JPH0616449A - Synthetic quartz glass optical member for excimer laser and its production - Google Patents

Abstract

PURPOSE:To provide the synthetic quartz glass optical member for an excimer laser which is adequately usable for a stepper lens of a lithographic device using an excimer laser beam and other optical members thereof. CONSTITUTION:This synthetic quartz glass optical member for the excimer laser has 10 to 100ppm content of OH groups, <=200ppm content of chlorine, <=1X10<16> molecular number/cm<3> hydrogen molecule content, homogeneity of <=5X10<-6> refractive index in DELTAn and <=5nm/cm double refractions. This optical member is produced by flame-hydrolyzing a volatile silicon compd. by an oxyhydrogen flame, depositing the formed particulate silica on a heat resistant base body to produce a poroous silica base material, subjecting this poroous silica base material to high-temp. dehydrating and degassing, then subjecting the base material to a homogenization treatment, molding the resulted highly homogeneous quartz glass and subjecting the molded highly homogeneous quartz glass to an annealing treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical quartz glass member having excellent stability against irradiation with an ultraviolet laser beam having an oscillation wavelength of 300 nm or less and a method for producing the same, and particularly to irradiation with a KrF or ArF excimer laser. The present invention relates to an optical member made of synthetic quartz glass having excellent stability with respect to the above and a manufacturing method thereof. Further, the present invention is a method for manufacturing a quartz glass member, which is preferably used for optical members such as windows, mirrors, lenses and prisms, which constitute an optical system of a lithographic apparatus using an excimer laser as a light source, for manufacturing a semiconductor chip. It is about.

[0002]

2. Description of the Related Art In recent years, with the high integration of LSIs, in an optical lithography technique for drawing an integrated circuit pattern on a wafer, that is, a lithography technique, for example, an accurate image is formed by a line having an extremely fine line width of submicron unit. Drawing technology has been required. Therefore, in the photolithography technology, in order to accurately draw an image with such a line having an extremely fine line width, the wavelength of the light of the light source of the exposure system is being shortened. For example, a stepper lens for lithography has excellent transparency to ultraviolet rays, especially ultraviolet rays, in order to clearly and accurately display an undistorted, accurate image of an integrated circuit pattern on a wafer with fine line widths without light and shade. The homogeneity of the refractive index distribution with respect to the ultraviolet laser light and the strong durability against the irradiation with the ultraviolet laser light are required.

However, a conventional lens using general optical glass has a very poor ultraviolet ray passing property, and for example,
When ultraviolet rays having a wavelength range shorter than 365 nm (i-line) are used, the transmittance of ultraviolet rays sharply decreases during use, and it is practically difficult to use as a stepper lens. In particular, when ultraviolet rays in the wavelength range shorter than 365 nm (i-line) are used, the lens heats up due to the absorption of ultraviolet rays, and the optical characteristics of the optical glass change, which causes the focal length of the lens to change. ing. For this reason, quartz glass has been used as an ultraviolet transmitting material. However, quartz glass manufactured from natural quartz has poor optical transparency to ultraviolet rays in the wavelength range of 250 nm or less, and furthermore, the irradiation of ultraviolet rays causes a new absorption of light in the ultraviolet ray area, and Since the transmittance is further reduced, it is practically difficult to use as a stepper lens. Absorption of light in the ultraviolet region in the quartz glass produced by this natural quartz,
Because it is thought that it is due to impurities in the quartz glass,
Synthetic quartz glass having a low content of impurities, that is, synthetic silica glass is used for optical members used in the ultraviolet region.

This synthetic quartz glass is usually a high-purity volatile silicon compound, which is chemically synthesized and purified by distillation, in order to avoid the inclusion of metallic impurities that cause ultraviolet absorption, generally. Is, for example, silicon tetrachloride (SiCl
₄ ) silicon halide such as ethoxysilane (Si
(OC ₂ H ₅ ) ₄ ), methoxysilane (Si (OC
H _{3) 4)} alkoxysilanes such as, further such as methyl trimethoxy silane _{(SiCH 3 (OCH 3) 3} ),
Ethyltriethoxysilane (SiC ₂ H ₅ (OC
The vapor of alkylalkoxysilanes such as ₂ H ₅ ) ₃ ) is directly introduced into an oxyhydrogen flame and flame hydrolyzed by the oxyhydrogen flame, and the glass particles decomposed and produced here are directly rotated into a heat-resistant rod shape. It is manufactured into transparent glass by melting and depositing it on the core member and vitrifying it. It is also possible to deposit the above glass fine particles on a heat-resistant rod-shaped core member to prepare porous glass, and heat and melt it in an electric furnace to produce transparent glass.

The transparent synthetic quartz glass produced in this manner is extremely high in purity, contains almost no metal impurities, and exhibits good light transmittance up to a short wavelength region of about 190 nm. Laser light, such as KrF (248 nm), XeCl (3
08 nm), XeBr (282 nm), XeF (35
1, 353 nm), ArF (193 nm) and other excimer laser lights, and YAG fourth harmonics (250 nm) and the like are used as transmission materials. For example, by increasing the purity of silicon tetrachloride as a raw material and adjusting the conditions of flame hydrolysis by an oxyhydrogen flame, the content of metal impurity elements is 0.1 ppm or less, and the content of O of a predetermined concentration is reduced.
Attempts have been made to synthesize a high-purity quartz glass containing an H group, and thereby to manufacture an optical quartz glass member having improved durability against ultraviolet laser light (Japanese Patent Application Laid-Open No. HEI-1).
No. 167258).

However, although the quartz glass member for optics manufactured by these methods is excellent in durability against ultraviolet laser light, the number of manufacturing steps increases, which is a technical problem. There are problems in terms of time, time, and economy. By the way, when synthetic quartz glass is also irradiated with ultraviolet rays, a new absorption band of light is generated in the ultraviolet region. The new absorption band of light in the ultraviolet region in this synthetic quartz glass is, for example, SiO in the quartz glass.
Structures other than SiO ₂ , such as H and SiCl, or Si-
It is believed that intrinsic defects due to oxygen deficiency or oxygen excess structure such as Si and Si-O-O-Si are generated by causing paramagnetic defects by photoreaction. Light absorption due to such paramagnetic defects in synthetic quartz glass includes, for example, E'center (Si.) And NBOHC (S).
i-O.) and the like have been identified so far in ESR spectra and the like.

As described above, the paramagnetic defect generally has an optical absorption band. Therefore, when the quartz glass is irradiated with ultraviolet rays, as the absorption band which becomes a problem in the ultraviolet region due to the paramagnetic defect of the quartz glass, for example,
The E'center is 215 nm, which is 260 nm although it has not been accurately identified. These absorption bands are relatively broad and generate strong absorption, which is a serious problem when used as a transmissive material for ArF lasers (193 nm) and KrF lasers (248 nm), for example.
For this reason, the synthetic quartz glass used in the excimer laser is required to have higher UV durability, which does not cause a new absorption band, for example, even when it is irradiated with strong UV rays, such as UV laser light. . The present invention is
In an optical quartz glass member used in an optical system using an ultraviolet laser represented by an excimer laser as a light source,
It is intended to solve the problem of the decrease in transmittance caused by such ultraviolet irradiation.

[0008]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive studies and as a result, as a result of the fact that hydroxyl groups (OH
Group) and chlorine to reduce the OH group content in the synthetic quartz glass to 10 to 100 ppm, and the chlorine content in the synthetic quartz glass to 200 p
By reducing to pm or less, Δn is 5 × 1
By 0 ^-6 to have homogeneity and 5 nm / cm or less in birefringence of the following refractive index profile, found that resistance to excimer laser with excellent quartz glass is obtained, in which have reached the present invention. The present invention provides a synthetic quartz glass used as an optical member for an excimer laser, in which a decrease in light transmittance in an ultraviolet region caused by irradiation of excimer laser light is reduced as much as possible, and a method for producing the same. In particular, the present invention provides an optical quartz glass member that can be suitably used for a stepper lens for an excimer laser, and a method for producing the same.

That is, the present invention relates to an optical member for excimer laser made of synthetic quartz glass, which is 10 to 100 pp.
OH group content of m, chlorine content of 200 ppm or less, hydrogen molecule content of 1 × 10 ¹⁶ molecules / cm ³ or less, homogeneity of refractive index distribution of 5 × 10 ⁻⁶ or less in Δn and 5 nm / An excimer laser optical member made of synthetic silica glass, which has a birefringence of not more than cm.
Further, the present invention is to produce a porous silica matrix by subjecting a volatile silicon compound to flame hydrolysis by an oxyhydrogen flame and depositing the resulting fine particle silica on a heat-resistant substrate to produce the porous silica matrix. At a high vacuum of 1 × 10 ⁻² Torr or higher.
By heating to a temperature of 00 ° C. or higher, dehydration and degassing, vitrification is performed, and then the dehydrated and degassed transparent quartz glass is homogenized to have striae in at least one direction. Forming a high-homogeneous quartz glass which is not formed, then shaping the obtained high-homogeneous quartz glass, and annealing the shaped high-homogeneous quartz glass, the content of OH group of 10 to 200 ppm, OH group content of preferably 10 to 100 ppm, 200 pp
Synthesis with chlorine content of m or less, hydrogen molecule content of 1 × 10 ¹⁶ molecules / cm ³ or less, homogeneity of refractive index distribution of 5 × 10 ⁻⁶ or less in Δn, and birefringence of 5 nm / cm or less A method of manufacturing an optical member for excimer laser made of quartz glass.

The inventors of the present invention have further improved stability against irradiation of excimer laser light when the synthetic quartz glass constituting the optical member has an internal transmittance of light at a wavelength of 245 nm of 99% or more. I found a thing. It is generally said that the absorption band at 245 nm is absorption due to oxygen deficiency, and it has been found that an optical member without this absorption is preferable in constructing an optical member for excimer laser.

The inventors have found that the smaller the OH group content and the chlorine content in the synthetic quartz glass, the better (eg, both are 5 ppm or less) in terms of durability against excimer laser. It has been found that when the content of OH groups in the molded product is 10 to 100 ppm and the content of chlorine is 200 ppm or less, good transmittance stability can be obtained in the excimer laser. In particular, regarding the content of OH groups related to light absorption due to intrinsic defects, it has been discovered that the content of OH groups of 10 to 200 ppm is acceptable in terms of durability against excimer laser. However, for long-term use, optical absorption due to intrinsic defects does not appear, and good homogeneity and birefringence of the refractive index are maintained for a long time, making it a more stable optical member for excimer laser light. Preferably has an OH group content of 10 to 100 ppm.

In the present invention, the hydrogen molecule content is 1 ×.
The number is 10 ¹⁶ molecules / cm ³ or less. The hydrogen content is
When it is 1 × 10 ¹⁶ molecules / cm ³ or less, the increase in the pulse number of the excimer laser light to be irradiated decreases the light transmittance in the ultraviolet region which occurs when the pulse number exceeds 1 × 10 ⁵ pulses at 500 mJ. Can be suppressed. Generally, in an optical member used in a semiconductor lithography apparatus, in order to achieve uniform exposure, homogeneity in the member is strictly required so that there is no variation in excimer laser resistance characteristics. Especially
The refractive index distribution on the light transmitting surface of the synthetic quartz glass optical member is Δn = 5 ×, where Δn is the difference between the maximum and minimum values of the refractive index.
It has been found that the excimer laser resistance characteristic in the optical member can be regarded as uniform if it is 10 ⁻⁶ or less. That is, Δ
When n = 5 × 10 ⁻⁶ or less, OH groups and chlorine, which are not preferable for stability against ultraviolet irradiation, are in a state of being almost evenly distributed in the synthetic quartz glass optical member. In, even excimer laser resistance can be obtained. Furthermore, the homogeneity of the refractive index distribution is a preferable characteristic in the case of an optical member such as a lens.

In the present invention, as a raw material of quartz glass for producing such an optical synthetic quartz glass member, for example, methyltrimethoxysilane [Si (CH ₃ ) (OC
H ₃ ) ₃ ), tetramethoxysilane [Si ((OC
Alkyl polyalkoxysilanes or alkoxysilanes such as H ₃ ) ₄ ] or other silane compounds or volatile silicon compounds such as volatile inorganic silicon compounds such as silicon tetrachloride are used. In the present invention, the volatile silicon compound is
It is volatilized and hydrolyzed by a direct flame hydrolysis method to produce fine particle silica glass, and this silica glass is deposited on a heat-resistant substrate to form a rod-shaped porous base material of synthetic silica glass, so-called soot. To manufacture.

In the present invention, the porous synthetic silica glass base material can be produced, for example, by a vapor phase axial attachment method (VAD method) and an external CVD method. Of course, the porous synthetic silica glass base material in the present invention is Since a porous aggregate of synthetic silica glass is sufficient, it is not limited to these production methods. In the present invention, since the OH groups formed by the oxyhydrogen flame are mixed in this porous synthetic silica glass base material, in order to avoid the generation of intrinsic defects due to the OH groups, OH in the synthetic silica glass is avoided. Removal of groups is performed. Conventionally, for example, in glass for optical fibers, in order to reduce OH groups in the glass as much as possible, chlorine gas (Cl ₂ ) is used as a dehydrating agent in the step of synthesizing porous silica glass or the step of transparent vitrification, and chlorine gas is used. The method of heat-treating is performed in it. However, in this method, even if OH is reduced, chlorine remains in the glass, and the generation of intrinsic defects cannot be avoided. Even if the heat treatment is carried out in an inert gas, as long as the heat treatment is carried out under normal pressure, the gas dissolves in the glass, and in this case also, intrinsic defects are generated.

On the other hand, the porous silica glass base material contains OH
In addition to the base, a significant amount of molecular hydrogen from the oxyhydrogen flame is in solution. Regarding the so-called residual hydrogen molecules that remain as a solid solution in the silica glass base material, for example, in synthetic quartz glass by the direct method, the residual hydrogen molecules are present at a hydrogen molecule concentration of 5 × 10 ¹⁶ molecules / cm ³ or more. It has been found that when it forms a solid solution in the silica glass base material, the generation of absorption bands in the ultraviolet region is suppressed (US Pat. No. 5,083).
6,352). However, 5 × 10 ¹⁶ molecules /
When the residual hydrogen molecules form a solid solution in the silica glass base material at a hydrogen molecule concentration of ³ cm ³ or less, the suppression of the generation of the absorption band in the ultraviolet region is not observed, but rather the generation of the absorption band in the ultraviolet region does not occur. It has been found to be on the rise.

On the other hand, the present inventors have obtained 1 × 10 ¹⁶
It has been found that when residual hydrogen molecules form a solid solution in the silica glass base material at a hydrogen molecule concentration of not more than the number of molecules / cm ³ , generation of an absorption band in the ultraviolet region is suppressed. Therefore, in the present invention, the synthetic silica glass is
For example, 1350 to 17 in a high vacuum degree of ^10-2 Torr or more, that is, in an atmosphere having a pressure of ^110-2 Torr or less.
Transparent vitrification is carried out by heating to a temperature within the temperature range of 00 ° C. The degree of vacuum and the heating temperature for the transparent vitrification treatment of the synthetic silica glass are selected so that the OH groups and metal impurities contained in the synthetic silica glass can be removed by volatilization and removal. With respect to the size of the base material and the transparent vitrification treatment time, it is preferable to set the temperature range as low as possible within the above temperature range.

The vitrification of the porous base material of the synthetic silica glass is based on the dehydration condensation reaction of the silanol group (SiOH) represented by the following reaction formula on the surface of the synthetic silica glass fine particles of the base material. 2SiOH → SiOSi + H ₂ O Since the water generated by the dehydration condensation reaction of the silanol groups is removed by diffusing outside between the silica glass fine particles, the generated water molecules are removed between the silica glass fine particles to remove the OH groups. It is necessary to carry out a transparent vitrification treatment during the time of diffusion from the outside. Therefore, when the vitrification temperature is 1700 ° C. or higher during this reaction,
On the silica glass surface, while the dehydration condensation reaction is not completed sufficiently, the sintering reaction between the silica glass fine particles progresses rapidly, and the porous silica glass base material is transparentized into a synthetic quartz glass. Therefore, the OH group remains without being removed.

On the other hand, the above silanol group dehydration condensation reaction proceeds even at a temperature lower than the sintering temperature, for example, at a temperature of about 800 ° C. Therefore, in order to remove the OH group from the synthetic quartz glass, silica glass While the sintering between the fine particles does not proceed, complete the dehydration condensation reaction of the silanol group,
It is necessary to diffuse and remove the OH group.
Therefore, in order to remove the OH group from the quartz glass, for example, the temperature is kept within a temperature range of 800 to 1200 ° C. for a certain period of time to accelerate the dehydration condensation reaction of the silanol group, and then heated to a higher temperature. Then, it is preferable to perform a two-step transparent vitrification, that is, to perform transparent vitrification by sintering the silica glass fine particles.

When the synthetic silica glass is made transparent by vitrification by the zone melt method, it is necessary to make it transparent under the condition that the dehydration condensation reaction of the silanol group is carried out as gently as possible. That is, the heating area should be moved as slowly as possible or the heating temperature should be as low as possible. Generally, the larger the porous silica glass base material, the slower the movement of the heating region. Water (H ₂ O) generated by the dehydration condensation reaction of silanol groups at the time of vitrification is at least 10 in order to diffuse it as quickly as possible and release it to the outside.
It has been found necessary to maintain a high vacuum atmosphere above ^-2 Torr during the vitrification process. What is important here is that the dehydration condensation reaction of the silanol group and the transparent vitrification reaction have a high vacuum degree of 10 ⁻² Torr or more, that is, 10 ⁻² Torr or more.
^-It is necessary to keep the pressure below ^-2 Torr. In addition,
When the porous base material of the silica glass to be treated is large, the amount of H ₂ O produced is considerably large. Therefore, the vacuum evacuation device to be used should have a higher evacuation rate than a high evacuation degree. It is valid.

The synthetic quartz glass produced in this manner has a low OH concentration, that is, the OH content in the synthetic quartz glass is 50 ppm or less, preferably 30 p.
pm or less, the content of metal impurities is extremely low,
It is a high-purity transparent quartz glass. Quartz glass manufactured by the CVD method has density fluctuations in the silica glass fine particle deposits on the heat-resistant substrate due to temperature changes during its manufacture, but these fluctuations remain as striae after transparent vitrification. In general, transparent quartz glass produced by the CVD method generally has striae.

However, this striae must be removed to form an optical member such as a stepper lens. Therefore, in the present invention, the high-purity transparent quartz glass is used, for example, in US Pat. No. 2,904,713, US Pat. No. 3,128,166, and US Pat. No. 3,128,1.
No. 69, U.S. Pat. No. 3,485,613, and the like to remove the striae by treatment according to the method disclosed therein. For example, a rod-shaped transparent synthetic quartz glass having a striae is held by a lathe, and a method of heating a local portion of the rod-shaped transparent quartz glass by a burner or electric heating, at least transparent synthetic quartz glass is heated to a softening point or higher, There is a method of rotating a lathe and twisting a rod-shaped synthetic quartz glass until the striae disappear.

In this method, when the striae are removed, the heating position of the rod-shaped synthetic quartz glass is sequentially moved so that the entire rod-shaped synthetic quartz glass is finally homogenized. The heating temperature at this time needs to be higher than the softening point of the quartz glass, for example, 1600 ° C. or higher.
Of course, the moving speed of the heating position on the synthetic quartz glass,
It is appropriately selected depending on the shape and weight of the quartz glass member to be treated. The striae-cleared transparent synthetic quartz glass is then formed into a shape and size suitable for use in a final product, such as a stepper lens.
This molding is generally carried out by placing the striae-free transparent synthetic quartz glass in a crucible of a desired shape, heating it to at least 1500 ° C. in a heating furnace, and molding the quartz glass by its own weight. In this case, a carbon crucible can generally be used as in the conventional method. Further, as the heating furnace, one having a carbon heater specification can be used as in the conventional method. Therefore, the molding is performed in a vacuum or an atmosphere of an inert gas such as He or N ₂ . Molding conditions such as heating temperature and heating time during this molding are appropriately selected according to the desired size and shape of the molded body.

Generally, the optical material is required to have a strain of 5 nm / cm or less. Therefore, in the present invention, the molding strain of the molded transparent synthetic quartz glass can be removed by annealing treatment. is necessary. This molding strain is removed by heating the molded transparent synthetic quartz glass to a temperature higher than the strain point of the quartz glass, and then gradually cooling the molded transparent synthetic quartz glass.
Generally, since the strain point of synthetic quartz glass is about 1025 ° C., in the present invention, the molded transparent synthetic quartz glass has a strain point of 11% in order to remove the molding strain almost completely.
It is heated to a temperature within the range of 00 ° C to 1250 ° C and then gradually cooled. The slow cooling is preferably performed as slowly as possible. In the present invention, the annealing treatment also contributes to making the refractive index distribution in the synthetic quartz glass uniform.

The refractive index distribution of synthetic quartz glass is
Impurity content such as OH and chlorine and fictive temperature
IVE temperature).
Of these, OH of the synthetic quartz glass optical member of the present invention
Since the amount of the group is several tens of ppm or less, it can be ignored, and other impurities in the case of the synthetic quartz glass optical member of the present invention are
The setting of the fictive temperature during the annealing is important because it can be substantially ignored. That is, in order to obtain a uniform refractive index distribution, the entire fictive temperature of the molded synthetic quartz glass to be processed, that is, the synthetic quartz glass molded body must be uniform. For this reason, the synthetic quartz glass compact is once heated to a temperature equal to or higher than the annealing point, and then kept at that temperature for a certain period of time to make the temperature distribution inside the synthetic quartz glass compact uniform, and then the temperature is lowered as slowly as possible. This is for minimizing the temperature difference in the entire quartz glass molded body. In this case, if the temperature decreasing rate is increased, a temperature difference occurs at an arbitrary position in the synthetic quartz glass molded body, and as a result, different virtual temperatures are set, and a uniform refractive index distribution cannot be obtained.

In the present invention, the heating temperature in the above-mentioned annealing treatment is about 1200 ° C., and the heating time and the temperature lowering speed are appropriately selected in consideration of the size and shape of the synthetic quartz glass compact to be annealed. . Generally, the larger the synthetic quartz glass molded body,
It is preferable to lengthen the heating time and slow the temperature lowering speed. The synthetic quartz glass optical member according to the present invention is
Since the content of the group is 10 to 100 ppm or less and the content of chlorine is 200 ppm or less, the total amount of paramagnetic defects caused by the irradiation of ultraviolet rays can be reduced, and stable for a long time under the irradiation of excimer laser light. Optical characteristics can be obtained. Moreover, since the synthetic quartz glass optical member for excimer laser according to the present invention has a refractive index distribution Δn of 5 × 10 ⁻⁶ or less on the light transmitting surface thereof, the entire optical member is irradiated with the excimer laser light. Therefore, uniform excimer laser stability can be obtained.

In the present invention, the volatile silicon compound is
Flame-hydrolysis by an oxyhydrogen flame and fine particles of synthetic silica produced are deposited on a heat-resistant substrate to produce a porous base material of synthetic silica glass, and the porous base material of the synthetic silica glass is 1 × 10 ^{−. By} heating under a high degree of vacuum of ² Torr or more to form a transparent synthetic quartz glass and subjecting the transparent synthetic quartz glass to a homogenizing treatment, a high degree of striae which has no striae in at least one direction, preferably three directions. Since the homogeneous synthetic quartz glass is formed, then the highly homogeneous synthetic quartz glass is molded, and annealed after the molding, the synthetic quartz glass optical member obtained has an intrinsic defect which is a source of paramagnetic defects generated by ultraviolet irradiation. Inherent defects due to other impurities such as SiOH and chlorine are reduced, and as a result, generation of paramagnetic defects is suppressed. As described above, the silica glass member for excimer laser produced by the present invention has good homogeneity and is excellent in excimer laser resistance, in particular,
It is suitable as quartz glass for a stepper lens that uses an excimer laser as a light source, and can also suppress an increase in absorption in the ultraviolet region due to ultraviolet irradiation.

[0027]

EXAMPLES The embodiments of the present invention will be described below with reference to examples, but the present invention is not limited to the following descriptions and examples. Example 1. Silicon tetrachloride was introduced into an oxyhydrogen burner and fine silica particles obtained by flame hydrolysis were deposited on a rotating target to form a porous synthetic silica deposit weighing 1 Kg. The porous synthetic silica deposit was placed in an atmosphere furnace, heated to 800 ° C., kept as it was, while flowing a mixed gas of chlorine, oxygen, nitrogen and 1: 1: 8 at a flow rate of 10 liter / min for 10 hours. After the heat treatment, the porous synthetic silica was taken out, placed in a vacuum furnace, heated to a temperature of 1600 ° C. under a vacuum of 1 × 10 ⁻² , held for 1 hour, and then cooled to obtain a transparent rod-shaped synthesis. Quartz glass was created.

Both ends of the synthetic quartz glass are fixed to a lathe,
The homogenization treatment was carried out while rotating the lathe while heating with a propane gas burner above the softening point. The homogenized synthetic quartz glass was set in a graphite mold, heated and molded at 1700 ° C. in a nitrogen atmosphere, and then annealed in the atmosphere. The annealing treatment was carried out by holding at 1100 ° C. for 20 hours and then cooling to 0.5 ° C./min to 600 ° C.
After collecting an analytical sample from the obtained synthetic quartz glass molded body, the outer peripheral portion was ground, and the end surface was mirror-polished to give an outer diameter of 8
A synthetic quartz glass molded body for an excimer laser optical window having a thickness of 0 mm and a thickness of 20 mm was prepared. When the OH group content of the obtained synthetic quartz glass molded body for an excimer laser optical window was measured by an infrared spectrophotometric method, it was 20 ppm,
The hydrogen molecule concentration of residual hydrogen molecules measured by Raman scattering was 1 × 10 ¹⁶ molecules / cm ³ or less. Further, when the ultraviolet transmittance of the synthetic quartz glass molded body for an optical window was measured by an ultraviolet spectrophotometer, no absorption at 245 nm was observed and the internal transmittance was 99% or more. Figure 1
The transmittance curve of the synthetic quartz glass molded body for an optical window of Example 1 is shown in FIG. The internal transmittance is the transmittance obtained by subtracting the loss due to the reflection of the sample from the transmittance shown in FIG. 1 and converted into the transmittance at a thickness of 1 cm.

The sample for analysis was decomposed with hydrofluoric acid and the chlorine concentration was measured by the silver nitrate nephelometry to find that it was 100 ppm. Further, the refractive index distribution of the synthetic quartz glass molded body for the optical window was measured by a Fizeau interferometer by an oil-on-plate method using HeNe laser light.
n was 1 × 10 ⁻⁶ and the birefringence was 2 nm. The synthetic quartz glass molding for an optical window was irradiated with KrF excimer laser at a fluence of 500 mJ / cm ² p, 100 Hz, and the change in absorbance in the ultraviolet region was measured. The measurement results are shown in FIG. In Fig. 2, the absorption wavelength of the E'center is 2
It shows the change with time in the number of shots of the absorbance (-Log (internal absorption)) at 15 nm. Compared with Comparative Example 1 to be described later, the change in absorbance with respect to irradiation was small, and good characteristics as an optical member were exhibited.

In this example, the hydrogen molecule concentration of residual hydrogen molecules in the synthetic quartz glass was measured by the Raman scattering method (Zhurnal Prikladnoi Sp.
ektroskopii vol. 46, No. 6, p
p. 987 to 991, jun 1987). This method is to determine the hydrogen molecule concentration in synthetic quartz glass by the ratio of the Raman band intensity of 800 cm ⁻¹ for SiO ₂ and the intensity of 4135 cm ⁻¹ for hydrogen molecules contained in the synthetic quartz glass. Yes, the hydrogen molecule concentration C is calculated by the following equation (1). C = kI ₄₁₃₅ / I ₈₀₀ (1) (In the formula (1), I ₄₁₃₅ is the area intensity of the Raman band at ₄₁₃₅ cm ^−1. I ₈₀₀ is ₈₀₀ cm ^−1.
Is the Raman band area intensity. k is a constant, 1.
It is 22 × 10 ²¹ . ) The hydrogen molecule concentration calculated by this formula is indicated by the number of hydrogen molecules per volume of 1 cm ³ . In this example,
The measuring instrument used to measure the hydrogen molecule concentration by the Raman scattering method is a Raman scattering spectrometer NR- manufactured by JASCO Corporation.
1100 double monochrome type, the detector is a photomultiplier tube R943-02 manufactured by Hamamatsu Photonics K.K., and the laser beam used for the measurement is an Ar ion laser (488 nm).

Example 2. A porous synthetic silica deposit was prepared in the same manner as in Example 1 above, kept at 800 ° C. in an atmospheric furnace, and then chlorine,
After heat treatment for 10 hours while flowing a mixed gas of oxygen, nitrogen and 1: 2: 7 at a flow rate of 10 liters / minute, the porous synthetic silica was taken out and placed in a vacuum furnace under a vacuum of 1 × 10 ⁻² to 1600. The temperature was raised to a temperature of ° C, the temperature was maintained for 1 hour and then cooled to prepare a transparent rod-shaped synthetic quartz glass. The synthetic quartz glass was molded in the same manner as in Example 1 and annealed to prepare a sample for analysis and a synthetic quartz glass molded body for an excimer laser optical window having an outer diameter of 80 mm and a thickness of 20 mm.
The obtained synthetic quartz glass molding for an excimer laser optical window had an OH group content of 90 ppm and a chlorine content of 20 ppm. In addition, in the synthetic quartz glass molded body for an optical window, the internal transmittance at 245 nm was 99% or more. When the synthetic quartz glass molded body for an optical window was irradiated with a KrF laser under the same conditions as in Example 1, the change in absorbance at 248 nm was measured.
The result is similar to the above, and shows good stability.

Example 3 In a transparent synthetic quartz glass prepared in the same manner as in Example 1,
The treatment time in homogenization was halved, and the other conditions were the same as in Example 1, and a series of treatments were performed, and a sample for analysis and a synthetic quartz glass molding for an excimer laser optical window with an outer diameter of 80 mm and a thickness of 20 mm were used. It was created. The obtained synthetic quartz glass molding for an excimer laser optical window had an OH group content of 90 ppm and a chlorine content of 20 ppm. Also, in this synthetic quartz glass molding for optical windows, 245
The internal transmittance in nm was 99% or more, and the birefringence was 2 nm. The refractive index distribution Δn of the synthetic quartz glass molded body for an optical window was measured and found to be 5 × 10 ^−6.
Met. The interference fringes showing the refractive index distribution are shown in FIG. From the central part and the outer peripheral part of the synthetic quartz glass molding for the optical window, 1
FIG. 4 shows the change in absorbance at 248 nm when a 0 mm × 10 mm × 40 mm sample was cut out and subjected to KrF laser irradiation under the same conditions as in Example 1. It can be said that the uniformity as the optical member is maintained because the central portion and the outer peripheral portion both show good stability and the changes in the absorbance are similar.

Comparative Example 1. A porous synthetic silica was prepared in the same manner as in Example 1, heated in a vacuum furnace to a temperature of 1600 ° C. under a vacuum of 1 × 10 ⁻² , held for 1 hour, and then cooled to obtain a transparent rod-shaped synthetic quartz. I made glass. The synthetic quartz glass was treated in the same manner as in Example 1 to prepare a sample for analysis and a synthetic quartz glass molding for an optical window having an outer diameter of 80 mm and a thickness of 20 mm. The optical window thus obtained had an OH group content of 200 ppm and a chlorine content of 10 ppm. Also in the synthetic quartz glass molding for the optical window, 245n
The internal transmittance at m was 99% or more. Under the same conditions as in Example 1, the synthetic quartz glass molded body for an optical window was subjected to KrF.
The change in absorbance at 248 nm when laser irradiation is performed is shown in FIG. 2 together with the case of Example 1. In Comparative Example 1, Example 1
Increase in absorbance at 215 nm compared to
It can be seen that the optical member for excimer laser does not have sufficient stability.

Comparative Example 2. A porous synthetic silica deposit was prepared in the same manner as in Example 1, kept at 800 ° C. in an atmospheric furnace, and then heat treated for 5 hours while flowing a mixed gas of chlorine, nitrogen and 1: 9 at a flow rate of 10 liters / minute. After that, the porous synthetic silica was taken out, and 160% under a vacuum of 1 × 10 ^{−2 in} a vacuum furnace.
The temperature was raised to 0 ° C., the temperature was maintained for 1 hour, and then cooled to prepare a transparent rod-shaped synthetic quartz glass. The synthetic quartz glass was molded in the same manner as in Example 1 and annealed to prepare a sample for analysis and a synthetic quartz glass molded body for an optical window having an outer diameter of 80 mm and a thickness of 20 mm. The obtained synthetic quartz glass molding for an optical window had an OH group content of 1 ppm and a chlorine content of 400 ppm. The internal transmittance at 245 nm of the molded synthetic quartz glass for optical windows was also 94.7%. FIG. 5 shows a transmittance curve in the ultraviolet region of the synthetic quartz glass molding for the optical window. 245
An absorption band having an absorption center of nm appears. The synthetic quartz glass molding for the optical window was subjected to KrF under the same conditions as in Example 1.
The change in absorbance at 215 nm when laser irradiation is performed is shown in FIG. 6 together with Example 1. A sharp increase in the absorbance at 248 nm was observed, indicating that the optical member for excimer laser does not have sufficient stability.

Example 4. After removing impurities by distilling silicon tetrachloride, using this as a raw material, the outer shape 15
A cylindrical porous synthetic quartz glass base material having a length of 0 mm and a length of 600 mm was produced. The porous synthetic quartz glass base material was placed in a vacuum furnace with a carbon heater specification and evacuated to 10 ⁻⁵ torr. Then, the heater was heated to heat the porous synthetic quartz glass base material. The heating conditions were 10 ° C./min up to 800 ° C., heating was performed at a temperature rising rate of 1 ° C./min from 800 to 1400 ° C., heating was stopped when 1400 ° C. was reached, and natural cooling was performed. A cylindrical transparent synthetic quartz glass having an outer diameter of 105 mm and a length of 550 mm was obtained. The OH content of the obtained transparent synthetic quartz glass was about 25 ppm.
Support rods made of quartz glass were attached to both ends of the cylindrical transparent synthetic quartz glass, and fixed to a chuck of a lathe. The transparent glass portion produced from the above-mentioned porous synthetic quartz glass base material was heated with a propane gas burner, the lathe was rotated, and the transparent synthetic quartz glass portion was twisted. The working temperature at this time was about 2000 ° C. No striae was observed in the twisted transparent glass part in three directions. After a while,
The transparent quartz glass portion was cut out and molded in a heating furnace with a carbon heater specification to obtain a cylindrical synthetic quartz glass molded body having an outer diameter of 250 mm and a length of 75 mm. The molding temperature at this time was about 1700 ° C., and the molding was performed in a nitrogen gas atmosphere.

The synthetic quartz glass molded body was annealed and heat treated to remove the strain. As the annealing heat treatment condition, the temperature was raised to 1100 ° C. and then lowered to 600 ° C. at 0.1 ° C./min. The heat treatment was performed in the atmosphere. Birefringence of the obtained synthetic quartz glass molded body is 2 nm
/ Cm or less, the refractive index distribution was substantially uniform, and the difference between the maximum value and the minimum value of the refractive index was 1 × 10 ^-6 or less. Further, the hydrogen molecule concentration of residual hydrogen molecules contained in this synthetic quartz glass was measured by Raman scattering method to be 1
It was x10 ¹⁶ molecules / cm ³ or less.

In order to investigate the generation of paramagnetic defects due to ultraviolet irradiation, a part of the above-mentioned transparent quartz glass molded body was cut out, and the boundary surface was polished to form a 10 mm × 10 mm × 40 mm transparent synthetic quartz glass molded body. . The synthetic quartz glass molded body was irradiated with an ArF laser, and changes in the transmittance of light at 193 nm were examined. The irradiation conditions of ArF laser are
Energy density 200 mJ / cm ² pulse, frequency 1
I went at 00 hertz. FIG. 7 shows the 193 nm absorption intensity with respect to the number of ArF irradiation pulses. The absorption intensity on the vertical axis is represented by the absorbance (-Log (internal transmittance)) per cm thickness of the sample.

Example 5. After removing impurities by distilling silicon tetrachloride, using this as a raw material, the outer diameter of 7
A cylindrical porous synthetic quartz glass base material having a length of 0 mm and a length of 600 mm was produced. The porous synthetic quartz glass base material was placed in a vacuum furnace with a carbon heater specification and evacuated to 10 ⁻⁵ torr. After that, the heater was heated to heat the base material. Heating condition is 800 ℃, 10 ℃ / min, 800
To 1400 ° C., heating at a heating rate of 1 ° C./min.
When the temperature reached 00 ° C, the heating was stopped and the mixture was naturally cooled. A cylindrical transparent synthetic quartz glass having an outer diameter of 50 mm and a length of 550 mm was obtained. The OH content of the obtained transparent glass was about 15 ppm.

The cylindrical transparent synthetic quartz glass was homogenized in the same manner as in Example 4, and then the transparent quartz glass portion was cut out and molded in a heating furnace with a carbon heater specification, an outer diameter of 120 mm and a length of 80 mm. A cylindrical synthetic quartz glass molded body of was obtained. Molding temperature at this time is about 1700 ℃
In a nitrogen gas atmosphere. The synthetic quartz glass molded body was annealed and heat treated to remove its distortion.
The annealing heat treatment conditions are as follows:
The temperature was lowered to 600 ° C. at a rate of 0.2 ° C./min. The heat treatment was performed in the atmosphere. The birefringence of the obtained synthetic quartz glass molded body is 2 nm / cm or less, the refractive index distribution is substantially uniform, and the difference (Δn) between the maximum value and the minimum value of the refractive index is 0.8 × 10. It was ^-6 . The synthetic quartz glass of this example was irradiated with an ArF laser under the same conditions as in Example 4, and the change in the transmittance of 193 nm light was examined.
The results are shown together in FIG. 7.

Comparative Example 3. The porous synthetic quartz glass base material produced in the same manner as in the case of the above-mentioned Example 4 was put in a furnace with carbon specifications to be transparent vitrified in a He gas atmosphere. The heating condition is that the temperature is raised to 1600 ° C. at a rate of 10 ° C./minute,
When the temperature reached 00 ° C, the heating was stopped and the mixture was naturally cooled.
The obtained transparent synthetic quartz glass has an OH content of about 300 p.
It was pm. Then, under the same conditions as in Example 1, a homogenizing step, a molding step, and an annealing step were performed. The birefringence and the refractive index distribution were almost the same as in the case of the synthetic quartz glass of Example 1. The synthetic quartz glass of this example was irradiated with an ArF laser under the same conditions as in Example 4, and the change in the transmittance of 193 nm light was examined. The results are shown together in FIG.

Comparative Example 4. A synthetic quartz glass molding for optics, which is generally used, was irradiated with an ArF laser under the same conditions as in Example 1 above and evaluated. This is a synthetic quartz glass obtained by synthesizing silicon tetrachloride by a direct flame hydrolysis method (a direct method using an oxygen / hydrogen flame).
The OH content of this glass was about 900 ppm. The synthetic quartz glass was subjected to a homogenizing step, a forming step and an annealing step under the same conditions as in Example 1. The birefringence and refractive index distribution of the obtained synthetic quartz glass molded body were almost the same as those of the synthetic quartz glass of Example 1. Further, the hydrogen molecule concentration of residual hydrogen molecules in the synthetic quartz glass was measured by Raman scattering method and found to be 3 × 10 ¹⁶ molecules / cm ³ . The synthetic quartz glass of this example was irradiated with an ArF laser under the same conditions as in Example 4, and the change in the transmittance of 193 nm light was examined. The results are collectively shown in FIG. 7 together with Example 4 and Example 5.

In Examples 4 and 5 and Comparative Examples 3 and 4, the birefringence and the refractive index distribution showed almost the same value. However, as shown in the results of FIG. 7, the resistance to ArF laser irradiation increased the absorbance in Examples 4 and 5, and was significantly suppressed as compared with the other Comparative Examples 3 and 4. Especially when compared with Comparative Example 4, the increase in absorbance of Examples 4 and 5 was suppressed to about 1/4. This is because the optical members of Examples 4 and 5 have a low production amount of paramagnetic defects generated by ArF laser irradiation, and are more susceptible to excimer laser light irradiation due to transparent vitrification treatment in a vacuum atmosphere. On the other hand, it shows that stable glass can be produced.

In these Examples and Comparative Examples, the hydrogen molecule concentration was 1 × 10 ¹⁶ molecules / c except for Comparative Example 4.
It was m ³ . The refractive index distribution Δn is 1 × 10 in Example 2.
^-6 , Comparative Example 1 is 1 × 10 ⁻⁶ , Comparative Example 2 is 5 ×
It was 10 ⁻⁶ . The chlorine concentration is 10 ppm in each of Examples 4 and 5 and Comparative Example 3, but is 8 in Comparative Example 4.
It was 0 ppm.

[0044]

Industrial Applicability The synthetic quartz glass optical member according to the present invention has an OH group content of 10 to 100 ppm, a chlorine content of 200 ppm or less, a homogeneity of a refractive index distribution of 5 × 10 ^{−6 in} Δn and 5 nm / n. Since it has a birefringence of not more than cm, it can be used without a decrease in light transmittance under irradiation of excimer laser light for a long time as compared with a conventional synthetic silica glass optical member. In semiconductor lithographic apparatus, it can be used for a long time, reducing the number of times to replace optical members,
Stable exposure can be performed, and the processing efficiency of semiconductor lithography can be improved. Further, the synthetic quartz glass optical member for excimer laser according to the present invention has a refractive index distribution Δn of 5 × 10 ⁻⁶ or less on the light transmitting surface thereof, and therefore can be achieved by the conventional synthetic quartz glass optical member. It was possible to perform uniform UV laser transmission over the entire optical member under the irradiation of excimer laser light, which was not possible, for example, in a semiconductor lithography apparatus, it is possible to perform uniform exposure for a long time. Therefore, the yield of semiconductor lithography can be improved.

In the present invention, a high-purity volatile silicon compound such as high-purity silicon tetrachloride is subjected to flame hydrolysis by an oxyhydrogen flame, and fine particle silica produced by this decomposition is deposited on a heat-resistant substrate. A porous base material of silica glass is manufactured, and the porous base material of silica glass is heated at a high vacuum degree of 1 × 10 ⁻² Torr or more to form transparent quartz glass, and the transparent quartz glass is homogenized. By the chemical treatment, a highly homogeneous quartz glass having no striae in at least one direction is formed, and since the highly homogeneous quartz glass is annealed after being molded, compared with a conventional production method of the excimer laser quartz glass member. It is possible to suppress the mixture of impurities as much as possible,
In addition, it is possible to produce glass having a low intrinsic defect concentration of glass. As a result, according to the present invention, as compared with the conventional method, it is possible to suppress the generation of paramagnetic defects due to the irradiation of excimer laser light, and it is possible to obtain quartz glass having excellent excimer laser resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a transmittance curve in an ultraviolet region of a 10 mm-thick sample of the synthetic quartz glass molding for an optical window of Example 1 of the present invention. FIG. 2 is a diagram showing changes in absorbance at a wavelength of 248 nm for the synthetic quartz glass molded bodies for optical windows of Example 1 and Comparative Example 1 of the present invention. FIG. 3 is a view showing interference fringes showing a refractive index distribution of a synthetic quartz glass molded body for an optical window of Example 3 of the present invention. FIG. 4 shows the wavelength 24 for the central portion and the outer peripheral portion of the synthetic quartz glass molded body for an optical window of Example 3 of the present invention.
It is a figure which shows the light absorbency change in 8 nm. FIG. 5 is a diagram showing a transmittance curve in an ultraviolet region of a 1.0 cm-thick sample of the synthetic quartz glass molded product for an optical window of Comparative Example 2. FIG. 6 shows a wavelength of 248 n for the synthetic quartz glass molded bodies for optical windows of Example 1 and Comparative Example 2.
It is a figure which shows the light absorbency change in m. FIG. 7 shows ArF in Examples 4 and 5 of the present invention and Comparative Examples 3 and 4.
It is a figure which shows the absorption curve of the light of 193 nm with respect to a laser irradiation pulse number.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kyoichi Inagi Kanayama, Tamura-cho, Koriyama-shi, Fukushima 88 Kawakubo, Shin-Etsu Quartz Co., Ltd. (72) Toshiyuki Kato Kawakubo, Kawamura, Tamura-cho, Koriyama, Fukushima 88 Shin-Etsu Quartz Co., Ltd.Koriyama Plant (72) Inventor Atsushi Shimada 88 Kawakubo, Kanaya, Tamura-cho, Koriyama City, Fukushima Prefecture Shin-Etsu Quartz Co., Ltd., Koriyama Plant

Claims (7)

[Claims] 1. An excimer laser optical member made of synthetic quartz glass, having an OH group content of 10 to 100 ppm, a chlorine content of 200 ppm or less, and a hydrogen molecule content of 1 × 10 ¹⁶ molecules / cm ³ or less. , Δn is 5 × 10
An optical member for excimer laser made of synthetic silica glass, which has a homogeneity of a refractive index distribution of ^-6 or less and a birefringence of 5 nm / cm or less. 2. The synthetic quartz glass optical member for an excimer laser according to claim 1, which has an internal transmittance of 99% or more for light having a wavelength of 245 nm. 3. The excimer made of synthetic quartz glass according to claim 1, wherein the synthetic quartz glass optical member for excimer laser is a window, a mirror, a lens and a prism for excimer laser having a wavelength of 300 nm or less. Optical member for laser. 4. A volatile silicon compound is flame-hydrolyzed by an oxyhydrogen flame, and the resulting fine particle silica is deposited on a heat-resistant substrate to produce a porous silica base material. 1400 under high vacuum of 1 × 10 ^-2 Torr or more
Highly homogeneous quartz glass having no striae in at least one direction by heating to a temperature of ℃ or higher to dehydrate and degas, and then subjecting the dehydrated and degassed transparent quartz glass to homogenization treatment. And then forming the obtained high-homogeneous quartz glass, and annealing the formed high-homogeneous quartz glass.
OH group content of 0 ppm, chlorine content of 200 ppm or less, hydrogen molecule content of 1 × 10 ¹⁶ molecules / cm ³ or less, homogeneity of refractive index distribution of Δn of 5 × 10 ⁻⁶ or less, and 5 nm / A method of manufacturing an optical member for excimer laser made of synthetic silica glass having a birefringence of not more than cm. 5. The method for producing an optical member for excimer laser made of synthetic quartz glass according to claim 5, wherein the homogenizing treatment of the quartz glass is performed at a temperature of 1600 ° C. or higher. 6. The molding of highly homogeneous quartz glass is 1500 ° C.
The method for producing a silica glass optical member for excimer laser according to claim 5, wherein the method is performed at the above temperature. 7. The annealing treatment is 800 ° C. to 1250 ° C.
The method for producing an optical member for excimer laser made of synthetic quartz glass according to claim 5, wherein the method is performed under a temperature range of