JP3403317B2 - High power synthetic silica glass optical material for vacuum ultraviolet light 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 synthetic silica glass optical material for high power vacuum ultraviolet rays, more specifically, a wavelength of 165 to 165.
The present invention relates to an optical material such as a lens, a prism, a window, a reflector, and a tube which is incorporated in an irradiation device using a high-output vacuum ultraviolet ray as a light source such as an 195 nm excimer laser and an excimer lamp, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, ultraviolet rays from a mercury lamp such as g-line and i-line have been used as a light source of an optical lithography apparatus for drawing an electronic circuit pattern on a silicon wafer. Lines and i-lines have a limited resolution, and excimer lasers with shorter wavelengths are drawing attention, and an optical lithography apparatus using a KrF excimer laser (248 nm) has been developed and is in the implementation stage. However, the degree of integration of semiconductor devices is expected to increase in the near future, and the line width of 0.2μ
A light source capable of drawing a fine pattern of m or less is required. As the light source, an ArF excimer laser (193n
m), mainly Xe ₂ excimer laser (172 nm), A
rCl excimer laser (175 nm), Xe ₂ excimer lamp (172 nm), ArCl excimer lamp (17 nm)
5 nm) and other high-output vacuum ultraviolet rays having a wavelength of 165 to 195 nm are considered, and their development has started. However,
Since the high-power vacuum ultraviolet ray has a higher output than the ultraviolet ray used in the conventional photolithography apparatus, the optical material irradiated with the high-power vacuum ultraviolet ray is rapidly damaged by a decrease in transmittance, an increase in refractive index, a distortion, and the like. Therefore, it cannot be used as an optical material.

At present, as a cleaning method for semiconductor devices, ArF excimer laser (193 nm), Xe ₂ excimer laser (172 nm), ArCl excimer laser (1
75 nm), Xe ₂ excimer lamp (172 nm), A
Wavelength of 165 such as rCl excimer lamp (175 nm)
A dry cleaning method using high-output vacuum ultraviolet rays of 195 nm is being developed, but in this cleaning processing apparatus, a large optical material is required for the window and the tube. However,
As the optical material becomes larger, the damage caused by high-output vacuum ultraviolet rays becomes more serious and it cannot be used as an optical material. Under such circumstances, there has been an eager desire to develop an optical material that is less damaged even by the high-output vacuum ultraviolet ray.

[0004]

DISCLOSURE OF THE INVENTION As an optical material which meets the above demands, the present inventors have disclosed in Japanese Patent Publication No. 6-48734 that the hydrogen gas concentration is at least 5 × 10 ¹⁶ (molecu).
les / cm ³ ) or more, OH group concentration is 100 wtppm
The above optical members for laser light are also described in Japanese Patent Publication No. 6-2701.
No. 3, the hydrogen gas concentration is at least 5 × 10 ¹⁶ (mo
ules / cm ³ ) or more, OH group concentration is 50 wt
ppm or more, the refractive index variation distribution based on the fictive temperature is canceled by the refractive index variation distribution based on the concentration distribution of the OH group, and a synthetic silica glass optical body having substantially no refractive index variation distribution is proposed. For example, diameter 200
mm, a large optical material with a thickness of over 30 mm,
A non-uniform distribution occurs in the concentration of hydrogen molecules and OH groups contained, a difference occurs in the initial transmittance, and the durability regarding the transmittance and the refractive index decreases. Further, when the silica glass optical material is contained in the silica glass optical material at a high concentration of 100 wtppm or more, the initial transmittance becomes low in the vacuum ultraviolet region and the durability is deteriorated. That is, the optical material proposed in the above publication is 165 to 195.
There is a problem that the initial transmittance in the nm range is low and the durability is low.

Accordingly, the inventors of the present invention have conducted extensive studies, and as a result, have made the impurity concentration of the optical material higher than that of the optical material described in the above publication, and have the OH group concentration and the hydrogen molecule concentration within a specific range. It was found that a synthetic silica glass optical material having high transmittance and excellent durability can be obtained by making the concentration distribution uniform and reducing the content of chlorine element. In addition, by limiting the OH group concentration in the synthetic silica glass optical material to a range narrower than the above range, the initial transmittance is high and the durability is maintained high even for high-output vacuum ultraviolet rays having a wavelength of 165 to 175 nm. The inventors have also found out what can be done and completed the present invention. That is,

An object of the present invention is to provide a silica glass optical material having a high initial transmittance for high-power vacuum ultraviolet rays having a wavelength of 165 to 195 nm and excellent durability.

The present invention also has a wavelength of 165 to 175 nm.
It is an object of the present invention to provide a silica glass optical material which has a high initial transmittance with respect to the high output vacuum ultraviolet ray and has excellent durability.

A further object of the present invention is to provide a method for producing the above silica glass optical material.

[0009]

DISCLOSURE OF THE INVENTION The present invention which achieves the above-mentioned object is a wavelength 165 made of synthetic silica glass of ultra-high purity.
In the synthetic silica glass optical material for high output vacuum ultraviolet rays of ˜195 nm, the OH group concentration is 5 to 300 wtppm,
OH group concentration fluctuation range (ΔOH / cm) is 10 wtppm or less, OH group concentration fluctuation range (ΔOH) of the entire optical material is 30
wtppm or less, hydrogen molecule concentration 1 × 10 ¹⁷ to 1 × 10
¹⁹ molecules / cm ³ , hydrogen molecule concentration fluctuation range (ΔH ₂ / cm) of 1 × 10 ¹⁷ molecules / cm ³ or less, hydrogen molecules of the entire optical material
The present invention relates to a large-sized synthetic silica glass optical material for high-output vacuum ultraviolet rays, which has a concentration fluctuation range (ΔH ₂ ) of 3 × 10 ¹⁷ molecules / cm ³ or less and a chlorine element content of 50 wtppm or less.

The synthetic silica glass optical material of the present invention is a synthetic silica glass optical material having a high initial transmittance with respect to high-output vacuum ultraviolet rays and excellent durability, and the high-output vacuum ultraviolet rays are ArF excimer lasers. (193 nm), X
e ₂ excimer laser (172 nm), ArCl excimer laser (175 nm), Xe ₂ excimer lamp (172
nm), an ArCl excimer lamp (175 nm) or the like having a wavelength of 165 to 195 nm. The ultra-high purity means that the concentration of each alkali metal element of Li, Na, and K is 5
wtppb or less, the concentration of each alkaline earth metal element of Mg, Ca, Sr is 1 wtppb or less, Ti, Cr, Mn, F
The concentration of each transition metal element of e, Co, Ni, and Cu is 0.1 w
It is less than or equal to tppb. The synthetic silica glass optical material of the present invention has the above-mentioned ultra-high purity, an OH group concentration of 5 to 300 wtppm, and an OH group concentration fluctuation range (ΔO
H / cm) is 10 wtppm or less, hydrogen molecule concentration is 1 ×
10 ¹⁷ to 1 × 10 ¹⁹ molecule / cm ³ , the hydrogen molecule concentration fluctuation range (ΔH ₂ / cm) is 1 × 10 ¹⁷ molecule / cm ³ or less, and the chlorine element content is 50 wtppm or less.

Generally, the OH group becomes the terminal end of the structure in the silica glass network structure, but if this OH group is contained in the silica glass in an appropriate amount, the internal strain in the network structure is removed, and Si--O--Si is removed. Bond angle of Si approaches the stable value and Si
The average binding energy of —O increases. On the other hand, O
The H group has a function of shifting the ultraviolet absorption edge of silica glass to the long wavelength side, and if contained in a high concentration, the transmittance will be reduced. Therefore, in the synthetic silica glass optical material of the present invention, the OH group concentration is in the range of 5 to 300 wtppm. Particularly in the case of an optical material for high-output vacuum ultraviolet rays having a wavelength of 165 to 175 nm, the OH group concentration is 5 to 100.
It is good to set it as wtppm. If there is a difference in the OH group concentration, a difference in the transmittance, the absolute refractive index, the hydrogen molecule concentration, or the like occurs, and the initial characteristics of the optical material deteriorate. Further, under irradiation with high-output vacuum ultraviolet rays, a difference in decrease in light transmittance and a difference in increase in refractive index occur in the optical material, resulting in very poor durability. Therefore, the fluctuation range (ΔOH / cm) of OH group concentration per 1 cm viewed from the direction of the light incident axis is set to 10 wtppm or less, and the fluctuation range of OH group concentration (ΔOH) of the entire optical material is set to 30 wtppm or less. Moreover, synthetic since silica glass hydrogen molecules to the generation of the dissolved E ^'center absorption band is ^{suppressed, 1 × 10 17 ~1 × 10} 19 molecules of hydrogen molecules In the synthetic silica glass optical material of the present invention The content is in the range of / cm ³ . Of course, the dissolved hydrogen molecules need to be uniform, and the fluctuation range of hydrogen molecule concentration per 1 cm (ΔH ₂ / cm) as viewed from the direction of the light incident axis (ΔH ₂ / cm) is 1 × 10 ¹⁷ molecules / cm ³ or less. Hydrogen molecule concentration fluctuation range (ΔH ₂ ) is 3
× preferably set to 10 ¹⁷ molecules / cm ³ or less.

In addition to the above, the synthetic silica glass optical material of the present invention has a chlorine element content of 50 wtppm or less. The chlorine atom in the silica glass becomes the terminal end of the silica glass network structure like the OH group, but since the bond energy of Si-Cl is smaller than the bond energy of Si-OH, it is exposed to high power vacuum ultraviolet rays. At Si-
Cl absorption band of 210 nm, a precursor of the so-called E ^'center absorption band generation. In order to suppress it, the content of chlorine element is set within the above range.

The synthetic silica glass optical material of the present invention has a fictive temperature of 700 to 1000 in order to further improve its durability.
℃, the fluctuation range is set within 50 ℃. Although the durability of synthetic silica glass increases by setting the fictive temperature low,
To lower the fictive temperature, it is necessary to lengthen the heat treatment time, and it is preferable to set the lower limit of the fictive temperature to 700 ° C. for practical use.

When the synthetic silica glass optical material of the present invention is used as an optical material for a lithographic apparatus, in addition to the above characteristics, three-direction striae-free and refractive index fluctuation width (Δ
It is preferable that n) is 2 × 10 ⁻⁶ or less and the birefringence amount is 1 nm / cm or less.

The synthetic silica glass optical material for high power VUV of the present invention can be manufactured by the following method. Ie

(I) Soot remelting method SiCl ultra-purified by means such as distillation_Four, HSiC
l₃, (CH₃)₂SiCl₂, CH₃SiCl₃, CH₃S
i (OCH₃)₃, H Si (OCH₃)₃, Si (OC
H₃)_FourA silicon compound such as, preferably CH₃Si (OC
H₃)₃, H Si (OCH₃)₃, Si (OCH₃)_FourChlorine
Oxyhydrogen gas or propane gas containing no silicon compounds
Flame hydrolysis to form a white opaque soot body
After adjusting the OH group concentration in the electric furnace,
In the same electric furnace, in a vacuum atmosphere at 1300 to 1700 ° C
Production of bubble-free synthetic silica glass ingot by heating
However, it is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-88742, US Patent
Extends into a rod shape as described in U.S. Pat. No. 3,485,613
Place the stretched silica glass ingot on a lathe and
The silica glass ingot is band-shaped by heating with a burner.
Sequentially soften and melt into the rod-shaped silica glass ingot
The floating zone melting method (FZ method) of rotating and stirring is used to equalize the OH group concentration.
Perform unification processing. Uniform OH group concentration by the floating zone melting method
In addition to striking, striae can be removed. Silica obtained
Hydrogen gas atmosphere under normal pressure or pressure in glass ingot
Medium, heated to 600-1200 ℃ in an electric furnace and concentrated hydrogen molecules
After uniforming the temperature and the virtual temperature, cutting and grinding
Machining and polishing to process silica glass optical material of specified size
how to.

(Ii) Direct Method Glass fine particles obtained by spraying the above ultrahigh-purity silicon compound into an oxyhydrogen gas or propane gas flame and hydrolyzing it are deposited on a target to directly obtain a transparent synthetic silica glass ingot. After making it and subjecting it to uniformization of OH group concentration and striae removal treatment by the floating zone melting method in the same manner as above,
Makes the hydrogen molecule concentration uniform and sets the virtual temperature,
A method to cut, grind, and polish it into a silica glass optical material of specified dimensions.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail based on specific examples, but the present invention is not limited thereto.

[0019]

【Example】

Examples 1 to 4 (1) Preparation of soot body Ultrahigh-purity CH ₃ Si (OCH ₃ ) ₃ gas obtained by distillation purification was fixed at 100 l / min in total, and total oxygen gas and total hydrogen gas were respectively fixed. 10 to 100 liters / minute, 30
The soot body was prepared by supplying the burner to a plurality of burners at a rate of up to 300 liters / minute. OH group content is several tens
A white soot body containing 0 wtppm was formed.

(2) Manufacture of silica glass ingot The above-mentioned soot body is installed in a stainless steel electric furnace containing a cylindrical high-purity graphite heater, and the inside of the electric furnace is set to a vacuum degree of about 10 ³ Pa or less. 600
The heat treatment was performed at a predetermined temperature in the range of up to 900 ° C. to adjust the OH group concentration. The OH group concentration was controlled by adjusting the degree of vacuum, temperature and time during the treatment. Then, in a electric furnace, it was heated and remelted at about 1400 to 1600 ° C. under vacuum to obtain a transparent silica glass ingot.

(3) OH group concentration homogenizing treatment and striae removing treatment The silica glass ingot is formed into a rod-shaped body having a diameter of about 60 mm, which is placed on a lathe, and the OH group is produced by a floating zone melting method by heating an oxyhydrogen burner. After performing the homogenizing treatment and the striae removing treatment of (1), the material was molded into a cylindrical shape having a diameter of 300 mm and a thickness of 60 mm.

(4) Uniformization of Hydrogen Molecule Concentration Treatment and Virtual Temperature Setting Treatment The above cylindrical silica glass ingot was introduced into an electric furnace of a tungsten mesh heater with a stainless steel jacket, and the internal atmosphere was 1 kgf / c in Example 1.
m ² , 100% hydrogen gas, 10 kgf / c in Example 2
m ² , 100% hydrogen gas, first heated to 1100 ° C. and maintained for 50 hours, then 200 to 1000 up to 800 ° C.
The temperature was gradually increased within the range of time, and then the temperature was allowed to cool to room temperature while maintaining the atmosphere. After that, the cylindrical silica glass ingot was subjected to outer circumference grinding and parallel surface grinding to obtain a diameter of 250 mm,
A silica glass optical material having a thickness of 50 mm was prepared.

Examples 5 and 6 (1) Manufacture of silica glass ingot The ultrahigh-purity CH ₃ Si (OCH ₃ ) ₃ gas obtained by distillation purification was fixed at 150 liters / min, and oxygen gas and hydrogen gas were fixed. 30 to 100 l / min and 100 to 300 l / min were supplied to the burner, and a transparent silica glass ingot was prepared by the direct method.

(2) OH group concentration homogenizing treatment and striae removing treatment The above transparent silica glass ingot was formed into a rod-shaped body having a diameter of about 60 mm, which was placed on a lathe and subjected to OH by a floating zone melting method by heating with an oxyhydrogen burner. After subjecting the base to homogenization treatment and striae removal treatment, it was molded into a cylindrical shape having a diameter of 300 mm and a thickness of 60 mm.

(3) Hydrogen molecule concentration homogenizing treatment and virtual temperature setting treatment In Example 5, the cylindrical silica glass ingot was introduced into an electric furnace of a tungsten mesh heater with a stainless steel jacket, and the internal atmosphere was 10 kgf /.
cm ² , 100% hydrogen gas, first heated to 1100 ° C., held for 50 hours, then heated to 800 ° C. 100-50
The temperature was gradually decreased within the range of 0 hour, and then allowed to cool to room temperature while maintaining the atmosphere. In Example 6, the cylindrical silica glass ingot was placed in a stainless steel autoclave, and the internal atmosphere was 500 kgf / cm ² , 100%.
Using hydrogen gas, first raise the temperature to 1100 ° C with an external heater, hold for 50 hours, and then increase to 800 ° C for 100 to 5 ° C.
The temperature was gradually decreased within the range of 00 hours, and then allowed to cool to room temperature while maintaining the atmosphere. The cylindrical silica glass ingot thus obtained was then subjected to outer circumference grinding and parallel surface grinding to obtain a diameter of 25
A silica glass optical material having a thickness of 0 mm and a thickness of 50 mm was prepared.

Regarding the silica glass optical material, the OH group average concentration, OH group concentration fluctuation range (ΔOH / cm), OH group concentration fluctuation range (ΔOH) of the entire optical material, hydrogen molecule average concentration, hydrogen molecule concentration fluctuation range (ΔH) ₂ / cm), fluctuation range of hydrogen molecule concentration in the entire optical material (ΔH ₂ ), chlorine element content,
Fictitious temperature (T _f ), fluctuating temperature range (ΔT _f ), refractive index difference (Δn), birefringence amount in visible light (nm / c)
m), the transmittance for ArF excimer laser irradiation, Xe ₂ excimer laser irradiation, etc. were measured. The results are shown in Table 1.

When the impurity element concentrations of the silica glass optical material of Example 3 and the silica glass optical material of Example 5 were measured, Li was 1 wtp for the former.
pb, Na 4wtppb, K <1wtppb, Mg
And Ca are <1 wtppb and Sr are <0.1 w, respectively.
tppb, Ti, Cr, Mn, Fe, Co, Ni, Cu
Were <0.1 wtppb respectively. Regarding the latter, Li is 1 wtppb, Na is 2 wtppb, K
<1 wtppb, Mg and Ca <1 wtppb, S
r is <0.1 wtppb, Ti, Cr, Mn, Fe, C
o, Ni, and Cu were <0.1 wtppb, respectively.

[0028]

[Table 1] Note): Remelting method Indicates the soot remelting method. DQ method is die
The Rect method is shown.

Comparative Example 1 An ultrahigh-purity synthetic silica glass ingot was formed by using the ultrahigh-purity silicon compound used in Example 1 to form a soot body and a soot remelting method including dehydration treatment in a hydrogen chloride gas atmosphere. It was created. OH to the silica glass ingot
Other than not subjecting the group concentration and hydrogen molecule concentration to uniformization,
Similar to Example 1, 250 mm in diameter and 50 mm in thickness
Optical material was obtained. Regarding the optical material, its OH group average concentration, OH group concentration fluctuation range (ΔOH / cm), OH group average concentration fluctuation range (ΔOH), hydrogen molecule average concentration, hydrogen molecule concentration fluctuation range (ΔH ₂ / cm) ), Hydrogen molecule concentration fluctuation range (ΔH ₂ ) of the entire optical material, chlorine element content, refractive index difference (Δn), fictive temperature (T _f ) and fictive temperature fluctuation range (ΔT _f ), birefringence amount in visible light (Nm /
cm), ArF excimer laser irradiation, Xe ₂ excimer laser irradiation, and the like. The results are shown in Table 2.

Comparative Example 2 An OH group-free synthetic silica glass ingot was prepared in the same manner as in Comparative Example 1 and subjected to striae removal treatment, hydrogen molecule concentration homogenization treatment and virtual temperature setting treatment, and then a diameter of 2
An optical material was prepared by cutting into 50 mm and a thickness of 50 mm, grinding and polishing. OH group average concentration, OH group concentration fluctuation range (ΔOH / cm), OH group concentration fluctuation range (ΔOH) of the entire optical material, hydrogen molecule average concentration, hydrogen molecule concentration fluctuation range (ΔH ₂ / cm), Fluctuation range of hydrogen molecule concentration (ΔH ₂ ) in the entire optical material, chlorine element content,
Refractive index difference (Δn), fictive temperature (T _f ) and fluctuating temperature range (ΔT _f ), birefringence amount in visible light (nm / c)
m), the transmittance for ArF excimer laser irradiation, Xe ₂ excimer laser irradiation, etc. were measured. The results are shown in Table 2.

Comparative Examples 3 and 4 A synthetic silica glass ingot was prepared in the same manner as in Example 3, and in Comparative Example 3, OH group concentration homogenization treatment, striae removal treatment, and virtual temperature setting treatment by heating in the atmosphere were performed. In Comparative Example 4, after the hydrogen molecule concentration homogenization treatment and the virtual temperature setting treatment were performed, the diameter was 250 mm and the thickness was 50 m.
An optical material is prepared by cutting into m, grinding and polishing, and the optical material has an OH group average concentration, an OH group concentration fluctuation range (ΔOH / cm), and an OH group concentration fluctuation range (ΔOH) for the entire optical material. , Hydrogen molecule average concentration, hydrogen molecule concentration fluctuation range (ΔH ₂ / cm), hydrogen molecule concentration fluctuation range of the entire optical material (ΔH ₂ ), chlorine element content, refractive index difference (Δn), fictive temperature (T _f ). The fluctuating temperature range (ΔT _f ), the amount of birefringence in visible light (nm / cm), the transmittance of ArF excimer laser irradiation, and the transmittance of Xe ₂ excimer laser irradiation were measured. The results are shown in Table 2.

Comparative Examples 5 and 6 Synthetic silica glass ingots were prepared by the direct method in the same manner as in Example 5. In Comparative Example 5, hydrogen molecule concentration homogenizing treatment and virtual temperature setting treatment were performed, and in Comparative Example 6, OH.
After performing the group concentration uniforming treatment, the striae removing treatment, the hydrogen molecule concentration uniformizing treatment and the virtual temperature setting treatment, cutting, grinding and polishing treatments were performed to prepare an optical material having a diameter of 250 mm and a thickness of 50 mm. OH group average concentration, OH group concentration fluctuation range (ΔOH / cm), OH group concentration fluctuation range (ΔOH) of the entire optical material, hydrogen molecule average concentration,
Fluctuation range of hydrogen molecule concentration (ΔH ₂ / cm), Fluctuation range of hydrogen molecule concentration of entire optical material (ΔH ₂ ), chlorine element content, refractive index difference (Δn), fictive temperature (T _f ) and fluctuating range of temperature ( ΔT _f ), the amount of birefringence in visible light (nm / c
m), the transmittance for ArF excimer laser irradiation, Xe ₂ excimer laser irradiation, etc. were measured. The results are shown in Table 2.

[0033]

[Table 2] Note): Remelting method Indicates the soot remelting method. DQ method is die
The Rect method is shown.

The physical properties of each of the above Examples and Comparative Examples are measured by the following methods.

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

(Ii) Method of measuring fluctuation range of OH group concentration In a cylindrical silica glass optical material having a diameter of 250 mm and a thickness of 50 mm, 1 in the diameter direction as viewed from the rotational symmetry axis direction.
The OH group concentration is measured at 25 points at 0 mm intervals. From the two adjacent OH group concentration values, the fluctuation range (ΔOH / cm) of OH group per 1 cm is calculated from the maximum and minimum OH group concentration values at 25 points (ΔOH / cm).
OH) is a measurement method for calculating the OH group average concentration from the arithmetic average value of the OH group concentrations at 25 points.

(Iii) Method for measuring hydrogen molecule concentration. V. K. KHOTIMCHENKO, et al. ，
Determin-ing the content
of hydrogendissolved in q
uartz glass using themes
ods of Raman scattering an
d massspectrometry, Journ
al of Applied Spectroscop
y, Vol. 46, No. 6, (1987) pp
632-635, the measurement method described in the literature.

(Iv) Method for measuring the fluctuation range of hydrogen molecule concentration. In a cylindrical silica glass optical material having a diameter of 250 mm and a thickness of 50 mm, 1 in the diameter direction when viewed from the rotational symmetry axis direction.
The H ₂ concentration is measured at 25 points at 0 mm intervals. From the H ₂ concentration values of two neighbors, the fluctuation range of H ₂ concentration per 1 cm (Δ
Of H ₂ / cm), concentration of H ₂ fluctuation range in the entire optical material is obtained from the maximum and minimum values of the concentration of H ₂ at 25 points to (ΔH _2), and H ₂ average density from the arithmetic mean value of the concentration of H ₂ at 25 points Measuring method to calculate.

(V) Method for measuring chlorine concentration. After decomposition with HF aqueous solution, measurement method by nephelometry with addition of AgNO ₃ .

(Vi) Impurity measurement in silica glass Na, K, Mg, Ca, Ti and Fe are measured by atomic absorption spectrophotometry, Li, Sr, Cr, Mn, Co, Ni and C.
u is measured by plasma mass spectrometry (ICP-MS
Law).

(Vii) Measuring method of refractive index fluctuation width (Δn) Measuring method by optical interferometry using a He-Ne laser (633 nm) as a light source.

(Viii) Method for measuring birefringence amount Retardation measurement method using a polarizing plate strain gauge.

(Ix) Method of measuring fictive temperature A. E. Geissberger and F.G. L. G
arener, Raman studies of
vitreous SiO ₂ Versusfitt
Ive temperature, Physical
Review B, Vol. 28, No. 6
(1983) pp. 3266 ^ 3271 Reference method.

(X) Method of measuring fluctuating temperature range and fictive temperature In a silica glass optical material having a diameter of 250 mm and a thickness of 50 mm, measurement is carried out at two points of the central part and the outer peripheral part, and the virtual temperature is calculated by the difference. Law. Also, a measurement method of obtaining a virtual temperature average value from the arithmetic average value of two points.

(Xi) Method for measuring transmittance at 193 nm before and after irradiation with ArF excimer laser. Size 30 × 20 × thickness 10 mm, double-sided mirror-polished sample, wavelength 193 nm, wavelength half width 3 nm, pulse life half width 17 nsec, energy density 50 mJ /
cm ² / shot, 193 nm when irradiated with a laser having a frequency of 100 Hz and an irradiation shot number of 1 × 10 ⁶ shots
A measuring method to measure the transmittance in the.

(Xi) A method for measuring the transmittance at a wavelength of 172 nm before and after irradiation with the Xe ₂ excimer lamp. A measurement method of measuring the transmittance at 172 nm when a sample having a size of 30 × 20 × thickness of 10 mm and a double-sided mirror-polished finish is irradiated with a wavelength of 172 nm, a wavelength half-value width of 14 nm and a lamp energy density of 10 mW / cm ² for 14 days.

<Evaluation> As is clear from the above Tables 1 and 2, the optical materials of the present invention are excellent in excimer light resistance even if they are large in size. Especially, the optical materials of Examples 3 and 4 have ArF excimer laser resistance. It can be seen that the optical materials of Examples 2 and 3 are excellent in Xe ₂ excimer lamp resistance. Furthermore, the optical materials of Examples 3 and 4 have a stable distribution of Δn of 2 × 10 ⁻⁶ without any change in the refractive index after irradiation with ArF excimer laser.

On the other hand, the synthetic silica glass optical materials of Comparative Examples 1 to 6 are inferior in ArF excimer laser resistance and Xe ₂ excimer lamp resistance, and the refractive index distribution after ArF excimer laser irradiation is not uniform. .

[0050]

The synthetic silica glass optical material of the present invention is
It exhibits excellent initial transmittance with respect to high-output vacuum ultraviolet rays having a wavelength of 165 to 195 nm and has excellent durability, and is useful as an optical material for high-output vacuum ultraviolet rays. Moreover, the optical material can be easily manufactured by using a conventionally known flame hydrolysis method or the like using an ultrahigh-purity silicon compound as a raw material, and there is a material having a high industrial value.

Front page continued (72) Inventor Mitsuha Kuriyama 88, Kawakubo, Kanaya, Tamura-cho, Koriyama-shi, Fukushima Shin-Etsu Quartz Co., Ltd. Quartz Technology Laboratory (56) Reference JP-A-9-12323 (JP, A) JP-A 5-58667 (JP, A) JP-A-9-124337 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03B 8 / 04,20 / 00 C03C 3/06

Claims (5)

(57) [Claims] 1. A synthetic silica glass optical material for high-power vacuum ultraviolet rays having a wavelength of 165 to 195 nm, which is made of ultra-high purity synthetic silica glass and has an OH group concentration of 5 to 300 wtp.
pm, OH group concentration fluctuation range (ΔOH / cm) is 10 wtp
pm or less, OH group concentration fluctuation range of the entire optical material (ΔOH)
Is 30 wtppm or less, and the hydrogen molecule concentration is 1 × 10 ¹⁷ to 1
× 10 ¹⁹ molecule / cm ³ , fluctuation range of hydrogen molecule concentration (ΔH ₂ / c
m) is 1 × 10 ¹⁷ molecules / cm ³ or less, water of the entire optical material
Elemental molecule concentration fluctuation range (ΔH ₂ ) is 3 × 10 ¹⁷ molecule / cm ^{3 or} less
Below, a large-scale synthetic silica glass optical material for high-power vacuum ultraviolet rays, which has a chlorine element content of 50 wtppm or less. 2. The OH group concentration is 5 to 100 wtppm.
The large-sized high-output vacuum ultraviolet according to claim 1, wherein
Synthetic silica glass optical material for wire. 3. The concentration of each alkali metal element in the synthetic silica glass is 5 wtppb or less, the concentration of each alkaline earth metal element is 1 wtppb or less, and each transition metal element concentration is 0.1 wt.
It is below ppb, The large-sized synthetic silica glass optical material for high power vacuum ultraviolet rays of Claim 1 or 2 characterized by the above-mentioned. 4. The fictive temperature (Tf) of the optical material is 700 to 1.
000 ℃, fictitious temperature fluctuation range (ΔTf) of the entire optics is 50
The large-scale synthetic silica glass optical material for high-power vacuum ultraviolet rays according to any one of claims 1 to 3, wherein the temperature is not higher than ° C. 5. The fluctuation range (Δn) of the refractive index of the entire optical material is 2
The large-scale synthetic silica glass optical material for high-power high-vacuum ultraviolet light according to any one of claims 1 to 4, which has a refractive index of ^{x10 -6} or less and a birefringence of 1 nm / cm or less.