JP2005298330A - Synthetic quartz glass and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synthetic quartz glass excellent in homogeneity and resistance to ultraviolet rays. <P>SOLUTION: The synthetic quartz glass is for optical use and used by irradiating it with a light ranging from an ultraviolet region to a vacuum ultraviolet region, which is formed by a synthetic quartz glass containing OH groups and fluorine where a variation range of the OH group content is ≤15 ppm, a variation range of the fluorine content is ≤15 ppm, and a chlorine content is ≤25 ppm in a region using the light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a synthetic quartz glass used for an optical member of an apparatus using an ultraviolet ray having a wavelength of 400 nm or less as a light source, and a method for producing the same. More specifically, excimer laser (XeCl: 308 nm, KrF: 248 nm, ArF: 193 nm), F ₂ laser (157 nm), low-pressure mercury lamp (185 nm), Xe ₂ ^* excimer lamp (172 nm), deuterium lamp (110-400 nm) ) Etc. Lenses (projection system, illumination system), prism, etalon, photomask, pellicle (pellicle material, pellicle frame or both), window material, etc. The present invention relates to a synthetic quartz glass used as an optical member (including a commercialized product and a semifinished product) and a method for producing the same.

  Synthetic quartz glass is a transparent material over a wide wavelength range from the near infrared region to the vacuum ultraviolet region, has a very low thermal expansion coefficient and excellent dimensional stability, and contains almost no metal impurities. It is characterized by high purity. Therefore, synthetic quartz glass has been mainly used as an optical member of an optical device using conventional g-line (436 nm) and i-line (365 nm) as a light source.

In recent years, along with the high integration of LSI, optical lithography technology that draws an integrated circuit pattern on a wafer requires a finer drawing technology with a narrower line width. Is being promoted. For example, KrF excimer lasers and ArF excimer lasers are being used in place of conventional g-line and i-line as light sources for lithography steppers, and F ₂ lasers are being used.

Low-pressure mercury lamps, Xe ₂ ^* excimer lamps and deuterium lamps are used in 1) equipment for photo-CVD, 2) ashing and etching equipment for silicon wafers, or 3) ozone generators, etc. Development is underway to apply to photolithography technology. Synthetic quartz glass is also used for optical members that are irradiated with these short-wavelength light, such as gas-filled tubes used in low-pressure mercury lamps, excimer lamps, deuterium lamps, or optical devices using the short-wavelength light sources described above. There is a need.

Synthetic quartz glass used in these optical members is required to have light transmittance at wavelengths ranging from the ultraviolet region to the vacuum ultraviolet region, and the transmittance is not lowered by ultraviolet irradiation (hereinafter simply referred to as “ultraviolet resistance”). ) Is required. Optical members used for irradiation with light such as ArF excimer laser, F ₂ laser, low-pressure mercury lamp, Xe ₂ ^* excimer lamp, deuterium lamp, etc. are light transmissive in the vacuum ultraviolet region with a wavelength of 200 nm or less. (Hereinafter simply referred to as “vacuum ultraviolet ray permeability”). In addition, an optical member used for light with a wavelength of 200 nm or less is required to have a smaller refractive index fluctuation range (Δn) than before (hereinafter referred to as “homogeneity”).

  In conventional synthetic quartz glass, for example, when high energy light emitted from a light source such as a KrF excimer laser or an ArF excimer laser is irradiated, a new absorption band is generated in the ultraviolet region, and an optical system using ultraviolet light as a light source is constructed. There was a problem as an optical member. That is, when ultraviolet rays are irradiated for a long time, an absorption band of about 215 nm called E ′ center (≡Si ·) and an absorption band of about 260 nm called NBOHC (non-bridging oxygen radical: ≡Si—O ·) are generated. To do.

  The causes of these absorption bands can be broadly classified into two types: one is a structural defect in synthetic quartz glass, that is, a reduced defect such as ≡Si—Si≡ (oxygen-deficient defect) or ≡Si—H, Alternatively, it is due to an oxidation type defect such as ≡Si—O—O—Si≡, and another is due to an unstable structure in the synthetic quartz glass, that is, a three-membered ring structure or a four-membered ring structure. As shown in the following formulas (1) to (4), these defects are cut by irradiation with ultraviolet rays to generate paramagnetic defects (E ′ center and NBOHC). If there are paramagnetic defects, the transmittance decreases. It is considered that the ultraviolet resistance decreases, the absolute refractive index increases, the refractive index distribution fluctuates and fluorescence occurs.

≡Si-Si≡ + hν → 2≡Si · (1)
≡Si-H + hν → ≡Si · + H · (2)
≡Si-O-O-Si≡ + hν → 2≡Si-O. (3)
≡Si-O-Si≡ + hν → ≡Si · + ≡Si-O · (4)

Various methods have been studied in order to solve these problems, and it is known that hydrogen molecules may be contained in some form in synthetic quartz glass. For example, Patent Document 1 discloses a method for suppressing a decrease in transmittance due to ultraviolet irradiation by containing 5 × 10 ¹⁶ molecules / cm ³ or more of hydrogen molecules in synthetic quartz glass and 100 ppm or more of OH groups. It is disclosed.

However, the OH group in the synthetic quartz glass is a problem because the reaction of the following formula (5) proceeds due to ultraviolet irradiation, NBOHC is generated, and 260 nm absorption and 650 nm fluorescence are generated.
≡Si-OH + hν → ≡Si-O · (NBOHC) + H · (5)

Even if hydrogen molecules were contained, the reaction of formula (5) could not be completely prevented, and particularly when the OH group concentration was high, the 650 nm fluorescence became strong, which was a problem. In addition, when the OH group concentration is high, the light transmittance at 150 to 180 nm is lowered, which is a problem particularly when used in an apparatus using a low pressure mercury lamp, Xe ₂ ^* excimer lamp, F ₂ laser or the like as a light source. there were.

  In order to solve such a problem, Patent Document 2 proposes a synthetic quartz glass having an OH group concentration of 10 ppm or less and a halogen concentration of 400 ppm or more and containing hydrogen molecules. According to this synthetic quartz glass, since the OH group concentration is low, it is excellent in ultraviolet resistance, and a high transmittance is obtained at 150 to 180 nm.

  This Patent Document 2 includes (1) a step of flame hydrolysis of a glass forming raw material to form a porous quartz glass body, and (2) a porous quartz glass body at 800 to 1250 ° C. in a halogen-containing atmosphere. A step of dehydrating by heating at a temperature; (3) a step of raising the temperature of the dehydrated porous quartz glass body to a transparent vitrification temperature and converting it to transparent vitrification; and (4) hydrogenation of the synthetic quartz glass converted to transparent glass. The manufacturing method characterized by including the process of heat-processing at the temperature of 500-1100 degreeC in the atmosphere to contain and containing hydrogen is proposed.

  Furthermore, when synthetic quartz glass is held in an atmosphere containing hydrogen at a high temperature, reduced defects of ≡Si—Si≡ and ≡Si—H are likely to be generated. Almost the same as the method, there has been proposed a production method in which a fluorine-containing quartz glass that has been made into a transparent glass is formed, and hydrogen is contained in an atmosphere containing hydrogen at a temperature of 500 ° C. or lower.

  However, as a result of studying the methods described in Patent Document 2 and Patent Document 3, the present inventors have found that sufficient UV resistance may not always be obtained. That is, when the porous quartz glass body is treated at a high temperature of 800 to 1250 ° C. in an atmosphere containing a fluorine compound, the ≡Si—Si≡ defect is generated. This ≡Si—Si≡ defect is a problem because it not only generates an E ′ center by ultraviolet irradiation as described above but also has absorption at 245 nm and 163 nm.

The ≡Si—Si≡ defect is a problem because ≡Si—H is generated by the following formula (6) even if hydrogen-containing treatment is performed, and this ≡Si—H also generates an E ′ center by ultraviolet irradiation. It was.
≡Si-Si≡ + H ₂ → ≡Si-H + ≡Si-H (6)

On the other hand, in order to improve the vacuum ultraviolet ray permeability, Patent Document 4 discloses that the OH group concentration is 200 ppm or less, the chlorine concentration is 2 ppm or less, and the ≡Si—Si≡ concentration is 1 × 10 ¹⁵ atoms / cm ³ or less. A synthetic quartz glass has been proposed. Patent Document 5 proposes a synthetic quartz glass having an OH group concentration of 10 to 400 ppm and a concentration of reduced defects and oxidized defects of 5 × 10 ¹⁶ pieces / cm ³ or less. Patent Document 6 proposes a synthetic quartz glass having an OH group concentration of 100 to 2000 ppm and containing a transition metal, an alkali metal, and an alkaline earth metal at a predetermined concentration or less.
All of these conventional synthetic quartz glasses are intended to improve the vacuum ultraviolet transmittance by setting the OH group concentration within a predetermined range, but a high transmittance is not necessarily obtained in the vacuum ultraviolet region.

Further, as a method for ensuring the homogeneity of the synthetic quartz glass, Patent Document 7 proposes a method of adjusting the fluctuation range of the OH group and chlorine concentration by including OH groups and chlorine in the synthetic quartz glass. . However, chlorine is present in synthetic quartz glass in the form of ≡Si—Cl, and this ≡Si—Cl bond has a weak bond energy of 7 to 8 eV and is easily cleaved as shown in the following formula by ultraviolet irradiation. After all, E 'center occurs.
≡Si-Cl + hν → ≡Si · (E 'center) + Cl ·
Therefore, although the method disclosed in the above-mentioned patent document can obtain a synthetic quartz glass excellent in homogeneity, there is a problem in ultraviolet resistance.

Japanese Patent Laid-Open No. 3-88742 JP-A-6-227827 JP-A-8-75901 JP-A-8-91867 JP-A-9-235134 JP-A-7-267654 Japanese Patent Publication No. 6-27014

The present invention provides a synthetic quartz glass with reduced generation of E ′ center and fluorescence and excellent in ultraviolet resistance.
The present invention also provides a synthetic quartz glass excellent in vacuum ultraviolet ray permeability.
The present invention provides a synthetic quartz glass excellent in homogeneity.
The present invention provides a suitable method for producing these synthetic quartz glasses.

  The present inventors have conducted detailed studies on the influence of the halogen concentration in the synthetic quartz glass and the influence of the unstable structure in the synthetic quartz glass on the ultraviolet resistance and ultraviolet transmittance. As a result, in synthetic quartz glass, fluorine exists in the form of ≡Si-F, and this ≡Si-F bond is very strong with a bond energy of 20 eV or more and is not cleaved by ultraviolet irradiation. I found that there was no problem. Furthermore, although the mechanism is not clear, it has been found that fluorine reduces the distorted structure in quartz glass and improves the UV resistance.

The present invention contain fluorine, the value of the scattering peak intensity I ₂₂₅₀ of 2250 cm ^-1 relative to the scattering peak intensity I ₈₀₀ of the 800 cm ^-1 in the laser Raman spectrum (I ₂₂₅₀ / I ₈₀₀₎ is 1 × 10 ^-4 or less A synthetic quartz glass having a light absorption coefficient of 245 nm (hereinafter simply referred to as an absorption coefficient of 245 nm) is 2 × 10 ⁻³ cm ⁻¹ or less.

Scattering peak of 800 cm ^-1 is a peak indicating the bond of ≡Si-O-(fundamental vibration between silicon and oxygen), the scattering peak of 2250 cm ^-1 is the binding of ≡Si-H is a reduction type defects The value of I ₂₂₅₀ / I _{800 is} an index of ≡Si—H defect concentration (≡Si—H concentration). In the present invention, it is important that I ₂₂₅₀ / I ₈₀₀ is 1 × 10 ⁻⁴ or less. If it ^exceeds 1 × 10 ⁻⁴ , the E ′ center is likely to occur.

The absorption coefficient of 245 nm is an index of the concentration of ≡Si—Si≡ defect, which is also a reduced defect. In the present invention, it is important that the absorption coefficient at 245 nm is 2 × 10 ⁻³ cm ⁻¹ or less. If it ^exceeds 2 × 10 ⁻³ cm ⁻¹ , the E ′ center is likely to occur. If it exceeds 2 × 10 ⁻³ cm ⁻¹ , it will be difficult to achieve high transparency at 150 to 180 nm. Moreover, it is preferable that absorption of light of 163 nm is also reduced.
The definition of the scattering peak at 2250 cm ⁻¹ and the absorption coefficient at 245 nm in the present invention define the amount of reduced defects.

The concentration of the E ′ center is obtained by measuring the transmittance of 214 nm light immediately after the shot irradiation with KrF excimer laser light with an ultraviolet-visible spectrophotometer, and obtaining the absorption coefficient change Δk ₂₁₄ [cm ⁻¹ ] before and after the irradiation. Can be evaluated. Δk ₂₁₄ is preferably 1 × 10 ⁻¹ or less. In particular, it is preferably 1 × 10 ⁻² or less.

The degree of fluorescence emission is measured by measuring ₆₅₀ nm fluorescence intensity L ₆₅₀ and KrF excimer laser scattered light intensity S ₂₄₈ when shot with KrF excimer laser light from a direction perpendicular to the incident axis of KrF laser light, and KrF laser (248 nm) scattering. It can be evaluated by determining the ratio L ₆₅₀ / S ₂₄₈ of the fluorescence intensity at 650 nm to the light intensity. L ₆₅₀ / S ₂₄₈ is preferably 5 × 10 ⁻⁴ or less, and particularly preferably 1 × 10 ⁻⁴ or less.

In addition, as a result of further detailed examination of the influence of the halogen concentration and OH group concentration in the synthetic quartz glass on the ultraviolet resistance, the present inventors have different effects in fluorine and chlorine in the synthetic quartz glass, Chlorine is present in synthetic quartz glass in the form of ≡Si—Cl, and this ≡Si—Cl bond has a weak bond energy of 7-8 eV.
≡Si-Cl + hν → ≡Si · (E 'center) + Cl · (7)
It was found that it was easily cleaved to produce the E ′ center as shown in FIG.

A synthetic quartz glass containing no chlorine and produced using a glass raw material not containing chlorine has also been proposed (Japanese Patent Laid-Open No. 7-291635). This is because the fluorine concentration is set to 1000 ppm or more in order to suppress the decrease in the transmittance due to the irradiation of the high energy beam, and the OH group concentration is set to 50 ppm or more in order to suppress the absorption at 245 nm due to the oxygen deficient defect ≡Si—Si≡. However, it does not mention the problem of a decrease in transmittance at 150 to 180 nm, and there is a problem in using it in a device using a low-pressure mercury lamp, Xe ₂ ^* excimer lamp, F ₂ laser or the like as a light source. .

  Therefore, in order to suppress the formation of paramagnetic defects and achieve an essential improvement in UV resistance, it is necessary to optimize the OH group, chlorine and fluorine concentrations in the synthetic quartz glass. As a result of further studies on this point, it was found that if the fluorine concentration in the synthetic quartz glass is increased and the chlorine concentration is reduced, a synthetic quartz glass excellent in UV resistance can be obtained even if the OH group concentration is slightly reduced. I found it.

That is, the present invention provides a synthetic quartz glass containing fluorine, having reduced defects below a specific amount, and having a chlorine concentration of 100 ppm or less. In particular, the synthetic quartz glass is effective in suppressing the unstable structure, E ′ center, and fluorescence emission in synthetic quartz, and exhibits excellent UV resistance. The synthetic quartz glass has an OH group concentration of less than 50 ppm and a fluorine concentration of 100 ppm. As described above, a synthetic quartz glass having a chlorine concentration of 100 ppm or less and a hydrogen molecule concentration of 5 × 10 ¹⁶ molecules / cm ³ or more is preferable.

  In addition, the relationship between the effects of halogen concentration and hydrogen molecule concentration in synthetic quartz glass and the influence of unstable structure in quartz glass were investigated. As a result, the amount of unstable structure due to fluorine doping is reduced to a certain limit, and when combined with the repairing of paramagnetic defects due to the inclusion of hydrogen molecules, synthetic quartz glass with respect to light emitted from short-wavelength light sources can be used. It was found that the UV transmittance and UV resistance can be improved to a satisfactory level.

Therefore, among the synthetic quartz glass of the present invention, the scattering peak intensity of the quartz glass unstable structure to the scattering peak intensity of the laser Raman spectrum of 495cm ^-1 attributed in (I ₁₎ and 606 cm ^-1 and (I ₂₎ Synthetic quartz glass in which the intensity ratios I ₁ / I ₀ and I ₂ / I ₀ with respect to the scattering peak intensity (I ₀ ) of 440 cm ⁻¹ are in a specific range is effective in improving ultraviolet transmittance and ultraviolet resistance. I found out that there was.

The present invention is based on the findings, it contains fluorine, scattering peak intensity of scattering peak intensity of 495cm ^-1 to oxygen deficient defects as a specific amount or less, and in the laser Raman spectrum (I ₁₎ and 606 cm ^-1 Synthetic quartz glass characterized in that (I ₂ ) is I ₁ / I ₀ ≦ 0.585 and I ₂ / I ₀ ≦ 0.136, respectively, with respect to a scattering peak intensity (I ₀ ) of 440 cm ^−1. Also provide. In particular, it is preferable to contain 100 ppm or more of fluorine and 5 × 10 ¹⁶ molecules / cm ³ or more of hydrogen molecules.

  The synthetic quartz glass of the present invention preferably has a fluorine concentration of 100 ppm (meaning ppm by weight, the same applies to the following, and the same applies to ppb) or higher. If it is less than 100 ppm, the action of reducing the unstable structure in the synthetic quartz glass may not be sufficient. The fluorine concentration is more preferably 400 ppm or more, and particularly preferably in the range of 400 to 3000 ppm. When the concentration of fluorine exceeds 3000 ppm, there is a possibility that reduced defects are generated and the ultraviolet resistance is lowered.

The synthetic quartz glass of the present invention preferably has an OH group concentration of 100 ppm or less. If it exceeds 100 ppm, the transmittance in a wavelength region of about 170 nm or less is lowered, and for example, there is a possibility that it is not suitable as an optical member of an apparatus using a Xe ₂ ^* excimer lamp, F ₂ laser, or deuterium lamp as a light source. When the OH group concentration is 50 ppm or less, good ultraviolet resistance is obtained, and in terms of obtaining high transmittance in the vacuum ultraviolet region, it is preferably 20 ppm or less, and more preferably less than 10 ppm. In particular, the OH group concentration affects the light transmittance in the vacuum ultraviolet region with a wavelength of 200 nm or less, and the synthetic quartz glass used for light in the vacuum ultraviolet region with a wavelength of 175 nm or less may have an OH group concentration of less than 10 ppm. preferable. Furthermore, in the synthetic quartz glass used for light in the vacuum ultraviolet region having a wavelength of 160 nm or less, the OH group concentration is preferably 5 ppm or less.

In addition, oxygen-deficient defects (≡Si—Si≡) in the synthetic quartz glass have a great influence on the vacuum ultraviolet transmittance, and the oxygen-deficient defects have an absorption band centered at a wavelength of 163 nm. The internal transmittance T ₁₆₃ (% / cm) at a wavelength of ₁₆₃ nm is estimated as in the following formula (i) by the OH group concentration C _OH (ppm) in the synthetic quartz glass.
T ₁₆₃ (% / cm) ≧ exp (−0.02C _OH ^0.85 ) × 100 (i)

However, if there is an oxygen-deficient defect, since there is an absorption band centered at ₁₆₃ nm, the transmittance (T ₁₆₃ ) at the actual wavelength of ₁₆₃ nm is smaller than the value on the right side of the equation (i), Although it depends on the size of the absorption band, the transmittance at a wavelength of 200 nm or less decreases. Accordingly, it is important to obtain substantially no oxygen-deficient defects, in order to obtain excellent vacuum ultraviolet transmittance, and substantially no oxygen-deficient defects, that is, internal transmittance at a wavelength of 163 nm. It is preferable that the formula (i) is satisfied.

  In addition, the synthetic quartz glass according to the present invention preferably has an internal transmittance at 157 nm of 70% / cm, particularly preferably 80% / cm or more, from the viewpoint of vacuum ultraviolet light transmittance.

  In the synthetic quartz glass of the present invention, the smaller the chlorine concentration, the better. The chlorine concentration of 100 ppm or less provides good UV resistance, and from the point of homogeneity, 25 ppm or less is preferred, and particularly good. It is preferably 10 ppm or less from the viewpoint of obtaining vacuum ultraviolet transmittance. Furthermore, from the viewpoint of ultraviolet resistance in the vacuum ultraviolet region having a wavelength of 175 nm or less, chlorine is preferably as little as possible, specifically 100 ppb or less, particularly 50 ppb or less.

In the synthetic quartz glass of the present invention, when the hydrogen molecule concentration is 5 × 10 ¹⁶ molecules / cm ³ or more, an action of repairing paramagnetic defects generated by ultraviolet irradiation occurs. In particular, the hydrogen molecule concentration is 1 × 10 ¹⁷ molecules / cm ³ or more, further 1 × 10 ^{17 to} 5 × 10 ¹⁸ molecules / cm ³ , particularly 5 × 10 ^{17 to} 5 × 10 ¹⁸ molecules / cm ^3. preferable.

  On the other hand, the Si—O—Si bond angle in the ≡Si—O—Si≡ bond in the quartz glass network has a certain distribution. An unstable structure in synthetic quartz glass means a distorted ≡Si—O—Si≡ bond. The unstable structure in the synthetic quartz glass has a weaker binding energy than the normal structure. Therefore, the more the unstable structure is, the lower the vacuum ultraviolet ray transmittance is. This unstable structure depends on the fictive temperature of the synthetic quartz glass and is affected by the fluorine concentration in the synthetic quartz glass. That is, if synthetic quartz glass is doped with fluorine, unstable structures can be reduced, and the lower the fictive temperature, the more unstable structures are reduced. Specifically, if the fictive temperature of synthetic quartz glass is 1100 ° C. or lower, unstable structures can be reduced, and excellent vacuum ultraviolet ray permeability can be obtained. In this case, the fluorine concentration is preferably 100 ppm or more. In the present invention, the fictive temperature means A.I. The fictive temperature calculated | required using the method (J.Non-Cryst., 185,191,1995) of Agarwal et al.

  Metal impurities such as alkali metals, alkaline earth metals, and transition metals in the synthetic quartz glass of the present invention not only decrease the transmittance from the ultraviolet region to the vacuum ultraviolet region, but also cause a decrease in ultraviolet resistance. The concentration is preferably as low as possible. Specifically, the total amount of metal impurities is preferably 100 ppb or less, particularly preferably 50 ppb or less.

  In addition, in synthetic quartz glass, OH groups and fluorine in the quartz glass affect the refractive index. Therefore, if there is a distribution in the concentration of OH groups and fluorine, the homogeneity deteriorates.

Therefore, it is necessary to optimize the distribution of OH group and fluorine concentration in order to suppress the generation of paramagnetic defects and improve the UV resistance and to improve the homogeneity. Was examined. As a result, by controlling the distribution of the fluorine concentration and the OH group concentration in the region where light is transmitted, that is, the light use region, if the variation range of the fluorine concentration and the OH group concentration is both within 15 ppm, the homogeneity is improved. The knowledge that it can improve was obtained.
Further, in the region where light passes, when OH groups and fluorine are distributed so as to cancel out the concentration distribution, homogeneity can be improved even if the upper limit of the fluctuation range of the fluorine concentration and the OH group concentration is 25 ppm or less. I also got the knowledge.

Therefore, the present invention is an optical synthetic quartz glass used by irradiating light in the ultraviolet region to the vacuum ultraviolet region, and is formed of synthetic quartz glass containing OH groups and fluorine, and has an OH group concentration in the light use region. Provided is a synthetic quartz glass having a fluctuation range of 15 ppm or less, a fluorine concentration fluctuation range of 15 ppm or less, and a chlorine concentration of 25 ppm or less.
Furthermore, as a synthetic quartz glass excellent in homogeneity and UV resistance, it is formed of synthetic quartz glass containing OH groups and fluorine, and in the light usage region, OH groups and fluorine are distributed so as to cancel each other's concentration distribution. And a synthetic quartz glass having a fluctuation range of OH group concentration of 25 ppm or less, a fluctuation range of fluorine concentration of 25 ppm or less, and a chlorine concentration of 25 ppm or less.

In the present invention, a synthetic quartz glass in which both the fluctuation range of the OH group concentration and the fluctuation range of the fluorine concentration in the light use region are 15 ppm or less is preferable because excellent homogeneity can be stably expressed. Further, when the OH groups and fluorine are distributed so as to cancel each other in the light use region, the synthetic quartz glass having a fluctuation range of the OH group concentration of 25 ppm or less and a fluctuation range of the fluorine concentration of 25 ppm or less. Even so, excellent homogeneity can be stably expressed.
At this time, the refractive index fluctuation range (Δn) in a plane orthogonal to the incident light is preferably 20 × 10 ⁻⁶ or less, particularly 10 × 10 ⁻⁶ or less, and further 5 × 10 ⁻⁶ or less. And most preferably 2 × 10 ⁻⁶ or less.
From the viewpoint of Δn, it is particularly preferable that the total of the fluctuation range of the fluorine concentration and the fluctuation range of the OH group concentration in the light use region is 5 ppm or less.

According to the present invention, the ultraviolet ray transmission is excellent, and the transmittance reduction and the fluorescence emission due to the generation of the E ′ center due to the irradiation of high energy light or radiation from a light source such as an excimer laser are reduced, and the ultraviolet light resistance is reduced. Synthetic quartz glass excellent in performance can be obtained.
Moreover, according to this invention, the synthetic quartz glass excellent in vacuum ultraviolet-ray permeability can be obtained. In particular, a synthetic quartz glass having a high transmittance can be obtained even in a vacuum ultraviolet region having a wavelength of 200 nm or less.
Furthermore, according to the present invention, a synthetic quartz glass excellent in homogeneity and ultraviolet resistance can be obtained.
Therefore, the synthetic quartz glass of the present invention is extremely suitable as a member constituting an optical system used for light from the ultraviolet region to the vacuum ultraviolet region.
Further, according to the present invention, it is possible to easily produce the synthetic quartz glass having excellent ultraviolet resistance, vacuum ultraviolet transmittance, or homogeneity.

  In the present invention, the light use region refers to a region through which light from the ultraviolet region to the vacuum ultraviolet region is transmitted or reflected when synthetic quartz glass is used. Furthermore, in the present invention, the distribution of OH groups and fluorine so that the concentration distributions cancel each other out means that the fluorine concentration and OH group concentration in an arbitrary plane orthogonal to the incident light in the region through which the light of synthetic quartz glass passes. It means that they are in a distribution state in which the increase and decrease are complementary. That is, for example, when the fluorine concentration increases from the center of any plane toward the outside, the OH group concentration is distributed so as to decrease from the center of the plane toward the outside, or vice versa. State. Specifically, for the synthetic quartz glasses of Examples 82 to 94 described later, as shown in the graphs showing the distribution states of the fluorine concentration and the OH group concentration shown in Tables 14 to 17, in a plane orthogonal to the incident light, In contrast to the distribution curve in which the concentration of fluorine is in a complementary relationship, the concentration of fluorine is shown as an upward convex graph in which the concentration of fluorine is maximum at the center. A distribution state in which there is a complementary relationship or the reverse.

  In the present invention, examples of the method for producing synthetic quartz glass include a direct method, a soot method (VAD method, OVD method), a plasma method, and the like. The soot method is particularly preferable from the viewpoint that the temperature during production is low and contamination of impurities such as chlorine and metal can be avoided. According to the soot method, the OH group is substituted with fluorine by doping with fluorine. According to the soot method, the amount of fluorine doped and the amount of substituted OH groups are almost the same, and OH groups can be reduced efficiently, so synthetic quartz glass with low UV concentration and low OH group concentration is productive. Can get well.

A method for producing the synthetic quartz glass of the present invention by the soot method will be specifically described.
The production of synthetic quartz glass by this soot method is a method including the following steps (a), (b) and (c).
(A) a step of depositing and growing quartz glass fine particles obtained by flame hydrolysis of a quartz glass forming raw material on a substrate to form a porous quartz glass body;
(B) holding the porous quartz glass body in a fluorine-containing atmosphere to obtain a porous quartz glass body containing fluorine;
(C) Step of obtaining a transparent quartz glass body containing fluorine by raising the temperature of the porous quartz glass body containing fluorine to a transparent vitrification temperature to form transparent glass

When a hydrogen molecule is contained, it is produced by performing the following steps (a), (b ′), (c ′), and (d) in this order.
(A) A step of forming a porous quartz glass body by depositing and growing quartz glass fine particles obtained by subjecting a quartz glass forming raw material to flame hydrolysis on a substrate.
(B ′) A step of holding the porous quartz glass body at a temperature of 600 ° C. or less in a fluorine-containing atmosphere to obtain a porous quartz glass body containing fluorine.
(C ′) A step of raising the temperature of the porous quartz glass body containing fluorine to a transparent vitrification temperature in an atmosphere substantially free of fluorine to form transparent glass, thereby obtaining a transparent quartz glass body containing fluorine.
(D) A step of obtaining a synthetic quartz glass by holding a transparent quartz glass body containing fluorine at a temperature of 600 ° C. or less in an atmosphere containing hydrogen gas, and allowing the transparent quartz glass body containing fluorine to contain hydrogen.

  If the temperature at which the porous quartz glass body is held in an atmosphere containing a fluorine compound is high, ≡Si—Si≡ defects are likely to be generated. That is, when a porous quartz glass body is treated at a high temperature in an atmosphere containing a fluorine compound, the fluorine compound has a strong activity and tends to generate ≡Si—Si≡ defects according to the following formulas (8) and (9).

≡Si-O-Si≡ → ≡Si-Si≡ (8)
Fluorine compound ≡Si-OH → ≡Si-F (9)
Fluorine compound

  Therefore, if the porous quartz glass body is treated in an atmosphere containing a fluorine compound at a low temperature of 600 ° C. or lower, the activity of the fluorine compound can be suppressed, and the reaction of the above formula (9) can occur without causing the reaction of the formula (8). Since only the reaction occurs, no ≡Si—Si≡ defect is generated.

Hereinafter, each step will be described. In the step (a), a quartz glass forming raw material is supplied to a multi-tube burner by supplying oxygen gas and hydrogen gas to a multi-tube burner, and quartz glass fine particles obtained by flame hydrolysis are deposited and grown on a substrate to form a porous quartz glass body. Let it form. The quartz glass forming raw material is not particularly limited as long as it is a gasifiable raw material, but chlorides such as SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , and SiCH ₃ Cl ₃ , SiF ₄ , SiHF ₃ , SiH ₂ F _{2 are used.} fluorides such as, SiBr _4, bromides such as SiHBr _3, an iodide such as SiI _4, halogenated silicon compounds such or _{R n Si (oR) 4-} n ( here R, is an alkyl group having 1 to 4 carbon atoms , N is an integer of 0 to 3). As the substrate, a quartz glass seed rod (for example, a seed rod described in Japanese Patent Publication No. 63-24974) can be used. Moreover, you may use not only rod shape but a plate-shaped base material. The oxygen gas / hydrogen gas ratio is preferably an oxygen-excess atmosphere because reduced defects are generated in an hydrogen-excess atmosphere. Specifically, the ratio of hydrogen gas to oxygen gas is 1.6 to 1. 9 is preferred.

Next, in the step (b), the porous quartz glass body is held at a temperature of 600 ° C. or less in a fluorine-containing atmosphere to obtain a porous quartz glass body containing fluorine. As this fluorine-containing atmosphere, an inert gas atmosphere containing 0.1 to 100% by volume, particularly 1 to 20% by volume of a fluorine-containing gas (for example, SiF ₄ , SF ₆ , CHF ₃ , CF ₄ , F ₂ ) is preferable. . In these atmospheres, the treatment is preferably performed at a temperature of 600 ° C. or lower and a pressure of 0.1 to 10 atm for several tens of minutes to several hours. In particular, when fluorine doping is performed at a high temperature of 500 to 100 ° C., it is preferable to set the atmosphere containing 5 to 90% by volume of oxygen to suppress the generation of reduced defects. In the present specification, “atmospheric pressure” and “Torr”, which will be described later, both mean absolute pressure, not gauge pressure.

  Further, in the step (b), since the porous quartz glass body can be doped with fluorine uniformly in a short time, it is reduced to a predetermined temperature of 1200 ° C. or less, preferably 600 ° C. or less (preferably 100 Torr or less, particularly 10 Torr or less). ), And then it is preferable to introduce a fluorine-containing gas until a normal pressure is reached to obtain a fluorine-containing atmosphere.

  Next, in the step (c), the porous quartz glass body containing fluorine is heated to a transparent vitrification temperature in an atmosphere substantially free of fluorine to form a transparent glass, and the transparent quartz containing fluorine is obtained. A glass body is obtained. Transparent vitrification temperature is 1300 degreeC or more, Preferably it is 1300-1600 degreeC, It is especially preferable that it is 1350-1500 degreeC.

The atmosphere that does not substantially contain fluorine is that the fluorine-containing gas (for example, SiF ₄ , SF ₆ , CHF ₃ , CF ₄ , F ₂ ) is 0.1% by volume or less at the start of the treatment in step (c). There is no particular limitation, and an atmosphere containing a 100% inert gas such as helium or an atmosphere containing an inert gas such as helium as a main component is preferable. The pressure may be reduced pressure or normal pressure. In particular, helium gas can be used at normal pressure. In the case of reduced pressure, it is preferably 100 Torr or less, particularly 10 Torr or less.

  Further, it is preferable to further include a step (e) between the steps (b) and (c), wherein the atmosphere is reduced in pressure and the porous quartz glass body containing fluorine is allowed to stand for a predetermined time under reduced pressure. Specifically, the porous quartz glass body containing fluorine is several tens to several in an inert gas atmosphere at a pressure of 100 Torr or less, more preferably 10 Torr or less, at the temperature at which fluorine doping in the step (b) is performed. It is preferable to include a step of holding time. After step (b), it is necessary to remove fluorine from the atmosphere. Although normal pressure may be used, it takes a long time, so fluorine can be removed in a short time by reducing the pressure as in step (e).

  Next, in the step (d), the transparent quartz glass body containing fluorine obtained in the step (c) is heat-treated at a temperature of 600 ° C. or lower in an atmosphere containing hydrogen gas to obtain a synthetic quartz glass. obtain. The pressure is, for example, 1 to 30 atmospheres. By performing the hydrogen treatment at 600 ° C. or lower, it is possible to prevent the generation of reduced defects of ≡Si—H and ≡Si—Si≡. The atmosphere containing hydrogen gas is preferably an inert gas atmosphere containing 0.1 to 100% by volume of hydrogen gas. Further, in order to control the fictive temperature, it is preferable to perform the following step (f) on the transparent quartz glass body.

  Step (f): After holding the transparent quartz glass body containing fluorine at a temperature of 800 ° C. to 1100 ° C. for 5 hours or more, a heat treatment is performed to lower the temperature to 750 ° C. or less at a temperature lowering rate of 10 ° C./hr or less, Controls the fictive temperature of synthetic quartz glass. After cooling down to 750 ° C. or lower, it can be allowed to cool. The atmosphere in this case is preferably an atmosphere of 100% inert gas such as helium, argon or nitrogen, an atmosphere containing these inert gases as a main component, or an air atmosphere, and the pressure is preferably reduced or normal.

  In order to reduce OH groups as much as possible in the synthetic quartz glass of the present invention, after step (a), the porous quartz glass body is held at a temperature of 1000 to 1300 ° C. at a pressure of 1 Torr or less for a predetermined time. After dehydration, the temperature may be raised to a transparent vitrification temperature at a pressure of 1 Torr or less to form a transparent glass.

The synthetic quartz glass of the present invention is used for stepper lenses and other optical components.
In order to provide the optical characteristics necessary for this optical component, it is necessary to appropriately perform each heat treatment (hereinafter referred to as optical heat treatment) such as homogenization, molding, and annealing, but the optical heat treatment may be performed before step (d). It may be later.

However, since the optical heat treatment requires a high temperature of 800 to 1500 ° C., even if hydrogen is contained in the step (d), the concentration of hydrogen molecules may be lowered by the subsequent optical heat treatment. Therefore, when the optical heat treatment is performed after the step (d), it is preferably performed in an atmosphere containing 0.1 to 100% by volume of hydrogen gas and a pressure of 1 to 30 atm.
Moreover, when performing optical heat processing after a process (d), it is necessary to make the furnace for optical heat processing into an explosion-proof structure. Therefore, it is preferable to perform an optical heat treatment before the step (d).

In the present invention, more fluorine can be doped by doping boron. Examples of the boron source in the case of doping with boron include BF ₃ , BCl ₃ , and boron alkoxide.
Examples of the method of doping boron and fluorine include a method of first doping boron and then doping fluorine.
Specifically, for example, boron and fluorine are doped by the following method 1) or 2).

1) The porous quartz glass body obtained in step (a) is set in a pressure vessel, the pressure in the pressure vessel is reduced to about 1 Torr, and then a gas containing a boron source (for example, He or the like) BCl ₃ vapor diluted to about 5% by volume with an inert gas) is introduced.
When the pressure is close to normal pressure, the introduction of the gas containing the boron source is stopped, and the porous quartz glass body is doped with boron by leaving it for a predetermined time.
Next, fluorine is doped according to step (b).

2) The porous quartz glass body obtained in the step (a) is treated with a boron alkoxide vapor, and then in a humidified atmosphere, the boron alkoxide is hydrolyzed to form B in the porous quartz glass body. ₂ O ₃ fine particles are deposited.
Next, fluorine is doped according to step (b).

  By the above method 1) or 2), the porous quartz glass body doped with boron can be further doped with fluorine, and more fluorine can be doped. After fluorine doping, synthetic quartz glass for optical members can be obtained according to steps (c) and (d).

In this case, fluorine doping is performed by the following procedure, for example.
An inert gas (such as He or N ₂ ) is introduced into the pressure vessel, and the pressure is set to normal pressure. Again, the pressure in the pressure vessel is reduced to about 1 Torr, and then SiF ₄ gas diluted with an inert gas (such as He) is introduced.
When the pressure is close to normal pressure, the introduction of the SiF ₄ gas diluted with the inert gas is stopped and left for a predetermined time to dope the boron-containing porous quartz glass body with fluorine.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these. The synthetic quartz glass produced in the following examples was evaluated according to the following method.

(Evaluation)
(Evaluation 1) Measurement of fluorine concentration A synthetic quartz glass was heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid (volume ratio 1: 1) were added to the obtained melt to prepare a sample solution. An electromotive force of the sample solution was measured with a radiometer using No. 945-220 and No. 945-468 manufactured by Radiometer Trading Co. as a fluorine ion selective electrode and a reference electrode, respectively, and a calibration curve prepared in advance using a fluorine ion standard solution Based on the above, the fluorine concentration was obtained (Journal of the Chemical Society of Japan, 1972 (2), 350).

(Evaluation 2) Measurement of Hydrogen Molecule Concentration A Raman spectroscopic measurement was performed, and an intensity ratio between an intensity I ₄₁₃₅ detected by a scattering peak at ₄₁₃₅ cm ⁻¹ of a laser Raman spectrum and an intensity I ₈₀₀ of a scattering peak at ₈₀₀ cm ⁻¹ (= I ₄₁₃₅ / I ₈₀₀ ), the hydrogen molecule concentration [molecules / cm ³ ] was determined (VS Khotimchenko et.al., Zhurnal Prikladno Specktroskii, 46 (6), 987-997 (1986)). The detection limit by this method is 1 × 10 ¹⁶ molecules / cm ³ .

(Evaluation 3) Measurement of OH group concentration Measurement was carried out using an infrared spectrophotometer, and the OH group concentration was determined from the absorption peak at a wavelength of 2.7 μm (JP P. Williams et. Al., Ceram. Bull., 55 (5), 524 (1976)).

(Evaluation 4)
Perform Raman spectroscopy, the intensity I ₂₂₅₀ detected by scattering peak of the laser Raman spectrum of 2250 cm ^-1, ≡Si-H defects from divided by the intensity I ₈₀₀ of the scattering peak of ^{_{800cm -1 (I 2250 / I 800}} ) Concentration (≡Si—H concentration) was evaluated. Here, the detection limit is I ₂₂₅₀ / I ₈₀₀ = 1 × 10 ⁻⁴ . A smaller value of I ₂₂₅₀ / I ₈₀₀ is a better result.

(Evaluation 5)
Using a UV-visible spectrophotometer, the transmittance of light at 245 nm is measured for a sample with a thickness of 10 mm and a sample with a thickness of 35 mm, and an absorption coefficient at 245 nm is calculated from these transmittances to generate ≡Si-Si≡ defects. The presence or absence of was evaluated. A smaller value of the absorption coefficient at 245 nm is a better result.

(Evaluation 6) Reduction type defect Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research Co., Ltd.), the transmittance at a wavelength of 163 nm was measured for samples having a thickness of 10 mm and a thickness of 4 mm. The absorption coefficient (k ₁₆₃ ) was determined. When the relationship with the OH group concentration (C _OH , the unit is ppm) contained in the sample satisfies k ₁₆₃ ≧ 0.02 × (C _OH ) ^0.85 , the reduction type defect is “present”. Reduced defect “None”.

(Evaluation 7)
The sample was irradiated with light from a KrF excimer laser (LPX-120i manufactured by Lambda Fijk) under the conditions of an energy density of 100 mJ / cm ² / Pulse and a frequency of 200 Hz. The transmittance at 214 nm immediately after irradiation with 5 × 10 ⁶ shots of KrF excimer laser light was measured with an ultraviolet-visible spectrophotometer, and the 214 nm absorption intensity by the paramagnetic defect E ′ center caused by KrF excimer laser irradiation was measured before and after irradiation. The absorption coefficient change amount Δk ₂₁₄ [cm ⁻¹ ] was evaluated. A smaller value of Δk ₂₁₄ indicates that the E ′ center is reduced, which is a good result.

(Evaluation 8) Evaluation of fluorescence emission The sample was irradiated with a KrF excimer laser (LPX-120i manufactured by Lambda Fijk) under the conditions of an energy density of 100 mJ / cm ² / Pulse and a frequency of 200 Hz. The fluorescence intensity L _{650 at 650} nm and the scattered light intensity S ₂₄₈ at 248 nm when the KrF excimer laser was irradiated with 1 × 10 ⁶ shots were respectively measured using a fiber light guide type spectrophotometer, and the scattered light intensity S _{248 at 248} nm. The fluorescence intensity at ₆₅₀ nm was evaluated by determining the ratio L ₆₅₀ / S ₂₄₈ of the fluorescence intensity L ₆₅₀ at ₆₅₀ nm relative to. A smaller value of L ₆₅₀ / S ₂₄₈ indicates that fluorescence emission is suppressed, which is a good result.

(Evaluation 9) Internal transmittance of 172 nm Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research), 172 nm as an index of the transmittance in the vacuum ultraviolet region with a wavelength of 175 nm or less for samples having a thickness of 10 mm and 4 mm The internal transmittance of was measured.
(Evaluation 10) Internal transmittance of 157 nm Using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research Co., Ltd.) for a sample of 10 mm thickness and 4 mm, 157 nm as an index of transmittance in the vacuum ultraviolet region of wavelength 160 nm or less The internal transmittance was measured, and the internal transmittance at the same wavelength was determined by the following equation.
Internal transmittance (% / cm) = exp (ln (T ₁ / T ₂ ) / (d ₁ −d ₂ )) × 100
Here, T ₁ : transmittance (%) of a sample having a thickness d ₁ [cm]
T ₂ : Transmittance (%) of sample with thickness d ₂ [cm]
A higher transmittance is a better result.

(Evaluation 11)
A sample having a thickness of 10 mm was irradiated with a Xe ₂ ^* excimer lamp under the condition of 10 mW / cm ² for 3 hours. The transmittance at 163 nm before and after irradiation was measured, and the change in transmittance at ₁₆₃ nm (ΔT ₁₆₃ ) due to irradiation was calculated. As [Delta] T ₁₆₃ is smaller has excellent ultraviolet resistance.

(Evaluation 12) Measurement of virtual temperature It calculated | required using the method (J.Non-Cryst., 185,191,1995) of Agarwal et al. The mirror-polished quartz glass is immersed in a 10% HF-2.5% H ₂ SO ₄ aqueous solution to remove abrasive grains and scratches remaining on the surface. The reflection spectrum of the surface is acquired using an infrared spectrometer (Magna 760 manufactured by Nikolet). At this time, the incident angle of infrared light is fixed at 6.5 degrees, the data interval is about 0.5 cm ^−1, and an average value obtained by scanning 64 times is used. In the infrared reflection spectrum thus obtained, the largest peak observed at about 1120 cm ⁻¹ is due to stretching vibration due to the Si—O—Si bond of quartz glass. When this peak position is ν (cm ⁻¹ ), the fictive temperature (T _f , unit: K) is obtained by the following correlation equation.
ν = 1114.51 + (11603.51 / T _f ).

(Evaluation 13) Measurement of chlorine concentration Fluorescence X-ray analysis using the kα ray of Cr was performed, and the chlorine concentration in synthetic quartz glass was determined by measuring the characteristic X-ray intensity of chlorine. The detection limit by this method is 2 ppm.

(Evaluation 14) Evaluation of unstable structure Raman spectroscopic measurement (Ramonor T64000 manufactured by Jobin Ybon, excitation light source: argon ion laser (wavelength 514.5 nm)) was performed, and a scattering peak intensity I ₁ of 495 cm ⁻¹ and 605 cm ^{− in the} laser Raman spectrum. ¹ of the scattering peak intensity I _2, was determined intensity ratio I ₁ / I ₀ and I ₂ / I ₀ of the scattering peak intensity I ₀ of 440 cm ^-1. The smaller the intensity ratio I ₁ / I ₀ and the intensity ratio I ₂ / I ₀ , the better.

Incidentally, how to obtain the respective scattering peak intensity I _1, I _2, I ₀ is as follows.
Perform curve fitting by a single Lorentzian respectively scattering peak of scattering peak and 605 cm ^-1 of 495cm ^-1, the coefficients of the functions performed approximated as least square error is minimum between the actual spectrum Decided.
The synthesis of the Gaussian function of the three for scattering peak of 440 cm ^-1, also the residual (baseline), excluding the scattering peak of scattering peak and 440 cm ^-1 of the scattering peak and 605 cm ^-1 of 495cm ^-1 On the other hand, curve fitting was performed using a quadratic function, and approximation was performed so that the least square error with the actual spectrum was minimized, and the coefficient of each function was determined.
The intensity | strength of each scattering peak was calculated | required using the function calculated | required by the above.

(Evaluation 15)
The concentrations of Na, Ca, Mg, Fe, Ni, Cu, Zn, and Ti in the synthetic quartz glass were analyzed by ICP mass spectrometry (SPQ9000 manufactured by Seiko Instruments Inc.). The detection limit of these impurities is 0.1 ppb for Ni and Cu, and 0.3 ppb for the others.

(Evaluation 16)
With a Fizeau interferometer, helium neon laser light was perpendicularly applied to a 200 mmφ surface of a synthetic quartz glass sample by an oil-on-plate method, and the refractive index distribution in the 200 mmφ surface was measured.

(Example 1)
By a known method, quartz glass fine particles obtained by subjecting SiCl ₄ as a raw material for forming quartz glass to heat hydrolysis (flame hydrolysis) in an oxyhydrogen flame are deposited and grown on a base material, and the diameter is 35 cm and the length is 100 cm. A porous quartz glass body was formed (step (a)). The obtained porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, and after reducing the pressure to 10 Torr at room temperature and holding it for 1 hour, a mixed gas of He / SiF ₄ = 99/1 (volume ratio) was introduced. However, this atmosphere was maintained at room temperature and normal pressure for 5 hours to carry out fluorine doping (step (b)). Thereafter, the supply of SiF ₄ was shut off and held in a He 100% atmosphere for 10 hours, and then heated to 1450 ° C. in a He 100% atmosphere, held at this temperature for 10 hours to form a transparent glass, and a transparent quartz glass body containing fluorine was obtained. Obtained (step (c)).

  The obtained transparent quartz glass body containing fluorine is heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element, and is deformed by its own weight to form a block shape of 250 mm × 250 mm × 120 mm. Then, it was sliced into blocks having a thickness of 30 mm. The obtained 250 mm × 250 mm × 30 mm block was held in an atmosphere of 100% hydrogen, 10 atm, and 500 ° C. for 250 hours, and subjected to hydrogen doping treatment to obtain synthetic quartz glass (step (d)).

(Example 2)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and then He / SiF ₄ = 99/1 (volume). Ratio) gas mixture was introduced, and fluorine doping was performed in this atmosphere at 300 ° C. under normal pressure for 5 hours. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 3)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 500 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF ₄ = 99/1 (volume ratio). ) Was introduced and held in this atmosphere at 500 ° C. under normal pressure for 5 hours for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 4)
In the step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 700 ° C., depressurized to 10 Torr and held for 1 hour, He / SiF ₄ = 99/1 (volume ratio) ) Was introduced, and this atmosphere was maintained at 700 ° C. under normal pressure for 5 hours for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 5)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 1200 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF ₄ = 99/1 (volume ratio). ) Was introduced, and this atmosphere was maintained at 1200 ° C. under normal pressure for 5 hours for fluorine doping. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 6)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF ₄ = 99.9 / 0. A mixed gas of 1 (volume ratio) was introduced, and fluorine doping was performed in this atmosphere by maintaining at 300 ° C. and normal pressure for 1 hour. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 7)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF ₄ = 99.9 / 0. A mixed gas of 1 (volume ratio) was introduced, and fluorine doping was performed by maintaining at 300 ° C. and 300 Torr for 1 hour in this atmosphere. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 8)
In step (b) in Example 1, the porous quartz glass body was placed in an electric furnace, first heated to 300 ° C., depressurized to 10 Torr and held for 1 hour, and He / SiF ₄ = 99.9 / 0. A mixed gas of 1 (volume ratio) was introduced, and fluorine doping was performed in this atmosphere at 300 ° C. and 100 Torr for 1 hour. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 9)
In the step (d) in Example 1, hydrogen doping treatment was performed by maintaining for 250 hours in an atmosphere of 100% hydrogen, 1 atm, and 500 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 10)
In the step (d) in Example 1, hydrogen doping treatment was performed by holding for 250 hours in an atmosphere of a mixed gas of hydrogen / helium = 10/90 (volume ratio) at 1 atmosphere and a temperature of 500 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 11)
In the step (d) in Example 1, hydrogen doping treatment was performed by maintaining for 250 hours in an atmosphere of 100% hydrogen, 10 atm, and 700 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 12)
In the step (d) in Example 1, hydrogen doping treatment was performed by holding for 250 hours in an atmosphere of 100% hydrogen, 10 atm, and 900 ° C. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 13)
In Example 1, the step (b) was not carried out, and the temperature was raised to 1450 ° C. in a He 100% atmosphere, and this temperature was maintained for 10 hours to form a transparent glass. A synthetic quartz glass was produced in the same manner as in Example 1 except for this.

(Example 14)
After step (b) in Example 1, the supply of SiF ₄ was cut off, the pressure was reduced to 1 Torr, and this state was maintained for 1 hour (step (e)). Subsequently, He 100% was introduced and the pressure was returned to normal pressure, and then the pressure was reduced again to 1 Torr to obtain an atmosphere substantially free of fluorine. The temperature was raised to 1450 ° C. under the atmosphere, and the glass was kept at 1450 ° C. for 10 hours to be transparent vitrified to obtain a transparent quartz glass body containing fluorine (step (c)). Thereafter, the same processing as in Example 1 was performed to produce a synthetic quartz glass.

(Example 15)
After the step (b) in Example 1, the supply of SiF ₄ is cut off, maintained in a He 100% atmosphere for 10 hours, and further mixed gas atmosphere of He / SiF ₄ = 99.95 / 0.05 (volume ratio). And then heated to 1450 ° C. and held at 1450 ° C. for 10 hours to form a transparent glass to obtain a transparent quartz glass body containing fluorine (step (c)). Thereafter, the same processing as in Example 1 was performed to produce a synthetic quartz glass.

(Example 16)
After the step (b) in Example 1, the supply of SiF ₄ is cut off, maintained in a He 100% atmosphere for 10 hours, and further mixed gas atmosphere of He / SiF ₄ = 99.8 / 0.2 (volume ratio). And then heated to 1450 ° C. and held at 1450 ° C. for 10 hours to form a transparent glass to obtain a transparent quartz glass body containing fluorine (step (c)). Thereafter, the same processing as in Example 1 was performed to produce a synthetic quartz glass.

  The synthetic quartz glass obtained in Examples 1 to 16 was evaluated. The results of each evaluation are shown in Table 1. ND indicates that it is below the detection limit. Examples 1-3, Examples 6-7, Examples 9-10, and Examples 14-15 correspond to Examples, Examples 4-5, Example 8, Examples 11-13, and Example 16 correspond to comparative examples.

Examples 17 to 34 are experimental examples in which the influence of the OH group concentration, the chlorine concentration, and the fluorine concentration on the characteristics of the synthetic quartz glass was examined.
(Examples 17 to 31)
SiO ₂ fine particles formed by hydrolyzing SiCl ₄ or Si (CH ₃ O) ₄ in a 1200 to 1500 ° C. oxyhydrogen flame by a known soot method are deposited on a substrate to have a diameter of 500 mm and a length of A 600 mm porous quartz glass body was produced. The porous quartz glass body is installed in an electric furnace capable of controlling the atmosphere, and helium gas containing SiF ₄ in the ratio shown in Table 2 is introduced under a reduced pressure of 10 Torr or less. By holding for the time shown in Table 2, the porous quartz glass body was dehydrated and simultaneously doped with fluorine. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (diameter 200 mm, length 450 mm). Further, the obtained transparent quartz glass body was cut into a diameter of 200 mm and a thickness of 10 mm, and held at 500 ° C. for 30 hours under the hydrogen-containing atmosphere at the ratio shown in Table 2 at the pressure shown in Table 2. In the above production method, the OH group concentration and the fluorine concentration in the quartz glass are controlled by the flow rate ratio of oxygen and hydrogen gas to the raw material gas when producing the porous quartz glass, or in an atmosphere containing a fluorine compound. It carried out by adjusting the density | concentration and holding time of the fluorine compound at the time of hold | maintaining a quartz glass body. Further, the concentration of hydrogen molecules in the quartz glass was controlled by adjusting the hydrogen concentration and the total pressure in the atmosphere when kept in a hydrogen atmosphere. Details of the production conditions (glass forming raw material, flow rate ratio of oxygen and hydrogen gas, fluorine compound concentration and pressure, hydrogen concentration and pressure) are shown in Table 2.

(Examples 32-34)
By using a known direct method, SiCl ₄ is used as a glass forming raw material, and SiF ₄ is hydrolyzed and oxidized in an oxyhydrogen flame at 1800 to 2000 ° C. at a flow rate of oxygen and hydrogen gas with respect to the raw material gas in the ratio shown in Table 3. A transparent quartz glass body was produced directly on the substrate. In this manufacturing method, the fluorine concentration in the obtained quartz glass is controlled by adjusting the mixing ratio of SiCl ₄ and SiF _4, and the OH group concentration and the hydrogen concentration adjust the flow rate ratio of oxygen and hydrogen. Was done. Details of the production conditions (flow rate ratio of SiF ₄ , oxygen and hydrogen gas) are shown in Table 3.

  Table 4 shows the OH group concentration, chlorine concentration, fluorine concentration, and hydrogen molecule concentration in the synthetic quartz glass produced in Examples 17 to 34. In addition, each density | concentration is calculated | required by the said method, ND shows below a detection limit.

Next, with respect to the synthetic quartz glass produced according to Examples 17 to 34, the scattering peak intensity ratio (I ₁ / I ₀ , I ₂ / I ₀ ), Δk ₂₁₄ , L ₆₅₀ / S ₂₄₈ , and internal transmittance at a wavelength of 157 nm, respectively. The impurity concentration in the synthetic quartz glass was measured and evaluated.
The evaluation results are shown in Table 5. Of Examples 17-34, Examples 20, 21, 22, 32 and 34 have higher OH group concentration, Example 29 has higher chlorine concentration, and Examples 23 and 34 do not contain fluorine. The characteristics are inferior.

Examples 35 to 47 are experimental examples in which the influence of I ₁ / I ₀ and I ₂ / I ₀ on the characteristics of the synthetic quartz glass was examined.
(Example 35 to Example 47)
By a known soot method, SiCl ₄ was hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were deposited on a substrate to produce a porous quartz glass body of 500 mmφ × 600 mm in length (step (a )). The porous quartz glass body was installed in an electric furnace capable of controlling the atmosphere, and helium gas containing a fluorine compound was introduced at normal pressure from a reduced pressure state of 10 Torr or less at room temperature. By holding at atmospheric pressure and room temperature for several hours under this atmosphere, the porous quartz glass was dehydrated and simultaneously doped with fluorine (step (b)). Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (200 mmφ × 450 mm in length).

Further, the obtained transparent quartz glass body was cut into 200 mmφ × 10 mm thickness, held in a hydrogen-containing atmosphere for 30 hours at 500 ° C. under the conditions shown in Table 6, and doped with hydrogen in the quartz glass. The synthetic quartz glass of Examples 35-47 shown in 7 was obtained (step (c)).
In the above manufacturing method, the OH group concentration and the fluorine concentration in the quartz glass are controlled by adjusting the flow ratio of oxygen and hydrogen gas to the raw material gas in the step (a), the concentration of the fluorine compound in the step (b), and the treatment time. Was carried out. The concentration of hydrogen molecules in the quartz glass was controlled by adjusting the hydrogen concentration and total pressure in the atmosphere during the hydrogen treatment in step (c). Table 6 shows the details of the processing conditions in step (a), step (b), and step (c) of each example.

Next, for the samples prepared from the synthetic quartz glass of Examples 35 to 47, the OH group concentration, fluorine concentration, and hydrogen molecule concentration were measured according to the following methods. The scattering peak intensity ratios (I ₁ / I ₀ , I ₂ / I ₀ ), Δk ₂₁₄ , L ₆₅₀ / S ₂₄₈ , and internal transmittance at a wavelength of 157 nm were measured and evaluated. Table 7 shows the evaluation results. Among Examples 35 to 47, Examples 45 to 47 have inferior characteristics than the others because I ₁ / I ₀ and I ₂ / I ₀ are high.

Examples 48 to 65 are experimental examples in which the influence of the OH group concentration and the concentration of reducing defects on the characteristics of the synthetic quartz glass was examined.
(Examples 48-60)
By a soot method, SiCl ₄ was hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were deposited on a substrate to produce a porous quartz glass body of 400 mmφ × 600 mm in length. The porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, kept at a reduced pressure of 10 Torr or less at room temperature, and then helium gas containing SiF ₄ was introduced until the pressure became normal. Under this atmosphere, the porous quartz glass body was dehydrated by maintaining at atmospheric pressure and room temperature for several hours. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less in an atmosphere substantially free of fluorine, and this temperature was maintained for 10 hours to obtain a synthetic quartz glass (200 mmφ × length 450 mm). Produced.

  Furthermore, the obtained synthetic quartz glass was cut into 200 mmφ × thickness 10 mm, and held for 30 hours in a hydrogen-containing atmosphere under the conditions shown in Table 8 to dope the synthetic quartz glass with hydrogen.

  In the production process described above, the volume ratio of oxygen and hydrogen gas of the oxyhydrogen flame when producing the porous quartz glass body, and the concentration of the fluorine compound when holding the porous glass body in an atmosphere containing the fluorine compound, By adjusting the treatment time and treatment temperature, the OH group concentration and the reduced defect concentration in the resulting synthetic quartz glass were controlled. In addition, the concentration of hydrogen molecules in the synthetic quartz glass was controlled by adjusting the treatment temperature during hydrogen doping, the hydrogen concentration in the atmosphere, and the total pressure. The details of the processing conditions in the manufacturing process of each example are shown in Table 8.

(Examples 61 to 65)
By a soot method, SiCl ₄ was hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were deposited on a substrate to produce a porous quartz glass body of 400 mmφ × 600 mm in length. The porous quartz glass body is placed in an electric furnace capable of controlling the atmosphere, heated at a reduced pressure of 1 Torr or less, held at 1200 ° C. for a predetermined time, subsequently heated to 1450 ° C., and heated to 10 ° C. at this temperature. Synthetic quartz glass (200 mmφ × 450 mm in length) was produced by maintaining the time.
The obtained synthetic quartz glass was cut into 200 mmφ × 10 mm thickness, and kept in a hydrogen-containing atmosphere for 30 hours under the conditions shown in Table 9 to dope hydrogen into the synthetic quartz glass.

  In the production process described above, by adjusting the holding time at 1200 ° C., the OH group concentration and the concentration of reduced defects in the synthetic quartz glass were controlled. In addition, the concentration of hydrogen molecules in the synthetic quartz glass was controlled by adjusting the treatment temperature during hydrogen doping, the hydrogen concentration in the atmosphere, and the total pressure. The details of the processing conditions in the manufacturing process of each example are shown in Table 9.

The OH group concentration, hydrogen molecule concentration, 163 nm internal transmittance, and presence or absence of reduced defects of the synthetic quartz glass obtained in Examples 48 to 65 were determined according to the above-described methods. Also, ΔT ₁₆₃ was measured as an internal transmittance of 172 nm, an internal transmittance of 157 nm, and an ultraviolet resistance index, and vacuum ultraviolet transmittance of wavelength 175 nm or less, vacuum ultraviolet transmittance of wavelength 160 nm or less, and ultraviolet resistance, respectively. Evaluated. Each evaluation result is shown in Table 10 and Table 11. Of Examples 48 to 65, Examples 52 to 54 have reductive defects, so Examples 55 to 58 and Example 64 have a relatively high OH group concentration and therefore have lower internal transmittance than the others.

Examples 66 to 81 are experimental examples in which the influence of the fluorine concentration, the OH group concentration, the fictive temperature, and the presence or absence of reducing defects on the characteristics of synthetic quartz glass was examined.

(Examples 66 to 81)
SiCl ₄ is used as a glass forming material, and SiO ₂ fine particles formed by hydrolyzing SiCl ₄ in an oxyhydrogen flame at 1200 to 1500 ° C. by a known soot method are deposited on a substrate to be 300 mmφ × length 800 mm A porous quartz glass body was prepared. The conditions of the oxyhydrogen flame are shown in step (a) of Table 12. Step (a) in Table 12 shows the volume ratio of oxygen and hydrogen to SiCl ₄ which is a glass forming raw material.
The porous quartz glass body is installed in an electric furnace capable of controlling the atmosphere, and dehydration (OH group reduction) is performed in the porous quartz glass body in the atmosphere, processing temperature, and processing time shown in step (b) of Table 12. At the same time, fluorine was doped. In step (b) of Table 12, the atmosphere is indicated by volume%. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (105 mmφ × length 650 mm).
Further, the obtained transparent quartz glass body is heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element at 100% nitrogen gas and normal pressure, and is deformed by its own weight in the growth axis direction. Molded into blocks. Subsequently, the temperature of the electric furnace was treated at the treatment temperature and treatment time described in the step (d) of Table 12 with the forming block being installed in the electric furnace, and then the room temperature was measured according to the temperature drop profile described in the step (d) of Table 12. The virtual temperature was controlled by lowering the temperature.

In the above manufacturing process, the flow rate ratio of oxygen and hydrogen gas to the raw material gas when manufacturing the porous quartz glass body, or the atmospheric gas composition when holding the porous quartz glass body in an atmosphere containing a fluorine compound The OH group concentration and fluorine concentration in the resulting synthetic quartz glass were controlled by adjusting the temperature. The fictive temperature was controlled by adjusting the temperature and temperature drop profile when the molded cylindrical block was kept at a high temperature.
The synthetic quartz glass obtained in each example was measured for fluorine concentration, OH group concentration, fictive temperature, and presence or absence of reducing defects, and are shown in Table 13.
Further, the internal transmittance at a wavelength of 157 nm was measured as an index of the transmittance in the vacuum ultraviolet region having a wavelength of 200 nm or less. The evaluation results are shown in Table 14.
In Tables 12 to 14, of Example 67 to Example 81, Example 66 and Example 73 have a high OH group concentration, Example 73 has a low fluorine concentration, and Example 74 has a high fictive temperature. Are inferior in properties to others due to reductive defects.

(Example 82 to Example 86)
By a known direct method, SiCl ₄ and SiF ₄ were hydrolyzed and oxidized in an oxyhydrogen flame at 1800 to 2000 ° C., and 250 mmφ transparent quartz glass was directly synthesized on the substrate. The transparent quartz glass was stretched into a 200 mmφ rod-shaped body, and then kneaded and homogenized by a horizontal zone melting method (FZ method). Next, it was set in an electric furnace, held at 1250 ° C. for a certain time, slowly cooled to 800 ° C. at a cooling rate of 1 ° C./hr, and then allowed to cool to obtain a synthetic quartz glass.
In the above manufacturing process, the fluorine concentration and its distribution are controlled by adjusting the mixing ratio of SiCl ₄ and SiF _4, and the OH group concentration and its distribution are controlled by adjusting the flow rate ratio of oxygen and hydrogen. The synthetic quartz glass shown in Examples 82 to 86 in Tables 15 and 16 was obtained by controlling the hydrogen molecule concentration.

(Example 87 to Example 94)
A porous quartz glass body of 300 mmφ × 800 mm in length is produced by depositing SiO ₂ fine particles formed by hydrolyzing SiCl ₄ in an oxyhydrogen flame at 1200 to 1500 ° C. by a known soot method. did. The porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere, and helium gas containing 1% by volume of a fluorine compound was introduced under a reduced pressure of 10 Torr or less. By holding at atmospheric pressure and room temperature for several hours under this atmosphere, the porous quartz glass was dehydrated and simultaneously doped with fluorine. Subsequently, the temperature was raised to 1450 ° C. while maintaining a reduced pressure of 10 Torr or less, and this temperature was maintained for 10 hours to produce a transparent quartz glass body (105 mmφ × length 650 mm).

  Furthermore, the obtained transparent quartz glass body was heated to 1750 ° C. above the softening point in an electric furnace having a carbon heating element, and was deformed by its own weight in the growth axis direction to form a cylindrical block. Subsequently, the temperature of the electric furnace is lowered to 1250 ° C. with the molding block installed in the electric furnace, and then gradually cooled at a cooling rate of 1 ° C./hr. When the temperature in the furnace reaches 800 ° C., power supply is stopped. did. The obtained quartz block was cut to a thickness of 30 mm, held in a hydrogen-containing atmosphere at 500 ° C. for 240 hours to dope hydrogen into the quartz glass, and the synthetic quartz glass of Examples 87 to 94 in Tables 16 to 19 Got.

  In the above manufacturing process, the flow rate ratio of oxygen and hydrogen gas to the raw material gas when producing the porous quartz glass body, or the concentration of the fluorine compound when holding the porous quartz glass body in an atmosphere containing the fluorine compound And by adjusting the holding time, the OH group concentration and the fluorine concentration in the resulting synthetic quartz glass were controlled. In addition, the fluctuation range of the OH group concentration and the fluorine concentration in the synthetic quartz glass was controlled by adjusting the size at the time of molding. Furthermore, the hydrogen molecule concentration in the synthetic quartz glass was controlled by adjusting the conditions for heat treatment in a hydrogen-containing atmosphere.

  The synthetic quartz glass obtained in Examples 82 to 94 was measured for fluorine concentration and its fluctuation range, OH group concentration and its fluctuation range, chlorine concentration, and hydrogen molecule concentration.

Next, the refractive index distribution, L ₆₅₀ / S ₂₄₈ , and internal transmittance at 157 nm were measured and evaluated for samples prepared from the synthetic quartz glasses of Examples 82 to 94.
The results of each evaluation are shown in Tables 15-21. Examples 82 to 84, Examples 87 to 91, and Example 94 correspond to examples of the present invention, and the others correspond to comparative examples.

Claims (8)

  In the synthetic quartz glass for optics used by irradiating light in the ultraviolet region to the vacuum ultraviolet region, it is formed of a synthetic quartz glass containing OH groups and fluorine, and the fluctuation range of the OH group concentration in the light use region is 15 ppm or less, A synthetic quartz glass having a fluctuation range of fluorine concentration of 15 ppm or less and a chlorine concentration of 25 ppm or less.   In optical synthetic quartz glass used by irradiating light in the ultraviolet to vacuum ultraviolet region, it is formed of synthetic quartz glass containing OH groups and fluorine, and in the light use region, the concentration distribution of OH groups and fluorine mutually. A synthetic quartz glass which is distributed so as to cancel each other, and has a fluctuation range of OH group concentration of 25 ppm or less, a fluctuation range of fluorine concentration of 25 ppm or less, and a chlorine concentration of 25 ppm or less.   The synthetic quartz glass according to claim 1 or 2, wherein the total of the fluctuation range of the fluorine concentration and the fluctuation range of the OH group concentration in the light use region is 5 ppm or less. The synthetic quartz glass according to any one of claims 1 to 3, wherein a refractive index fluctuation range (Δn) in a plane orthogonal to incident light is 20 x 10 ^-6 or less. The synthetic quartz glass according to any one of claims 1 to 3, wherein a refractive index fluctuation range (Δn) in a plane orthogonal to incident light is 5 × 10 ^-6 or less. A method for producing the synthetic quartz glass according to any one of claims 1 to 5,
(A) a step of depositing and growing quartz glass fine particles obtained by hydrolyzing a quartz glass forming raw material on a substrate to form a porous quartz glass body;
(B) holding the porous quartz glass body in a fluorine-containing atmosphere at 600 ° C. or less to obtain a porous quartz glass body containing fluorine;
(C) The production of synthetic quartz glass, comprising a step of heating a porous quartz glass body containing fluorine to a transparent vitrification temperature to obtain a transparent quartz glass body containing fluorine. Method. A method for producing the synthetic quartz glass according to any one of claims 1 to 5,
(A) a step of depositing and growing quartz glass fine particles obtained by hydrolyzing a quartz glass forming raw material on a substrate to form a porous quartz glass body;
(B) holding the porous quartz glass body in a fluorine-containing atmosphere containing 5 to 90% by volume of oxygen to obtain a porous quartz glass body containing fluorine;
(C) The production of synthetic quartz glass, comprising a step of heating a porous quartz glass body containing fluorine to a transparent vitrification temperature to obtain a transparent quartz glass body containing fluorine. Method. The method for producing synthetic quartz glass according to claim 6 or 7, wherein the following step (e) is further performed between step (b) and step (c).
(E) A step of reducing the atmosphere and leaving the porous quartz glass body containing fluorine under reduced pressure for a predetermined time.