JP3274955B2 - Method for producing synthetic quartz glass base material for optical components for use in ultraviolet region, and method for producing synthetic quartz glass material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a synthetic quartz glass preform, and more particularly, to a lens, a mirror, a prism, a window member, and the like of an apparatus utilizing light in a wide wavelength range from an ultraviolet region to an infrared region. The present invention relates to a method for producing a synthetic quartz glass base material which is a raw material of a synthetic quartz glass material used for forming the optical component.

[0002]

The present invention relates to processes for the preparation of an optical component for synthetic quartz glass preform, and the optical component of quartz glass material
Regarding the manufacturing method , more specifically, synthesis for optical components in the ultraviolet region used as a raw material of synthetic quartz glass material used for forming optical components such as lenses, mirrors, prisms, and window members of equipment utilizing light in the ultraviolet region. Method for producing quartz glass base material , and synthetic quartz glass material for optical components for use in ultraviolet region
And a method for producing the same .

Utilizing such excellent characteristics, it is used for optical components such as lenses, mirrors, prisms, and window members of devices utilizing light in a wide wavelength range from the ultraviolet region to the infrared region.

[0004] Quartz glass materials used for forming these optical components are required to have various characteristics, but in particular, homogeneity of refractive index and high light resistance at the wavelength used (transmissivity after light irradiation). Is difficult to lower).

[0005] Synthetic quartz glass is an example of quartz glass that 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, depending on the purity of the raw materials and the manufacturing method, there are various grades of impurity element concentration (metal element concentration, non-metal element concentration), defect concentration, and the like in the manufactured synthetic quartz glass. Quartz glass cannot 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 for an optical system. There are various types such as a CVD method, a plasma CVD method, and a gas phase axial method (VAD method). The impurities such as metals, OH groups, Cl, H ₂ , O
_2. Concentrations of oxygen excess defects, oxygen deficiency defects, ring structure defects, etc. are different. It is known that the concentration of these impurities and defects has a great influence on optical characteristics such as light absorption, fluorescence and refractive index of synthetic quartz glass.

[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 a porous synthetic quartz glass, and then heated to be transparent and vitrified.However, when silicon tetrachloride is used as a silicon compound, chlorine or OH groups are used. And the like remain in the synthetic quartz glass, the concentration of which tends to be non-uniform, and there is a problem in that the refractive index and the like are distributed due to 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 caused by the distribution of the OH group and the refractive index distribution caused by the slow cooling after the vitrification of the transparent glass overlap, 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 resulting from 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 in that the equipment itself becomes expensive, and thus the synthetic quartz glass obtained becomes very expensive.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an optical section for use in an ultraviolet region capable of obtaining a synthetic quartz glass having a uniform refractive index and almost no refractive index distribution.
For manufacturing synthetic quartz glass base material for products and applications in the ultraviolet region
It is an object of the present invention to provide a method for producing a synthetic quartz glass material for an optical component .

[0014]

SUMMARY OF THE INVENTION According to the present invention, there is provided a light source for use in an ultraviolet region.
The production method of the synthetic quartz glass preform for optical parts is to add a porous synthetic quartz glass formed by a gas phase axial method under a pressure of 1.5 to 50 Pascal as a preliminary calcination step.
A heat treatment is performed at 300 to 1400 ° C. for 1 to 5 hours to homogenize the density.
After removing water and the like by heating at a temperature of 00 to 1300 ° C. for 10 to 40 hours, the temperature is increased at a rate of 0.5 to 5 ° C./min, and a clearing step is further performed to form a transparent glass. I have. In addition, according to the present invention, there is provided an optical component for an ultraviolet region.
The method for producing synthetic quartz glass material is as described above for synthetic quartz for optical parts.
Synthetic quartz glass manufactured by the method of manufacturing a glass base material
The base material is formed by heating to a temperature of 1600 to 2000 ° C.
After that, cool to a temperature of 1500 to 1600 ° C and equalize the temperature.
Then, from a temperature of at least 1500 ° C., 5 ° C. /
Cooling at a rate of less than 1 minute, and then 1 × 10 ³ -1 × 10 ⁶
Heat at 610-790 ° C under Pascal's hydrogen gas atmosphere
Is characterized by doping with hydrogen
You.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, as a high-purity silicon compound to be used as a raw material, for example, silicon tetrachloride can be mentioned, and 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, N
each content of a, K, and Li is 0.008 ppm or less;
Ca, Fe, Ti, Cr, Ni, P, B, Mg, Cu,
It is preferable that each content of 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 the 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 hydrolysis may be carried out using a normal oxyhydrogen flame by a gas phase axial method.

Next, the synthetic quartz glass material is manufactured by subjecting the porous synthetic quartz glass (soot body) obtained in the above process to a heat treatment or the like under vacuum. Calcination, calcination, temperature rise, and the manufacturing process of the synthetic quartz glass base material by the process of transparency, and after performing processing and the like using the base material, heat forming, cooling, soaking,
It is divided into a step of manufacturing a synthetic quartz glass product by cooling.

The voids in 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 decreases gradually toward the center. , Getting bigger toward the center.

Therefore, in the pre-calcining step, an operation of rapidly increasing the density of the portion having the lowest density around the soot body as compared with the other portions, that is, baking is performed to make the density of the soot body uniform. To By this preliminary calcination, the dehydration effect of the slow sintering in the subsequent calcination step can be made to proceed almost uniformly throughout the soot body, and the OH group concentration in the synthetic quartz glass after vitrification becomes transparent. Can be set to have a desired distribution.

The heating at this time is preferably carried out at 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 particularly, the baking of the peripheral portion of the soot body rapidly progresses, so that the surface layer portion becomes transparent vitrified, and the subsequent calcining and clearing process are sufficient. A desired synthetic quartz glass cannot be obtained because a dehydration effect 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 smaller than about 1.5 Pascal, oxygen tends 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 calcining, the OH group concentration increases as approaching the central portion, there is a portion where the OH concentration reaches a maximum value in the central portion, and conversely, the OH group concentration decreases toward the peripheral portion. A distribution is formed.

Next, the calcined quartz glass is heated under the same vacuum condition to increase the temperature at a rate of 0.5 to 5 ° C./min. The clearing process is performed in the temperature range for 3 to 8 hours. When the temperature for the transparency is less than about 1420 ° C., the densification hardly proceeds and the productivity is deteriorated, while the temperature for the transparency is about 1600 ° C.
Exceeding the cost increases due to power consumption.

After the above step, the transparent synthetic quartz glass base material is manufactured by slow cooling at about 0.5 to 5 ° C./min.

Since the synthetic quartz glass base material produced by the above method has a very small content of metal impurities and the like, it can be used as a normal quartz glass material. However, since the distribution of the refractive index is formed by controlling the distribution of the OH group concentration, the synthetic quartz glass base material has a virtual Preferably, a temperature distribution is formed, whereby a synthetic quartz glass material having a uniform refractive index as a whole can be manufactured.

In this case, first, the synthetic quartz glass base material is heat-molded under the following conditions, cooled slowly, and then cut to a predetermined size to manufacture a product. Of course, it is also possible to perform processing under the same conditions without cooling the obtained synthetic quartz glass base material.

At the time of molding, the above-mentioned base material is
A large lens by heating to a temperature of 000 ° C. and pressing using a mold made of, for example, high-purity carbon,
It is shaped into an optical member such as a mirror or a window member. The molded optical synthetic quartz glass is temporarily
Cooling is performed to about 1500 to 1600 ° C. under the condition of 30 ° C./min, and a soaking process of maintaining the temperature in this temperature range for 0 to 10 hours is performed. 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. However, here, the temperature equalization process is also included including the case of 0 hour. .

If the temperature in the soaking process is lower than about 1500 ° C., the temperature before the slow cooling is too low, so that it is difficult to form a virtual temperature distribution in the state described below.

After the soaking treatment, at least 1500
From a temperature of not less than 5 ° C / min, preferably from 0.1 to
By cooling at a temperature of less than 4 ° C./min, a virtual temperature distribution of the synthetic quartz glass material is formed.

The properties of the quartz glass at room temperature, such as the density and the refractive index, 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).

[0033] Figure 1 is a graph relationship, and showing how the change in density upon cooling the temperature and density of the quartz glass described in the publication, g ^s, the temperature t indicated by g ^t is ,
The glass transition temperature for slow cooling and the glass transition temperature for fast cooling, respectively, are shown.

According to the aforementioned R. Bruckner, 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. The virtual temperature having a correlation with the density also produces the same distribution as the density, and it becomes possible to specify the refractive index distribution caused by the virtual temperature by measuring the virtual temperature. Thus, when cooling from a temperature higher than about 1500 ° C., the internal virtual temperature distribution becomes lower than the surrounding virtual temperature distribution,
A state in which the inner density is larger than the surrounding density, that is, a distribution having a higher refractive index in the inner part than the surroundings is generated, which is opposite to the refractive index distribution caused by the OH group concentration distribution. It is possible to cancel each other out and to form a very uniform refractive index distribution.

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 becomes large, 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.

By the above-described manufacturing process of the synthetic quartz glass material or the synthetic quartz glass product for optical use (hereinafter, also referred to as a synthetic quartz glass material including both), the refractive index distribution based on the distribution of the OH group concentration is canceled. Manufacture of a synthetic quartz glass material that can form a refractive index distribution caused by a virtual temperature distribution, has a very small variation in refractive index, and does not reduce the transmittance of vacuum ultraviolet light to ultraviolet light even by laser irradiation. Becomes possible.

The maximum value of the OH group concentration in the synthetic quartz glass material produced by the above process is preferably about 60 ppm or less, more preferably about 20 to 45 ppm. The difference between the maximum value and the minimum value of the OH group concentration is 45
ppm or less, and more preferably 30 ppm or less.

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 fluctuation distribution of the refractive index based on the distribution of the OH group concentration by adjusting the virtual temperature distribution.

The synthetic quartz glass material for optics thus obtained is excellent in homogeneity and has a very small fluctuation range (Δn) in refractive index. 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 production conditions, it is extremely excellent in three-way stria-free and extremely excellent in homogeneity. Become.

In the synthetic quartz glass material according to the present invention, the obtained soot is made transparent through the steps of preliminary calcination, calcination, temperature rise, and transparency. The distribution of the base concentration has no inflection point.

The chlorine concentration can also be removed to a considerable extent by heat treatment after the formation of the soot body, and 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 largely depend on the content of the metal impurities in the raw material, and are not so much influenced by the production method itself. Therefore, in any of the manufacturing methods, the total content of metal impurities in the synthetic quartz glass material is 0.15 p.
pm or less, the content of Al is 0.01 ppm or less,
Each content of Na, K, and Li is 0.02 ppm or less;
Ca, Fe, Ti, Cr, Ni, P, B, Mg, Cu,
It is preferable that each content of Zr and Zn is 0.008 ppm or less.

In addition, hydrogen is contained in the synthetic quartz glass material for optics in order to prevent problems such as light absorption and fluorescent light emission due to the occurrence of defects in the glass structure upon irradiation with a laser beam as described later. 5 × 10 ¹⁵ to 1 × 10 ¹⁹ mo
l / cm ³ . As described in the specification of Japanese Patent Application No. 6-216233 filed by the inventor of the present application, ≡Si—O ° (non-bonded oxygen) ) Defects and ΔS
Defects such as i · (E ′ center) defects are easily generated,
Hydrogen (H ₂ molecule or H atom) in synthetic quartz glass,
In particular, when an appropriate amount of molecular hydrogen (H ₂ molecules) is dissolved, non-oxygen bond defects among the above defects can be suppressed during laser irradiation. Its preferred H ₂ molecular content of 10
^In order to obtain about ¹⁵ to 10 ¹⁸ / cm ³ , the hydrogen content needs to be about 5 × 10 ¹⁵ to 1 × 10 ¹⁹ mol / cm ³ .

When 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. The non-bonded oxygen vacancies can be reduced to a minimum concentration by producing a synthetic quartz glass material under the above conditions.

[0048]

Embedded image −Si—H → ≡Si · (E ′ center) + H ·

[0049]

According to the method of the present invention for producing a synthetic quartz glass preform for an optical component for use in the ultraviolet region, a porous synthetic quartz glass formed by a vapor phase axial method is preliminarily calcined. 1300-140 under pressure of 5-50 Pascal
Heat treatment at 0 ° C. for 1 to 5 hours to homogenize the density,
Next, as a calcination step, under the same pressure, 1200 to 1400
After removing water and the like by heating at a temperature of 10 ° C. for 10 to 40 hours, the temperature is increased at a rate of 0.5 to 5 ° C./min, and a clearing step is performed to form a transparent vitreous. The material has an extremely low content of impurities such as chlorine and metal, and has a region having a maximum in the central portion, and a distribution of the OH group concentration which gradually decreases from the region toward the peripheral portion is formed.

After heating to a temperature of 1500 to 2000 ° C. using the synthetic quartz glass base material for optical parts for use in the ultraviolet region, it is gradually cooled from a temperature of at least 1500 ° C. to room temperature at a rate of 5 ° C./min or less. Then, by forming a virtual temperature distribution so as to cancel the refractive index distribution based on the distribution of the OH group concentration, an ultraviolet region having an extremely uniform refractive index can be obtained.
It is possible to manufacture a synthetic quartz glass material for an optical component for use in a region .

[0051]

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

[Examples 1 to 13 and Comparative Examples 1 to 14]
Porous synthetic quartz glass (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 calcined in advance, calcined, heated, and heated under the conditions shown in Table 1 below.
It was made transparent and cooled to produce a synthetic quartz glass base material having the dimensions shown in Table 3 below. The properties of this synthetic quartz glass preform are also shown in Table 3 below.

Next, the synthetic quartz glass base material manufactured in the above process is cut, processed, and the like.
Under the heat molding conditions shown in Table 1, heating, molding and soaking were performed. Thereafter, cooling was performed at the rate shown in Table 1 to form a virtual temperature distribution. Next, using the synthetic quartz glass material 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 with hydrogen. The properties of the obtained synthetic quartz glass for optical use are shown in Table 5 below.

Further, the synthetic quartz glass material according to the comparative example, in which the refractive index fluctuation width (Δn) is larger than that of the synthetic quartz glass material according to the embodiment, is also manufactured under the conditions for manufacturing the synthetic quartz glass material, heat molding conditions, and hydrogen. Table 2 below shows the doping conditions.
Table 4 shows the properties of the synthetic quartz glass base material, and Table 6 below shows the properties of the synthetic quartz glass product.

The fictive temperature is 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.

FIG. 2 is a graph showing the density distribution of the synthetic quartz glass after completion of the predetermined steps in the method of manufacturing the synthetic quartz glass base material according to the example and the comparative example. In FIG. 2, the solid line shows the density distribution in the case of Example 1, where the porous synthetic quartz glass (soot body) before the heat treatment and the porous synthetic quartz glass after the pre-calcining treatment (the pre-temporary The soot body after sintering) shows the synthetic quartz glass body after the calcination treatment, and the dotted line in the figure shows the synthetic quartz glass body without pre-sintering (Comparative Example 1).

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

[0062]

[Table 4]

[0063]

[Table 5]

[0064]

[Table 6]

As is clear from the results shown in Tables 3 and 5, the region where the OH group concentration is maximized is located in the central portion of the optical synthetic quartz glass base material and the optical synthetic quartz glass product according to the examples. Exists, and the OH group concentration gradually decreases toward the peripheral portion around the region, and there is a concentration distribution at which the concentration becomes the minimum value on the wall surface portion. The refractive index distribution based on this OH group concentration distribution is Since the refractive index distribution due to the virtual temperature distribution is formed so as to cancel out, the refractive index of the entire inside of the synthetic quartz glass material becomes extremely uniform (refractive index fluctuation width Δn ≦ 0.9 × 10 ⁻⁶ ). . Further, the chlorine concentration is less than 1 ppm, the birefringence is extremely small at 3 nm / cm or less, and the striae is free in three directions and has excellent homogeneity. Furthermore, although not shown in the table, the total content of metal impurities in the synthetic quartz glass product for optics according to the examples is less than 0.15 ppm, and the content of each metal impurity is such that the content of Al is 0.1%. 01 ppm or less, each content of Na, K, and Li is 0.02 ppm or less, Ca, Fe, Ti, Cr, Ni, P, B, Mg, C
Each content of u, Zr, and Zn was 0.008 ppm or less. 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.

As shown in FIG. 2, in the manufacturing method according to the embodiment, a porous body having a uniform bulk density was obtained over almost the entirety by the pre-calcining step. Since there is no change, the dehydration can be performed slowly, the concentration of the OH group can be reduced, and the concentration distribution can be controlled.

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 variation in the refractive index formed by the OH group concentration distribution and 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.

[0069]

As described in detail above, the ultraviolet region according to the present invention
In the method for producing a synthetic quartz glass base material for optical components for use in a region, a porous synthetic quartz glass formed by a vapor phase axial method is subjected to a pre-calcination step under a pressure of 1.5 to 50 Pascal. Heat treatment at 1300 to 1400 ° C for 1 to 5 hours to homogenize the density. Then, as a calcination step, heat at 1200 to 1400 ° C for 10 to 40 hours under the same pressure to remove moisture and the like. After that, the temperature is increased at a rate of 0.5 to 5 ° C./min, and further a transparentizing step is performed to form a transparent vitreous, so that the content of impurities such as chlorine and metal in the synthetic quartz glass base material is extremely small, There is a region having a maximum value in the central portion, and an OH group concentration distribution that gradually decreases from the region toward the peripheral portion can be formed.

Therefore, using this synthetic quartz glass base material, after heating to a temperature of 1500 to 2000 ° C., it was gradually cooled from the heating temperature to room temperature at a rate of 5 ° C./min or less, and the OH group concentration was lowered. By forming the virtual temperature distribution so as to cancel the refractive index distribution based on the distribution, it is possible to manufacture a synthetic quartz glass material for an optical component for an ultraviolet region having an extremely uniform refractive index.

[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.

FIG. 2 is a graph showing a density distribution of a synthetic quartz glass after a predetermined process is completed in the method of manufacturing a synthetic quartz glass base material according to the examples and the comparative examples.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuyuki Nakamura 1 Higashi-Muko, Higashi-Mukojima, Hyogo Prefecture Sumikin Quartz Co., Ltd. (56) References JP-A-62-182126 (JP, A) 24854 (JP, A) JP-A-9-52723 (JP, A) JP-A-9-52722 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03B 8/04 C03B 20 / 00 C03B 37/014

Claims (2)

(57) [Claims] 1. A porous synthetic quartz glass formed by a gas phase axial method is subjected to a heat treatment at 1300 to 1400 ° C. for 1 to 5 hours under a pressure of 1.5 to 50 Pascal as a pre-calcining step. At the same pressure and at a temperature of 1200 to 1300 ° C.
After heating for 40 hours to remove moisture and the like, 0.5 to 5 ° C /
A method for producing a synthetic quartz glass base material for an optical component for use in an ultraviolet region , wherein the temperature is raised at a speed of one minute, and further a transparentizing step is performed to form a transparent glass. 2. The synthetic quartz glass for an optical component according to claim 1.
Synthetic quartz glass base material manufactured by the method of manufacturing base material
Was heated to a temperature of 1600 to 2000 ° C. and molded.
After that, it is cooled to a temperature of 1500 to 1600 ° C. and made uniform.
Then, from a temperature of at least 1500 ° C., 5 ° C. /
1 min. ^Three ~ 1 × 10 ⁶
Heat at 610-790 ° C under Pascal's hydrogen gas atmosphere
Characterized by doping with hydrogen by doping
Manufacturing method of synthetic quartz glass material for optical components for area use.