JP2001180962A - Synthesized quartz glass and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthesized quartz glass without decrease of transmission factor by an ultraviolet irradiation of wavelength 150-200 nm and the manufacturing method. SOLUTION: A synthesized quartz glass is characterized by an OH group concentration of 100 ppm or less, hydrogen molecule concentration less than 1×1017 molecule/cm3, and no reduction type of defect substantially, therein; and by that change of absorbance index in 150-200 nm after irradiation of an ultraviolet ray of wavelength 172 nm at an illuminance of 10 mW/cm2 for 15 kJ/cm2 is 0.2 cm-1 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
More specifically, the present invention relates to a synthetic quartz glass for an optical member used in a device using a 0 nm ultraviolet ray as a light source and a method for producing the same.
F excimer laser (193 nm), F ₂ laser (157
nm), low-pressure mercury lamp (185 nm), Xe ₂ ^* excimer lamp (172 nm), etc.
The present invention relates to a synthetic quartz glass used as an optical component such as a pellicle and a method for producing the same.

[0002]

2. Description of the Related Art Synthetic quartz glass is a transparent material over a wide wavelength range from near infrared to vacuum ultraviolet, has a very small coefficient of thermal expansion, has excellent dimensional stability, and has a high level of metal impurities. It has features such as high purity with little content. Therefore, the conventional g-line, i
Synthetic quartz glass has been mainly used as an optical member of an optical device using a line as a light source.

In recent years, with the increase in integration of LSIs, a finer drawing technique with a smaller line width is required in an optical lithography technique for drawing an integrated circuit pattern on a wafer. Are being shortened. That is, for example, the light source of the lithography stepper is a conventional g-line (436 nm), i-line (365n).
Starting from m), an ArF excimer laser or an F ₂ laser is being used.

[0004] Low-pressure mercury lamps and Xe ₂ ^* excimer lamps are used in devices such as photo-CVD, cleaning silicon wafers or ozone generators, and are being developed for application to photolithography technology in the future. ing.
It is necessary to use synthetic quartz glass for a gas-filled tube of a lamp used for a low-pressure mercury lamp or an excimer lamp, or an optical element used for an optical device using the above-mentioned short-wavelength light source.

[0005] The synthetic quartz glass used in these optical systems is required to have light transmittance at wavelengths ranging from the ultraviolet region to the vacuum ultraviolet region, and has high light resistance at the wavelength used (the transmittance after light irradiation). Is not reduced).

In conventional synthetic quartz glass, when an ultraviolet ray is irradiated from a high energy light source such as an ArF excimer laser or an F ₂ laser, a new absorption band is generated in an ultraviolet region, so that an ArF excimer laser or an F ₂ laser is used as a light source. However, there is a problem as an optical member when constructing the optical system described above.

When an ArF excimer laser or an F ₂ laser is irradiated for a long time, the so-called E ′ center (≡Si.)
Absorption band centered at 214 nm (hereinafter referred to as 21
An absorption band centered on 260 nm (hereinafter referred to as 260 nm absorption band) called NBOHC (non-crosslinked oxygen radical: ≡Si—O.) Is generated.

As a technique for suppressing the generation of these absorption bands and improving the resistance to ultraviolet light, there is substantially no reduction type defect or oxidation type defect, and an OH group in the synthetic quartz glass is 10%.
0 ppm or more, containing 5 × 10 ¹⁶ hydrogen molecules / c
m ³ method of incorporating more has been proposed (JP-3-
101282). Hydrogen molecules in the synthetic quartz glass have the effect of repairing defects such as E ′ center and NBOHC generated by ultraviolet irradiation, and OH groups are defects that become defects such as E ′ center and NBOHC when irradiated with ultraviolet light. It is said to have an effect of reducing the concentration of the precursor.

However, the present inventors have conducted a detailed study on the change in light transmittance of synthetic quartz glass due to ultraviolet irradiation, and as a result, the absorption band generated in synthetic quartz glass has 214
It was found that an absorption band centered at 163 nm (hereinafter referred to as a 163 nm absorption band) was generated in addition to the nm absorption band and the 260 nm absorption band. When used as an optical member of a device using ultraviolet light having a wavelength of 200 nm or more as a light source, the wavelength used is 163 nm apart from the 163 nm absorption band.
Although there is almost no effect of transmittance decrease due to the generation of the m absorption band, when used as an optical member of a device using ultraviolet light having a wavelength of 200 nm or less as a light source, the transmittance around the used wavelength decreases due to the generation of the 163 nm absorption band. I do.

[0010]

SUMMARY OF THE INVENTION The present invention has a wavelength of 150.
It is intended to provide a synthetic quartz glass which is used in an apparatus using ultraviolet light of from 200 to 200 nm as a light source and does not decrease in transmittance near a used wavelength even when irradiated with ultraviolet light of an ultraviolet light having a wavelength of from 150 to 200 nm, and a method for producing the same. I do.

[0011]

Means for Solving the Problems The inventors of the present invention have a wavelength of 15 nm.
Initial transmittance at 0 to 200 nm (hereinafter, referred to as ultraviolet transmittance) and transmittance decrease due to ultraviolet irradiation (hereinafter, referred to as ultraviolet transmittance).
A detailed study was also conducted on the relationship between the UV resistance and the composition of the synthetic quartz glass. As a result, the UV transmittance was determined by the concentration of OH groups and reduced defects in the synthetic quartz glass. We found that the concentrations of OH groups and hydrogen molecules in quartz glass affected each other, and that there was an optimal relationship between the amount of UV irradiation and the concentration of hydrogen molecules in synthetic quartz glass, especially for UV resistance. Was found.

That is, according to the present invention, a wavelength of 150 to 200 n
m is irradiated with ultraviolet rays, the synthetic quartz glass has an OH group concentration of 100 ppm or less, a hydrogen molecule concentration of less than 1 × 10 ¹⁷ molecules / cm ³ , and is substantially reduced. Contains no mold defects and has a wavelength of 172 nm
The synthetic quartz glass is characterized in that the amount of change in the extinction coefficient at a wavelength of 150 to 200 nm after irradiating 10 kJ / cm ² with an illuminance of 10 mW / cm ² is 0.2 cm ⁻¹ or less.

The present invention also provides a synthetic quartz glass used by irradiating ultraviolet rays having a wavelength of 150 to 200 nm,
The synthetic quartz glass has an OH group concentration of 100 ppm or less, a hydrogen molecule concentration of 1 × 10 ¹⁷ molecules / cm ³ or more, substantially does not contain reduced defects, and emits ultraviolet light having a wavelength of 172 nm at an illuminance of 10 mW / cm ^2. The synthetic quartz glass is characterized in that the amount of change in the extinction coefficient at a wavelength of 150 to 200 nm after irradiating with 3 kJ / cm ² is 0.05 cm ⁻¹ or less.

[0014] The cause of the decrease in transmittance due to ultraviolet irradiation is the generation of two absorption bands due to ultraviolet irradiation. That is,
Irradiation with ultraviolet rays causes reduction-type defects {Si—Si}
A 63 nm absorption band and a 214 nm absorption band by the E ′ center are generated, and the generation of these absorption bands causes a wavelength of 150 to 20 nm.
The transmittance at 0 nm decreases. The amount of these absorption bands generated depends largely on the concentration of hydrogen molecules and reduced defects in the synthetic quartz glass and the amount of UV irradiation. There is a need to.

That is, when the synthetic quartz glass contains 1 × 10 ¹⁷ molecules / cm ³ or more of hydrogen molecules, generation of a 214 nm absorption band is suppressed up to a certain irradiation amount, and
Since almost no nm absorption band is generated,
The transmittance at 0 nm hardly decreases. But,
When irradiation is performed beyond a certain amount, a 163 nm absorption band is rapidly generated, and the transmittance at 150 to 200 nm is greatly reduced. On the other hand, the hydrogen molecule concentration in the synthetic quartz glass is 1 ×
If it is less than 10 ¹⁷ molecules / cm ³ , a 220 nm absorption band is generated even with a relatively small irradiation dose, and the transmittance at 150 to 200 nm is also reduced. However, the generation amount of these absorption bands is saturated when the irradiation amount exceeds a certain irradiation amount, and the 163 nm absorption band is not generated, so that a decrease in transmittance at 150 to 200 nm can be suppressed to some extent or less.

Specifically, for example, as an optical member of an optical device using ultraviolet light having a wavelength of 172 nm at an illuminance of 10 mW / cm ² , when the total irradiation amount is less than 7 kJ / cm ² , the hydrogen molecule concentration Is 1 × 10 ¹⁷ molecules / cm ³
As described above, ultraviolet light having a wavelength of 172 nm, which does not substantially contain reduced defects, is irradiated with 3 kJ / cm ² at an illuminance of 10 mW / cm ^2.
Synthetic quartz glass in which the change in the absorption coefficient at a wavelength of 150 to 200 nm after irradiation with cm ² is 0.05 cm ⁻¹ or less is preferable.

When the total irradiation amount is in the range of 7 kJ / cm ² or more, the hydrogen molecule concentration is less than 1 × 10 ¹⁷ molecules / cm ³ , and substantially contains no reduced defects.
And a wavelength of 150 to 200 nm after irradiating an ultraviolet ray having a wavelength of 172 nm with an illuminance of 10 kJ / cm ² at an illuminance of 10 mW / cm ^2.
It is preferable to use a synthetic quartz glass having a change in the extinction coefficient at 0.2 cm ^-1 or less.

Further, reduced defects (欠 陥 S
(i-Si≡ bond) forms ≡Si
−Si≡ + hν → ≡Si ・ + ≡Si ・ causes a 214 nm absorption band (≡Si ・) to be generated, and the wavelength 15
It reduces the transmittance of ultraviolet light at 0 to 200 nm.
Furthermore, since this reduced defect has an absorption band at a wavelength of 163 nm, the initial ultraviolet transmittance is reduced. Therefore, in the present invention, it is important that the synthetic quartz glass does not substantially contain reduced defects, that is, it is 5 × 10 ¹⁶ / cm ³ or less. The concentration of reduced defects was 163
(Phy)
s. Rev .. B38, 12772 (1988)).

The OH group concentration in the synthetic quartz glass is 10
It is important that the content is 0 ppm or less, and the wavelength is 180 nm.
When used as an optical member of a device using ultraviolet light in the vacuum ultraviolet region as a light source, the OH group concentration is preferably 50 ppm or less, and 10 ppm is used as an optical member of a device using ultraviolet light having a wavelength of 170 nm or less as a light source. Less than is preferred. The lower the OH group concentration, the higher the transmittance for ultraviolet rays in the vacuum ultraviolet region. The OH group concentration also affects the UV resistance, and the lower the OH group concentration, the better the UV resistance.

In the present invention, metal impurities (alkali metal, alkaline earth metal, transition metal, etc.) and chlorine in the synthetic quartz glass not only reduce the transmittance from the ultraviolet region to the vacuum ultraviolet region, but also resist ultraviolet rays. It is preferable that the concentration is low, because it may cause the property to be reduced. The concentration of the metal impurity is preferably 100 ppb or less, particularly preferably 10 ppb or less. The chlorine concentration is 100 ppm or less, particularly 10 ppm
ppm or less, more preferably 2 ppm or less.

The synthetic quartz glass of the present invention can be produced by a direct method, a soot method (VAD method, OVD method) or a plasma method. In particular, the soot method is preferable because the OH group concentration in the synthetic quartz glass can be relatively easily controlled, and the temperature at the time of synthesis is low, which is advantageous in avoiding contamination of impurities such as chlorine and metal.

The present invention also provides: 1) a step of depositing and growing quartz glass fine particles obtained by flame hydrolysis of a glass forming raw material in an oxidizing atmosphere on a substrate to form a porous quartz glass body; (2) a step of heating the porous quartz glass body to a temperature of 900 to 1300 ° C. for dehydration, and (3) a step of removing the dehydrated porous quartz glass body by one step.
And a step of obtaining a transparent glass body by heating to 400 ° C. or higher.

The raw material for forming the glass is not particularly limited as long as it is a raw material that can be gasified, but SiCl ₄ , SiHC
chlorides such as l ₃ , SiH ₂ Cl ₂ , CH ₃ SiCl ₃ , S
Fluoride such as iF ₄ , SiHF ₃ , SiH ₂ F ₂ , SiB
r _4, bromides such as SiHBr _3, halogenated silicon compounds such as an iodide such as SiI _4, or R _n Si
(OR) _4-n (where R is an alkyl group having 1 to 4 carbon atoms,
and n is an integer of 0 to 3). In particular, an alkoxysilane containing no chlorine is preferable. As the base material, a seed rod made of quartz glass (for example, a seed rod described in JP-B-63-24973) can be used. Further, the substrate is not limited to the rod shape, and a plate-shaped substrate may be used.

The atmosphere in the step (2) is preferably an atmosphere containing 100% of an inert gas such as helium or nitrogen, or an atmosphere mainly containing an inert gas such as helium. For pressure, 10 Torr (1 To
(rr = 133.3224 Pa) or less, and preferably 1 Torr or less.

The atmosphere in the step (3) is as follows.
An atmosphere containing 100% of an inert gas such as helium or an atmosphere mainly containing an inert gas such as helium is preferable. The pressure may be reduced pressure or normal pressure. In particular, in the case of normal pressure, helium gas can be used.
Further, the pressure reduction is preferably 100 Torr or less.

In the present invention, the following step (2 ') can be performed instead of step (2). (2 ′) a step of exposing the porous quartz glass body to a fluorine compound-containing gas atmosphere at 1200 ° C. or lower to dehydrate it.

The fluorine compound-containing gas atmosphere may be a fluorine compound (for example, SiF ₄ , SF ₆ , CHF ₃ , CF ₄ ,
F ₂₎ are preferred atmosphere containing 0.1 to 100 vol%. At this time, the porous quartz glass body is doped with fluorine. In this case, the dilution gas is preferably an inert gas such as nitrogen, argon, or helium, or oxygen. Under this atmosphere, dehydration is performed at a temperature of 1200 ° C. or less at which the porous quartz glass body does not sinter. Pressure 0.1 to 10 atm (1 atm =
(1.01325 × 10 ⁵ Pa) for several tens minutes to several hours. In the present invention, pressure units such as “atmospheric pressure” and “Torr” are not gauge pressures but absolute pressures.

In the step (2 '), since the porous quartz glass body can be uniformly doped with fluorine in a short time, the fluorine-containing gas is brought to a normal pressure while maintaining the temperature at 1200 ° C. or less and under reduced pressure. And it is preferable to introduce a fluorine-containing atmosphere. In this case, the pressure at the time of decompression is 1
00 Torr or less is preferable, and especially 10 Torr or less is preferable.

In the present invention, the following step (4) can be performed after the step (3). (4) A step of heating the transparent glass body in an atmosphere containing hydrogen to dope hydrogen. In this case, the heating temperature is 600 ° C
The following is preferred. If the treatment is performed at a temperature of 600 ° C. or more, there is a possibility that reduced defects are generated.

Since the synthetic quartz glass obtained by the above method is used as a stepper lens or other optical members, it is subjected to various heat treatments such as homogenization and molding to give optical properties necessary for the optical members (hereinafter referred to as optical heat treatment). ) Must be performed appropriately. Optical heat treatment is step (4)
Can be done before or after. However, since the optical heat treatment requires a high temperature of 800 to 1800 ° C., it is preferable to perform it before the step (4).

[0031]

EXAMPLES In the following examples, Examples 8, 15 and 16 correspond to comparative examples, and others correspond to examples. (Examples 1 to 8 and 16) Quartz glass fine particles formed by hydrolyzing silicon tetrachloride in an oxyhydrogen flame at 1200 to 1500 ° C. at an oxygen gas / hydrogen gas ratio shown in Table 1 are deposited on a substrate. Then, a porous quartz glass body having a size of 500 mmφ × 600 mm was produced (step (l)). The obtained porous quartz glass body is placed in an atmosphere controllable electric furnace,
The treatment was carried out under the conditions shown in Table 1 under a reduced-pressure atmosphere of 100% inert gas or an atmosphere containing a fluorine compound (step (2) or step (2 ')).

Subsequently, the temperature was raised to 1450 ° C. while maintaining the pressure at a reduced pressure of 10 Torr or less.
Hold the transparent quartz glass body (105mmφ x length 65)
0 mm) (step (3)). The obtained transparent quartz glass body was cut into 200 mmφ × 10 mm to obtain a synthetic quartz glass.

(Examples 9 to 15) After the step (3) in Examples 1 to 8, the obtained transparent quartz glass body was removed by 200 mm.
It was cut into φ × 10 mm, treated under the conditions shown in Table 1, and doped into synthetic quartz glass with hydrogen molecules (step (4)).

Table 2 shows the OH group concentration, hydrogen molecule concentration, fluorine concentration, oxidized defect concentration, and reduced defect concentration in the synthetic quartz glass obtained in Examples 1 to 16. The OH group concentration, fluorine concentration and hydrogen molecule concentration were determined by the following methods.

(OH Group Concentration) Measurement was carried out with an infrared spectrophotometer, and the OH concentration was determined from the absorption peak at a wavelength of 2.7 μm (Cer. Bull., 55 (5), 524, 524).
(1976)).

(Hydrogen molecule concentration) Raman spectroscopy was performed,
From the intensity ratio (I ₄₁₃₅ / I ₈₀₀ ) between the intensity I ₄₁₃₅ detected by the scattering peak at ₄₁₃₅ cm ⁻¹ in the laser Raman spectrum and the intensity I ₈₀₀ of the scattering peak at ₈₀₀ cm ⁻¹ which is the fundamental vibration between silicon and oxygen. , Hydrogen molecule concentration [molecules / cm ³ ] was determined (Zhurn Priklad).
noi Spektroskopii, 46 (6), 9
87 (1986)). The detection limit by this method is 5 × 1
0 ¹⁶ molecules / cm ³ .

(Fluorine concentration) Journal of the Chemical Society of Japan, 1972
According to the method described in (2), 350, synthetic quartz glass was heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid (1 + 1) were added to the obtained melt to prepare a sample solution. The electromotive force of the sample solution was measured using a No. No. manufactured by Radiometer Trading Co. as a fluorine ion selective electrode and a reference electrode. 945-220 and No. Each of the samples was measured with a radiometer using 945-468, and the fluorine concentration was determined based on a calibration curve prepared in advance using a fluorine ion standard solution.

Further, a sample for evaluation of 30 mmφ × 10 mm was cut out from the center of the obtained synthetic quartz glass of 200 mmφ × 10 mm, and the surface of 30 mmφ was mirror-polished for the following evaluation.

A wavelength of 150 to 200 nm was measured using a vacuum ultraviolet spectrophotometer (VTMS-502 manufactured by Acton Research).
Was measured for ultraviolet transmittance. Wavelength 150-200nm
Was evaluated by representing the transmittance of ultraviolet rays at wavelengths of 157 nm and 172 nm. The UV resistance was evaluated based on the change in absorption coefficient at a wavelength of 172 nm after irradiation with Xe ₂ ^* excimer lamp light (illuminance: 10 mW / cm ² ) having a wavelength of 172 nm for 3 to 200 kJ / cm ² . Table 3 shows the evaluation results of the initial transmittance and the ultraviolet light resistance at wavelengths of 157 nm and 172 nm.

In Examples 8 and 15, since the OH group concentration was high, a decrease in the initial transmittance was observed. Further, since Example 16 contains reduced defects, not only the initial transmittance but also a decrease in UV resistance is observed. Practically, the initial transmittance is 60% or more at a wavelength of 157 nm and 172 nm, although it depends on the application.
Is preferably 80% or more.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

According to the present invention, a wavelength of 150 to 200 n
m used as a light source, and a wavelength of 150 to
The present invention provides a synthetic quartz glass and a method for producing the same in which the transmittance near the used wavelength does not decrease even when irradiated with ultraviolet light using ultraviolet light of 200 nm as a light source.

Continued on the front page (72) Inventor Akio Masui 2-13-9-404 Himonya, Meguro-ku, Tokyo F-term (reference) 4G014 AH11 AH21 4G062 AA04 BB02 CC07 MM02 NN01 NN16

Claims (6)

[Claims] 1. A synthetic quartz glass used by irradiating ultraviolet rays having a wavelength of 150 to 200 nm, wherein the synthetic quartz glass has an OH group concentration of 100 ppm or less and a hydrogen molecule concentration of 1 ppm.
Less than × 10 ¹⁷ molecules / cm ³ , substantially free from reduced defects and having an illuminance of 10 m
W / cm ² at 10kJ / cm ² wavelength after irradiation 150
Synthetic quartz glass characterized in that the amount of change in the extinction coefficient at 200 nm is 0.2 cm ^-1 or less. 2. A synthetic quartz glass used by irradiating ultraviolet rays having a wavelength of 150 to 200 nm, wherein the synthetic quartz glass has an OH group concentration of 100 ppm or less and a hydrogen molecule concentration of 1 ppm.
× 10 ¹⁷ molecules / cm ³ or more, substantially free from reduced defects and having an illuminance of 10 m
W / cm ² in 3kJ / cm ² wavelength after irradiation 150-2
Synthetic quartz glass characterized in that the variation of the extinction coefficient at 00 nm is 0.05 cm ^-1 or less. 3. The synthetic quartz glass according to claim 1, wherein the OH group concentration is less than 10 ppm. 4. A method for producing a synthetic quartz glass according to claim 1, wherein: (1) quartz glass fine particles obtained by flame hydrolysis of a glass forming raw material in an oxidizing atmosphere are deposited on a substrate. Growing the porous quartz glass body to form a porous quartz glass body; (2) heating the porous quartz glass body to a temperature of 900 to 1300 ° C. to dehydrate; and (3) removing the dehydrated porous quartz glass body. A process of heating to 1400 ° C. or higher to obtain a transparent glass body, in this order. 5. A method for producing a synthetic quartz glass according to claim 2, wherein: (1) depositing quartz glass fine particles obtained by flame hydrolysis of a glass-forming raw material in an oxidizing atmosphere on a substrate. Growing the porous quartz glass body to form a porous quartz glass body; (2) heating the porous quartz glass body to a temperature of 900 to 1300 ° C. to dehydrate; and (3) removing the dehydrated porous quartz glass body. A method for producing synthetic quartz glass, comprising: heating a transparent glass body at 1400 ° C. or higher to obtain a transparent glass body; and (4) heating the transparent glass body in an atmosphere containing hydrogen to dope hydrogen. 6. The process for producing a synthetic quartz glass according to claim 4, wherein, instead of the step (2), a step of exposing the porous quartz glass body to a gas atmosphere containing a fluorine compound at 1200 ° C. or lower to perform dehydration is performed. Method.