JP4111940B2 - Method for producing synthetic silica glass large plate for high output vacuum ultraviolet light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a silica glass large-sized plate material having high initial transmittance to high output vacuum UV in the range of 160-200 nm wavelength and having excellent durability and uniformity. <P>SOLUTION: In the method, a cylindrical synthetic silica glass body is manufactured by forming a white soot body by an oxyhydrogen flame hydrolysis method by using a high purity silicon compound as a raw material and adjusting an OH group concentration of the soot body and vitrifying the soot body, then forming a synthetic silica glass tube by horizontal tube drawing, then molding the tube to the large-sized plate material by tube opening treatment in a tangential direction of the tube. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

  The present invention relates to a method for producing a synthetic silica glass large plate, more specifically, to an irradiation apparatus for dry cleaning and photo-CVD using high-power ultraviolet rays having a wavelength range of 160 to 200 nm, particularly high-power vacuum ultraviolet rays such as excimer lasers and excimer lamps. The present invention relates to a method for producing a synthetic quartz glass large plate to be used.

Currently, a dry cleaning apparatus using vacuum ultraviolet rays is being developed as a cleaning processing means in a method of manufacturing a silicon semiconductor element, and an ArF excimer laser (193 nm) having a wavelength of 160 to 200 nm, an Xe ₂ excimer laser (172 nm), ArCl excimer laser (175 nm), Xe ₂ excimer lamp (172 nm), ArCl excimer lamp (175 nm) and the like are considered. The dry cleaning device requires a large glass plate for the window, but when the window is made of commercially available window glass, the ultraviolet radiation emitted by the dry cleaning device is short wavelength, and the irradiation energy is mercury because of high output. Larger than lamps and CW lasers, it becomes damaged and becomes unusable. Therefore, it has been studied to form a window with silica glass that is less damaged against the high-power vacuum ultraviolet rays. However, conventional large silica glass introduces a high-purity silicon compound into an oxyhydrogen flame so that it can be hydrolyzed. By the direct method of directly depositing the obtained glass fine particles on the target or the VAD method of transparently solidifying a white opaque soot body obtained by hydrolyzing a high purity silicon compound with an oxyhydrogen flame in a vacuum atmosphere in an electric furnace A synthetic silica glass ingot is formed, heated and press-molded in a vacuum electric furnace using a graphite mold, cut into a thin plate, and polished. was there. Furthermore, the silica glass plate material obtained by the former direct method has a high OH group content of 400 to 1000 wtppm, damage is caused by irradiation with high-power vacuum ultraviolet rays for a long time, and light transmittance is lowered by solarization. Since it is formed in a layer shape, the OH group content can vary from 100 to 400 wtppm at the center and outer edge of the plate material, and the vacuum ultraviolet light transmittance and UV resistance are non-uniform in the plate material. It was not satisfactory for a window such as. In addition, the silica glass plate material obtained by the latter VAD method has an OH group content of 100 to 400 wtppm, which is smaller than that of the direct method, and the fluctuation range of the OH group is as small as 50 to 200 wtppm. The amount of variation in the amount and OH group concentration was large, and the transmittance and ultraviolet resistance of vacuum ultraviolet rays were not uniform in the plate material, which was a major obstacle. Therefore, development of a large-sized silica glass plate material with little damage to the high-power vacuum ultraviolet rays, high transmittance, and excellent uniformity thereof has been eagerly desired.

  In view of the current situation, the present inventors have conducted extensive research and as a result, formed a white soot body by a oxyhydrogen flame hydrolysis method using a high-purity silicon compound as a raw material, and adjusted the OH group concentration of the soot body. A cylindrical synthetic silica glass body is produced by transparent vitrification, and after it is made into a synthetic silica glass tube by horizontal tube drawing, a wavelength of 160 to 200 nm is formed by molding into a large plate material by a tube opening process in the tangential direction of the tube. The present invention has been completed by finding that a synthetic silica glass large plate material that is stable and has high transmittance can be produced even with high-power vacuum ultraviolet rays in the region. Ie

  An object of the present invention is to provide a method for producing a synthetic silica glass large plate having high initial transmittance with respect to high-power vacuum ultraviolet rays in a wavelength range of 160 to 200 nm, excellent durability, and uniformity thereof. To do.

  The present invention for achieving the above object is to form a white soot body by a oxyhydrogen flame hydrolysis method using a high-purity silicon compound as a raw material, adjust the OH group concentration of the soot body, convert it into a transparent glass, and form a cylindrical synthetic silica. The present invention relates to a method for producing a synthetic silica glass large plate material, which comprises producing a glass body, forming a synthetic silica glass tube by horizontal tube drawing, and then molding the glass body into a large plate material by a tube opening process.

The synthetic silica glass large plate obtained by the production method of the present invention is a high-purity synthetic silica glass plate that is stable against high-power vacuum ultraviolet rays. The high-power vacuum ultraviolet rays are ArF excimer laser (193 nm), It refers to ultraviolet rays having a wavelength of 160 to 200 nm, such as Xe ₂ excimer laser (172 nm), ArCl excimer laser (175 nm), Xe ₂ excimer lamp (172 nm), ArCl excimer lamp (175 nm). The high purity means that the concentration of alkali metal elements such as Li, Na and K and alkaline earth metal elements such as Mg and Ca in the silica glass plate is 10 wtppb or less, and transition metals such as Ti, Cr, Mn and Fe. The element concentration is 1 wtppb or less, and the concentration of transition metal elements such as Co, Ni, and Cu is 0.1 wtppb or less. When the alkali metal element and alkaline earth metal element concentration in the large-sized synthetic silica glass plate of the present invention exceeds the above range, recrystallization of silica glass is promoted and cristobalite is easily generated, and white devitrification occurs. . On the other hand, if the transition metal element concentration exceeds the above range, it absorbs ultraviolet rays and shifts the ultraviolet absorption edge to the longer wavelength side, leading to a decrease in transmittance, which is not preferable.

  In addition to the above, the synthetic silica glass large plate of the present invention must have an OH group concentration of 5 to 300 wtppm and an OH group concentration fluctuation range (ΔOH / cm) per cm of 10 wtppm or less. In general, the OH group is the terminal part of the structure in the silica glass network structure. If an appropriate amount of the OH group is contained in the silica glass, the internal strain in the network structure is removed, and the bonding angle of Si—O—Si. However, it is said that the average bond energy of Si—O increases as the value approaches a stable value. However, the OH group has an action of shifting the ultraviolet absorption edge of the silica glass to the long wavelength side, and when it is contained in a high concentration, the transmittance is lowered. Therefore, in the synthetic silica glass large plate of the present invention, the OH group concentration is in the range of 5 to 300 wtppm. In particular, when used for high-power vacuum ultraviolet rays having a wavelength of 160 to 180 nm, the OH group concentration is preferably 5 to 100 wtppm. Further, if the OH group concentration is not uniform, the transmittance, the absolute refractive index and the like are uneven depending on the position of the plate material, and as a result, the initial characteristics are deteriorated. Therefore, in the synthetic silica glass large plate of the present invention, the fluctuation range of OH group concentration per 1 cm (ΔOH / cm) is set to 10 wtppm or less. Furthermore, it is preferable that the OH group concentration fluctuation range (ΔOH) of the entire plate material is 50 wtppm or less.

Further, the concentration of hydrogen molecules contained in the large-sized synthetic silica glass plate of the present invention is set in the range of 1 × 10 ¹⁷ to 1 × 10 ²⁰ molecules / cm ³ . By containing the hydrogen molecule at the above concentration, the generation of the E ^′ center absorption band is suppressed, and the transmittance is less likely to decrease. Furthermore, when the water molecule concentration is 1 × 10 ¹⁷ or less, the shift of the ultraviolet absorption edge to the long wavelength side caused by water molecules can be suppressed, which is preferable. However, the water molecule referred to here is not an OH group bonded to Si but a molecule dissolved in a gap in a silica glass network structure.

Moreover, it is good for the synthetic silica glass large-sized board | plate material of this invention to contain the chlorine element content to 50 wtppm or less. Si—Cl formed by chlorine element serves as a precursor for generating a 210 nm absorption band, so-called E ^′ center absorption band, but if it is within the above range, the generation of the precursor can be suppressed and the decrease in transmittance can be suppressed.

  In the present invention, a large silica glass cylinder is formed by using a soot remelting method known from the past using an ultra-high purity silicon compound as a raw material. A synthetic silica glass large-sized plate can be manufactured by a simple method of performing a direction-opening treatment.

  The synthetic silica glass large plate of the present invention is produced by the following production method. Ie

(I) Manufacture of synthetic silica glass cylinder Ultra-high purity SiCl ₄ , HSiCl ₃ , (CH ₃ ) ₂ SiCl ₂ , CH ₃ SiCl ₃ , CH ₃ Si (OCH ₃ ) ₃ , HSi (OCH) ₃ ) ₃ and a silicon compound such as Si (OCH ₃ ) ₄ , preferably a silicon compound containing no chlorine such as CH ₃ Si (OCH ₃ ) ₃ , HSi (OCH ₃ ) ₃ , and Si (OCH ₃ ) ₄ oxyhydrogen gas Alternatively, flame hydrolysis is performed using propane gas, and the OH group concentration in the axial direction is made uniform by a burner swing by a preparation method described in, for example, JP-A-4-260618, US Pat. No. 5,609,666. On the other hand, a white opaque large soot body is formed on the rod-shaped target. In the formation of the large soot body, the OH group concentration is adjusted according to the temperature, time and vacuum degree in the electric furnace. Subsequently, it is heated and melted at 1500 to 1700 ° C. in a vacuum atmosphere in the same electric furnace to obtain a cylindrical synthetic silica glass body having an outer diameter of 80 to 200 mm and a wall thickness of about 20 to 70 mm without bubbles. In the present invention, the method for producing the synthetic silica glass is referred to as a soot remelting method.

(Ii) Manufacture of a large plate of synthetic silica glass Heated while adjusting the internal pressure of the large cylindrical synthetic silica glass body with N2 gas, and formed into a large tube having an outer diameter of 200 to 400 mm and a wall thickness of about 3 to 10 mm by pipe drawing. To do. The resulting large tube is cut in a predetermined width in the tube axis direction, and pulled in the tangential direction of the tube while heating and softening with a strip burner in the tube circumferential direction from the inside and outside of the cut portion to the entire width in the tube axis direction. As shown in FIG. 1, it is flattened by a tube opening process to obtain a large synthetic silica glass plate. In FIG. 1, 1 is a silica glass tube, 2 is the direction in which the plate is pulled, 3 is a heating means, 4 and 8 are support pieces of the quartz glass plate, and 5 is a notch. The obtained synthetic silica glass large plate is subjected to strain removal treatment in an electric furnace, etched and heat-treated, and then mirror polished to have a size of 300 × 300 mm square to 1000 × 1000 mm square and a thickness of 2 to 8 mm. Finish the board. The obtained large plate has a flat OH group concentration fluctuation range of 10 wtppm or less per cm since the axial direction in which the OH group concentration is adjusted becomes the plate surface. On the other hand, the large fluctuation range of the OH group concentration in the radial direction of the tube is the fluctuation width in the thickness direction of the large plate. The plate material is thin with a thickness of 2 to 8 mm, and the OH group concentration is gradually increased or decreased uniformly. Therefore, the transmittance of the high-power vacuum ultraviolet ray and the degree of solarization caused thereby are less uneven and uniform in the plate surface direction. Has characteristics.

  The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.

Examples 1-6
(1) Preparation of synthetic silica glass cylinder Ultra high-purity CH ₃ Si (OCH ₃ ) ₃ gas obtained by distillation purification is fixed at a total of 150 liters / minute, and the total of oxygen gas and total of hydrogen gas is 10 to 100 respectively. Liter / minute, supplied to a plurality of burners at a rate in the range of 30 to 300 liter / minute, and the OH group content is several hundred wtppm by an external method as described in JP-A-4-260618 while swinging the burner. The white large soot body was formed. The large soot body is installed in a stainless steel electric furnace equipped with a cylindrical high-purity graphite heater, and the electric furnace is evacuated to about 10 ³ Pa or less and at a predetermined temperature in the range of about 600 to 900 ° C. The OH group concentration was adjusted by heat treatment. The OH group concentration was controlled by adjusting the degree of vacuum, temperature and time during processing. Subsequently, it was heated and remelted at about 1500 to 1700 ° C. under vacuum in an electric furnace to produce a synthetic silica glass cylinder having an outer diameter of 150 mm and a thickness of 40 mm.

(2) Manufacture of silica glass tube While adjusting the internal pressure of the silica glass cylinder with nitrogen gas, it was heated through a graphite heater, and a large silica glass tube having a diameter of 250 mm, a length of 1600 mm, and a thickness of 7 mm was manufactured by horizontal tube drawing. .

(3) Manufacture of large synthetic silica glass plate The obtained large silica glass tube 1 is cut into a predetermined width in the axial direction as shown in FIG. While being heated and softened sequentially to 1800 to 2000 ° C. with a strip-shaped burner 3 in the circumferential direction, it was flattened by pulling in the tangential direction of the tube and molded into a large synthetic silica glass plate of 670 × 600 × thickness 7 mm. The synthetic silica glass large plate is annealed at 1150 ° C. for 30 minutes in an electric furnace to remove the distortion, then etched and washed with 5% HF for 30 minutes, and high purity carbon sheets are laid on the upper and lower sides of the plate. In order to further flatten the plate material while preventing contamination, the plate material was further sandwiched by another silica glass plate material from the outside , and was weighted from the top, and heated and pressurized at 1200 ° C. for 2 hours in an electric furnace. Both sides of the obtained large plate were mirror-polished to finish a synthetic silica glass large plate of 650 × 550 × thickness 5 mm.

Next, the samples of Examples 1 to 3 were annealed at 1 atm and hydrogen gas atmosphere at 600 ° C. for 3 hours, and in Example 4 at 100 atm and hydrogen gas atmosphere at 600 ° C. for 3 hours. To dope hydrogen molecules. For the obtained samples of Examples 1 to 4 and the samples of Examples 5 and 6 that were not subjected to the hydrogen doping treatment, the OH group concentration, the OH group concentration fluctuation width per cm (ΔOH / cm), the OH group concentration in the whole plate material The fluctuation width (ΔOH), hydrogen molecule concentration, water molecule concentration, chlorine element content, transmittance for Xe ₂ excimer lamp and ArF excimer laser irradiation were measured, and the results are shown in Table 1.
(Table 1)

Further, impurity element concentrations were measured for the synthetic silica glass large plate materials of Examples 5 and 6, and the results are shown in Table 2.
(Table 2)

註: The unit of the impurity element is wtppb.

Comparative Examples 1-4
In Comparative Examples 1 and 2, a white soot body is formed using the high-purity silicon compound used in Example 1 as a raw material, dehydrated in an electric furnace in a chlorine gas atmosphere, and further transparently solidified in a vacuum atmosphere. Create a synthetic silica glass cylinder (soot method) and make a large synthetic silica glass tube by horizontal tube drawing, then open the tube, press mold, and mirror polish, 650 x 550 x 5 mm thick synthetic silica glass A board was obtained. In Comparative Example 2, the synthetic silica glass large plate was further annealed in a hydrogen gas atmosphere to dope hydrogen molecules. OH group concentration of the large synthetic silica glass plate, OH group concentration fluctuation width per 1 cm (ΔOH / cm), OH group concentration fluctuation width (ΔOH) of the whole plate material, hydrogen molecule concentration, water molecule concentration, chlorine element content, The transmittance for Xe ₂ excimer lamp and ArF excimer laser irradiation was measured, and the results are shown in Table 3.

In Comparative Example 3, an ingot was produced by using an ultra-high purity SiCl ₄ as a raw material by the direct method of the oxyhydrogen flame hydrolysis method, and in Comparative Example 4, the ingot was formed by the VAD method of the oxyhydrogen flame hydrolysis method. After performing this, it was hot press molded in a vacuum electric furnace using a graphite mold, cut into a thin layer plate, and a synthetic silica glass large plate was produced by mirror polishing. For each sample obtained, OH group concentration, OH group concentration fluctuation width per 1 cm (ΔOH / cm), OH group concentration fluctuation width (ΔOH) in the whole plate material, hydrogen molecule concentration, water molecule concentration, chlorine element content, The transmittance for Xe ₂ excimer lamp and ArF excimer laser irradiation was measured, and the results are shown in Table 3.
(Table 3)

  The measuring method of each physical property value in the above Examples and Comparative Examples is as follows.

(I) OH group concentration measurement method M.M. DODD and D.D. B. FRASER, Optical determination of OH in fused silica, Journal of Applied Physics, Vol. 37 (1966) p. Measurement method described in 3911 literature.

(Ii) Measuring method of fluctuation range of OH group concentration In a large silica glass plate of 650 × 550 × 5 mm thickness, 85 points of OH group concentration are measured at 10 mm intervals in the diagonal direction of the face plate. The OH group concentration fluctuation range per 1 cm (ΔOH / cm) from the two OH group concentration values of neighboring neighbors, and the OH group concentration fluctuation range (ΔOH) of the entire plate from the maximum and minimum values of the OH group concentration at 85 points. The measurement method to calculate.

(Iii) Measuring method of hydrogen molecule concentration.
V. K. KHOTIMCHENKO, et al. , Determine-ing the content of hydrogen
dissolved in quadz glass using the methods of Raman scattering and mass spectroscopy, Journal of Applied
Spectroscopy, Vol. 46, no. 6, (1987) pp 632-635.

(Iv) Measuring method of water molecule concentration.
Y. MORIMOTO, et al. , Analysis of gas release from vitreous silica,
Journal of Non-Crystalline Solids,
139 (1992) 35-46.

(V) Measuring method of chlorine concentration.
Measurement method by turbidimetric method with AgNO ₃ addition after decomposition with HF aqueous solution.

(Vi) Measurement of impurities in silica glass Na, K, Mg, Ca, Ti and Fe are measured by atomic absorption photometry, and Li, Sr, Cr, Mn, Co, Ni and Cu are measured by plasma mass spectrometry ( ICP-MS method).

(Vii) Measurement method of transmittance at 193 nm before and after ArF excimer laser irradiation Size 30 × 20 × thickness 5 mm, double-sided mirror polished sample, wavelength 193 nm, wavelength half width 3 nm, pulse lifetime half width 17 nsec, energy density 50 mJ / A measurement method for measuring the transmittance at 193 nm when the laser irradiation with the number of irradiation shots of 1 × 10 ⁶ shots is performed at cm ² / shot and the frequency of 100 Hz.

(Viii) Measuring method of transmittance at wavelength 172 nm before and after Xe ₂ excimer lamp irradiation Size φ40 × thickness 5 mm, sample finished with double-sided mirror polishing, wavelength 172 nm, wavelength half width 14 nm, average lamp energy density 7 mW / cm ² A measurement method for measuring the transmittance at 172 nm when irradiated for a day.

<Evaluation>
As is apparent from Tables 1 and 3, the synthetic silica glass large plate of the present invention is excellent in excimer light resistance and uniformity. In particular, Examples 1, 2, and 4 are more excellent in excimer light resistance because the OH group concentration is low and the H ₂ molecule concentration is high.

  On the other hand, the synthetic silica glass large plate materials of Comparative Examples 1 and 2 are inferior in initial characteristics and excimer light resistance, and the synthetic silica glass large plate materials in Comparative Examples 3 and 4 are inferior in excimer light resistance and change in OH group concentration. The width is large and the transmittance is distributed and non-uniform.

  The synthetic silica glass large plate obtained by the production method of the present invention is useful as a member such as a window of a dry cleaning using high-power vacuum ultraviolet rays such as an excimer laser or an excimer lamp, or a photo-CVD irradiation apparatus.

It is the schematic of pipe opening shaping | molding in the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silica glass tube 2 Direction which pulls a board | plate material 3 Heating means 5 Cutting part

Claims (2)

A white soot body is formed by oxyhydrogen flame hydrolysis using a high-purity silicon compound as a raw material, and the OH group concentration of the soot body is 5 to 300 wtppm of the OH group concentration of a large plate, and the fluctuation range of OH group concentration per 1 cm (ΔOH / Cm) is adjusted to 10 wtppm or less, and is made into a transparent glass to produce a cylindrical synthetic silica glass body, which is then formed into a synthetic silica glass tube by horizontal tube drawing, and then molded into a large plate by a tube opening process. A method for producing a synthetic silica glass large plate for high-power vacuum ultraviolet rays . 2. The high-power vacuum ultraviolet ray according to claim 1 , wherein hydrogen molecules are doped so that the hydrogen molecule concentration in the synthetic silica glass large plate is in the range of 1 × 10 ¹⁷ to 1 × 10 ²⁰ molecules / cm ³ . A method for producing a synthetic silica glass large plate.