JP3274954B2 - Synthetic quartz glass material for optics and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz glass material for optical use and a method for producing the same, and more particularly, to an excimer laser (XeCl: 308 nm, KrF: 248 nm,
ArF: 193 nm), low-pressure mercury lamp (185 n)
m), an optical synthetic quartz glass material used as an optical component such as a lens for vacuum ultraviolet light to ultraviolet light such as an excimer lamp (Xe-Xe: 172 nm), a prism, and a window material, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Synthetic quartz glass has a thickness of about 150 nm to about 5 μm.
It has a wide range of applications because it transmits light over a wide wavelength range of m. It has a small thermal expansion coefficient, so it can be used to construct a high-precision optical system with a small deviation of the optical axis. It has a number of very good properties, such as being able to be used, and being resistant to damage even when irradiated with high energy light because of high purity silicon dioxide.

Taking advantage of such excellent characteristics, the synthetic quartz glass is used as an optical material of a lithography apparatus for exposing and drawing an integrated circuit pattern such as an LSI.
Conventionally, as an exposure light source of this lithography apparatus, Hg
G-line (435.8 nm) and i-line (36
5 nm), and optical glass composed of multiple components was used as the optical glass material. However, recently, there has been a tendency to shorten the wavelength of light used for exposure in order to further improve the degree of integration of a circuit.
It becomes necessary to use synthetic quartz glass having low light absorption in the ultraviolet region for the illumination optical system and the exposure optical system. Further, a low-pressure mercury lamp (185 nm) and an excimer lamp (Xe-Xe:
172 nm) is used for photo-CVD, ashing, etching of silicon wafers, and ozone generators, or is being developed to be applied to the above-mentioned applications in the future. This also requires the use of the synthetic quartz glass.

[0004] The quartz glass material used for forming these optical parts is required to have high light resistance at the used wavelength (the transmittance is hardly reduced after light irradiation) and is used as a lens or a prism. In addition, in addition to the above-mentioned properties, homogeneity of the refractive index is also required. Regarding the light fastness, it is required that light absorption is practically not detected and fluorescence is not detected in a wavelength region of light to be used, and that a light absorption band is not induced even after long-time light irradiation, and KrF excimer is required. When a laser (248 nm) is used, the most severe condition is an energy density of 400.
mJ / cm ^2, reduction of the transmittance at 248nm after ¹⁰⁶ shots of was carried out in the conditions of radiation frequency 100Hz is required to be 0.5% or less. further,
It is desired to develop a material that can withstand shorter-wavelength light even under longer-density irradiation conditions for a longer time.

[0005] Synthetic quartz glass is usually mentioned as a quartz glass which can meet such severe conditions. In general, the term synthetic quartz glass is applied to all quartz glass that does not use a natural silica material as a starting material, but there are various methods for producing this synthetic quartz glass. Therefore, due to the purity of the raw material and the manufacturing method, there are various grades of impurity element concentration (metal element concentration, nonmetal element concentration) and defect concentration present in the manufactured synthetic quartz glass, Not all synthetic quartz glass can be the ideal glass material for transmission optics.

[0006] Synthetic quartz glass production methods are roughly classified into a gas phase method and a liquid phase method, and a gas phase method is mainly used as a method for producing a material used in an optical system. There are a synthesis method, a plasma CVD method, a soot method, etc., and impurities such as metals, OH groups, Cl, H ₂ , O ₂ , oxygen excess defects, oxygen deficiency defects, The concentrations of ring structure defects and the like are different. The concentration of these impurities and defects is determined by the light absorption, fluorescence,
It is known that it has a great effect on optical characteristics such as a refractive index, and thus also has a great effect on light resistance against the irradiation with the above-mentioned high-energy light (a degree of decrease in transmittance after irradiation).

[0007]

For example, in the VAD method, a raw material gas such as a silicon compound, hydrogen, or oxygen is supplied from a burner to a vertically suspended seed rod, and the silicon compound is supplied to an oxygen-hydrogen flame. Attach the fine particles of quartz glass produced by hydrolysis in the lower end of a seed rod made of quartz, etc.
This is a method for producing synthetic quartz glass, which is formed by depositing to form porous quartz glass and then heating it to make it viscous.When silicon tetrachloride is used as the silicon compound, chlorine and OH groups are used. Remains in the synthetic quartz glass, the concentration of which tends to be non-uniform, and there is a problem in that distribution of the refractive index and the like is caused by these impurities.

[0008] In general, the vitrification of the transparent glass is 1420 to 1
This is performed in a temperature range of 600 ° C., but a distribution occurs in the refractive index due to a difference in cooling rate between the inside and the outside of the synthetic quartz glass body during the subsequent slow cooling. Usually, since the distribution of the refractive index mainly generated by the distribution of the OH group and the refractive index distribution generated by the slow cooling after the vitrification are added together, there is a problem that a larger refractive index distribution is easily generated. .

[0009] The refractive index distribution caused by the residual impurity concentration distribution and the refractive index distribution caused by the thermal history such as the cooling conditions in the manufacturing process are erased as contradictory distributions. A method has been proposed in which the cooling rate is adjusted to obtain an optical quartz glass having a small actual refractive index distribution and good quality (Japanese Patent Application Laid-Open Nos. 2-102139 and 2-239127).

In the invention described in Japanese Patent Application Laid-Open No. 2-102139, an OH group concentration distribution in which a minimum concentration area of OH groups exists in the central portion of the glass and the concentration gradually increases as approaching the peripheral portion. To form At this time, the refractive index distribution caused by the OH group concentration distribution has a local maximum value at the center portion, and has a distribution (hereinafter, referred to as a convex distribution) that decreases as approaching the peripheral portion. On the other hand, a refractive index distribution is formed by selecting a heat treatment condition so as to cancel the refractive index distribution caused by the OH group concentration distribution. In other words, after heating to a temperature in the range of 800 to 1300 ° C. for a predetermined time, the virtual temperature distribution is controlled by a method of gradually cooling at a predetermined speed, and has a local minimum value caused by the virtual temperature distribution, A refractive index distribution (hereinafter, referred to as a concave distribution) that increases as approaching is formed.
By forming the refractive index distribution caused by such contradictory impurity concentrations and the refractive index distribution caused by the virtual temperature distribution, a synthetic quartz glass for optics having a small overall refractive index distribution and good quality is obtained. It is described in the publication that this is possible.

In the invention described in Japanese Patent Application Laid-Open No. 2-239127, the refractive index distribution caused by the OH group concentration and the chlorine concentration is set as a convex distribution, and the convex refractive index distribution is canceled. It is described that by controlling a virtual temperature distribution, a concave refractive index distribution is formed, the refractive index distribution is reduced overall, and a synthetic quartz glass for optics of good quality can be obtained.

However, as described above, the OH group concentration and the chlorine concentration in the synthetic quartz glass manufactured by the ordinary method are more likely to remain in the interior of the glass lump. The concentration gradually decreases as approaching the peripheral portion, and the refractive index distribution caused by the OH group concentration distribution and the chlorine concentration distribution becomes concave. Therefore, it is difficult to form an OH group concentration distribution and a chlorine concentration distribution having a minimum value in the central portion of the glass lump, and it is more difficult to control the concentration distribution. The method is not a practical method, and even if it can be manufactured, there is a problem that the equipment cost is very high because of the equipment cost.

[0013] On the other hand, the decrease in transmittance caused by the laser light irradiation is considered to be one of the causes of oxygen excess defects, oxygen deficiency defects, chlorine and the like contained in the synthetic quartz glass material for optics. Although depending on the manufacturing conditions of the synthetic quartz glass material for optical use, the manufactured synthetic quartz glass material for optical use is usually used as it is, and thus has a problem that the transmittance is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a uniform refractive index, has no refractive index distribution, and has almost no decrease in transmittance even when irradiated with laser light or the like. It is intended to provide a material and a method for producing the same.

[0015]

In the synthetic quartz glass material for optics according to the present invention, there is a region where the OH group concentration is maximized in the center portion, and O is gradually increased from the region toward the peripheral portion.
The H group concentration gradually decreases, and the refractive index distribution based on the distribution of the OH group concentration and the internal virtual temperature are higher than the surrounding virtual temperature.
Internal refractive index due to low virtual temperature distribution
Large refractive index distribution and is formed than the rate, 5 × 1 hydrogen
0 ¹⁵ It is characterized in containing ^{~1 × 10 19 mol / cm 3} .

The method for producing a synthetic quartz glass material for optics according to the present invention is the method for producing a synthetic quartz glass material for optics, wherein a region where the OH group concentration is maximum exists in a central portion. The OH group concentration gradually decreases toward the peripheral portion around the region, and the refractive index distribution based on the distribution of the OH group concentration and the virtual temperature inside are lower than the virtual temperature around. And the internal refractive index is
The synthetic quartz glass material for optics having a large refractive index distribution is doped with hydrogen by performing a heat treatment at 610 to 790 ° C. in a hydrogen gas atmosphere of 1 × 10 ³ to 1 × 10 ⁶ Pa. It is characterized by:

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the synthetic quartz glass material for optics according to the present invention, first, there is a region where the OH group concentration is maximum in the center portion, and the region is centered on the peripheral portion. The imaginary OH group concentration gradually decreases, and the internal virtual
Due to the virtual temperature distribution where the temperature is lower than the surrounding virtual temperature
Thus, a refractive index distribution in which the internal refractive index is larger than the surrounding refractive index is formed.

The synthetic quartz glass material for optics is usually V
It is produced by an AD method or a direct synthesis method. In any of the above-mentioned methods, usually, silicon tetrachloride is produced by hydrolysis using an oxygen-hydrogen flame, so that a Si-OH group is formed partially and chlorine remains, but the production method The degree varies greatly.

First, an optical synthetic quartz glass material manufactured by the VAD method will be described. In the VAD method, first, a porous synthetic quartz glass, a so-called soot body, is formed. Therefore, when densification is performed by performing various heat treatments, the OH group concentration and its distribution can be controlled. Although a detailed description of the manufacturing method will be described later, a region where the OH group concentration has a maximum value is formed in the central portion of the cylindrical optical synthetic quartz glass material by this manufacturing method, and the peripheral portion is centered on the region. , The distribution of the OH group concentration is gradually reduced.

In this case, the difference between the maximum value and the minimum value of the OH group concentration is preferably 45 ppm or less, and 30 pp.
m or less is more preferable. In order to obtain such a difference in the OH group concentration, it is desirable that the maximum value of the OH group concentration is about 60 ppm or less. However, even when the OH group concentration is 60 ppm or more, the difference is preferably in the range of 45 ppm. The value is not particularly limited.

When the difference between the maximum value and the minimum value of the OH group concentration is about 45 ppm, the fluctuation range (Δn) of the refractive index is about 4.5.
If it is larger than × 10 ⁻⁶ , it becomes difficult to cancel the refractive index distribution based on the distribution of the OH group concentration by adjusting the virtual temperature distribution.

The optical synthetic quartz glass material according to the present invention comprises:
The internal refractive index is larger than the surrounding refractive index due to the virtual temperature distribution where the internal virtual temperature is lower than the surrounding virtual temperature so as to cancel the refractive index distribution based on the OH group concentration distribution.
A sharp refractive index distribution is formed, but after the vitrification, or after once cooling, the temperature is raised to a temperature of 1500 ° C. or higher, and only after heating, or after heat molding, etc., the cooling rate is reduced. By adjusting, the virtual temperature distribution can be adjusted. The method of adjusting the virtual temperature distribution will be described later.

The optical synthetic quartz glass material thus obtained is excellent in homogeneity and has a very small refractive index variation width (Δn). The variation width (Δn) of the refractive index varies depending on the size, for example, the diameter is about 200 to 300 mm.
The fluctuation width (Δn) of the refractive index is about 1 × 10 ⁻⁶ even in a large size having a length of about 60 to 150 mm.
Less than and small. If the size is smaller than the above size, the fluctuation range of the refractive index is naturally smaller than about 1 × 10 ⁻⁶ and the birefringence is also about 3 nm / cm or less.

Further, since the synthetic quartz glass material for optics has such homogeneity, it is at least one-way stria-free and, depending on the manufacturing conditions, a three-way stria-free and extremely excellent in homogeneity. Become.

The optical synthetic quartz glass material according to the present invention comprises:
The soot body obtained is clarified through pre-calcination, calcination, temperature rise, and a process similar to the process of transparency, and the OH group concentration distribution becomes inflection point by such a continuous treatment. Do not have.

The concentration of chlorine can be removed to a considerable extent by heat treatment after the formation of the soot body. The final concentration of the synthetic quartz glass material is preferably 10 ppm or less, and more preferably 1 ppm or less. Is more preferable. The difference between the maximum value and the minimum value of the chlorine concentration is 1
It is preferably at most ppm. Chlorine concentration is 10pp
m, the difference between the maximum and minimum values of chlorine concentration is 1p
pm or less in some cases. If the difference between the maximum value and the minimum value of the chlorine concentration exceeds 1 ppm, the non-uniformity of the chlorine concentration affects the refractive index, and it is difficult to keep the refractive index small.

The metal impurities are greatly affected by the content of the metal impurities in the raw material, and are not significantly affected by the production method itself. Therefore, in any of the manufacturing methods, the total content of metal impurities in the synthetic quartz glass material for optics is 0.1%.
15 ppm or less, the content of Al is 0.01 ppm
Hereinafter, each content of Na, K, and Li is 0.02 ppm.
Hereinafter, Ca, Fe, Ti, Cr, Ni, P, B, Mg,
It is preferable that each content of Cu, Zr, and Zn is 0.008 ppm or less.

Next, an optical synthetic quartz glass material manufactured by a direct method will be described.

[0029] In the direct method, the oxygen-
It is produced by hydrolysis using a hydrogen flame, and the silica particles generated at that time are deposited on a substrate to directly produce a transparent synthetic quartz glass ingot. Therefore, unlike the case of the VAD method, the OH group and the like cannot be removed in the process up to the transparency, so that the concentration of the OH group is extremely higher than that of the VAD method. Therefore, the OH group concentration distribution is adjusted by adjusting the flow rates of oxygen, hydrogen, and the like during the hydrolysis.

The concentration of the OH group in the optical synthetic quartz glass material thus manufactured is usually from 600 to 1000.
ppm, and a preferable maximum value of the OH group concentration is about 800 ppm. The difference between the maximum value and the minimum value of the OH group concentration is the same as in the case of the VAD method.

When the OH group concentration exceeds about 800 ppm, the dispersion of the OH group concentration in the quartz glass increases, and O
It tends to be difficult to control the difference between the maximum value and the minimum value of the H group concentration to 45 ppm or less.

The chlorine concentration is usually 20 to 100 p
pm and the chlorine concentration is preferably as low as possible, but the minimum value is about 20 ppm. As described above, the impurity concentrations of OH groups and chlorine are different from those of the VAD method, but other characteristics are the same as those of the synthetic quartz glass in the case of the VAD method. In order to make the refractive index uniform, the difference between the maximum value and the minimum value of the chlorine concentration is preferably less than 1 ppm. However, when the chlorine concentration in the manufactured optical synthetic quartz glass material is high, defects are easily generated due to transmission of laser light and the like, so that the concentration is preferably as low as possible. The obtained synthetic quartz glass material for optics is more preferable.

In addition, hydrogen is contained in the synthetic quartz glass material for optics in order to prevent problems such as light absorption and fluorescence emission due to the occurrence of defects in the glass structure during laser irradiation as described later. 5 × 10 ¹⁵ to 1 × 10 ¹⁹ mo
l / cm ³ . As described in Japanese Patent Application No. 6-216233 previously filed by the inventor of the present application, 合成 Si—O ° (non-bonded oxygen) defects and ≡Si ・ (E '
Although a defect such as a center) defect is likely to be generated, if hydrogen (H ₂ molecule or H atom), particularly molecular hydrogen (H ₂ molecule), is dissolved in an appropriate amount in the synthetic quartz glass, among the above defects during laser beam irradiation, In particular, non-oxygen bond defects can be suppressed. Its preferred H ₂ molecular content of 10 ¹⁵ to 10 ¹⁸
In order to obtain about 1 / cm ³ , the hydrogen content is 5 × 1
About 0 ¹⁵ to 1 × 10 ¹⁹ mol / cm ³ is required. The non-bonded oxygen vacancies can be reduced to a minimum concentration by producing a synthetic quartz glass material under the above conditions.

The hydrogen content is 5 × 10 ¹⁵ mol / c
If it is less than m ³ , a defect or the like is likely to be generated upon irradiation with a laser beam or the like, and the transmittance tends to decrease significantly, while the hydrogen content is 1 × 10 ¹⁹ mol / cm ^3.
Exceeds, the content of atomic hydrogen (H atom) increases,
Upon irradiation with laser light, the reaction of the following chemical formula 1 proceeds and E '
Central defects are easily generated.

[0035]

## STR1 ## Next, a method of manufacturing a synthetic quartz glass material for optics having such characteristics will be described. First, the optics by the VAD method is described. A method for producing a synthetic quartz glass material for use will be described.

As described above, examples of the high-purity silicon compound as a raw material include silicon tetrachloride.
The total content of metal impurities in the raw material is 0.05 ppm or less, the content of Al is 0.005 ppm or less, Na, K,
And Li content is 0.008 ppm or less, Ca, F
It is preferable that each content of e, Ti, Cr, Ni, P, B, Mg, Cu, Zr, and Zn is 0.003 ppm or less.

The concentration of impurities in the raw material is determined by
It can be measured by heating to about 1000 ° C. in a furnace to deposit on a substrate, and analyzing the amount of metal impurities in the deposited metallic silicon by activation analysis.

In the synthesis of the porous synthetic quartz glass, no special conditions are required, and the hydrolysis may be performed by a usual oxyhydrogen flame.

Next, the porous synthetic quartz glass (soot body) obtained in the above process is subjected to a heat treatment or the like under vacuum to produce an optical synthetic quartz glass material. The process includes the steps of manufacturing a synthetic quartz glass base material by pre-calcining, calcining, heating, and clearing, and processing and the like using the base material, followed by heat molding, cooling, and soaking. And production of synthetic quartz glass products by cooling and cooling.

The voids of the soot body obtained by hydrolysis of the silicon compound have a non-uniform distribution, many voids in the peripheral portion, and the number of voids gradually decreases toward the center. , Getting bigger toward the center.

Therefore, by the above-mentioned preliminary calcination, an operation of concentrating other parts mainly on the part having the lowest density around the soot body to increase the density, that is, performing baking, is performed.
Uniform density of soot body. By this pre-calcination,
The dehydration effect due to the slow sintering in the subsequent step of calcination can be made to proceed almost uniformly throughout the soot body, and the OH in the synthetic quartz glass after vitrification becomes transparent.
The base concentration can be set to have a desired distribution.

The heating at this time is preferably carried out under a pressure of about 1.5 to 50 Pascal at about 1300 to 1400 ° C. for 1 to 5 hours, and at a temperature slightly higher than the calcination performed later, for a short time. When the temperature of the pre-calcination is less than about 1300 ° C,
The baking effect of the pre-calcination is small, while about 13
If the heating time exceeds 5 hours even at a low temperature of 00 ° C., not only the peripheral portion where the density of the soot body is low, but also the entire soot body is slowly baked, so that the target soot body density tends to be hardly uniform. . The pre-calcination temperature is about 1
When the temperature exceeds 400 ° C., the shrinkage of the voids rapidly progresses, and especially the baking of the soot body peripheral portion progresses rapidly. Synthetic quartz glass cannot be obtained. On the other hand, even at a high temperature of 1400 ° C., if the heating time is less than 1 hour, the baking effect cannot be obtained, and the density of the soot body cannot be made uniform.

If the pressure during the preliminary calcination is less than about 1.5 Pascal, oxygen is more likely to escape from the quartz glass during heating, thereby causing oxygen deficiency defects and causing ultraviolet and vacuum ultraviolet light. If the pressure during the preliminary calcination exceeds about 50 Pascal, the effect of baking the soot body is small, and it is difficult to make the density of the soot body uniform.

Thereafter, the calcination is performed for about 1 hour under the same vacuum conditions.
The reaction is carried out at 200 to 1300 ° C. for about 10 to 40 hours, and the Si—OH partially contained in the fine silica glass particles in the soot body is converted to
Change to i-O-Si or vaporize and degas attached water,
The water generated at that time is removed and dehydrated. Further, the distribution of the OH group concentration in the soot body is adjusted by this calcining treatment. If the calcination temperature is less than about 1200 ° C., the removal of water proceeds only slowly, the OH group concentration does not sufficiently decrease, and the concentration distribution cannot be adjusted well. On the other hand,
When the temperature of the calcination exceeds 1300 ° C., densification occurs before moisture is sufficiently removed from the inside, so that a high concentration of OH groups also remains.

By this calcination, the OH group concentration distribution is such that the OH group concentration is higher as approaching the central portion, there is a portion where the OH concentration reaches a maximum value in the central portion, and conversely, the concentration decreases toward the peripheral portion. Is formed.

It is also possible to carry out only calcination without pre-calcination. In this case, heat treatment is carried out at a temperature of about 1200 to 1400 ° C. for 10 to 40 hours under the same vacuum conditions as described above. Do.

The calcination under the above-mentioned conditions makes the density uniform and the removal of moisture simultaneously. However, compared to the two-stage heating of the preliminary calcination and the calcination, the density uniformity is completely advanced. It is difficult, and the time of the transparency processing may be long.

Subsequently, the calcined quartz glass was heated under the same vacuum conditions to raise the temperature at 0.5 to 5 ° C./min.
The clearing process is performed in a temperature range of about 1240 to 1600 ° C. for 3 to 8 hours. If the temperature for the transparentization is less than about 1420 ° C., the densification hardly proceeds and the productivity is deteriorated. On the other hand, if the temperature for the transparentization exceeds about 1600 ° C., the cost increases due to power consumption.

After the above step, the optically cooled synthetic quartz glass base material is manufactured by slow cooling at about 0.5 to 5 ° C./min. In addition, the temperature of the said transparentization is 1500 degreeC or more, and about 0.5-5 degreeC after this process.
Since the base material gradually cooled under the conditions of / min satisfies the fictive temperature condition described later,
It is also possible to obtain a product of synthetic quartz for optics by performing cold working such as cutting to make it a predetermined size.

Then, the base material of the synthetic quartz glass material for optics is heated and formed under the following conditions, cooled slowly, and then cut to a predetermined size to produce a product. Of course, it is also possible to continue the treatment under the following conditions at a high temperature without cooling the obtained base material of the synthetic quartz glass material for optics.

At this time, the above-mentioned base material is added to about 1600 to 20
It is heated to a temperature of 00 ° C. and pressed using a mold made of, for example, high-purity carbon to form a large-sized lens, mirror, window member or other optical member. The molded optical synthetic quartz glass is temporarily
Cooling is performed to about 1500 to 1600 ° C. at a rate of 30 ° C./min, and a soaking process is performed in which the temperature is kept at 0 to 10 hours. Here, in the case of 0 hour, the temperature equalization process is not strictly performed, and only the cooling rate is switched at this temperature. I do.

If the temperature of the soaking treatment is less than about 1500 ° C., the temperature before the slow cooling is too low, so that it is difficult to form the following virtual temperature distribution.

After the temperature equalization treatment, the fictive temperature distribution of the synthetic quartz glass material for optics is adjusted by cooling at a temperature of less than 5 ° C./min, preferably 0.1 to 4 ° C./min.

The characteristics such as the density and refractive index of quartz glass at room temperature reflect the heat history of the glass in the high temperature range in the past manufacturing process and the cooling process from the high temperature range to room temperature. Virtual temperature (Fictive Temperatu
re) means the temperature at which the glass has been adapted in the past thermal history, that is, the temperature at which the above characteristic values have been determined (R. Bruckner, J. Non-Crystaline Solids,
5,1970, pp.133-134). This concept of virtual temperature is a concept that applies not only to quartz glass but also to glass in general.
To put it more simply, it means that the characteristic values such as the glass density and the refractive index at room temperature are the characteristic values in the equilibrium state of the glass at the virtual temperature (higher than room temperature).

FIG. 1 is a graph showing the relationship between the temperature and the density of the quartz glass described in the above-mentioned publication and how the density changes during cooling. The temperature t shown by g ^s and g ^t is shown in FIG.
Indicates the glass transition temperature for slow cooling and the glass transition temperature for fast cooling, respectively.

According to R. Bruckner described above, as shown in FIG. 1, quartz glass has a minimum density at about 1500 ° C. and cools from a temperature higher than 1500 ° C.
It is known that the state of distribution of density in quartz glass differs between when cooling from a temperature lower than 1500 ° C.
That is, when cooling from a temperature lower than 1500 ° C., the surroundings are cooled faster because the surroundings are cooled faster, and when cooling from a temperature higher than 1500 ° C., the surroundings are cooled. Cooling faster than inside is the same as in the above case, but the density is lower around the periphery than inside. Refraction correlated with density
The index also produces a distribution similar to the density, and measuring the density makes it possible to identify the refractive index distribution due to the fictive temperature, but, as in the case of the present invention, about 150 μm.
When cooled from a temperature higher than 0 ° C., the inside virtual temperature distribution is lower than the surrounding virtual temperature distribution, and the inside density is larger than the surrounding density, that is, the inside has a higher refractive index than the surroundings. Since a high distribution is generated and the refractive index distribution is opposite to the refractive index distribution generated by the OH group concentration distribution, fluctuations in the refractive index of each other are canceled out, and a very uniform refractive index distribution can be formed.

In the case of the direct method, as described above, silica particles are directly deposited on a base by hydrolysis of silicon tetrachloride to produce a transparent ingot. Therefore, VA
Although it is not necessary to perform a treatment such as calcination until the transparent glass is obtained as in the case of the method D, the distribution of the OH group concentration and the chlorine concentration cannot be adjusted by the above process instead. Therefore, the distribution of the OH group concentration, the chlorine concentration, and the like are controlled by setting the temperature of the oxygen-hydrogen flame and the flow ratio of oxygen to hydrogen to predetermined values when performing the hydrolysis.

The cooling of the ingot produced in the case of the direct method is usually performed under the condition of cooling in the furnace which is close to the air-cooled state, since the heating furnace is open-to-atmosphere, and it is difficult to control the cooling rate. is there. Therefore, in the base material of the synthetic quartz glass material manufactured by the direct method, the virtual temperature distribution described later is not formed in the state of the heat history as it is. Therefore, in the case of the direct method, it is necessary to perform heating again and perform cooling or formation and cooling described later to form a virtual temperature distribution. The conditions such as heating, molding, and cooling in this case are the same as in the case of the above-described VAD method.

As described above, the manufacturing process of the synthetic quartz glass material for optics or the synthetic quartz glass material for optics (hereinafter, also referred to as the synthetic quartz glass material for optics including both) is performed by
The internal refractive index is larger than the surrounding refractive index due to the virtual temperature distribution where the internal virtual temperature is lower than the surrounding virtual temperature so as to cancel the refractive index distribution based on the distribution of the OH group concentration.
A sharp refractive index distribution can be formed, and it becomes possible to manufacture a synthetic quartz glass material for optics having a very small fluctuation range of the refractive index.

Next, the thus-produced synthetic quartz glass material for optics is doped with hydrogen by heating at 610 to 790 ° C. in a hydrogen gas atmosphere of 1 × 10 ³ to 1 × 10 ⁶ Pa.

When the hydrogen gas atmosphere exceeds 1 × 10 ⁶ Pa, the rate of hydrogen doping is too fast to control the doping amount. On the other hand, when the hydrogen gas atmosphere is less than 1 × 10 ³ Pa, volatilization of the dissolved hydrogen gas is difficult. Accelerated and difficult to dope.

When the heating temperature exceeds 790 ° C., the ratio of (atomic hydrogen / molecular hydrogen) in the doped hydrogen increases, and the doping amount of molecular hydrogen effective for improving the laser light resistance is reduced. If the heating temperature is lower than 610 ° C., the doping speed is too slow and the doping time is too long. Since heating in a temperature range of 610 to 790 ° C. is relatively low, it does not change the virtual temperature distribution in the quartz glass generated in the previous step.

According to the synthetic quartz glass material for optics according to the present invention, there is a region where the OH group concentration is maximum at the center portion, and the OH group concentration gradually decreases around the region toward the peripheral portion, The internal virtual temperature is changed to the surrounding virtual temperature so as to cancel the refractive index distribution based on the OH group concentration distribution.
Internal refractive index due to virtual temperature distribution lower than
Since a refractive index distribution larger than the surrounding refractive index is formed and hydrogen is contained at 5 × 10 ¹⁵ to 1 × 10 ¹⁹ mol / cm ³ , the refractive index of the whole inside of the synthetic quartz glass material for optics is extremely low. In addition to being uniform, defects and the like hardly occur even by continuous irradiation with a laser beam or the like, and light transmittance is excellent without a decrease in transmittance.

In the method of manufacturing an optical synthetic quartz glass material according to the present invention, there is a region where the OH group concentration is maximized in the center portion, and O is gradually increased from the region toward the peripheral portion.
As the H group concentration gradually decreases and the refractive index distribution based on the OH group concentration distribution is cancelled, the internal virtual temperature increases
Internal refraction due to virtual temperature distribution lower than virtual temperature
1 × 10 ³ to 1 × 10 ³ for an optical synthetic quartz glass material having a refractive index distribution whose refractive index is larger than the surrounding refractive index.
^Since hydrogen is doped by performing heat treatment at 610 to 790 ° C. in a hydrogen gas atmosphere of ⁶ Pa, the refractive index of the entire inside is extremely uniform, and defects are generated even by continuous irradiation with laser light or the like. It is possible to produce a synthetic quartz glass material for optical use which is difficult to reduce the transmittance and has excellent light resistance.

[0065]

EXAMPLES AND COMPARATIVE EXAMPLES Hereinafter, a synthetic quartz glass material for optics and a method for producing the same according to examples of the present invention will be described.

[Examples 1 to 13 and Comparative Examples 1 to 14]
A porous synthetic quartz glass base material (soot body) was synthesized by the AD method.

Using silicon tetrachloride (SiCl ₄ ), which is a high-purity silicon compound, as a raw material, quartz glass fine particles are synthesized by a gas phase chemical reaction in an oxygen-hydrogen flame, and the quartz glass fine particles are adhered and deposited around a seed rod. Porous synthetic quartz glass (soot body) was synthesized.

Next, the synthesized porous synthetic quartz glass was preliminarily calcined, calcined, heated, transparentized, and cooled under the conditions shown in Table 1 to produce an optical synthetic quartz glass base material. did.

Next, the synthetic quartz glass base material for optics manufactured in the above process is cut, processed, etc., and the obtained members are heated, formed, and uniformly heated under the forming conditions shown in Table 1. After performing the warming process, cooling was performed at the rate shown in Table 1 to form a virtual temperature distribution. Next, using the synthetic quartz glass material for optics in which the virtual temperature distribution was formed, hydrogen gas treatment was performed under the conditions shown in Table 1 to dope the synthetic quartz glass material for optics with hydrogen. The properties of the obtained optical synthetic quartz glass product are shown in Table 3 below.

The optical synthetic quartz glass material according to the comparative example, in which the refractive index fluctuation width (Δn) is larger than that of the optical synthetic quartz glass material according to the example, is also manufactured under the conditions for manufacturing the optical synthetic quartz glass material. Tables 2 and 4 show the heat molding conditions, hydrogen doping conditions and product characteristics.

The virtual temperature was determined by a method using an infrared spectrophotometer proposed by KDavis et al.
and M. Tomozawa New Glass Forum 1993 4th Silica Glass Workshop pp. 215-255 199
The refractive index fluctuation width (Δn)
About the Fizeau type interferometer manufactured by Zygo (Mar
k-IV), and the birefringence is measured by a high-sensitivity birefringence measuring device (ADR-30) manufactured by Oak Manufacturing Co., Ltd.
0). Regarding the amount of hydrogen gas released, mass spectrometry of the amount of released gas proposed by Morimoto et al. (Yukihiro Morimoto et al. Journal of the Illuminating Engineering Institute of Japan Tokyo Section 16-25)
1989) and laser Raman scattering measurement.

[Examples 14 to 17 and Comparative Examples 15 to 1]
8] Next, a transparent synthetic quartz glass base material for optics was produced directly by a direct method.

First, silica glass fine particles were synthesized by a gas phase chemical reaction in an oxygen-hydrogen flame using silicon tetrachloride (SiCl ₄ ), which is a high-purity silicon compound, and deposited on a base. A synthetic quartz glass base material was manufactured.

At this time, the impurity concentration of silicon tetrachloride is about 0.01 ppm or less, the impurity concentration in hydrogen gas is about 50 ng / Nm ³ or less, and the impurity concentration in oxygen gas is about 50 ng / Nm ³ or less. Was. The analysis of impurities in the hydrogen gas or oxygen gas was performed by bubbling a gas through a nitric acid solution, injecting the solution into a high frequency inductively coupled plasma (ICP) mass spectrometer, and measuring each element. The lower limit of measurement is approximately 0.02 to 0.005 ng /
It is about Nm ³ .

Next, the synthetic quartz glass base material for optics manufactured in the above process is cut, processed, etc., and the obtained members are heated, formed, and soaked under the heat forming conditions shown in Table 5. After the heat treatment, a fictive temperature distribution was formed by cooling at a rate of less than 5 ° C./min. Next, using the synthetic quartz glass material for optics in which the virtual temperature distribution was formed, hydrogen gas treatment was performed under the conditions shown in Table 5 to dope the synthetic quartz glass material for optics with hydrogen. The properties of the obtained synthetic quartz glass product for optical use are shown in Table 6 below.

The optical synthetic quartz glass material according to the comparative example, in which the refractive index variation distribution (Δn) is larger than that of the optical synthetic quartz glass material according to the example, is also subjected to heat molding conditions, hydrogen doping conditions and products. The characteristics are shown in Tables 5 and 6 below.
Is shown in

[0077]

[Table 1]

[0078]

[Table 2]

[0079]

[Table 3]

[0080]

[Table 4]

[0081]

[Table 5]

[0082]

[Table 6]

As is clear from the results shown in Table 3 above, there is a region where the OH group concentration has a maximum value in the central portion of the synthetic quartz glass product for optics according to the example. The OH group concentration gradually decreases as going to the part, and there is a concentration distribution with the minimum concentration at the wall part,
The internal virtual temperature is lower than the surrounding virtual temperature so as to cancel the refractive index fluctuation distribution based on the OH group concentration distribution (refractive index fluctuation width Δn: 1.0 × 10 ^{−6 to} 5.0 × 10 ⁻⁶ ). Due to the low virtual temperature distribution, the internal refractive index is higher than the surrounding refractive index.
Also large refractive index distribution Ri (refractive index fluctuation width [Delta] n: -1.5 ×
10 ⁻⁶ to −4.5 × 10 ⁻⁶ ), the refractive index of the entire inside of the synthetic quartz glass material for optics is extremely uniform (refractive index variation Δn ≦ 0.9 × 10 ⁻⁶ ). become. Further, the birefringence is extremely small at 3 nm / cm or less, and the material is free from striae in three directions and excellent in homogeneity. further,
The metal impurity content of the synthetic quartz glass product for optics according to the example is less than 0.15 ppm as a total amount,
The content of each metal impurity is such that the content of Al is 0.01 ppm.
Hereinafter, each content of Na, K, and Li is 0.02 ppm.
Hereinafter, Ca, Fe, Ti, Cr, Ni, P, B, Mg,
Each content of Cu, Zr, and Zn was 0.008 ppm or less. In addition, the concentration of chlorine was less than 1 ppm for those manufactured by the VAD method, and 20 to 40 ppm for those manufactured by the direct method, and the difference in concentration between the maximum value and the minimum value was less than 1 ppm. The impurity concentration in this synthetic quartz glass product for optics was measured by a plasma emission (ICP) analysis method and an activation analysis method.

Further, the synthetic quartz glass material for optics according to the examples contains 5 × 10 ¹⁵ to 1 × 10 ¹⁹ mol / cm ^{3 of} hydrogen, so that it has excellent resistance to laser and at least K
rF light laser (wavelength: 248 nm) is about 400 mJ /
Even when irradiation was performed at 1 × 10 ⁶ shots or more at an irradiation light energy density of cm ^2, the internal transmittance at 248 nm was less than 0.5%.

On the other hand, in the synthetic quartz glass product for optics according to the comparative example, the difference in concentration between the maximum value and the minimum value of the OH group is too large, or the fluctuation distribution of the refractive index formed by the OH group concentration distribution. Since the refractive index fluctuation distribution due to the formed virtual temperature distribution is in the form of being added, the entire refractive index fluctuation width is a value exceeding three times the optical synthetic quartz glass product according to the embodiment. I have. If the cooling rate after the temperature equalization is too fast, the birefringence is 10%.
The anisotropy is large at nm / cm or less. further,
About KrF laser is about 400
By irradiating 1 × 10 ⁶ shots at an irradiation light energy density of mJ / cm ² , there is a case where the internal transmittance is reduced by 0.5% or more, and the laser resistance is poor.

[0086]

As described in detail above, in the synthetic quartz glass material for optics according to the present invention, there is a region where the OH group concentration is maximum at the center portion, and the region goes to the peripheral portion around this region. OH group concentration decreases gradually in accordance with the so as to cancel the refractive index distribution based on the OH group concentration distribution, the interior of the virtual
Due to the virtual temperature distribution where the temperature is lower than the surrounding virtual temperature
A refractive index distribution in which the internal refractive index is larger than the surrounding refractive index is formed, and hydrogen is supplied in an amount of 5 × 10 ¹⁵ to 1 × 10 ¹⁹ mol / c.
Since m ³ contains, it is possible to very the refractive index of the entire inner optical synthetic silica glass material uniform, continuous even transmittance by irradiation of a laser beam or the like is excellent in light resistance does not decrease Things.

In the method for producing a synthetic quartz glass material for optics according to the present invention, there is a region where the OH group concentration is maximum in the center portion, and the O.sub.
As the H group concentration gradually decreases and the internal refractive index distribution based on the OH group concentration distribution cancels out ,
Internal refraction due to virtual temperature distribution lower than virtual temperature
1 × 10 ³ to 1 × 10 ³ for an optical synthetic quartz glass material having a refractive index distribution whose refractive index is larger than the surrounding refractive index.
^Since hydrogen is doped by performing heat treatment at 610 to 790 ° C. in a hydrogen gas atmosphere of ⁶ Pa, the refractive index of the entire inside is extremely uniform, and the transmittance is reduced even by continuous irradiation with laser light or the like. An optical synthetic quartz glass material having excellent light resistance is manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the temperature and the density of quartz glass and how the density changes during cooling.

Continuation of the front page (72) Inventor Tetsuyuki Nakamura 1 Higashi-Mukojima Higashinoshima-cho, Amagasaki-shi, Hyogo Sumikin Quartz Co., Ltd. (56) References JP-A-5-24856 (JP, A) JP-A-3-88743 (JP JP-A-3-109233 (JP, A) JP-A-3-23236 (JP, A) JP-A-3-52722 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB Name) C03C 1/00-14/00 C03B 8/04 C03B 20/00

Claims (2)

(57) [Claims] 1. A region where the OH group concentration is maximum exists in a central portion, and the OH group concentration increases from the region toward the peripheral portion.
The base concentration gradually decreases, and the refractive index distribution based on the distribution of the OH group concentration and the internal virtual temperature are lower than the surrounding virtual temperature.
The internal refractive index is the surrounding refractive index
The refractive index distribution is greater than the formation, 5 × 10 hydrogen
An optical synthetic quartz glass material characterized by containing ¹⁵ to 1 × 10 ¹⁹ mol / cm ³ . 2. A region where the OH group concentration is maximum is present in the center portion, and the OH group concentration is increased from the region toward the peripheral portion.
The base concentration gradually decreases, and the refractive index distribution based on the distribution of the OH group concentration and the internal virtual temperature are lower than the surrounding virtual temperature.
The internal refractive index is the surrounding refractive index
The synthetic quartz glass material for optics having a larger refractive index distribution is doped with hydrogen by performing a heat treatment at 610 to 790 ° C. in a hydrogen gas atmosphere of 1 × 10 ³ to 1 × 10 ⁶ Pa. A method for producing a synthetic quartz glass material for optics, comprising: