JP2010150097A - Method of producing synthetic quartz glass member for optics, and synthetic quartz glass member for optics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synthetic quartz glass member for optics having high laser resistance, which can be favorably used as a material for a variety of parts for a semiconductor aligner, and a method of producing the same. <P>SOLUTION: The method of producing a synthetic glass member for optics comprises: a process (a) of making a porous base material by hydrolyzing a volatile silicon compound with oxyhydrogen flame, and depositing fine particles of silica on a heat resistant base substance; a process (b) of dehydration heating treatment step in a vacuum or in an inactive gas containing atmosphere; a process (c) of obtaining a transparent quartz glass by heating; a process (d) of removing striae by carrying out a zone melting rotation stirring treatment by flame heating; a process (e) of forming in a cylindrical column; a process (f) of removing an external layer by grinding top and bottom surfaces and a periphery surface of the quartz glass; a process (g) of once keeping the quartz glass at a temperature of not lower than a slow cooling point, and thereafter slowly cooling; and a process (h) of carrying out heat treatment in an atmosphere containing a hydrogen gas at a pressure range of 0.0098-0.98 MPa at a temperature of not higher than 723 K to permeate with hydrogen molecules. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for producing synthetic quartz glass and a synthetic quartz glass member that are suitably used particularly as lenses and other optical components of lithography exposure apparatuses using excimer lasers for producing semiconductor chips. More specifically, it has excellent light transmission and homogeneity for a long period of time with excimer laser light such as KrF and ArF, and has characteristics suitable as a lens and other optical components of a lithography exposure apparatus. The present invention relates to an optical synthetic quartz glass manufacturing method and an optical synthetic quartz glass member.

With the progress of miniaturization of the exposure pattern accompanying the high integration of VLSI, an exposure light source is required to have a shorter wavelength even in an exposure apparatus that draws a circuit pattern on a semiconductor wafer. As a result, the ArF excimer laser (wavelength 193 nm) has now become the mainstream as a light source for the exposure apparatus, from the conventional I-line (wavelength 365 nm) and KrF excimer laser (wavelength 248 nm), and in recent years we have aimed for higher NA. An immersion lithography apparatus has also been put into practical use.

With the shortening of the wavelength of the light source and the increase in NA due to the immersion technique, higher precision is required for optical components such as lenses, windows, and prisms used in the optical system of the exposure apparatus. Yes.

Regarding laser resistance, these optical characteristics are required to be stable over a long period of time with respect to ArF excimer laser irradiation. In order to reduce exposure cost, ArF excimer laser, which is an exposure light source, has been increased in frequency in the latest exposure apparatus, and an excimer laser with a very high frequency of 6 kHz has recently been developed. The stability with respect to the number of excimer laser irradiation pulses required for the optical member to be used is extremely demanding that various optical characteristics do not change with an enormous irradiation of 3 to 1 × 10 ¹² shots or more. .

There are several types of changes in optical properties of quartz glass due to ArF excimer laser irradiation, such as a decrease in ultraviolet transmittance due to the formation of paramagnetic defects, and a change in volume of quartz glass called laser compaction and laser rarefaction. The increase and decrease of the refractive index and the change of birefringence.

The generation of paramagnetic defects in quartz glass by excimer laser irradiation means that, for example, in the case of ArF excimer laser irradiation with a wavelength of 193.4 nm, the energy as ultraviolet rays is very high. This is a phenomenon in which a bond is broken and a paramagnetic defect called an E ′ center is generated. Here, since the E ′ center has an absorption center at a wavelength of 215 nm, the transmittance of ultraviolet rays in this wavelength region is lowered.

When such a decrease in the transmittance of ultraviolet rays occurs in an optical component, the optical component absorbs a part of the energy of the excimer laser light that should be transmitted originally, but the absorbed energy is absorbed because it is converted into heat. The portion is heated to cause a change in refractive index, and as a result, highly accurate exposure cannot be performed. For these reasons, a synthetic quartz glass material that forms an optical component used in an excimer laser exposure apparatus is required to have a material that is unlikely to cause paramagnetic defects such as E 'center even after long-term excimer laser irradiation. Yes.

Laser compaction is a phenomenon in which quartz glass becomes dense with the excimer laser light irradiation. The fact that the quartz glass is densified literally means that the density of the quartz glass through which the excimer laser is transmitted increases, and the network structure of the quartz glass is cut and rearranged into a more dense structure at that portion.

As the quartz glass is densified, the refractive index of the quartz glass increases. Further, in the laser compaction, the densification of the quartz glass occurs only in the laser irradiated portion, so that stress is generated at the boundary with the unirradiated portion of the laser, and this is observed as birefringence. As described above, laser compaction causes a double change in optical characteristics, that is, a change in refractive index and a change in birefringence.

Laser rare faction is not a conventional accelerated test for quartz glass irradiation testing, but a low energy density that is almost the same as the energy density transmitted through optical components in actual exposure. This phenomenon is observed when irradiation is performed for a long time, and is a phenomenon in which the refractive index of the quartz glass irradiation portion is decreased in the opposite direction to laser compaction. Rare faction is an important problem when considering the optical stability of the ArF exposure apparatus, as is the compaction characteristic. The refractive index change behavior when irradiated for a long time at a low energy density is affected by the physical properties of the quartz glass and the laser irradiation conditions, and either a compaction or rare fact phenomenon is observed. In other words, compaction and rare faction are contradictory laser characteristics, and they cancel each other out, and the one with the larger contribution is apparently observed.

The change in the transmitted wavefront means that the refractive index of the quartz glass at the irradiated part changes. That is, when the transmitted wavefront is delayed, the refractive index of that portion is increased, and conversely, when the transmitted wavefront is advanced, the refractive index is decreased. When a refractive index change occurs only in a part of the lens (irradiation part) due to damage by laser irradiation, the imaging performance is greatly affected, and an accurate pattern cannot be formed. Therefore, in order to maintain high imaging performance, it is not only necessary to use a quartz glass material having a high refractive index homogeneity, but also a material in which the refractive index does not change by laser irradiation, in other words, the transmitted wavefront does not change. It is important to choose. For this purpose, a material with small characteristics of both compaction and rare faction with suppressed refractive index change is required.

In recent years, illumination light from conventional circularly polarized light to linearly polarized light has been used as a laser light source for higher resolution. In this case, as a more specific phenomenon, it has been found that extremely strong birefringence is generated over the entire irradiated portion in addition to a decrease in refractive index. A characteristic of birefringence when using this polarized illumination is that the birefringence direction (for example, the direction of the slow axis) is parallel to the laser polarization direction at the center of the laser irradiation part (in the actual lens, the center of the lens). In the intensity distribution that gives the maximum value. Therefore, even if the amount of birefringence is small, an enormous retardation (optical path difference between the fast axis and the slow axis) is generated over the entire long optical path length of the projection optical system. Thus, a failure such as a decrease in contrast occurs, and the exposure characteristics are significantly impaired. This characteristic is generally called polarization induced birefringence.

In order to provide a synthetic quartz glass member for optical use and a method for producing the same, in which a decrease in ultraviolet transmittance, compaction, rare faction, and polarization-induced birefringence do not substantially occur when laser irradiation is performed at a low energy density. In Japanese Unexamined Patent Application Publication No. 2004-269287, the amount of OH groups is in the range of more than 10 wtppm to 400 wtppm, fluorine is 30 to 1000 wtppm, hydrogen molecules are 0.1 × 10 ¹⁷ to 10 × 10 ¹⁷ (number of molecules / cm ³ It is clearly shown that the amount of change in transmitted wavefront at 632.8 nm per 1 cm thickness of quartz glass due to ArF excimer laser irradiation can be kept low.

In JP-A-2003-221245, the internal transmittance for ultraviolet light having a wavelength of 193.4 nm is 99.7% or more, the amount of OH groups is 5 wtppm or more and 300 wtppm or less, and the hydrogen molecule concentration is 1 × 10 ^16. By making the molecule / cm ³ or more and less than 2 × 10 ¹⁷ molecules / cm ³ , the laser rare faction that induces a great amount of birefringence does not occur, and the minute laser compaction within the range that hardly affects the lens characteristics. It is clearly shown that an optical system with stable exposure characteristics can be obtained over a long period of time by selecting the resulting synthetic quartz glass.

The present invention provides an optical synthetic quartz glass member with high laser resistance that can be suitably used as various optical materials for a semiconductor exposure apparatus when irradiated with an excimer laser such as ArF or KrF, and a method for producing the same. Is the purpose. Specifically, a synthetic quartz glass member for optical use that does not substantially cause a decrease in ultraviolet transmittance, a compaction, a rare faction, or a transmitted wavefront change due to polarization-induced birefringence when irradiated with an excimer laser, and its manufacture A method is provided.

The above object is achieved by a method for producing an optical synthetic quartz glass member according to the present invention having the following constitutions (1) to (10) and an optical synthetic quartz glass member produced by the method.
(1) A method for producing an optical synthetic quartz glass member including the following steps a) to h):
a) a step of hydrolyzing a volatile silicon compound with an oxyhydrogen flame, and depositing fine particle silica to be produced on a heat-resistant substrate to form a porous base material;
b) a step of subjecting the porous base material to a dehydration heat treatment in a vacuum or an inert gas-containing atmosphere;
c) A step of heating the porous base material subjected to the dehydration heat treatment to obtain a transparent quartz glass body (the heating temperature regulation is deleted)
d) a step of removing the striae by subjecting the transparent quartz glass body to a band-like melt-rotation stirring process by flame heating;
e) a step of molding the quartz glass body from which the striae has been removed into a cylindrical shape;
f) A step of removing the outer layer where the reducing defects introduced into the quartz glass body in the step d are removed by grinding and removing the upper and lower surfaces and the outer peripheral surface of the quartz glass body molded into the columnar shape,
g) The step of setting the fictive temperature to 1373 K or less by temporarily cooling the quartz glass body that has been ground and removed to a temperature equal to or higher than the annealing point and then cooling it, and h) the transparent in which the fictive temperature is set A step of heat-treating the quartz glass body in a hydrogen gas-containing atmosphere at a pressure of 0.0098 MPa to 0.98 MPa and a temperature of 723 K or less to contain hydrogen molecules.
(2) In the step f), the cylindrical quartz glass body is uniformly removed from each of the upper surface and the lower surface with a width of 8% or more of the height and from the outer peripheral portion of the cylindrical quartz glass body with a width of 5% or more of the diameter. The manufacturing method of the optical synthetic quartz glass member of Claim 1 (3) The optical synthetic quartz glass member manufactured by the manufacturing method of said (1) or (2).
(4) The amount of OH groups is in the range of more than 5 wtppm and not more than 100 wtppm, the difference between the maximum value and the minimum value of OH groups in quartz glass is within 10 wtppm, and the hydrogen molecules are 0.2 × 10 ^{17 to} 20 × 10. ¹⁷ (number of molecules / cm ³ ) The synthetic quartz glass member for optics according to (3) above, which has a fictive temperature of 1373 K or less.
(5) The amount of decrease in absorbance at a wavelength of 215 nm when an ArF excimer laser is irradiated with an energy density of 20 mJ / cm ² · pulse per pulse and a frequency of 200 Hz at a wavelength of 215 nm is 0.003 (/ cm) or less The synthetic quartz glass member for optics according to (3) or (4).
(6) When the ArF excimer laser is irradiated with 10,000,000 pulses at an energy density of 20 mJ / cm ² · pulse and a frequency of 200 Hz, the decrease in absorbance at a wavelength of 215 nm is 0.01 (/ cm) or less. The optical synthetic quartz glass member according to the above (3) or (4).
(7) When the ArF excimer laser is irradiated with 1 × 10 ⁷ pulses at an energy density of 10 mJ / cm ² · pulse and a frequency of 2000 Hz, the amount of change in the transmitted wavefront at 632.8 nm is 0 to 1 cm per thickness. The synthetic quartz glass member for optics according to any one of the above (3) to (6), which is in the range of +4 nm.
(8) When an ArF excimer laser is irradiated with 4 × 10 ¹⁰ pulses at an energy density of 0.05 mJ / cm ² · pulse or less and a frequency of 2000 Hz, the amount of change in the transmitted wavefront at 632.8 nm is 1 cm thick. The optical synthetic quartz glass member according to any one of the above (3) to (6), which is in the range of -0.5 to +0.5 nm per unit.
(9) When the ArF excimer laser is irradiated with 4 × 10 ¹⁰ pulses at an energy density of 0.05 mJ / cm ² · pulse and a frequency of 2000 Hz, the birefringence change at the center of the irradiated portion is 0.3 nm / The optical synthetic quartz glass member according to any one of (3) to (8), which is not more than cm.
(10) The synthetic quartz glass member for optical use according to any one of (4) to (9), wherein the fictive temperature is 1323K or less.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings, but the following description is given by way of example, and it goes without saying that various modifications are possible without departing from the technical idea of the present invention.

Hereinafter, the manufacturing method of the synthetic quartz glass member for optics by embodiment of this invention is demonstrated.
The method for producing an optical synthetic quartz glass member according to an embodiment of the present invention is as follows.
A step of hydrolyzing a volatile silicon compound with an oxyhydrogen flame, and depositing the resulting fine particle silica on a heat-resistant substrate to form a porous base material a),
A step b) of subjecting the porous base material to a dehydration heat treatment in a vacuum or an inert gas-containing atmosphere;
C) a step of heating the porous base material subjected to the dehydration heat treatment to obtain a transparent quartz glass body;
A step d) of removing the striae by subjecting the transparent quartz glass body to a band-like melt-rotating stirring process by flame heating;
A step e) of forming the quartz glass body from which the striae has been removed into a cylindrical shape;
A step f) of removing the outer layer having the reducing defects introduced into the quartz glass body in the step d) by grinding and removing the upper and lower surfaces and the outer peripheral surface of the quartz glass body formed into the cylindrical shape.
Step g) of setting the fictive temperature to 1373 K or lower by temporarily cooling the quartz glass body that has been ground and removed to a temperature equal to or higher than the annealing point, and then cooling it, and transparent quartz glass having the fictive temperature set. The body is heat-treated in a hydrogen gas-containing atmosphere at a pressure of 0.0098 MPa to 0.98 MPa and at a temperature of 723 K or less to contain hydrogen molecules h)
Is provided.

Examples of the volatile silicon compound in step a) are, for example, silicon compounds containing chlorine such as silicon tetrachloride [SiCl ₄ ] and methyltrichlorosilane [CH ₃ SiCl ₃ ]. is not limited, to other, tetramethoxysilane _{[Si (OCH 3) 4]} , alkoxysilanes such as methyl trimethoxysilane _{[(CH 3) Si (OCH} 3) 3], hexamethyldisilazane [( An organic silane compound such as CH ₃ ) ₃ SiNHSi (CH ₃ ) ₃ ] can be used. Moreover, although there exist VAD method, OVD method, etc. about the preparation method of a porous preform | base_material, it may be based on any method.

In step b), the porous base material is subjected to dehydration heat treatment in a vacuum or an inert gas-containing atmosphere, and the heat treatment temperature and treatment time are controlled so as to obtain a desired OH group concentration. Generally, heat treatment at a high temperature for a long time makes it easier to lower the OH concentration, and the addition of a dehydrating agent such as fluorine or chlorine makes it possible to lower the OH concentration.

In step c), transparent vitrification of the porous base material is performed in a heating furnace, and the heat treatment temperature and treatment time are controlled so as to obtain a desired OH group concentration. The heating atmosphere is generally treated in an inert gas atmosphere such as He or Ar, or in a vacuum atmosphere, but is not particularly limited. The heating temperature is not particularly limited, but if it is too low, transparent vitrification does not proceed sufficiently, and if it is too high, the glass body is deformed and it is difficult to maintain its shape. Substantially, the preferred temperature range is 1623K to 1873K.

Since the content of OH groups is determined by the heat treatment conditions and transparent vitrification conditions of the porous base material, a quartz glass material suitable for optics can be obtained by optimizing the treatment conditions at this time. For example, when setting the content of OH groups low. The dehydration process in step b) sufficiently promotes dehydration over a long period of time, and in the transparent vitrification process in step c), the optimization of the process conditions such as slow vitrification over time, It is possible to control the content of OH groups.

As a specific method for removing the striae in step d), it is preferable to employ the striae removal method described in JP-A-7-267661 as follows. That is, both ends of the synthetic silica glass ingot in the longitudinal direction are supported by the support member, and while rotating around the axis connecting the support ends, a melting zone is formed in the synthetic quartz glass ingot with a burner and the pressure is applied in the direction of the support axis. This is a method in which the same treatment as before is performed after protruding outward in the melting zone and then supporting the side surface on the support. In this method, quartz glass is physically mixed well in the melting zone, so that the striae structure itself is also mixed, and the striae substantially disappears by applying a treatment for a predetermined time or longer. In addition, since the OH groups, chlorine, and other impurities in the quartz glass that were originally distributed unevenly are also mixed uniformly, the refractive index change caused by these is also reduced, and a highly homogeneous quartz glass member is obtained. can get.

In particular, the glass physical property that greatly affects the refractive index homogeneity is an OH group, and it is desirable to make this concentration distribution as uniform as possible. The refractive index homogeneity of the quartz material suitably used for the lens material of the exposure apparatus for manufacturing LSI needs to be set to at least 2 × 10 ⁻⁶ or less as the difference between the maximum value and the minimum value of the refractive index. In this case, the difference between the maximum value and the minimum value of the OH group concentration (hereinafter abbreviated as ΔOH) is preferably 10 wtppm or less, more preferably 5 wtppm or less.

The quartz glass member that has been subjected to the striae removal process of step d) generally has an oval shape with both ends connected to a support rod. In order to use this as an optical quartz glass member, particularly a lens material, which is suitably used in a semiconductor exposure apparatus, it is preferably molded into a cylindrical shape. Therefore, the quartz glass member that has undergone striae removal processing is placed in the cylindrical mold by the molding step of step e), and a weight is placed from above or deformed into a cylindrical shape by high-temperature heat treatment by its own weight.

Here, for the first time this time, it has been found that a very strong reducing defect is formed on the outer peripheral portion by the striae removing process in the step d). This reducing defect causes a strong absorber having a central wavelength at 215 nm by excimer laser irradiation, which is reversibly generated by ON / OFF of laser irradiation, and has a very bad influence on laser resistance. The amount of this reducing defect is an initial sharp increase in absorption at a wavelength of 215 nm when irradiated with an ArF excimer laser under the conditions of an energy density of 20 mJ / cm ² · pulse and a frequency of 200 Hz and 1 × 10 ⁵ pulses (in this patent, the initial increase in ArF) Measured as absorption). FIG. 1 shows the distribution of the ArF initial absorption amount in the quartz glass body after molding and before the peripheral grinding removal. The initial absorption amount, that is, the amount of reducing defects, has a stronger distribution toward the outer peripheral portion, but is hardly observed in the central portion.

Although this reducing defect is formed even in a quartz glass member having an OH concentration exceeding 200 wtppm, the amount of the defect is not so strong, and the high temperature heat treatment for setting the virtual temperature in the subsequent step g) is performed. It has the property of being easily removed by external diffusion. Therefore, when a quartz glass member having an OH concentration exceeding 200 wtppm is manufactured, there is no practical problem even if no specific measures are taken. That is, the ease of generation of reducing defects and the ease of diffusion removal by heat treatment depend on the OH concentration of the quartz glass body, and quartz glass having a low OH concentration of 5 to 100 wtppm as defined in this patent. It has been found that in the member, reducing defects are more easily generated and are not easily diffused and removed by heat treatment. This indicates that the lower the OH concentration of the quartz glass member, the more sites where the reducing defects exist in the outer peripheral portion, and the more easily affected by the reducing defects.

Although the cause of this reductive defect generation is not yet clear, H ₂ O produced by combustion of the burner gas by igniting from the outside with a burner in the striae removal step of step d) is produced by quartz glass by a high-temperature burner flame. It is presumed that a defect related to H such as SiH or two-coordinate silicon was formed.

As a countermeasure against this reducing defect, a method of grinding and removing a defect generation site is conceivable. Defect generation occurs in the striae removal process, and it may be removed by grinding the outer periphery after removing the striae, but generally the quartz glass member after striae removal has an oval shape, and its outer periphery It is difficult and time-consuming to uniformly remove the material. Therefore, in this patent, reduction is performed by grinding and removing the upper and lower surfaces and the outer peripheral surface of the quartz glass body formed into a cylindrical shape after the molding step of step e), not after the striae removal step of step d). A step f) for removing the outer layer in which sexual defects exist is newly provided. As the amount of grinding, it was found that if the portion where the ArF initial absorption amount of the outer peripheral portion exceeds 0.02 / cm is removed, the final quartz glass member thereafter is hardly affected by reducing defects. Considering the distribution of the ArF initial absorption of the quartz glass member in this patent, this depends on the size of the quartz glass member, but it is 8% or more of the height from the upper and lower surfaces of the cylindrical quartz glass body. In addition, it was found that removal from the outer peripheral portion of the cylindrical quartz glass body uniformly with a width of 5% or more of the diameter is sufficient as a countermeasure for reducing defects.
In addition, in the past, in order to prevent impurity contamination in the vicinity of the surface of the quartz glass member at the time of molding, the surface was sometimes ground and removed by grinding 10 mm from all surfaces of the upper and lower and outer peripheral portions. . However, it did not pay attention to the remaining problem of reducing defects more serious than that, and the actual grinding removal amount was insufficient.

The designated heat treatment in step g) is mainly intended to improve the refractive index homogeneity and birefringence of the obtained quartz glass member, but the fictive temperature is set to 1373K or lower, more preferably 1323K or lower. By doing so, it is one of the purposes to stabilize the glass structure of the final quartz glass body and to give the effect of improving the laser resistance. Details of this will be described later.

Specifically, a quartz glass member is placed in a heating furnace, heated to a temperature above the annealing point, once held at a temperature above the annealing point for a certain period of time, and then gradually cooled to a temperature of 1373K or less. By doing so, it is possible to set the fictive temperature to 1373K or lower, preferably 1323K or lower. The temperature and time for holding above the annealing point are optimized depending on the size of the quartz glass member to be treated.

In general, in the case of a quartz glass body having a large weight, the time for holding it at an annealing point or higher is set longer. Moreover, the fictive temperature can be set to 1423K or less by setting also the slow cooling rate in the range of 0.1 degreeC / hour-5 degreeC / hour. Also for the slow cooling rate, it is preferable to set the quartz glass body having a large weight low.

Step h) is a treatment for containing hydrogen molecules to improve damage resistance due to excimer laser irradiation. Specifically, the pressure is 723 K or less in a hydrogen-containing atmosphere having a pressure in the range of 0.0098 MPa to 0.98 MPa. This is achieved by applying a heat treatment at a temperature. Here, when the pressure is less than 0.0098 MPa, it is difficult to contain a sufficient amount of hydrogen, so that the laser resistance is insufficient. On the other hand, when the treatment is performed at a pressure exceeding 0.98 MPa, a large amount of hydrogen molecules can be contained. However, in order to easily deteriorate the homogeneity and birefringence, it is desirable to perform the hydrogen molecule-containing treatment in the above pressure range.

Regarding the processing temperature in step h), if the processing temperature is too high, the laser resistance deteriorates due to the generation of reducing defects described later. In particular, when the OH group concentration is as low as less than 100 wtppm, reducing defects are more likely to occur. Therefore, the treatment temperature is desirably 723 K or less. The lower limit temperature should be determined in consideration of the size of the sample to be processed and the production time, but if the temperature is too low, the diffusion of hydrogen into the quartz glass will be extremely slow, resulting in very high productivity. Worse. In practice, it is reasonable to set the lower limit to 523K.

In the quartz glass member according to the manufacturing method of this patent, the amount of OH groups is in the range of more than 5 wtppm to 100 wtppm, the difference between the maximum value and the minimum value of OH groups in the quartz glass is within 10 wtppm, and hydrogen molecules are 0 .2 × 10 ^{17 to} 20 × 10 ¹⁷ (number of molecules / cm ³ ) and the optical synthetic quartz glass member satisfying that the fictive temperature is 1373 K or less is particularly suitable as a quartz glass member for an exposure apparatus. It turned out to be.

The present inventors investigated the behavior of the transmitted wavefront when irradiated with ArF laser at a low energy density, and investigated quartz glass prepared with several different manufacturing parameters. It has been found that the concentration of OH is a particularly important physical property in order to improve. Of course, not only the OH concentration, but also the hydrogen concentration, fictive temperature, etc., it is possible to obtain a comprehensively optimized quartz member that is resistant to damage such as solarization, compaction, and rarefaction during low energy density irradiation. I found.

That is, it was found that a quartz glass member having excellent laser resistance can be obtained by limiting the amount of OH to more than 5 wtppm and not more than 100 wtppm. As an even more preferable range, by setting the amount of OH to more than 10 wtppm and not more than 50 wtppm, hydrogen molecules to 0.2 × 10 ^{17 to} 20 × 10 ¹⁷ (molecules / cm ³ ), and virtual temperature to 1373 K or less, It has been found that an optical synthetic quartz glass member that can be suitably used as an optical member of an ArF excimer laser exposure machine is obtained.

In such a quartz glass member, with respect to excimer laser resistance of transmittance change, for ArF initial absorption, an ArF excimer laser was irradiated with 100,000 pulses at an energy density of 20 mJ / cm ² · pulse at a frequency of 200 Hz. When the decrease in absorbance at 215 nm is 0.003 (/ cm) or less, ArF excimer laser is irradiated with 10,000,000 pulses at an energy density of 20 mJ / cm ² · pulse and a frequency of 200 Hz for ArF long-term resistance. As a result, the decrease in absorbance at 215 nm was 0.01 (/ cm) or less, which was found to be a level that can be suitably used as an optical material for an ArF excimer laser exposure apparatus.

Hydrogen molecules in quartz glass are effective in reducing the ultraviolet transmittance and increasing the resistance to compaction. In general, the decrease in ultraviolet transmittance is caused by the formation of paramagnetic defects caused by excimer laser irradiation. A paramagnetic defect that particularly affects 193.4 nm is a structure called an E ′ center (Si ·), and has a broad absorption band with a center wavelength of 210 to 215 nm.

Although hydrogen molecules are thought to be dispersed in the SiO ₂ network, it is thought that the generation of absorption bands is suppressed by changing the defect type of Si · and SiO · that occurs with laser irradiation to SiH and SiOH. Yes. Thus, in order to eliminate the defect species generated by the laser irradiation, it is necessary to contain a certain amount or more of hydrogen molecules. If the molecular weight of the hydrogen is too small, the effect will be insufficient due to insufficient hydrogen to bond to the generated defects. On the other hand, if the amount of hydrogen molecules is too large, the resistance to the rare faction will be deteriorated. It has also been found that the initial transmittance of the region is reduced (see, for example, Patent Document 5). Therefore, the appropriate amount of hydrogen molecules is preferably set in the range of 2 × 10 ¹⁶ to 2 × 10 ¹⁸ (molecules / cm ³ ).

In addition, unstable O—Si—O bonds in quartz glass (structures in which the bond distance, bond angle, and the like are distorted from normal values) are easily broken by excimer laser irradiation, and laser resistance is deteriorated. Cause. Therefore, as a means for improving excimer laser resistance, it is possible to eliminate unstable O—Si—O bonds and to make the O—Si—O structure as stable as possible. The O—Si—O bond is related to the fictive temperature of the glass, and reducing the fictive temperature has a more stable structure and increases the laser resistance. In this patent, by optimizing the high-temperature heat treatment of the quartz glass member as described above (paragraphs [0031] and [0032]) and the subsequent cooling temperature, the fictive temperature of the quartz glass member is more preferably 1373 K or less. Is set to 1323K or less. If the fictive temperature is higher than this, laser resistance, particularly long-term resistance, is adversely affected. On the other hand, the lower limit value is not particularly limited, but is substantially limited to about 1173 K from the cooling process of quartz glass.

Further, in the quartz glass member in this patent, even if ArF excimer laser with an energy density per pulse of 0.05 mJ / cm ² · pulse or less is irradiated with 4 × 10 ¹⁰ pulses at a frequency of 2000 Hz, the thickness of the quartz glass is 1 cm. The amount of change in the transmitted wavefront at 632.8 nm is within the range of −0.5 to +0.5 nm, and the change in birefringence occurring at the center of the irradiated portion when irradiated under the same condition is 0.3 nm / cm. It became the following, and it turned out that it is a level which can be used suitably for the optical material of an ArF excimer laser exposure apparatus.

Further, when used for a relatively high energy density, the damage due to the change in the refractive index is dominated by compaction. However, in the optical synthetic quartz glass member of the present invention, the energy density is 10 mJ / cm ² · pulse and the frequency is 2000 Hz. The amount of change in transmitted wavefront per 1 cm thickness of quartz glass when irradiated with 1 × 10 ⁷ pulses is in the range of 0 to +4 nm, and this level can be suitably used for the illumination system portion of the ArF excimer exposure apparatus. It was a level.

There are still many unclear points about the damage mechanism of rare-faction and polarization-induced birefringence, but experimentally, OH concentration and hydrogen molecular weight are the dominant causes. I know it will happen.

The optimum range of OH is more than 5 wtppm and not more than 100 wtppm, but it is more preferable to set the lower limit value to 10 wtppm and the upper limit value to about 50 wtppm. If the OH concentration becomes too low, oxygen defects such as Si-Si are likely to be generated, and compaction damage is likely to occur when irradiated with a low energy density ArF laser. Is preferred. On the other hand, if the OH concentration becomes too high, the amount of change of the transmitted wavefront due to rarefaction deteriorates beyond −0.5 nm per 1 cm thickness, and the polarization-induced birefringence deteriorates beyond 0.3 nm / cm. For this reason, it is preferable to set at most 100 wtppm, more preferably about 50 wtppm.

Examples of the present invention will be described below with reference to examples. However, the present invention is not limited to the following descriptions and examples.
The measured values of physical properties shown in the examples and comparative examples of the present specification are based on the following measuring methods.

ii) assessment of striae;
Visual observation with crossed Nicols polarizing plate.

iii) assessment of homogeneity;
Evaluation by measurement of refractive index difference at He-Ne laser wavelength (632.8 nm). Measured with a Fizeau interferometer (Mark IV, manufactured by Zygo).

iv) measurement of hydrogen molecule concentration;
Measurement by laser Raman scattering spectroscopy (see Non-Patent Document 2). This method obtains the concentration of hydrogen molecules in the synthetic quartz glass from the ratio of the intensity of the Raman band with a wave number of 800 cm ⁻¹ relating to SiO ₂ and the intensity of 4135 cm ⁻¹ relating to the hydrogen molecules contained in the synthetic quartz glass. Yes, the hydrogen molecule concentration C is calculated by the following equation (1).

V. S. Khotimchenko et al. , J. et al. Appl. Spectroscopy, 4,632-635 (1987)

C = k × I ₍₄₁₃₅₎ / I ₍₈₀₀₎ (1)
(In formula (1), I ₍₄₁₃₅₎ is the area intensity of the Raman band of ₄₁₃₅ cm ⁻¹ , I ₍₈₀₀₎ is the area intensity of the Raman band of ₈₀₀ cm ⁻¹ , k is a constant, 1.22 × 10 ²¹ )

The hydrogen molecule concentration calculated by this equation is indicated by the number of hydrogen molecules per volume of 1 cm ³ . In the following examples, the measuring instrument used for measuring the hydrogen molecule concentration by the Raman scattering method is a Raman scattering spectrometer NR-1100 double monochrome type manufactured by JASCO Corporation, and the detector is a photoelectron manufactured by Hamamatsu Photonics Corporation. It is a multiplier tube R94-03-02, and the laser beam used for the measurement is an Ar ion laser (488 nm).

v) measurement of the amount of birefringence;
Measurement with Exicor 350AT birefringence automatic measuring device manufactured by HINDS.

vi) Initial transmission measurements at 193.4 nm;
Measurement by Cary4E visible / ultraviolet spectrophotometer manufactured by Varian. Measured with a sample that was optically polished on both sides at a thickness of 10 mm. Using the theoretical transmittance of 90.86% of quartz glass at 193.4 nm (a value obtained by subtracting the loss due to multiple reflection on the surface from 100%), the apparent transmittance T% at a thickness of 10 mm is (T / 90.86). ) X100.

vii) measurement of OH groups;
Calculated from the intensity of the 2.7 micron OH stretching vibration band using an infrared absorption spectrum spectrophotometer (IR-700, manufactured by JASCO Corporation).

ix) measurement of virtual temperature;
Measured by laser Raman scattering spectroscopy. Quantified from the intensity of the D1 and D2 Raman scattering bands of quartz glass. A calibration curve is created from a quartz glass sample in which the virtual temperature is forcibly set by quenching, and the virtual temperature is calculated from the measured value of the actual sample.

Example 1
Silicon tetrachloride is flame-hydrolyzed in an oxygen / hydrogen flame to form fine soot-like silica, and the resulting fine-particle silica is deposited on a heat-resistant substrate to form a cylindrical porous mother having an outer diameter of 300 mm and a length of 1200 mm Made the material. The obtained porous base material was subjected to a dehydration heat treatment in a N ₂ gas atmosphere at a temperature of 1373 K for 24 hours, and then heated to a temperature of 1773 K in vacuum to effect transparent vitrification. The obtained quartz glass body was subjected to strip melting and rotating stirring treatment by the method disclosed in Japanese Patent Application Laid-Open No. Hei 7-267661, and after removing the striae, it was placed in a high purity graphite mold and 2070 K using an electric furnace. Was deformed by its own weight at a temperature of 380 mm and formed into a cylindrical shape having a diameter of 380 mm and a thickness of 120 mm. The cylindrical quartz glass body was ground and removed by 10 mm on each of the upper surface and the lower surface and an even 25 mm width from the outer peripheral portion in order to remove the generation site of the reducing defects present on the outer peripheral portion. The quartz glass body that has been ground and removed is stored in a quartz glass container, held in an electric furnace at 1423K for 45 hours, slowly cooled to 1273K at a temperature drop rate of 1 K / hour, and then the furnace is deenergized. Naturally cooled. Further, this quartz glass body was subjected to a heat treatment for 1500 hours at a pressure of 0.5 MPa and a temperature of 673 K in an atmosphere containing hydrogen gas to contain hydrogen molecules. In addition, in order to make the hydrogen concentration distribution in the glass body uniform, the gas pressure and the hydrogen gas ratio were changed as needed. Table 1 summarizes the manufacturing conditions in the manufacturing process of these series of quartz glass bodies.

When the obtained cylindrical quartz glass body (diameter 330 mm, thickness 100 mm) was visually observed through a polarizing plate, no striae was observed.

Furthermore, from the obtained synthetic quartz glass body, a 10 mm × 10 mm × 50 mm square column-shaped sample was used for various physical property evaluations, and a 60 mm diameter × 10 mm-thick cylindrical sample was used for initial transmittance evaluation. Polishing was performed, and various characteristics were measured. The measurement results are shown in Table 2. In the synthetic quartz glass body prepared in Example 1, the amount of OH groups is 90 wtppm, the difference between the maximum value and the minimum value of OH groups in the quartz glass is 8 wtppm, and hydrogen molecules are 2 × 10 ¹⁷ (number of molecules / cm ³ ). The fictive temperature was 1293 K, and the internal transmittance per cm at 193.4 nm was 99.80%. These satisfy | filled all the structural components of the quartz glass body of this invention.

Further, from the columnar quartz glass member obtained in Example 1, a 10 mm × 10 mm × 50 mm square column-shaped sample was cut out for evaluation of ArF long-term durability and initial absorption, and its side surface (10 mm × 50 mm surface) ) Was polished so that light could pass through all four surfaces. A laser irradiation test of the prepared sample was performed using an excimer laser manufactured by Lambda Physic Co., Ltd. at a repetition frequency of 200 Hz.

For the evaluation of long-term durability and initial absorption, an excimer laser beam is incident from one direction of the four-side polished surface, an ultraviolet beam with a wavelength of 215 nm using a D2 lamp as a light source is irradiated on the orthogonal surface, and the sample is irradiated with an ArF laser. The transmittance was measured from the lamp light intensity ratio before and after. Here, since the measurement of the light intensity ratio is synchronized with the oscillation pulse of the excimer laser, the transmittance can be measured simultaneously with the laser irradiation. In the evaluation of long-term durability, an energy density of 20 mJ / cm ² · pulse and a frequency of 200 Hz is 1 × 10 ⁷ pulses, and the initial absorption is measured at an energy density of 20 mJ / cm ² · pulse and a frequency of 200 Hz under 1 × 10 ⁵ pulses. While irradiating with an ArF excimer laser, a change in transmittance at 215 nm was measured. The measured values are the changes in absorbance at a wavelength of 215 nm, and the results are shown in Table 2. The ArF long-term resistance in the quartz glass member of Example 1 was 0.0055 / cm, and the ArF initial absorption amount was 0.0008 / cm, both satisfying the constituent requirements of the quartz glass body of the present invention.

For the evaluation of laser compaction, laser rarefaction, and polarization-induced birefringence, a 30 × 30 × L80 mm square columnar sample was cut out from the cylindrical quartz glass member obtained in Example 1, and 2 in the longitudinal direction. The surface was optically polished. Using an excimer laser manufactured by Lambda Physic, an ArF excimer laser whose energy density was appropriately adjusted was repeated at a frequency of 2000 Hz, and a laser irradiation test of the prepared sample was performed.
For compaction evaluation, evaluation of rare-faction and polarization-induced birefringence at a high energy density laser irradiation condition with an energy density per pulse of 10 mJ / cm ² · pulse, 1 × 10 ⁷ pulses at a frequency of 2000 Hz Therefore, as a laser irradiation condition at a low energy density, the energy density per pulse is 0.05 mJ / cm ² · pulse and the frequency 2000 Hz is irradiated with 4 × 10 ¹⁰ pulses. , The amount of change in the transmitted wavefront at 632.8 nm after ArF excimer laser irradiation was measured using an interferometer (Zygo
In Mark IV), for the evaluation of polarization-induced birefringence, the birefringence change at the center of the irradiated portion after ArF excimer laser irradiation was evaluated by an Exicor 350AT birefringence automatic measuring device manufactured by HINDS. The evaluation data is expressed as the amount of change in the transmitted wavefront of the laser irradiation part, and the results are shown in Table 2. Compaction is 3 nm / cm, rare facts are not observed, and polarization-induced birefringence is 0.2 nm / cm, both of which are satisfactory. These are all the constituents of the quartz glass body of the present invention. It was.
Thus, it was found that the quartz glass member according to Example 1 satisfies all the structural requirements of the present invention and is suitable as a quartz glass member for an exposure apparatus.

(Example 2)
A porous base material prepared in the same manner as in Example 1 was subjected to a dehydration heat treatment at a temperature of 1473 K for 120 hours in an N ₂ gas atmosphere, and then heated to a temperature of 1823 K in a vacuum to form a transparent glass body. It was created. Further, in the same manner as in Example 1, the OH group concentration of the transparent quartz glass obtained by adding hydrogen molecules to this quartz glass body is lower than that in Example 1, and thus zero defects are more easily generated. The ease of diffusion removal was 20 wtppm, which satisfied the constituent requirements of the quartz glass body of the present invention.
The obtained quartz glass body was subjected to striae removal processing, molding processing, and outer periphery grinding in exactly the same manner as in Example 1, and in the virtual temperature setting processing, the furnace cooling temperature was increased to 1333 K, 60 K higher than that in Example 1, and heat-treated. Thereafter, annealing was performed in the same manner as in Example 1 to obtain a cylindrical quartz glass body having a diameter of 330 mm and a thickness of 100 mm. A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
The synthetic quartz glass body prepared in Example 2 satisfies all the structural requirements of the present invention as in Example 1, and was found to be suitable as a quartz glass member for an exposure apparatus.

(Example 3)
A transparent glass body was prepared in exactly the same manner as in Example 1. The obtained transparent quartz glass has an OH group concentration of 90 ppm which is more easily generated than the same 90 wt as in Example 1, and is easily diffused and removed. It fulfilled the requirements of.
The obtained quartz glass body was subjected to striae removal processing, molding processing, and outer periphery grinding in exactly the same manner as in Example 1, and in the virtual temperature setting process, the furnace cooling temperature was held at 1423 K for 45 hours, and then from Example 1 After gradually cooling to 1333 K, which is a higher temperature, at a rate of 1 K / hour, the furnace was turned off and naturally cooled. A cylindrical quartz glass body having a diameter of 330 mm and a thickness of 100 mm was obtained. A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
The synthetic quartz glass body prepared in Example 3 satisfies all the structural requirements of the present invention as in Example 1, and was found to be suitable as a quartz glass member for an exposure apparatus.

Comparative example

(Comparative Example 1)
In the same manner as in Example 2, a porous base material was prepared, and after dehydrating heat treatment, a transparent glass body was prepared.
The obtained transparent quartz glass has an OH group concentration of 20 wtppm, which is more likely to generate defects than those in Example 2, and is easily diffused and removed, and the quartz glass body of the present invention. It fulfilled the requirements of.

After the obtained quartz glass body was subjected to striae removal processing and molding processing in exactly the same manner as in Example 1, the outer peripheral grinding after molding was 5 mm from each of the upper and lower surfaces of the cylindrical quartz glass body and the outer peripheral portion. Therefore, the outer peripheral grinding removal amount was reduced more than that of Examples 1 and 2. Thereafter, in the same manner as in Example 1, a virtual temperature setting process and gradual cooling were performed to obtain a cylindrical quartz glass body having a diameter of 360 mm and a thickness of 110 mm. Further, hydrogen molecules were contained in the quartz glass body.
A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
The synthetic quartz glass body produced in Comparative Example 1 had a reducing defect remaining because the grinding removal amount of the outer peripheral portion after molding was insufficient, and the ArF initial absorption amount was 0.0008 to 0.005 / cm depending on the location. Strongly observed. As shown in FIG. 3, the distribution of initial absorption in the quartz glass body has a characteristic distribution shape in which there is almost no outermost peripheral portion and a central portion and a strong portion exists in the middle portion. This is because the reducing defects remaining on the outer peripheral portion due to insufficient outer peripheral grinding are thermally diffused by the heat treatment in the subsequent virtual temperature setting step, and the outermost layer is diffused and removed to the outside, but in the internal direction of the quartz glass body. It seems to be the result of spreading. Once the reductive defects that have entered the quartz glass body are not removed no matter how much heat treatment is applied, they remain even after the hydrogen molecule containing step.
Further, this quartz glass member was also detected to have a large change in transmitted wavefront at 632.8 nm of 0.6 nm / cm with respect to refractive index change due to laser irradiation at a low energy density. This is thought to be due to the fact that the initial absorption due to reducing defects has the effect of increasing the contribution of compaction.
As described above, the ArF initial absorption amount and the refractive index fluctuation damage of the quartz glass member in Comparative Example 2 do not satisfy the constituent requirements of the present invention, and as a quartz glass member for a semiconductor exposure apparatus that requires high laser resistance. It turned out to be inappropriate.

(Comparative Example 2)
In the same manner as in Example 1, after preparing a porous base material, a transparent glass was formed at 1773 K without performing a dehydration heat treatment to prepare a glass body.
The obtained transparent quartz glass has an OH group concentration of more than 150 wt% higher than that of Example 1 and is more likely to generate zero defects, and is easily diffused and removed. It did not meet the body requirements.

The obtained quartz glass body was subjected to striae removal processing, molding processing, peripheral grinding after molding, virtual temperature setting processing and slow cooling in exactly the same manner as in Examples 1 and 2, and a cylindrical shape having a diameter of 330 mm and a thickness of 100 mm. A quartz glass body was obtained. Furthermore, hydrogen molecules were contained in this quartz glass body under the same conditions as in Example 1. A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
The synthetic quartz glass body prepared in Comparative Example 2 had a strong OH concentration distribution of 15 wtppm because the absolute value of OH concentration was as high as 150 wtppm. It is known that the OH concentration in the glass body affects various glass properties such as refractive index, fictive temperature, and laser resistance, and the distribution of the OH concentration causes variations in these characteristics.
In addition, the quartz glass member was observed to have a large change in transmitted wavefront at 632.8 nm of -1.0 nm / cm when the refractive index was changed by laser irradiation at a low energy density. It is known that there is a strong correlation between the OH concentration and the laser rare faction, and it is considered that the contribution of the laser rare faction is strengthened by the high OH concentration.
Further, the polarization-induced birefringence of this quartz glass member was observed as large as 0.6 nm / cm. This is known to have a strong positive correlation between the OH concentration and the polarization-induced birefringence, and the polarization-induced birefringence is 0.3 nm / cm when the OH concentration is 150 ppm, which is higher than the specified range of this patent. It is thought that it was because it deteriorated beyond this.
Thus, the quartz glass member in Comparative Example 2 does not satisfy the constituent requirements of the present invention in terms of OH concentration, OH concentration distribution, refractive index fluctuation damage, and polarization-induced birefringence, and is used as a quartz glass member for a semiconductor exposure apparatus. It turned out to be inappropriate.

(Comparative Example 3)
A synthetic quartz glass member was prepared in the same manner as in Example 1 except that the treatment conditions in the dehydration heat treatment step and the transparent vitrification step were changed. In the dehydration heat treatment step, the porous quartz glass base material is heat-treated at a temperature of 773 K for 8 hours in He gas containing 1.0% by volume of SiF _4, and then helium containing 10% by volume of oxygen while maintaining the temperature. Heat treatment was performed with gas for 8 hours. After cooling, the porous quartz glass base material was heated at 1723 K in vacuum to effect transparent vitrification.
The obtained transparent quartz glass has an OH group concentration of 3 ppm, which is considerably lower than that of Example 1 and is more likely to generate zero defects, and is easily diffused and removed. The constituent requirements of the glass body were not satisfied.

The obtained quartz glass body was subjected to striae removal processing, molding processing, peripheral grinding after molding, virtual temperature setting processing and slow cooling in exactly the same manner as in Example 1, and cylindrical quartz glass having a diameter of 330 mm and a thickness of 100 mm. Got the body. Furthermore, hydrogen molecules were contained in this quartz glass body under the same conditions as in Example 1. A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
In the synthetic quartz glass member prepared in Comparative Example 3, the amount of change in the transmitted wavefront at 632.8 nm was observed as large as +0.6 nm / cm in the refractive index change due to laser irradiation at a low energy density. As described above, it is known that there is a strong correlation between the OH concentration and the laser rare faction. Since the OH concentration is too low, 3 wtppm, the contribution of the laser rare faction is small, and it is contrary to this. It is thought that the contribution of compaction, which is a characteristic to be achieved, is relatively strengthened. Thus, the quartz glass member in Comparative Example 3 did not satisfy the constituent requirements of the present invention in terms of refractive index fluctuation damage, and was found to be unsuitable as a quartz glass member for a semiconductor exposure apparatus.
As is clear from Comparative Example 1 and Comparative Example 2, from the viewpoint of refractive index change due to laser irradiation at a low energy density, which is close to the irradiation conditions in an actual exposure apparatus, the OH concentration is too much or too little. However, the OH concentration range of 5 to 100 wtppm, which is a constituent requirement of this patent, is a suitable range.

(Comparative Example 4)
Exactly the same as in Example 1, the OH group concentration of the transparent quartz glass obtained by creating a porous base material and producing a transparent glass body by dehydration heat treatment is more than 0 defects as in Example 9. It was 0 wtppm in terms of ease of formation and diffusion removal. This satisfied the constituent requirements of the quartz glass body of the present invention.
The obtained quartz glass body was subjected to striae removal processing, molding processing, outer peripheral grinding removal, and virtual temperature setting processing in exactly the same manner as in Example 1 to obtain a cylindrical quartz glass body having a diameter of 330 mm and a thickness of 100 mm. However, in this comparative example 4, the subsequent treatment of containing hydrogen molecules was not performed. A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
The synthetic quartz glass body produced in Comparative Example 4 had a considerably poor ArF long-term resistance of 0.075 / cm in absorption. H ₂ molecules in quartz glass play an extremely important role in excimer laser resistance. That is, as described above in [0039] and [0040], the decrease in transmittance due to the excimer laser irradiation is caused by the paramagnetic defect called E ′ center having Si · structure due to destruction of the Si—O—Si structure of quartz glass. Generate. This has a strong absorption band in the vicinity of 215 nm, and this causes a decrease in transmittance. However, since the E ′ center generated by containing hydrogen molecules changes to a SiH structure, the transmittance decreases as a result. There is an inhibitory effect. The quartz glass member in Comparative Example 4 is considered to have deteriorated ArF long-term resistance because no hydrogen-containing treatment was performed.
Further, in the quartz glass member in Comparative Example 4, the change in the transmitted wavefront at 632.8 nm was observed to be as large as +1.0 nm / cm when the refractive index was changed by laser irradiation at a low energy density. Also, in the refractive index change characteristic by laser irradiation at a high energy density, the amount of change of the transmitted wavefront at 632.8 nm was observed as large as 5 nm / cm. The hydrogen concentration in quartz glass has a strong influence on both laser compaction and laser rarefaction, reducing the generation of compaction, and rarefaction is a phenomenon seen only in hydrogen-containing quartz glass. In the quartz glass member in Comparative Example 4, since the hydrogen-containing treatment was not performed, compaction was large, and no rare faction was generated. Therefore, it is considered that stronger compaction was observed.
As described above, the quartz glass member in Comparative Example 4 does not satisfy the constituent requirements of the present invention in terms of ArF long-term durability, low energy density, and refractive index change characteristics due to laser irradiation at high energy density. It was found to be unsuitable as a quartz glass member.

(Comparative Example 5)
In the same manner as in Example 1, a porous base material was prepared and subjected to dehydration heat treatment to prepare a transparent glass body.
The transparent quartz glass obtained had an OH group concentration of 0 wtppm, which is more likely to generate zero defects than the same 9 as in the Examples, and to be easily removed by diffusion. This satisfied the constituent requirements of the quartz glass body of the present invention.
The obtained quartz glass body was treated in exactly the same way as in Example 1 except that the fictive temperature setting heat treatment was not performed to obtain a cylindrical quartz glass body. A sample was cut out from the obtained cylindrical quartz glass body in the same manner as in Example 1, and the same physical property evaluation and laser resistance evaluation were performed. The results are shown in Table 2.
Since the synthetic quartz glass body produced in Comparative Example 5 was not heat-treated, its fictive temperature was as high as 1443K. In addition, the fictive temperature is related to the structural stability of the glass and this also affects the laser resistance. Therefore, the ArF long-term resistance is 0.012 / cm in terms of absorption, and the ArF initial absorption is 0.0045 / cm. It was.
Thus, it turns out that the quartz glass member in this comparative example 5 does not satisfy the constituent requirements of the present invention in the fictive temperature, ArF long-term durability, and ArF initial absorption, and is unsuitable as a quartz glass member for a semiconductor exposure apparatus. It was.


Table 1
Table 2

The present invention provides an optical synthetic quartz glass member with high laser resistance that can be suitably used as various optical materials for a semiconductor exposure apparatus when irradiated with an excimer laser such as ArF or KrF, and a method for producing the same. Is the purpose. Specifically, a synthetic quartz glass member for optical use that does not substantially cause a decrease in ultraviolet transmittance, a compaction, a rare faction, or a transmitted wavefront change due to polarization-induced birefringence when irradiated with an excimer laser, and its manufacture A method is provided. In particular, in the manufacturing process of a cylindrical quartz glass body used as a lens material for an exposure apparatus, it has become possible to effectively suppress the reduction defects.

The schematic diagram showing the distribution of the reducing defect in the quartz glass body molded into a columnar shape is shown. It is sectional drawing when the quartz glass body after shaping | molding is vertically divided by the radial direction center, and it represents that there are many reducing defects, so that a dark color part. The schematic diagram showing the distribution of a reducing defect in the quartz glass body of the comparative example 1 is shown. It is sectional drawing when the quartz glass body after annealing is divided vertically by the center in the radial direction, and the darker colored portion indicates that there are more reducing defects.

Claims (10)

The manufacturing method of the synthetic quartz glass member for optics including each process of following a) to h).
a) a step of hydrolyzing a volatile silicon compound with an oxyhydrogen flame, and depositing fine particle silica to be produced on a heat-resistant substrate to form a porous base material;
b) a step of subjecting the porous base material to a dehydration heat treatment in a vacuum or an inert gas-containing atmosphere;
c) a step of heating the porous base material subjected to the dehydration heat treatment to obtain a transparent quartz glass body;
d) a step of removing the striae by subjecting the transparent quartz glass body to a band-like melt-rotation stirring process by flame heating;
e) a step of molding the quartz glass body from which the striae has been removed into a cylindrical shape;
f) A step of removing the outer layer where the reducing defects introduced into the quartz glass body in the step d are removed by grinding and removing the upper and lower surfaces and the outer peripheral surface of the quartz glass body molded into the columnar shape,
g) The step of setting the fictive temperature to 1373 K or less by temporarily cooling the quartz glass body that has been ground and removed to a temperature equal to or higher than the annealing point and then cooling it, and h) the transparent in which the fictive temperature is set A step of heat-treating the quartz glass body in a hydrogen gas-containing atmosphere at a pressure of 0.0098 MPa to 0.98 MPa and a temperature of 723 K or less to contain hydrogen molecules. 2. In the step f, the cylindrical quartz glass body is uniformly removed with a width of 8% or more of its height from each of the upper and lower surfaces of the cylindrical quartz glass body and a width of 5% or more of its diameter from the outer peripheral portion of the cylindrical quartz glass body. The manufacturing method of the synthetic quartz glass member for optics as described in 2. An optical synthetic quartz glass member produced by the production method according to claim 1. The amount of OH groups is in the range of more than 5 wtppm and not more than 100 wtppm, the difference between the maximum value and the minimum value of OH groups in quartz glass is within 10 wtppm, and hydrogen molecules are 0.2 × 10 ^{17 to} 20 × 10 ¹⁷ (molecules The optical synthetic quartz glass member according to claim 3, which contains a few / cm ³ ) and has a fictive temperature of 1373 K or less. The amount of decrease in absorbance at a wavelength of 215 nm when an ArF excimer laser is irradiated with an energy density of 20 mJ / cm ² · pulse per pulse at a frequency of 200 Hz at a wavelength of 215 nm is 0.003 (/ cm) or less. 5. A synthetic quartz glass member for optical use according to 4. The amount of decrease in absorbance at a wavelength of 215 nm when an ArF excimer laser is irradiated with 10,000,000 pulses at an energy density of 20 mJ / cm ² · pulse and a frequency of 200 Hz per pulse is 0.01 (/ cm) or less. 5. A synthetic quartz glass member for optical use according to 3 or 4. When the ArF excimer laser is irradiated with 1 × 10 ⁷ pulses at an energy density of 10 mJ / cm ² · pulse and a frequency of 2000 Hz, the amount of change in transmitted wavefront at 632.8 nm is in the range of 0 to +4 nm per 1 cm thickness. The optical synthetic quartz glass member according to any one of claims 3 to 6. When an ArF excimer laser is irradiated with 4 × 10 ¹⁰ pulses at an energy density of 0.05 mJ / cm ² · pulse or less at a frequency of 2000 Hz, the amount of change in transmitted wavefront at 632.8 nm is −0 per 1 cm thickness. The optical synthetic quartz glass member according to any one of claims 3 to 6, which is in a range of 0.5 to +0.5 nm. When the ArF excimer laser is irradiated with 4 × 10 ¹⁰ pulses at an energy density of 0.05 mJ / cm ² · pulse and a frequency of 2000 Hz, the birefringence change amount at the center of the irradiated portion is 0.3 nm / cm or less. The optical synthetic quartz glass member according to any one of claims 3 to 8. The fictive temperature is 1323K or less, The optical synthetic quartz glass member according to any one of claims 4 to 9.