JP2980510B2 - High purity silica glass for ultraviolet lamp 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 silica glass for an ultraviolet lamp in a 0 nm region, particularly a high-purity silica glass for an ultraviolet lamp such as an excimer lamp, a deuterium lamp, a xenon lamp, and a mercury lamp.

[0002]

2. Description of the Related Art Ultraviolet rays are used in the semiconductor industry, food / medical hygiene field, laser optics field, and the like. For example, in the semiconductor industry, photo-CVD, optical cleaning, optical lithography, etc., and in the food / medical hygiene field, sterilization. It is used as a laser oscillator excitation light source in the field of laser optics for deodorization, water treatment and the like. As an element for generating the ultraviolet light, an ultraviolet lamp is generally used. Ultraviolet lamps include low-pressure mercury lamps that emit metal gas at a relatively low pressure and low temperature, deuterium lamps, excimer lamps, high-pressure mercury lamps that emit metal gas at a relatively high pressure and high temperature, and metal halide lamps. . Since all of the above-described lamps emit the generated ultraviolet light to the outside of the lamp tube, the tube material must have a good ultraviolet transmittance and a material that can sufficiently withstand the emission temperature. In addition, it is required to have excellent processing characteristics for processing into a lamp tube. Silica glass is a material that meets these requirements, and most ultraviolet lamp tubes have been made of silica glass.

However, silica glass contains trace amounts of impurities such as transition metal elements, alkali metal elements and alkaline earth metal elements, and these metal impurities absorb, for example, ultraviolet rays in the case of transition metal elements. In addition, in the case of alkali metal elements and alkaline earth metal elements, promote the recrystallization of silica glass to produce cristobalite,
In order to cause white devitrification, an ultraviolet lamp tube material having a small amount of metal element impurities is used. However, when the above silica glass is actually used as a tube material of an ultraviolet lamp and emits ultraviolet light for a long time, ultraviolet damage occurs in the lamp tube, so-called solarization.
The transmission caused a decrease in the transmittance of ultraviolet light. In particular, this solarization was remarkable in an ultraviolet lamp which emits light at low pressure and low temperature.

[0004]

In view of the current situation,
The present inventors have conducted intensive research on the production of an ultraviolet lamp having a long life by eliminating solarization caused by ultraviolet rays of an ultraviolet lamp (hereinafter, referred to as a low pressure lamp) emitting light at a relatively low pressure and a low temperature. The alkali metal element, alkaline earth metal element and transition metal element in the silica glass to be used are specified within a specific range, the non-mobile OH group concentration is also set to a specific range, and the fictive temperature of the silica glass is set. It has been found that, when it is within a certain range, ultraviolet damage is small, and a decrease in transmittance due to solarization is small. The present invention has been completed based on these findings.

According to the present invention, the ultraviolet light damage is small,
Providing high-purity silica glass for UV lamps with long lamp life
The purpose is to do.

Further , the present invention relates to a tube for an ultraviolet lamp.
The purpose is to provide.

Another object of the present invention is to provide a method for producing the above silica glass.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a UV lamp having a wavelength range of 150 to 400 nm.
In Kaglass, the content of each transition metal element is 50 w
tppb or less, alkali metal element and alkaline earth gold
The content of each element is 100 wtppb or less, non-mobile
OH group concentration is 5wtppm ~ 1,000wtppm,
With a virtual temperature of 1,000 to 1,300 ° C and oxygen gas release
The output is 5 × 10 ¹⁸ molecules / m ² or less.
High purity silica glass for ultraviolet lamp and its production
According to the method .

A low-pressure lamp made of the above silica glass, for example, an excimer lamp, particularly a KrCl excimer lamp (222 nm), a XeCl excimer lamp (308n)
m), and lamps that emit UV light from 150 nm to 400 nm show excellent solarization resistance and have a long lamp life.

The transition metal element impurities contained in the silica glass of the present invention include Ti, Cr, Fe, Ni, C
u, whose content is 50 wtppb or less,
Alkali metal elements such as Li, K, and Na;
a, the content of alkaline earth metal elements of Mg is 100
It is important that it is not more than wtppb. When the contents of the transition metal element and the alkali metal element / alkaline earth metal element are within the above ranges, ultraviolet absorption by the elements is reduced, and white devitrification due to the generation of cristobalite due to recrystallization is suppressed. The crystalline silica powder fused silica glass having an impurity content in this range can be obtained by subjecting the raw silica powder to a purification treatment by heating the atmosphere containing chlorine gas or hydrogen chloride gas. However, excessive purification treatment lowers the concentration of non-migrating OH groups, not only reduces the effect of solarization resistance due to the non-migrating OH groups, but also increases the production cost and is not economical. Therefore, the content of each transition metal element is 1 w
The content of each of the alkali metal element and the alkaline earth metal element should be 5 wtppb or more.

The content of non-mobile OH groups in the silica glass of the present invention is preferably from 5 wtppm to 1000 wtppm. Silica glass containing non-mobile OH groups in this range has a non-mobile OH group whose terminator is a glass network.
This relaxes the distortion in the silica glass and makes it less susceptible to damage by ultraviolet light. When the concentration of non-mobile OH groups is less than 5 wtppb, the above effect is not obtained.
If it exceeds 0 wtppb, the generation of hydrogen molecules and oxygen molecules increases, and black devitrification due to these molecules appears and the ultraviolet light resistance decreases.

Further, the fictive temperature range of the silica glass of the present invention needs to be 1,000 to 1,300 ° C. Silica glass having the above-mentioned virtual temperature range has little etching action due to the enclosed metal gas, and white devitrification is very unlikely to occur.

In addition to the above requirements, the amount of oxygen gas released from the silica glass of the present invention is set to 5 × 1 per m ² of glass surface.
0 ¹⁸ UV absorption of oxygen gas by suppressing below the number of molecules, in particular about the excitation of the oxygen gas itself due to the absorption of light of a wavelength of 150~300nm and the absorbed energy - silica glass without production of ozone by chemical reactions based on There is no destruction of the network. Therefore, ultraviolet damage can be further prevented.

The above-mentioned non-mobile OH group concentration refers to the OH group concentration present after a silica glass sample having a thickness of 2 mm is subjected to heat treatment at 1000 ° C. for 10 hours or more under a vacuum of 1 Torr or less. . The OH group measurement method is described in D.
M. Dodd, D.E. B. Fraser, Optical
Determinations of OH inF
used Silica J. Applied Ph
ysics, Vol 37, (1966) pp. 3911
Obey.

The fictive temperature of silica glass is a temperature at which it is assumed that physical properties such as density and refractive index of silica glass at room temperature are set, and differs depending on the heat history of the silica glass (R. Brukener Jour
nal of Non-Crystalline So
lids, Vol. 5, (1970) pp. 123
175).

The high-purity silica glass of the present invention is produced by the following several methods. That is, first, SiC
l ₄ , HSiCl ₃ , CH ₃ SiCl ₃ , (CH ₃ ) ₂ SiC
l ₂ , CH ₃ Si (OCH ₃ ) ₃ , Si (OCH ₃ ) _{4 and} other silicon compounds as raw materials, and then silica glass or natural crystalline silica powder synthesized by a flame hydrolysis method such as oxyhydrogen or propane. The silica raw material obtained by the purification treatment is melt vitrified by a flame Bernoulli method or an electric heating melting method to prepare a silica glass, which is formed into a tube by heat molding, and then, in an air or nitrogen atmosphere, preferably 1T.
10 to 1,000 to 1,300 ° C under a vacuum of orr
The heat treatment is carried out for up to 100 hours. The silica glass of the above-mentioned various production methods is prepared such that the content of each of the transition metal elements therein is 50 wtppb or less, and the content of each of the alkali metal element and the alkaline earth element is 100 wtppb or less. The heat treatment conditions are such that the concentration of immobile OH groups in the silica glass is 5 wtppm to 1,000 wt.
ppm, the amount of released oxygen gas is 5 × 10 ¹⁸ molecules / m ² or less, and the fictive temperature is selected from the conditions of 1,000 ° C. to 1,300 ° C. An oxyhydrogen flame hydrolysis method is preferred in the method of producing the synthetic silica glass. In other cases such as the plasma method, non-mobile OH in silica glass is used.
The radical concentration becomes extremely low, and solarization due to ultraviolet rays cannot be suppressed.

The physical properties in the silica glass of the present invention are measured by the following methods. 1) Non-mobile OH group concentration measurement: Infrared absorption spectrophotometry (DM Dodd, DB Fraser, supra).

2) Virtual temperature measurement: Raman scattering spectrophotometry (AE Geissberger, FL Galeener, Physical Review B, Vol. 28, No. 6 (1983) pp. 3266-3271).

3) Oxygen gas emission measurement: by gas mass analysis (Y. Morimoto, et al., Journal of Non-Crystalline Solids, Vol. 139 (1992) pp. 35-46).

4) Analysis method of Na, K, Ca, Cr, Fe, Ni, Cu: Atomic absorption spectrometry.

5) Li, Mg, Ti analysis: by IPC mass spectrometry.

6) Initial transmittance: by ultraviolet spectrophotometry.

7) KrCl excimer lamp irradiation experiment: KrCl excimer lamp, wavelength: 222 nm, light output: 2 W, light energy—density: 0.1 W / cm ² , irradiation time: after 1000 hours, transmittance measurement.

[0024]

EXAMPLES Examples 1 to 3 Using SiCl ₄ as a raw material, high-purity silica glass cylinders having the impurity concentrations shown in Table 1 were synthesized by an oxyhydrogen flame hydrolysis method. The obtained synthetic silica glass cylinder was inserted from the upper part of the cylindrical electric furnace and heated to a temperature higher than the softening point to obtain a diameter of 3 mm.
It was formed into a tube having a thickness of 0 mm, a thickness of 2 mm, and a length of 200 mm by heating. The tube was placed in an electric furnace with a molybdenum disilicide heater and heated at 1100 ° C. in air.
The heat treatment tube was further placed in a vacuum furnace having a tungsten mesh heater with a stainless steel jacket, and the tube was heated at a degree of vacuum of about 1 × 10 ^-2 Torr for 10 hours at 1000 hours. The heat treatment of ° C was performed. A low-pressure lamp was prepared using the obtained tube, and its performance was confirmed. Table 1 shows the results.

[0025] Ju was prepared in the same manner as in Examples 4 and 5 Examples 1-3 - Bed Example 4
After heating at 1200 ° C for 10 hours in the atmosphere,
Further, at a vacuum of about 1 × 10 ⁻³ Torr for 5 hours, 1000
The heat treatment of ° C was performed. On the other hand, in the fifth embodiment, the tube
The tube was subjected to a heat treatment at 1000 ° C. for 10 hours in a vacuum of about 1 Torr. Table 1 shows the results.

Comparative Examples 1 to 4 For comparison with the above Examples, a silica glass tube having an impurity content shown in Table 1 was subjected to a heat treatment under the conditions shown in the same Table. Table 1 shows the results.

[0027]

[Table 1] Note) (1) Initial transmittance is 2mm thickness, 222nm wavelength
Means the initial transmittance. (2) The transmittance of the excimer lamp is KrCl excimer lamp (222 nm), light energy density 0.1 W / cm
^2. Refers to the transmittance at 222 nm after irradiation for 100 hours.

As shown in the above table, the lamp made of the silica glass of the present invention has a slight decrease in transmittance even after lighting for 1000 hours. In contrast, the transmittance of lamps made of silica glass outside the scope of the present invention is significantly reduced.

[0029]

The silica glass for an ultraviolet lamp according to the present invention.
Has high purity and solarization resistance to ultraviolet rays
UV lamp tube made with it,
In particular, the low-pressure UV lamp tube depends on the contained metal gas.
In addition to being able to prevent etching, white devitrification
There is no decrease in transmittance, and lamp life can be maintained longer.
And the silica glass for the ultraviolet lamp is in a tubular shape.
Silica glass in a vacuum of 1 Torr or less from 1,000 to
Heat treatment at 1,300 ° C for 10 to 100 hours
It can be easily manufactured in a convenient way.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI H01J 61/30 H01J 61/30 C (58) Field surveyed (Int.Cl. ⁶ , DB name) C03C 3/06 C03B 20/00

Claims (3)

(57) [Claims] 1. An ultraviolet lamp having a wavelength of 150 to 400 nm.
In the silica glass for use, the content of each of the transition metal elements is 50 wtppb or less, the content of each of the alkali metal element and the alkaline earth metal element is 100 wtppb or less, and the non-mobile OH group concentration is 5 wtppm to 1,000 wtpp.
m, virtual temperature of 1,000 to 1,300 ° C, oxygen
A high-purity silica glass for an ultraviolet lamp, wherein a gas emission amount is 5 × 10 ¹⁸ molecules / m ² or less . 2. A method of producing a silicon compound from a silicon compound by a flame hydrolysis method.
After synthesizing transparent high-purity silica glass,
By thermoforming, it becomes tube-shaped transparent high-purity silica glass.
Then, in a vacuum of 1 Torr or less,
Heat treatment at 300 ° C. for 10 to 100 hours to obtain non-mobile OH
Base concentration is 5 to 1,000 wtppm, fictive temperature is 1.0
A method for producing high-purity silica glass for an ultraviolet lamp, wherein the temperature is set to 00 to 1,300 ° C. and the amount of released oxygen gas is set to 5 × 10 ¹⁸ molecules / m ² or less. 3. The highly purified crystalline silica powder is cylindrically transparent by a flame Bernoulli method or an electric heat melting method.
After synthesizing high-purity silica glass, heat molding
Into a tube-shaped transparent high-purity silica glass, then 1T
1,000 to 1,300 ° C in a vacuum of not more than orr, 10
Heat treatment for ~ 100 hours to reduce non-mobile OH group concentration
1,000 wtppm, fictive temperature of 1,000 to 1,3
A method for producing a high-purity silica glass for an ultraviolet lamp, wherein the temperature is set at 00 ° C. and the amount of released oxygen gas is 5 × 10 ¹⁸ molecules / m ² or less.