JPH02243535A - Production of glass matrix for ultraviolet ray - Google Patents

Abstract

PURPOSE:To obtain the subject glass matrix having an excellent ultraviolet ray-resistant characteristic by heat treating a silica glass lump of high purity having a specified OH content in an atmosphere containing hydrogen and hydrogen chloride, slowly cooling the heat treated silica glass lump while maintaining the atmosphere, preventing contamination of impurities and degassing and enabling to take place preferable internal diffusion of hydrogen. CONSTITUTION:A silica glass lump of high purity having >=about 300ppm OH content is heat treated at 1,000-1,200 deg.C, preferably >=1,120 deg.C in an atmosphere containing hydrogen and hydrogen chloride gases (preferably <=30mol% hydrogen chloride and >=70mol% hydrogen) followed by slow cooling to <=400 deg.C, preferably <=200 deg.C while maintaining the atmosphere, thus obtaining the objective glass matrix for ultraviolet ray for production of a lens, a window, a mirror, a prism, a filter, etc., used for laser of 400-200nm wave range.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is intended for manufacturing lenses, windows, mirrors, prisms, filters, etc. used for ultraviolet light, especially laser light in the wavelength range of 4QOn■ or less. The present invention relates to a method for producing a glass base material for ultraviolet light.

"Conventional technology" For example, with the miniaturization and higher integration of LSIs, there is an urgent need to develop submicron-level drawing technology in phosphorography technology, which draws integrated circuit patterns on wafers.
Considering recent steady progress in optical systems, light sources, photoresists, etc., it is presumed that optical lithography will become the mainstream.

It is true that optical lithography has the various conditions necessary to draw fine line widths, such as a relatively high-intensity light source, high-sensitivity resist, and stable optical materials.
As a drawback, since the exposure wavelength is large, the resolution is limited due to diffraction, and as a solution to this problem, progress is being made to shorten the exposure wavelength.

However, in order to shorten the exposure wavelength, 400n■
When the following ultraviolet rays are used, in lenses using conventional optical glass, the light transmittance decreases rapidly from the wavelength used around 385 nm (i-line), heat generation occurs due to light absorption, and the focal point of the lens and other characteristics.

For this reason, we changed the lens material from conventional optical glass to quartz glass, and in order to prevent the occurrence of chromatic aberration when using quartz glass, we used a high-power laser beam with a narrow spectral width as the light source, especially in the ultraviolet region. Although a pulsed laser is used, even when quartz glass is used, the transmittance rapidly decreases when the wavelength range of transmitted light is 190 nm or less.

Therefore, even when silica glass is used, the wavelength range of the transmitted light is approximately 200 to 400 nm, specifically, KrF (248nl1), Xe (41nm), etc.
(308nm), XeBr (282nm), XaF
Excimer laser light such as (351, 353ni+) and laser light such as YAG 4th harmonic (25Qnm) are targeted, but when such short wavelength laser light is used, the uniformity of the refractive index of the optical material is Compared to the case of the above-mentioned G-line, something several orders of magnitude higher is required.

For this reason, the quartz glass base material used to manufacture the lenses and the like is generally made of synthetic quartz glass, which is formed by reacting silicon tetrachloride in an oxyhydrogen flame, in order to achieve higher purity.
After the synthetic quartz glass is molded into a desired shape such as a substantially cylindrical, disk-shaped, or spherical shape, it is heated to about 1100°C in order to remove internal distortion and make the refractive index distribution uniform. Heat treatment is performed at high temperature.

``Problems to be Solved by the Invention'' However, when heat treatment is performed in the high-temperature range as described above, contamination occurs from within the furnace material, making it difficult to maintain high purity. The occluded hydrogen degasses, which adversely affects the ultraviolet ray resistance, including a decrease in transmittance and an increase in refractive index.

As a technique that can be applied to prevent such degassing of occluded hydrogen, for example, in Japanese Patent Publication No. 10228/1973, a quartz glass article is heated for 40 minutes in a hydrogen gas atmosphere.
A technique for preventing coloration due to the action of ionizing radiation by heating at 0 to 1000°C, particularly 500°C, has been disclosed. If the temperature exceeds .degree. C., there is a drawback that the light transmission characteristics deteriorate due to the contamination of impurities even in a hydrogen gas atmosphere. For this reason, such a technique cannot be applied as a method for manufacturing a glass base material for ultraviolet light that requires heat treatment in a high temperature range.

That is, in silica glass, the transition temperature range is 1025 to 11
Since the temperature is 20° C., if the heat treatment temperature is set to 1000° C. or lower, it is impossible to remove internal strain and achieve homogenization, and as a result, the above technique cannot be adopted.

In view of such prior art, the present invention enables hydrogen to be internally diffused more favorably than before the heat treatment without causing impurity contamination or degassing even when the heat treatment is performed, The object of the present invention is to provide a method for producing a glass base material for ultraviolet light that can obtain good ultraviolet light resistance.

Furthermore, another object of the present invention is to improve the ultraviolet ray resistance by not restricting the improvement of the ultraviolet ray resistance only by the heat treatment method, but by regulating the amount of a specific substance contained before the heat treatment, specifically, the OH group content. - Layer An object of the present invention is to provide a method for producing a glass base material for ultraviolet light, which can improve the preferable ultraviolet resistance properties.

``Means for Solving the Problems'' The present invention relates to a method of manufacturing a glass base material for ultraviolet light used for ultraviolet light in a specific wavelength range from approximately 20 nm to 400 nm.

That is, from the perspective of preventing impurity contamination during heat treatment, it is not necessary to specifically limit the wavelength range, but the present invention specifically aims to actively incorporate occluded hydrogen into the glass structure. Therefore, the wavelength range is also limited to a range in which a particularly large effect can be obtained when occluded hydrogen is contained, specifically, a wavelength range from about 2αGmm to 400 nm.

However, if the wavelength range is 400nm or more, the photon energy is small, so there is no need to consider the stability of optical properties, and if the wavelength range is about 200nm or less, there may be problems with light transmittance as described above. This is also because in such a vacuum ultraviolet region, resistance is sometimes better when the material does not contain occluded hydrogen.

The present invention for producing a glass base material for ultraviolet light used in such a wavelength range has the following features: (1) As a first feature, a high-purity quartz glass lump is produced based on a desired synthesis method; The point is that the OH group concentration is approximately 300 ppm or more.

It is a fact that the present inventors have previously discovered that UV resistance properties such as fluorescence properties, refractive index, and transmittance can be improved by increasing the OH group concentration in the glass structure. 323882), and in particular, by using a high-purity quartz glass block with an OH group concentration of about 300 ppp or more, a car can be created that suppresses fluorescence generation when irradiated with ultraviolet rays in the wavelength range from about 200 nm to 400 nm. This makes it possible to improve the stability of refractive index, transmittance, etc.

However, even if a synthetic quartz glass block with high purity and OH group concentration is used as described above, the effects of the invention cannot be achieved if contamination or degassing of occluded hydrogen occurs during heat treatment. .

(2) Therefore, the second feature is that the quartz glass lump is heat-treated at a temperature of 1000 to 1200° C. in an atmosphere containing hydrogen and hydrogen chloride.

That is, by performing heat treatment in an atmosphere containing hydrogen chloride, Na, Fe, and M diffused from the furnace material by high-temperature heating.
Impurity metal elements such as g combine with the C+ element in the hydrogen chloride and volatilize as chloride, and as a result, it is possible to prevent impurities from entering the glass structure. Incidentally, since the annealing point of synthetic quartz glass is 1120°C, it is preferable to carry out the heat treatment at a temperature of 1000 to 1200°C, particularly 1120°C or higher, as described above, since strain can be removed in a short time.

In this case, if the heat treatment is performed in the above-mentioned high temperature range, it will be degassed even in an atmosphere containing hydrogen gas, and if left as it is, fluorescence etc. will be generated and the ultraviolet ray resistance will deteriorate.

③Therefore, the third feature of the present invention is that while the atmosphere containing hydrogen and hydrogen chloride is maintained, slow cooling is performed until the treatment temperature is lowered to at least 400°C or lower, preferably 200°C or lower. be.

That is, slow cooling in a hydrogen-containing atmosphere promotes the diffusion and dissolution of hydrogen into the glass structure, and the slow cooling is continued to a temperature point where there is no risk of degassing of the hydrogen diffused in the mixed atmosphere. It is something to do.

In this case, since the atmosphere is hydrogen chloride-containing even during the slow cooling, contamination of impurities can be prevented as described above.

The reason for maintaining the slow cooling and mixed atmosphere until the temperature drops to 400°C or lower is that if the mixed atmosphere is replaced with other nitrogen gas or the like at 400°C or higher, This is because hydrogen gas dissolved in the glass easily separates.

Furthermore, regarding the blending ratio of hydrogen and hydrogen chloride, the higher the mixing ratio of hydrogen gas, the more advantageous it is.On the other hand, regarding the hydrogen gas, even if the mixing ratio is small, more specifically, the hydrogen chloride in the atmosphere is more advantageous. Even at a mixing ratio of 0.1 mo1%, there is a considerable effect of preventing impurity contamination, and conversely, even if hydrogen chloride is set to approximately 30 mo1% or more, the prevention effect does not improve. The mixing ratio of hydrogen is at least 0.1 mo1% hydrogen chloride, particularly preferably 0.5 mo1% or more (hydrogen 89%).
Although the upper limit of the mixing ratio of hydrogen chloride is not particularly limited, optimally, in order to more smoothly achieve the hydrogen occlusion effect described above, Hydrogen chloride is approximately 30 mo1% or less (hydrogen 70 no!
It is preferable to set it to %h).

Therefore, the present invention uses high-purity quartz glass containing OH groups to prevent contamination of impurities in a hydrogen chloride-containing atmosphere during heating and slow cooling, and to prevent hydrogen diffusion and dissolution in a hydrogen-containing atmosphere (during slow cooling). The gist of the present invention lies in the fact that the ultraviolet ray resistance is improved through effective combination, and this point is not disclosed in any of the above-mentioned conventional techniques.

"Experimental Example" The process leading to the present invention will be explained based on a specific experimental example.

After distilling the raw material silicon tetrachloride to remove impurities, we prepare high-purity silicon tetrachloride stored in a stainless steel container with a Teflon runner, and use the high-purity silicon tetrachloride raw material to perform the direct method and CVD suit. By remelting synthesis method,
A plurality of high-purity quartz glass blocks are synthesized.

Next, the quartz glass lumps produced by the above two types of synthesis methods are sequentially placed in a quartz glass chamber in an atmospheric heating furnace, and either a mixed gas of hydrogen gas and hydrogen chloride, or a mixture of hydrogen gas or hydrogen chloride gas is produced. or about 2 types after being kept at about 1100℃ for a certain period of time in the air atmosphere.
Slow cooling was performed according to a certain program until the temperature reached 00° C. or less, and then air cooling was performed.

Then, the thus formed silica glass lump free of residual strain is cut into a size of 40×30×tlO+u+, and both sides are mirror-finished to produce nine test pieces for each excimer laser irradiation experiment.

Next, for each of these eight test pieces, using a KrF excimer laser (248!11), the energy density per pulse was t00, 200, 400 (mJ/crnj11).
pulse) and number of irradiation pulses lX105, lX10
6. Irradiation was performed under the irradiation conditions consisting of a combination of 1×107 (pulse).

After the irradiation, the refractive index distribution of each specimen was changed using an interferometer, and solarization was observed using a transmittance meter.
Fluorescence intensity was measured using a fluorometer, and the results are shown in the experimental results table below.

As can be understood from the table below, it was synthesized by the direct method and the soot method, and the OH groups were 1000pp and 3.
The excimer laser resistance of the high-purity quartz glass ingot containing 0.00 pp heat-treated in an atmospheric atmosphere was poor, but the excimer laser resistance of the high-purity quartz glass ingot that was heat-treated in an atmosphere containing hydrogen and hydrogen chloride was poor. A uniform glass with significantly improved refractive index and no distortion was obtained (Experiments 1.4, 5.fl, ?) Next, a glass with 1000
The excimer laser resistance of high-purity quartz glass blocks containing pp-containing heat treated in a hydrogen chloride atmosphere or a hydrogen atmosphere was at an average level, but not at a satisfactory level. (Experiment 2.3) Furthermore, whether the high-purity anhydrous silica glass lump synthesized by the soot method is heat-treated in an atmosphere containing hydrogen chloride and hydrogen or in an air atmosphere, the KrF excimer laser resistance remains high. The value was significantly worse. (Experiment 8,
3) In order to confirm the effect of desorption of dissolved hydrogen gas, the quartz glass lump described in Experiment No. 1) was heated at approximately 1100°C for a certain period of time in a mixed gas atmosphere of hydrogen gas and hydrogen chloride. After holding, the sample was slowly cooled in the same atmosphere until it reached a temperature of about 500°C, and then slowly cooled in a nitrogen gas atmosphere.The excimer laser resistance of the sample was investigated.
It was confirmed that the transmittance, refractive index, and fluorescence characteristics were all lower than that of the previous one. (Experiment 1) "Effects of the Invention" As described above, according to the present invention, the impurity blocking effect in a hydrogen chloride-containing atmosphere and the hydrogen diffusion effect in a hydrogen-containing atmosphere can be efficiently achieved by using high-purity quartz glass containing OH groups. By performing heating and slow cooling treatment in a combinable manner, even when heat treatment is performed in a high temperature range, there will be no contamination of impurities or degassing, and on the contrary, hydrogen will be more preferable than before heat treatment. As a result, good ultraviolet light resistance can be obtained.

In addition, the present invention does not restrict the improvement of UV resistance properties only by the heat treatment method, but by specifying the OH group content before heat treatment, it is possible to improve the UV resistance properties of the - layer. It has various effects.

Claims (1)

[Claims] 1) In a method for producing a glass base material for ultraviolet light used for ultraviolet light in a specific wavelength range from approximately 200 nm to 400 nm, the OH group concentration is approximately 300p based on the desired synthesis method.
After producing a high-purity quartz glass lump containing pm or more, the quartz glass lump is heated in an atmosphere containing hydrogen and hydrogen chloride for about 10 min.
Production of a glass base material for ultraviolet light, characterized in that heat treatment is performed at a temperature of 00 to 1200°C, and then gradual cooling is performed while maintaining the atmosphere until the treatment temperature drops to at least 400°C or less. Method