JP3188624B2 - High purity synthetic silica glass for far ultraviolet rays 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 high-purity synthetic silica glass for far ultraviolet rays and a method for producing the same, and more particularly to an excimer laser in the deep ultraviolet region, a lamp having a high transmittance for excimer lamp light, an optical fiber, a lens, and the like. The present invention relates to a high-purity synthetic silica glass for a prism, a window, and a mirror and a method for producing the same.

[0002]

2. Description of the Related Art Heretofore, ultraviolet rays from a mercury lamp such as a g-line or an i-line have been used as light rays used in photolithography for drawing an electronic circuit pattern on a wafer.
However, in recent years, the miniaturization of semiconductor devices has increased, and today, mass production of ultra LSI using a fine pattern of quarter micron or less (0.25 μm or less) is about to begin. In order to form such an ultrafine pattern, the resolution of the currently used g-line and i-line is limited, and light of shorter wavelength is attracting attention. In particular, the most complete excimer laser attracts attention. Have been. The excimer laser is a high-power laser, and is conventionally known from KrF (248 nm) and XeCl (308 n) in terms of oscillation efficiency and gas life.
m) and XeF (351, 353 nm) were suitably used. However, the wavelength for forming a fine pattern of the quarter micron or less is insufficient, and the wavelength is 165 to 165 μm.
Xe ₂ excimer laser (172 nm), ArCl excimer laser (175 nm), ArF excimer laser (193 nm) oscillating at 195 nm (hereinafter referred to as far ultraviolet)
nm), Xe ₂ excimer lamp (172 nm) or Ar
The use of a Cl excimer lamp (175 nm) has been considered. Accordingly, a member which is not damaged by the far ultraviolet ray has been required for the optical member.

[0003]

As a silica glass member which is not damaged by the far ultraviolet rays, the inventors of the present invention have a high concentration of OH groups and hydrogen molecules and a content of transition metal elements etc. of 10 wtppb or less. No. 6-24997 and Japanese Patent Publication No. 6-48
No. 734. However, when a member for far ultraviolet rays is prepared and used by using the silica glass, a decrease in light transmittance occurs, an increase in absolute refractive index, an increase in birefringence occurs, and the service life of the member is short. Met. When the cause was examined, (i) when the OH group was contained in the silica glass at a high concentration, the wavelength 16
The transmittance of 5-195 nm far ultraviolet rays is reduced, the absorption of photon energy of used far ultraviolet rays is increased, and the damage of silica glass is increased, (i.
i) Inclusion of a high concentration of OH groups also includes water molecules at the same time, and the water molecules absorb far ultraviolet rays to increase the damage of silica glass. (iii) The mechanism is unknown, Silica glass containing oxygen and carbon dioxide at the same time as the concentration of hydrogen is easily damaged,
And so on.

Therefore, the present inventors have set the transition metal element concentration of the synthetic silica glass to 1 wtppb or less, the OH group content, the amount of carbon dioxide released, the oxygen-deficient defect concentration, and the concentration of water vapor released to specific ranges or less. As a result, they have found that a stable silica glass having a high transmittance to far ultraviolet rays and a small change in refractive index can be obtained. Furthermore, in addition to the above-mentioned limitation of silica glass, by setting the oxygen release amount and the hydrogen concentration in a specific range, the transmittance is higher even for higher output far ultraviolet rays, and the change in the refractive index is small and stabilized. The inventors have found that silica glass can be obtained, and have completed the present invention. That is,

It is an object of the present invention to provide a stable silica glass having a high purity, a high transmittance to irradiation of far ultraviolet rays, and a small change in refractive index.

An object of the present invention is to provide a stable silica glass having a high transmittance and a small change in refractive index with respect to irradiation with far ultraviolet rays having a wavelength of 165 to 195 nm.

[0007] The present invention also provides a light emitting device having a wavelength of 165 to 175 nm.
It is an object of the present invention to provide a stable silica glass having a high transmittance with respect to the irradiation of far ultraviolet rays and a small change in refractive index.

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

[0009]

In order to achieve the above object, the present invention provides a silica glass for far ultraviolet light, wherein the silica glass is a synthetic silica glass, and the OH group concentration of the silica glass is 1%.
0 to 400 wtppm, oxygen deficiency type defect concentration is 5 × 10
High-purity synthetic silica glass for deep ultraviolet rays having a carbon dioxide emission amount of ¹⁶ × 10 ³ / cm ³ or less, a carbon dioxide emission amount under a vacuum of 1000 ° C. of 5 × 10 ¹⁵ molecules / cm ² or less, and a water vapor emission concentration of 5 × 10 ¹⁷ molecules / cm ³ or less. And the silica glass has an oxygen release of 5 × 10 ¹⁴ molecules / cm ² or less and a hydrogen concentration of 1 ×
The present invention relates to a high-purity synthetic silica glass for far ultraviolet light having a range of 10 ¹⁶ molecules / cm ³ to 1 × 10 ²⁰ molecules / cm ^{3 and} a method for producing the same.

The silica glass of the present invention has a wavelength of 165.
A silica glass having a high transmittance and a small change in refractive index for far ultraviolet rays of up to 195 nm, in particular, excimer laser and excimer lamp light, and using a silicon compound as a raw material, aluminum, titanium, vanadium, chromium, manganese,
It is a synthetic silica glass having a transition metal element concentration of 1 wtppb or less, such as iron, cobalt, nickel, copper, or gallium. As described above, since the silica glass of the present invention must have high purity, natural silica having a high impurity content cannot be used as a raw material.

The silica glass of the present invention has a high purity as described above and an OH group concentration of 10 to 400 wtp.
pm, oxygen deficiency type defect concentration is 5 × 10 ¹⁶ defects / cm ³ or less, and water vapor emission concentration under vacuum at 1000 ° C. is 5 × 1
It is a synthetic silica glass having 0 ¹⁷ molecules / cm ³ or less. OH
When the group concentration is less than the above range, there is no effect of reducing the concentration of oxygen-deficient defects in the silica glass, and the OH group concentration is 40%.
If it exceeds 0 wtppm, the transmittance near the ultraviolet absorption edge is lowered by the OH group itself, which is not preferable. When the oxygen-deficient defect concentration in the silica glass exceeds the above range, 7.6 eV (163 nm) based on the oxygen-deficient defect is used.
A lot of absorption in the vicinity appears, leading to a decrease in the transmittance of far ultraviolet rays. Furthermore, if water molecules are present in the silica glass, 7.
Absorption occurs around 5 eV (165 nm), so that when the water vapor emission concentration exceeds the above range, the transmittance of far ultraviolet rays decreases. In order to use the silica glass of the present invention for higher output far ultraviolet rays, in addition to the above, the amount of released oxygen is 5 × 1
It is preferable to set the concentration of the hydrogen molecule to 0 ¹⁴ molecules / cm ² or less and 1 × 10 ¹⁶ molecules / cm ³ to 1 × 10 ²⁰ molecules / cm ³ . When the oxygen release amount exceeds 5 × 10 ¹⁴ molecules / cm ² , the ultraviolet absorbing effect becomes large, which is not preferable for silica glass for short wavelength. The effect of repairing damage to the network structure of the broken glass is undesirably reduced. In particular, xenon excimer lasers and xenon excimer lamps (1
72 nm), the OH group concentration is 10 to 100 wtppm and the oxygen deficiency defect concentration is 1 × 1
0 ¹⁶ / cm ³ or less, preferably set to release water vapor concentration 1 × 10 ¹⁷ molecules / cm ³ or less under 1000 ° C. vacuum. More preferably, in addition to the above, the amount of released oxygen is 1 ×
It is preferred that the concentration of hydrogen be 10 ¹⁴ molecules / cm ² or less and the concentration of hydrogen molecules be 1 × 10 ¹⁶ molecules / cm ³ to 1 × 10 ¹⁹ molecules / cm ³ . By satisfying the above range, a silica glass having a high transmittance even for far ultraviolet rays of 165 to 175 nm can be obtained.

The silica glass of the present invention is manufactured by the following manufacturing method. Ie

(I) Production of a soot body SiCl ₄ , HSiCl ₃ , which has been highly purified by means such as distillation,
(CH ₃ ) ₂ SiCl ₂ , CH ₃ SiCl ₃ , CH ₃ Si (O
A soot body is formed by forming soot from a silicon compound such as CH ₃ ) ₃ and Si (OCH ₃ ) ₄ by a flame hydrolysis method and depositing the soot. Examples of the flame hydrolysis method include an oxyhydrogen flame hydrolysis method and a propane flame hydrolysis. The OH group concentration contained in the soot body is controlled in the range of 10 to 400 wtppm by changing the ratio between the supply flow rate of the combustion gas supplied to the burner and the supply flow rate of the silicon compound. As the control method, for example, when increasing the OH group content in the silica glass, a method of increasing the supply flow rate of the oxyhydrogen gas or the propane gas with respect to the gas of the silicon compound is adopted.

(Ii) Production of silica glass ingot The soot body is heated in a vacuum at a temperature of 1300 to 1700 ° C., preferably 1400 to 1600 ° C., slowly from the bottom to the top by a zone heating method to remove transparent bubbles. A silica glass ingot containing no silica glass is produced. The degree of vacuum is 1
00Pa or less, preferably 10Pa or less is good. In the vitrification, the OH group content in the silica glass can be controlled by changing the degree of vacuum and the melting temperature. For example, when the degree of vacuum is lowered and the melting temperature is lowered, the OH group content increases.

(Iii) Production of silica glass The obtained silica glass ingot is heat-treated to remove internal strain in the silica glass ingot, and then cut.
It is ground and polished and processed into silica glass of a predetermined size.
As a heating temperature for removing the internal strain, a temperature of about 1100 ° C. is adopted.

(Iv) Degassing treatment The silica glass is then subjected to a vacuum degree of 100 Pa or less,
A degassing process is performed by heating at 00 to 1200 ° C. for 1 to 100 hours. By the degassing treatment, a silica glass having a higher transmittance can be obtained. Further, by performing the internal strain removal treatment (iii) under a high vacuum, degassing treatment can be performed at the same time.

(V) Hydrogen molecule doping treatment The degassed silica glass is treated at 100 to 900 ° C.
Under normal pressure or under pressure, preferably 100 to 500 ° C, 1 to 2
000 kgf / cm ² for 1 to 100 hours in a hydrogen-containing gas atmosphere to obtain a hydrogen concentration of 1 × 10 ¹⁶ molecules / cm ³ to
1 × 10 ²⁰ molecules / cm ³ , preferably 1 × 10 ¹⁶ molecules / cm ³
Silica glass in the range of cm ³ to 1 × 10 ¹⁹ molecules / cm ³ is produced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to specific examples, but the present invention is not limited thereto.

[0019]

【Example】

Examples 1 to 7 (1) Preparation of soot body Silicon tetrachloride (SiC) which was purified by distillation to remove transition metal concentration such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper or gallium
l ₄ ) Fix the gas at 2 liters / minute, supply oxygen and hydrogen gas to the burner at a rate of 2 to 20 liters / minute and 6 to 60 liters / minute respectively, and measure the OH group content number by the soot method. A soot body of 10 to several 100 wtppm was formed. Note that argon was used as a carrier gas.

(2) Production of silica glass ingot The soot body was placed in a stainless steel electric furnace equipped with a cylindrical high-purity graphite heater. It was heated and melted while slowly moving the temperature zone from below to above to produce a transparent silica glass ingot. Aluminum, titanium in the obtained silica glass ingot,
The concentration of transition metal element of vanadium, chromium, manganese, iron, cobalt, nickel, copper or gallium is 0.5wt
ppb or less, and the presence of air bubbles could not be confirmed visually.

(3) Processing of Silica Glass Ingot A sample was cut from the above silica glass and ground, and both surfaces thereof were mirror-polished to obtain a sample for measuring the OH group-containing concentration and oxygen-deficient defect concentration of 10 mm in length.
× 30 mm wide × 10 mm thick plate, 20 mm long × 20 m wide as sample for measuring water vapor and carbon dioxide emission concentration
mx 1mm thick plate and 20mm long x 30mm wide x 10m thick as Xe ₂ excimer lamp irradiation sample
m, and for each sample, OH
The group-containing concentration, oxygen-deficient defect content, water vapor release concentration, and transmittance of 172 nm light after irradiation with a Xe ₂ excimer lamp were measured. Table 1 shows the results. In addition, impurities contained in the silica glass manufactured under the manufacturing conditions of Examples 4, 5, and 7 were analyzed, and the results are shown in Table 2.

(4) Degassing treatment The OH group content produced by changing the supply amounts of silicon tetrachloride gas, oxygen and hydrogen gas in the above production method is 10 wtp.
pm, 50wtppm, 100wtppm, 200wt
Degassing treatment was performed on various types of silica glass samples of ppm and 350 wtppm by heating at 1000 ° C. for 5 hours at a degree of vacuum of 100 Pa or less.

[0023]

[Table 1]

Comparative Examples 1 to 5 A silica glass body was formed by a plasma method (Comparative Examples 1 and 2),
The direct method (Comparative Examples 3 and 4) and the soot body were formed by a soot method (Comparative Example 5) including performing a dehydration treatment by heat treatment in a chlorine-containing atmosphere before vitrification. To produce a transparent silica glass ingot. For Comparative Examples 2 and 4, degassing was further performed under the same conditions as in Examples 2, 4 to 7. The OH group content of the obtained silica glass ingot in the same manner as in Example 1,
The oxygen-deficient defect concentration, the water vapor emission concentration, and the transmittance of a 172 nm light beam after irradiation with a Xe ₂ excimer lamp were measured. The results are shown in Table 2.

[0025]

[Table 2]

Examples 8 to 15 A molded body having a diameter of 100 mm and a thickness of 30 mm was prepared from the transparent silica glass ingot produced in Example 6, and subjected to a degassing treatment and a hydrogen molecule doping treatment.

(I) Degassing treatment For the samples of Examples 8 to 15, in Examples 8 and 9, treatment at 800 ° C. and 10 ³ Pa for 10 hours;
For 0 to 12, treatment at 800 ° C. and 10 ² Pa for 20 hours;
In Examples 13 to 15, at 1000 ° C. and 10 ² Pa, 40
Time treatment.

(Ii) Hydrogen Molecule Doping Treatment The degassing-treated silica glass molded body was subjected to hydrogen doping treatment under the atmosphere gas, pressure, temperature, and time conditions shown in Table 3.

With respect to the silica glass subjected to each of the above treatments, the hydrogen molecule concentration, the water vapor release concentration, the oxygen release amount, the carbon dioxide release amount, the OH group concentration, the chlorine concentration, the birefringence, and the initial transmittance of far ultraviolet rays having a wavelength of 165 nm. The transmittance of far ultraviolet rays having a wavelength of 165 nm after irradiation with a Xe ₂ excimer lamp was measured. Table 3 shows the results.

[0030]

[Table 3]

Comparative Examples 6 to 10 Silica glass was produced by the synthesis methods shown in Table 4, and each of them was subjected to degassing treatment and hydrogen doping treatment. About the obtained silica glass, hydrogen concentration, water vapor release concentration, oxygen release amount, carbon dioxide release amount, OH group concentration, chlorine concentration, birefringence, initial transmittance of far-ultraviolet light having a wavelength of 165 nm, and X
The transmittance of far ultraviolet rays having a wavelength of 165 nm after irradiation with an e ₂ excimer lamp was measured. Table 4 shows the results.

[0032]

[Table 4]

The impurity metal concentrations in the silica glasses of Examples 1 to 15 and Comparative Example 10 were measured and are shown in Table 5.

[0034]

[Table 5]

The methods for measuring the physical properties of the above Examples and Comparative Examples are as follows.

(I) Method for measuring OH group content M. DODD and D. B. FRASE
R, Optical determination o
f OH in fused silica, Jour
nal of Applied Physics, Vo
l. 37 (1966) p. Measurement method described in 3911 document.

(Ii) Method for Measuring Oxygen-Deficient Defects HOSONO, et al. , Experime
ntal evidence for the Si-
Si bond model of the 7.6 eV
band in SiO ₂ glass, Phys
ical Review B, Vol. 44, No.
21 (1991) pp. 12043 to 45 Measurement method described in literature.

(Iii) one of water vapor, carbon dioxide and oxygen
Measurement of outgassing amount under vacuum at 000 ° C. MORIMOTO, et al. , Analysi
s of gas release from vit
reous silica, Journalof N
on-Crystalline Solids, Vo
l. 139 (1992) pp. Measurement methods described in 35-46 documents.

(Iv) A method for measuring the transmittance at a wavelength of 172 nm after irradiation with a Xe ₂ excimer lamp. Size 30 × 20 × 10mm, wavelength 172nm, lamp energy density 10m for double-sided mirror-polished sample
A measuring method for measuring the transmittance when silica glass is irradiated for 1000 hours using a W / cm ² Xe ₂ excimer lamp.

(V) 16 after irradiation with Xe ₂ excimer lamp
Method for measuring the transmittance at 5 nm. 172 nm wavelength, energy density 10 mW / c on a sample of size 30 × 20 × 10 mm, mirror-polished on both sides
165 nm when irradiated with excimer light of m ² for 500 hours
A measuring method for measuring transmittance. (Vi) Method for measuring hydrogen molecule concentration. V. K. KHOTICHENKO, et al. , D
terminatingthe content of
hydrogen dissolvedin quar
tz glass using the method
s of Raman scattering and
massspectrometry, Journal
of AppliedSpectroscopy,
Vol. 46, no. 6, pp 632-635
(1987) Measurement method described in the literature.

(Vii) Method for measuring chlorine concentration. Measurement method by turbidimetry.

(Viii) A method for measuring birefringence. A retardation measurement method using a polarizing plate strain meter.

(Ix) Measurement of transmittance at 165 nm A measuring method using a vacuum ultraviolet transmittance meter.

(X) Measurement of impurities in silica glass Measurement by plasma mass spectrometry (ICP-MS method) and measurement by atomic absorption spectrophotometry.

<Evaluation> As is clear from Tables 1 and 2, the silica glass of the present invention shows excellent transmittance for far ultraviolet rays having a wavelength of 172 nm, and the silica glasses of Examples 4 and 5 exceed 80%. Shows the transmittance. On the other hand, the conventional silica glass for ultraviolet rays containing a high concentration of OH groups (Comparative Examples 3 and 4) and the silica glass containing no OH groups (Comparative Examples 1, 2, and 5) show low transmittance. In particular, silica glass containing hydrogen and oxygen at the concentrations specified in the present invention has an excellent transmittance of 70% or more even with far ultraviolet rays of 165 nm, and does not cause an increase in birefringence.

[0046]

The silica glass of the present invention has a wavelength of 165 to 165.
It shows excellent transmittance to 195 nm ultraviolet light, and is useful as an optical material for far ultraviolet light. Moreover, the silica glass can be produced by using a conventionally known flame hydrolysis method using a high purity silicon compound as a raw material, and is excellent in productivity.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C03C 3/06 C03B 8/04 C03B 20/00

Claims (12)

(57) [Claims] 1. A synthetic silica glass having an OH group concentration of 10 to 400 wt ppm and an oxygen deficiency type defect concentration of 5
× 10 ¹⁶ atoms / cm ³ or less, far and wherein the carbon dioxide emissions under 1000 ° C. vacuum is 5 × 10 ¹⁵ molecules / cm ² or less and water vapor release concentration 5 × is 10 ¹⁷ molecules / cm ³ or less High purity synthetic silica glass for ultraviolet rays. 2. An OH group concentration of 10 to 100 wt ppm, an oxygen deficiency type defect concentration of 1 × 10 ¹⁶ / cm ³ or less,
A carbon dioxide emission amount under a vacuum of 0 ° C. is 1 × 10 ¹⁵ molecules / cm ² or less, and a water vapor emission concentration is 1 × 10 ¹⁷ molecules / c.
2. The high-purity synthetic silica glass for far ultraviolet rays according to claim 1, wherein m is ³ or less. 3. The high-purity synthetic silica glass for deep ultraviolet rays according to claim 1, wherein the amount of released oxygen is 5 × 10 ¹⁴ molecules / cm ² or less and the hydrogen concentration in the silica glass is 1 ×.
A high-purity synthetic silica glass for far ultraviolet rays, which has a molecular weight of 10 ¹⁶ molecules / cm ³ to 1 × 10 ²⁰ molecules / cm ³ . 4. The silica glass according to claim 3, wherein the amount of released oxygen is 1 × 10 ¹⁴ molecules / cm ² or less and the hydrogen concentration in the silica glass is 1 × 10 ¹⁶ molecules / cm ³ to 1 × 1.
A high-purity synthetic silica glass for far-ultraviolet light having a molecular weight of 0 ¹⁹ molecules / cm ³ . 5. The method according to claim 1, wherein the concentrations of the transition metal elements aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper and gallium are 1 wtppb or less. The high-purity synthetic silica glass for deep ultraviolet rays described above. 6. The high-purity synthetic silica glass for far ultraviolet rays according to claim 3, wherein the transmittance for far ultraviolet rays having a wavelength of 165 nm is 50 to 80% of silica glass having a thickness of 10 mm. 7. The high-purity synthetic silica glass for deep ultraviolet rays according to claim 3, wherein the birefringence is 10 nm / cm or less. 8. The high purity synthetic silica glass for deep ultraviolet rays according to claim 3, wherein the chlorine content is 50 wtppm or less. 9. An opaque white soot containing an OH group is prepared by a flame hydrolysis method using a silicon compound.
A method for producing a high-purity synthetic silica glass for far-ultraviolet light, wherein the glass is transparently vitrified by heating in a zone at a temperature of 700 ° C. 10. A silica glass obtained by zone-heating and melting a soot body is further subjected to a vacuum degree of 100 Pa or less and 800 to 120.
10. A degassing process at a temperature of 0 ° C.
The method for producing a high-purity synthetic silica glass for deep ultraviolet rays described above. 11. A high-purity synthesis for deep ultraviolet rays, wherein the silica glass degassed in claim 10 is further subjected to hydrogen doping in a hydrogen-containing gas atmosphere at 900 ° C. or lower at normal pressure or under pressure. A method for producing silica glass. 12. A hydrogen doping treatment at 100 to 500 ° C.,
The method for producing a high-purity synthetic silica glass for deep ultraviolet rays according to claim 11, wherein the treatment is performed at a pressure of 2000 kgf / cm ² for 1 to 100 hours.