it is possible to obtain a silica glass member excellent in refractive index homogeneity.
Further, by setting the OH group concentration to 10 ppm or less, a large amount of fluorine can be doped, which is preferable.

Here, it is desirable that the refractive index distribution in the surface of the member for light of wavelength 633 nm is 1 × 10 ⁻⁶ or less. Incidentally, the reason why the refractive index distribution in the surface of the member in the light having a wavelength of 633 nm is defined is that most of commercially available measuring devices adopt 633 nm. For example, although the wavelength of the ArF excimer laser used in use is 193 nm, the refractive index is larger at a wavelength of 193 nm.

In the method for producing a silica glass member of the present invention, the viscosity of the silica glass is 10 ^{14.5 at} a temperature of 400 ° C. or more and 1000 ° C. or less with respect to the base material having undergone the step of doping the porous silica base material to make it transparent. and D. heat treatment in a hydrogen atmosphere in a temperature range of dPa · s or less.

The method for producing silica glass according to the present invention can form a fluorine content distribution homogeneously and easily, and heat treatment in a hydrogen atmosphere so as not to cause radical defects in order to obtain a very small refractive index distribution. It is characterized in that
That is, according to the present invention, radical defects can be eliminated and the homogeneity of the refractive index can be enhanced by carrying out the step of performing heat treatment in a hydrogen atmosphere after producing fluorine-containing silica glass. .

It should be noted that the temperature range of 400 ° C. or more and 1000 ° C. or less and the viscosity of the silica glass of 10 ^14.5 dPa · s or less can not confirm the effect of hydrogen treatment below 400 ° C., and at a high temperature of more than 1000 ° C. This is because diffusion of hydrogen occurs.

It is preferable that the base material which passed through the said process to make it transparent is a porous silica base material manufactured by the soot method, and fluorine dope is performed in a fluorine-containing atmosphere.
Alternatively, the base material subjected to the above-mentioned step of clarifying is subjected to fluorine doping in a fluorine-containing atmosphere, or by the infiltration of a fluorine compound solution into a porous silica base material made of dry gel or sintered gel manufactured by sol-gel method. Is preferred.
Incidentally, even in the case of producing the porous silica matrix by the direct method, the present invention relates to the present invention if the nonuniformity of the content distribution of fluorine generated when depositing the silica glass fine particles on the target is alleviated. A method of producing silica glass can be applied.

In addition, it is desirable that the step of clarifying the porous silica matrix be performed under pressure.
Here, the pressure condition is preferably 1 atm to 2 atm. If the pressure is less than 1 atm, the distribution of the fluorine concentration becomes more than 100 ppm, and even if the pressure exceeds 2 atm, the distribution of the fluorine concentration becomes more than 100 ppm, which is not preferable.

  According to the present invention, a silica glass member excellent in refractive index homogeneity can be obtained, and a method of manufacturing a silica glass member capable of easily producing a silica glass member excellent in refractive index homogeneity is obtained. be able to.

  The silica glass member according to the present invention is a silica glass member used in a photolithographic process using vacuum ultraviolet light as a light source, and has a fluorine content of 1 wt% or more and 5 wt% or less, and maximum and minimum fluorine concentration values. The range of the value is 100 ppm or less, and the OH group concentration is 10 ppm or less.

Here, since the content of fluorine is 1 wt% or more and 5 wt% or less, it is possible to obtain an excellent silica glass member having a small fluorine concentration distribution.
When the content of fluorine is less than 1 wt%, the fluorine concentration distribution is more than 100 ppm, which is not preferable from the viewpoint of the homogeneity of the refractive index. On the other hand, when the content of fluorine exceeds 5 wt%, the fluorine concentration distribution exceeds 100 ppm, which is also not preferable from the viewpoint of homogeneity of refractive index.

When the width between the maximum value and the minimum value of the fluorine concentration exceeds 100 ppm, it is not possible to obtain a silica glass member excellent in refractive index homogeneity.
On the other hand, if the fluorine content in the silica glass member is made uniform, the homogeneity of the refractive index can be expected, but since it is difficult to be completely homogeneous in the industry, the width of the maximum value and the minimum value of the fluorine concentration is essentially Although it is preferable that it is 0, about 10 ppm is acceptable for obtaining the effects of the present invention.
Therefore, it is desirable that the range between the maximum value and the minimum value of the fluorine concentration is 100 ppm or less.

When the width between the maximum value and the minimum value of the fluorine concentration in the silica glass member is 100 ppm or less, the difference in refractive index can be suppressed to about 4.2 × 10 ⁻⁶ or less.
The maximum value of the fluorine concentration refers to the maximum value of the fluorine concentrations measured at each point in the use area. The minimum value of the fluorine concentration means the minimum value of the fluorine concentrations measured at each point in the use area. Further, the range between the maximum value and the minimum value of the fluorine concentration means the difference between the maximum value and the minimum value of the fluorine concentration.

The OH group concentration is preferably 10 ppm or less in order to set the fluorine concentration to 1 wt% or more.
Since the radical structure generated in the process of forming silica glass is treated with a hydrogen atmosphere to form an OH group structure, a very small refractive index distribution can be obtained.
The OH group concentration is preferably 10 ppm or less, and more preferably 5 ppm or less.

Next, a method of manufacturing a silica glass member according to the present invention will be described.
In the method for producing a silica glass member according to the present invention, the heat treatment is performed in a hydrogen atmosphere so as not to form radical defects, in order to obtain a very small distribution of refractive index as well as to uniformly form the content distribution of fluorine. There is a feature in the point.

As a method for producing a silica glass member, a combustion supporting gas, a flammable gas and a silica producing raw material gas are supplied from a burner to a reaction zone so as to uniformly contain fluorine, and flame hydrolysis of the silica producing raw material gas is performed in this reaction zone. It is possible to use a so-called soot method in which silica fine particles are generated by decomposition to produce a porous silica base material, and the base material is heated and melted in an atmosphere containing a fluorine compound gas to vitrify.
At this time, it is possible to achieve a uniform fluorine content by appropriately setting the amount of fluorine gas introduced during vitrification and by making it transparent under pressure conditions.

Specifically, for example, as described in JP-A-2001-342027, a silica glass forming raw material is subjected to flame hydrolysis to form a porous silica body (soot), and then a transparentizing treatment is performed. , So-called VAD method.
That is, after forming a soot, it is treated in a mixed gas atmosphere in which an inert gas such as helium and a SiF ₄ gas are mixed, after doping with fluorine, it is made transparent in a fluorine-containing atmosphere (mixed gas atmosphere), Further, a predetermined heat treatment is performed to manufacture a silica glass member.

10 vol%-35 vol% are preferable, and, as for the fluorine concentration (concentration ratio of SiF ₄ gas) in the said mixed gas, 25 vol%-35 vol% are more preferable.
Moreover, 1000 degreeC-1300 degreeC are preferable, and, as for introduction | transduction temperature of mixed gas, 1100 degreeC-1200 degreeC is more preferable. When the introduction temperature is less than 1000 ° C., diffusion of fluorine into the glass structure may be slow and not sufficiently doped. On the other hand, if the temperature is higher than 1300 ° C., sintering of soot may start, and diffusion of fluorine into the glass structure may be inhibited.

Even if it is difficult in principle to make the fluorine content distribution completely homogeneous at this time, the content of fluorine is 1 wt% or more and 5 wt% or less by introducing vitrified gas under pressurized conditions. In addition, it is possible to obtain a glass having a fluorine content of 100 ppm or less between the maximum value and the minimum value of the fluorine content, which is larger than that of the prior art and high in homogeneity.
As this pressurizing condition, 1 atm to 2 atm is desirable. If the pressure is less than 1 atm, the distribution of the fluorine concentration becomes more than 100 ppm, and even if the pressure exceeds 2 atm, the distribution of the fluorine concentration becomes more than 100 ppm, which is not preferable.

Although the present invention is premised on producing silica glass by the soot method, the silica glass according to the present invention may be used even if the porous silica matrix is produced by a known sol-gel method. The manufacturing method of a member can be applied.
Further, even in the case where the porous silica matrix is produced by the direct method, the present invention relates to the present invention, provided that the unevenness of the content distribution of fluorine generated when depositing the silica glass fine particles on the target is alleviated. The manufacturing method of a silica glass member can be applied.

  In the method for producing a silica glass member according to the present invention, after producing fluorine-containing silica glass, the heat treatment is further performed in a hydrogen atmosphere to eliminate radical defects and improve the homogeneity of the refractive index. It is based on knowledge. The reason why the homogeneity of the refractive index is improved by the addition of such treatment is not clear, but it is presumed as follows.

For example, it is known that when fluorine is contained in silica glass, strain bonding represented by a three-membered ring or a four-membered ring structure formed in a Si-O-Si network in glass is eliminated. In this reaction, part of the member ring structure is cleaved to generate the reaction of the formula (1), and it is described that the reaction of the formula (2) is generated by the fluorine (OPTRONICS (2004) 23 p 148).
-Si-O-Si- → -Si ···· O-Si- (1)
-Si * + * O-Si- + F2->-Si-F + F-Si- (2)

However, although (2) is a model in which the oxygen atom of O-Si structure is detached, even if the majority reaction occurs in (2), only a slight amount of .O-Si- structure remains. Is assumed.
In this case, it is considered that the refractive index is different in the portion where the radical structure remains. For this reason, in order to eliminate a radical structure, it is set as HO-Si- structure by heat-processing in a hydrogen atmosphere.

In addition, although the reason is not necessarily clear, it has been newly found that in the present invention, the remaining of the OH group contributes to the homogeneity of the refractive index rather than the remaining of the radical structure.
That is, in the manufacturing method according to the present invention, since the effect on the refractive index can be reduced when the hydrogen atmosphere is treated to form the OH group rather than the radical structure, the heat treatment in the hydrogen atmosphere is performed. To be done.

The heat treatment in the hydrogen atmosphere is performed in a temperature range where the temperature is 400 ° C. or more and 1000 ° C. or less and the viscosity of the silica glass is 10 ^14.5 dPa · s or less.
In addition, by processing in a temperature range of 400 ° C. or more and 1000 ° C. or less, diffusion of hydrogen at high temperature can be suppressed, and radical defects can be efficiently eliminated.

Since the strain point of silica glass having a fluorine concentration of 1 wt% or more and 5 wt% or less is 1000 ° C. or less, the temperature of the heat treatment is usually 1000 ° C. or less, preferably 800 ° C. or less, more preferably 600 ° C. to 400 ° C. Do between. The strain point is a temperature at which the viscosity becomes 10 ^14.5 dPa · s, the temperature at which viscous flow of the silica glass can not practically occur, and corresponds to the lower limit temperature in the slow cooling region.
Therefore, the radical structure in silica glass can be made into OH group structure in the temperature range which viscous flow of silica glass can not practically occur.

  EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited by the examples shown below.

Example 1
SiCl ₄ as a glass forming material was hydrolyzed in an oxyhydrogen flame, and the produced fine silica particles were deposited on a target made of quartz glass to obtain porous silica (soot) having a diameter of 200 mm and a length of 500 mm.
Next, the soot is put into a furnace and heated to 1250 ° C. at a heating rate of 400 ° C./h in a He gas atmosphere with a flow rate of 20 L / min, and then the atmosphere gas is mixed gas of 25 vol% SiF ₄ + 75 vol% He The fluorine doping process was performed by switching (flow rate 20 L / min) and holding at 1250 ° C. for 4 hours. The pressure in the furnace at this time was 1.2 atm.
After completion of the fluorine doping treatment, the atmosphere is kept as it is, and the temperature is raised to 1420 ° C. at a temperature rising rate of 400 ° C./h, held at 1420 ° C. for 2.5 hours to perform a clarifying treatment, diameter 120 mm, length A 230 mm silica glass ingot was obtained.
The ingot is once cooled to room temperature, processed and sliced to a substrate size of 152 mm × 152 mm, 6.4 mm thick, and then the thin plate is placed in an electric furnace and heated in a hydrogen atmosphere to 800 ° C. Held for 15 hours.

Furthermore, after cutting out a 20 mm x 40 mm x 6.4 mm strip-like sample and performing optical polishing, OH concentration by OH absorption peak was measured with an infrared spectrometer (Nicolet 6700). In addition, F concentration analysis was performed by ion chromatography.
The fluorine content at this time was 2.6 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 60 ppm or less. In addition, the OH group concentration was 1.5 ppm.

Furthermore, the refractive index distribution in the member surface in the light of wavelength 633 nm was measured. The measurement of the homogeneity of refractive index measured and evaluated in-plane 25 points using the optical measurement instrument (Zygo Verifire). As a result, the in-plane distribution of the refractive index was 0.5 × 10 ⁻⁶ . The results are shown in Table 1. The reason why the refractive index distribution in the surface of the member in the light having a wavelength of 633 nm is measured is that most of the commercially available measuring devices use 633 nm. For example, although the wavelength of the ArF excimer laser used in use is 193 nm, the refractive index is larger at a wavelength of 193 nm.

Example 2
A silica glass member was obtained in the same manner as Example 1, except that the fluorine doping process was performed with the ratio of SiF ₄ to He mixed gas being 35 vol%: 65 vol%.
Thereafter, the same measurement and evaluation as in Example 1 were performed.
The fluorine content at this time was 3.6 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 75 ppm or less. In addition, the OH group concentration was 1 ppm. The in-plane distribution of the refractive index was 0.7 × 10 ⁻⁶ . The results are shown in Table 1.

[Example 3]
After 1 mole of tetraethoxysilane, 10 moles of water and 0.002 moles of nitric acid are mixed and stirred, hydrolysis is allowed to proceed under an acid catalyst, and after the mixture is stabilized, 0.02 mole of ammonium acetate is added dropwise to make the solution basic The gelation was caused by The obtained gel was dried at 80 ° C. for 7 days to obtain porous silica having a diameter of 100 mm and a length of 100 mm.
Thereafter, the porous silica is put into a furnace as in the soot of Example 1, and the temperature is raised to 1250 ° C. at a heating rate of 400 ° C./h in a He gas atmosphere with a flow rate of 20 L / min. It switched to the mixed gas of ₄ 10 vol% + He 90 vol% (flow volume 20 L / min), and it hold | maintained at 1250 degreeC for 4 hours, and performed the fluorine dope process. The pressure in the furnace at this time was 1.1 atm. After completion of the fluorine doping treatment, the atmosphere is kept as it is, and the temperature is raised to 1420 ° C. at a temperature rising rate of 400 ° C./h and held at 1420 ° C. for 2.5 hours to perform a clarifying treatment, diameter 80 mm, length An 80 mm silica glass ingot was obtained.
The ingot is once cooled to room temperature, processed and sliced to a substrate size of 60 mm × 60 mm, 6.4 mm thick, and then the thin plate is placed in an electric furnace and heated in a hydrogen atmosphere to a temperature of 600 ° C. Held for 15 hours.
Furthermore, after cutting out a 20 mm x 40 mm x 6.4 mm strip-like sample and performing optical polishing, OH concentration by OH absorption peak was measured with an infrared spectrometer (Nicolet 6700). In addition, F concentration analysis was performed by ion chromatography. The fluorine content at this time was 1.0 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 25 ppm or less. In addition, the OH group concentration was 4 ppm. The results are shown in Table 1.

Example 4
The fluorine doping process is performed with the ratio of SiF ₄ to He mixed gas set to 35 vol%: 65 vol%, the atmosphere pressure at the time of transparency is 1.7 atm, and the hydrogen treatment temperature after the transparency is 400 ° C. In the same manner as in Example 1, a silica glass member was obtained.
Thereafter, the same measurement and evaluation as in Example 1 were performed.
The fluorine content at this time was 5.0 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 95 ppm or less. In addition, the OH group concentration was 1 ppm. The in-plane distribution of the refractive index was 0.9 × 10 ^-6 . The results are shown in Table 1.

[Example 5]
A fluorine doping process is performed with a ratio of SiF ₄ to He mixed gas of 15 vol%: 85 vol%, the atmosphere pressure at the time of clarification is 1.1 atm, and the hydrogen treatment temperature after the clarification is 600 ° C. In the same manner as in Example 1, a silica glass member was obtained.
Thereafter, the same measurement and evaluation as in Example 1 were performed.
The fluorine content at this time was 1.5 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 45 ppm or less. Also, the OH group concentration was 3 ppm. The in-plane distribution of the refractive index was 0.3 × 10 ⁻⁶ . The results are shown in Table 1.

[Example 6]
A fluorine doping process is performed at a ratio of 30 vol%: 70 vol% of SiF ₄ and He mixed gas, the atmosphere pressure at the time of transparency is 1.5 atm, and the hydrogen treatment temperature after the transparency is 400 ° C. In the same manner as in Example 1, a silica glass member was obtained.
Thereafter, the same measurement and evaluation as in Example 1 were performed.
The fluorine content at this time was 4.2 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 85 ppm or less. In addition, the OH group concentration was 1 ppm. The in-plane distribution of the refractive index was 0.8 × 10 ⁻⁶ . The results are shown in Table 1.

Comparative Example 1
Silica glass was obtained in the same manner as in Example 1 except that the fluorine doping process was performed in Example 1 in which the ratio of SiF ₄ to He mixed gas was 7 vol% and 93 vol%.
Thereafter, the same test and evaluation as in Example 1 were performed.
The fluorine content at this time was 0.7 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 120 ppm or less. The OH group concentration was 12 ppm. The in-plane distribution of the refractive index was 2.7 × 10 ⁻⁶ . The results are shown in Table 1.

Comparative Example 2
Silica glass was obtained in the same manner as in Example 1 except that the ratio of SiF ₄ to He mixed gas was 45 vol% and 55 vol% in Comparative Example 1.
Thereafter, the same test and evaluation as in Example 1 were performed.
The fluorine content at this time was 6 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 130 ppm or less. In addition, the OH group concentration was 1 ppm. In addition, the in-plane distribution of the refractive index was 1.5 × 10 ⁻⁶ . The results are shown in Table 1.

Comparative Example 3
A fluorine doping process is performed with a ratio of SiF ₄ to He mixed gas of 25 vol%: 75 vol%, the atmosphere pressure at the time of transparency is 0.5 atm, and the hydrogen treatment temperature after the transparency is 600 ° C. In the same manner as in Comparative Example 1, a silica glass member was obtained.
Thereafter, the same measurement and evaluation as in Comparative Example 1 were performed.
The fluorine content at this time was 0.8 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 120 ppm or less. The OH group concentration was 15 ppm. The in-plane distribution of the refractive index was 1.3 × 10 ^-6 . The results are shown in Table 1.

Comparative Example 4
The fluorine doping process is performed at a ratio of 25 vol%: 75 vol% of SiF ₄ and He mixed gas, the atmospheric pressure at the time of transparency is 1.2 atm, and the hydrogen treatment temperature after the transparency is 1100 ° C. In the same manner as in Comparative Example 1, a silica glass member was obtained.
Thereafter, the same measurement and evaluation as in Comparative Example 1 were performed.
The fluorine content at this time was 1.8 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 140 ppm or less. In addition, the OH group concentration was 2.5 ppm. The in-plane distribution of the refractive index was 1.6 × 10 ^-6 . The results are shown in Table 1.

Comparative Example 5
A fluorine doping process is performed with a ratio of SiF ₄ to He mixed gas of 35 vol%: 65 vol%, the atmosphere pressure at the time of transparency is 1.2 atm, and the hydrogen treatment temperature after the transparency is 300 ° C. In the same manner as in Comparative Example 1, a silica glass member was obtained.
Thereafter, the same measurement and evaluation as in Comparative Example 1 were performed.
The fluorine content at this time was 3.0 wt%. Further, the width between the maximum value and the minimum value of the fluorine concentration was 150 ppm or less. In addition, the OH group concentration was 1.5 ppm. The in-plane distribution of the refractive index was 1.8 × 10 ⁻⁶ . The results are shown in Table 1.

  The silica glass member of the present invention can be suitably used for photolithography using vacuum ultraviolet light such as ArF excimer laser (193 nm) or F2 laser (157 nm) as a light source.

Claims (6)

  A silica glass member used in a photolithographic process using vacuum ultraviolet light as a light source, wherein the content of fluorine is 1 wt% or more and 5 wt% or less, and the width between the maximum value and the minimum value of fluorine concentration is 100 ppm or less And an OH group concentration of 10 ppm or less. The silica glass member according to claim 1, wherein the refractive index distribution in the member plane of light having a wavelength of 633 nm is 1 × 10 ^-6 or less. In a temperature range where the viscosity of the silica glass is 10 ^14.5 dPa · s or less, the temperature is 400 ° C. or more and 1000 ° C. or less and the viscosity of the silica glass is 10 ^14.5 dPa · s or less. A step of heat treatment;
A method of manufacturing a silica glass member, comprising:   The silica glass member according to claim 3, wherein the base material subjected to the step of making transparent is a porous silica base material manufactured by a soot method, and fluorine doping is performed in a fluorine-containing atmosphere. Production method.   In the fluorine-containing atmosphere, or the porous silica base material made of a dry gel or sintered gel manufactured by a sol-gel method, the base material which has been subjected to the above-mentioned clearing step is subjected to fluorine doping by infiltration of a fluorine compound solution. The manufacturing method of the silica glass member of Claim 3 characterized by these.   The method for producing a silica glass member according to any one of claims 3 to 5, wherein the step of making the porous silica matrix transparent is performed under pressure.