JP2001311801A - Synthetic quartz glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic quartz glass excellent in vacuum UV transmittance. SOLUTION: The synthetic quartz glass used as an optical member of an optical device using F2 laser light as a light source has >=85%/cm internal transmittance at 157.6 nm wavelength and <=5%/cm variation of the internal transmittance at 157.6 nm by irradiation with UV from an F2 laser, an Xe2 excimer lamp or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a synthetic quartz glass optical member of the optical device as a light source an F ₂ laser (wavelength 157.6 nm), specifically the lens (projection system, the illumination system), a prism, Etalon, photomask substrate, pellicle (pellicle material, pellicle frame or both),
The present invention relates to a synthetic quartz glass for an optical member such as a window material.

[0002]

2. Description of the Related Art Conventionally, in an optical lithography technique, an exposure apparatus for transferring a fine circuit pattern onto a wafer to manufacture an integrated circuit has been widely used. In recent years, as integrated circuits have become more highly integrated and sophisticated, miniaturization of integrated circuits has progressed, and exposure apparatuses have been required to form high-resolution circuit patterns with a large depth of focus on a wafer surface. Shorter wavelength light sources are being promoted. Exposure light sources include conventional g-rays (wavelength 436 nm) and i-rays (wavelength 365
nm), a KrF excimer laser (wavelength 24
8.3 nm) or ArF excimer laser (wavelength 193.4)
nm) is about to be used. Further, in order to support a next-generation integrated circuit having a circuit pattern of 100 nm or less, an F ₂ laser (wavelength: 157.6) is used as an exposure light source.
nm) has begun to be considered.

An optical member used in an optical device using such a light source includes a working wavelength band, that is, 157.6 n.
It is required to have stable and excellent light transmittance in a wavelength range of m or less (hereinafter, simply referred to as “vacuum ultraviolet ray transmittance”).

[0004] In order to improve the vacuum ultraviolet ray transmittance, Japanese Patent Application Laid-Open No. Hei 8-91867 discloses that the OH group content is 200.
ppm or less, chlorine concentration is 2 ppm or less, and ΔSi-S
A synthetic quartz glass having an i≡ concentration of 1 × 10 ¹⁵ / cm ³ or less has been proposed. Also, Japanese Patent Application No. 10-370014.
In JP-A No. 2-2, a synthetic quartz glass having an OH group content of less than 10 ppm and containing substantially no reduced defects is proposed.

[0005] All of these conventional synthetic quartz glasses are intended to improve the vacuum ultraviolet transmittance by setting the component composition such as the OH group content within a predetermined range. However, ultraviolet rays having a wavelength of 180 nm or less are irradiated. In some cases, the vacuum ultraviolet light transmittance may increase or decrease, and stable vacuum ultraviolet light transmittance cannot be exhibited.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a synthetic quartz glass which stably exhibits excellent vacuum ultraviolet ray transmittance.

[0007]

The present inventors have SUMMARY OF THE INVENTION As a result of performing a detailed examination for VUV transparent synthetic quartz glass is irradiated with F ₂ laser, when improving the vacuum ultraviolet rays permeability, and vice For the first time, and found that both were related to the vacuum ultraviolet transmittance of synthetic quartz glass before irradiation with vacuum ultraviolet light.
That is, the higher the vacuum ultraviolet ray property before irradiation with vacuum ultraviolet light, the more stable the vacuum ultraviolet ray transmittance when vacuum ultraviolet light is applied is obtained.

Accordingly, the present invention relates to a synthetic quartz glass used for an optical member of an optical device using an F ₂ laser as a light source, wherein the internal transmittance at a wavelength of 157.6 nm is 88%.
157.6% during irradiation with a total of 20 kJ / cm ^{2 of} an F ₂ laser having a energy density of 1 mJ / cm ² / pulse or more, preferably 92% / cm or more and an energy density of 1 mJ / cm ² / pulse or less.
Provided is a synthetic quartz glass having a variation in nm internal transmittance of ± 4% / cm or less.

Further, according to the present invention, in a synthetic quartz glass used for an optical member of an optical device using an F ₂ laser as a light source, the internal transmittance at a wavelength of 157.6 nm is 88% /.
cm or more, 157.6 nm internal transmission between preferably a 92% / cm, and an illuminance 50mW / cm 20kJ / cm ^{2 2} The following Xe ₂ excimer lamp light in total, preferably of 54kJ / cm ² irradiation ± 5% / c fluctuation
m, preferably ± 3% / cm or less.

In the present invention, OH in synthetic quartz glass is used.
The group content affects the light transmittance at a wavelength of 180 nm or less, and the higher the OH group content, the lower the initial vacuum ultraviolet ray transmittance. The content is preferably 1 ppm or less, particularly preferably 0.1 ppm or less. The vacuum ultraviolet ray transmittance is also affected by the state of OH groups in the synthetic quartz glass, and a state in which adjacent OH groups are hydrogen-bonded to each other is more preferable than an isolated state.

In the present invention, the oxygen-deficient defect is defined as
Si-Si≡ has an absorption band centered on a wavelength of 163 nm. The internal transmittance T _{163 at 163} nm (%
/ Cm) is the OH group content C _OH (p
pm), it is estimated as follows. T ₁₆₃ (% / cm) ≧ exp (−0.02 C _OH ^0.85 ) × 100 (1) However, if there is an oxygen-deficient defect, the internal transmittance at an actual wavelength of 163 nm is determined by an absorption band centered at 163 nm. T ₁₆₃ ) is smaller than the value on the right side of Expression (1). Therefore, it is preferable that oxygen-deficient defects are not substantially contained, since excellent vacuum ultraviolet ray permeability can be obtained.

In the present invention, a distorted structure such as a three-membered ring structure or a four-membered ring structure in synthetic quartz glass has a wavelength of 165 nm.
m or less, there is a tendency that the light transmittance of m or less is reduced and the vacuum ultraviolet light transmittance is deteriorated. Scattering peak intensity I of the specific scattering peak intensity of 495cm ^-1 in the laser Raman spectrum is I ₁ and 606 cm ^-1
₂ preferably satisfies I ₁ / I ₀ ≦ 0.59 and I ₂ / I ₀ ≦ 0.15 for a scattering peak intensity I ₀ of 440 cm ⁻¹ .

[0013] In the present invention, chlorine in synthetic quartz glass impairs vacuum ultraviolet ray transmission and its stability.
It is preferable that the content is small. Specifically, the chlorine content in the synthetic quartz glass is 10 ppm or less, particularly 5 pp.
m or less, more preferably substantially not contained.

When fluorine is contained in synthetic quartz glass,
It has an effect of reducing the OH group content by substituting with an OH group, and further has an effect of reducing a distorted structure such as the above three-membered ring structure or four-membered ring structure, which is preferable. Specifically, the synthetic quartz glass of the present invention contains fluorine at 10 ppm or more, preferably 100 ppm or more, particularly preferably 200 ppm or more.

In the present invention, metal impurities such as alkali metals, alkaline earth metals, and transition metals in the synthetic quartz glass not only reduce the transmittance in the ultraviolet region to the vacuum ultraviolet region, but also reduce the ultraviolet resistance. Therefore, the content is preferably as small as possible. Specifically, the total content of metal impurities is preferably 100 ppb or less, particularly preferably 50 ppb or less.

As described above, the synthetic quartz glass contains OH groups.
With a content of 5 ppm or less, a chlorine content of 10 ppm or less,
Index I for four- and four-membered ring structures₁/ I₀And
And I _Two/ I₀Are 0.59 or less and 0.14 or less, respectively.
Below, and if the fluorine content is 10 ppm or more,
F_TwoLaser irradiation or Xe_TwoExcimer lamp irradiation
The rise or fall of the 157 nm internal transmittance
It is possible.

As a method for producing the synthetic quartz glass of the present invention, a direct method, a soot method (VAD method, OVD method), a plasma method and the like can be mentioned. The soot method is particularly preferred from the viewpoint that the production temperature is low and contamination of impurities such as chlorine and metal can be avoided. According to the soot method, even when silicon tetrachloride is used as a raw material, a synthetic quartz glass having a chlorine content of less than 10 ppm can be obtained.

At this time, it is effective to irradiate the obtained synthetic quartz glass with a low irradiation Xe ₂ excimer lamp for a relatively long time, since the synthetic quartz glass has improved vacuum ultraviolet transmittance and stability.

[0019]

Examples of the present invention will be described below. The present invention is not limited to these examples.

(Examples 1 to 19) The glass raw materials shown in Table 1, ie, silicon tetrachloride or hexamethyldisilazane were hydrolyzed in an oxyhydrogen flame, and the formed SiO ₂ fine particles were deposited on a substrate to obtain a diameter. 350mm, length 600mm
Was produced. At this time,
When silicon tetrachloride is used as a raw material, hydrolysis is performed in an oxyhydrogen flame in which the volume ratio of oxygen to hydrogen is 15:25 with silicon tetrachloride as 1, and when hexamethyldisilazane is used as a raw material, Hydrolysis was carried out in an oxyhydrogen flame in which the volume ratio of oxygen to hydrogen was 10:25 with hexamethyldisilazane being 1. Next, the porous quartz glass body was placed in an electric furnace capable of controlling the atmosphere and maintained under the conditions of dehydration treatment shown in Table 1 to dehydrate (low OH-based) the porous quartz glass body. .

Subsequently, the temperature was raised to 1450 ° C. while maintaining the pressure at 150 Pa or less, and the temperature was maintained at this temperature for 10 hours, and the transparent quartz glass body (180 mm in diameter, 400 mm in length) was formed.
mm). This transparent quartz glass body is heated to 1750 ° C. above the softening point in an electric furnace having a heating element made of carbon to cause its own weight deformation, and 200 mm × 250 mm
A synthetic quartz glass block sample was obtained by molding into a long block shape. Next, annealing was performed under the annealing conditions shown in Table 1.

Further, the synthetic quartz glass blocks of Examples 18 and 19 were sliced to a thickness of 30 mm and sliced from the vicinity of the center in the longitudinal direction.
For one block having a thickness of m, two surfaces of 200 mm square were mirror-polished, and then from the direction perpendicular to the surface of 200 mm square.
The sample was irradiated with a Xe ₂ excimer lamp under a nitrogen atmosphere under the conditions shown in (1) to obtain a synthetic quartz glass block sample.

From the vicinity of the center of the synthetic quartz glass block samples obtained in Examples 1 to 19, evaluation samples of 50 mm □ × 10 mm thickness and 50 mm □ × 3 mm thickness were cut out and evaluated as follows.

(Evaluation 1: Content of OH Group and Its Existence) Measurement was performed by an infrared spectrophotometer around the center of a 50 mm square of the evaluation sample, and the OH group content was determined from an absorption peak at a wavelength of 2.7 μm. TA (JPWiliams e
t. al., Ceramic Bulletin, 55 (5), 524,1976). The detection limit by this method is 0.1 ppm.

Regarding the existence state of the OH group, the wavelength 2
The determination was made based on the position of the absorption peak at 000 to 3000 nm. That is, the absorption peak is 2700-2730n
m, it exists in a free state without hydrogen bonding and has an absorption peak of 2730 to 27.
When it is located in the wavelength region of 67 nm, it exists in a hydrogen-bonded state.

(Evaluation 2: Chlorine Content) 50
GD-Mass analysis is performed about the center of the mm square,
The chlorine content in the synthetic quartz glass was determined. The detection limit by this method is 1 ppm.

(Evaluation 3: Fluorine content)
A sample of 10 mm × 10 mm × 10 mm was cut out from the center of the 0 mm square, and the fluorine concentration was analyzed. The method for analyzing the fluorine concentration is as follows. The Chemical Society of Japan, 1972
(2) According to the method described in 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 used as a fluorine ion selective electrode and a reference electrode by Radiometer Trading Co., Ltd. 9
No. 45-220 and No. 45. Each of the samples was measured with a radiometer using 945-468, and the fluorine content was determined based on a calibration curve prepared in advance using a fluorine ion standard solution. The detection limit by this method is 10 ppm.

(Evaluation 4: Reduction type defect) 50 of the evaluation sample
50 mm x 50 mm x 3 mm sample from the center of the mm square
And a sample of 50 mm × 50 mm × 10 mm, each of which is mirror-polished on two sides of 50 mm square, and a vacuum ultraviolet spectrophotometer (“UV201M” manufactured by Spectrometer Co., Ltd .; the same applies hereinafter) with the temperature of the sample kept at 25 ° C. Wavelength 16
The light transmittance at 3 nm was measured. The internal light transmittance T at a wavelength of 163 nm from the light transmittances T ₁ and T ₂ of the two types of samples having a thickness of 3 mm and a thickness of 10 mm.
₁₆₃ was determined according to equation (2), and it was examined whether or not the condition of equation (3) was satisfied. When the condition of Expression (3) is not satisfied, that is, when the value on the left side of Expression (3) is smaller than the value on the right side, it means that a reduced defect exists. T ₁₆₃ (% / cm) = exp (−ln (T ₁ / T ₂ ) /0.7) × 100 (2) T ₁₆₃ (% / cm) ≧ exp (−0.02C _OH ^0.85 ) × 100 (3) )

(Evaluation 5: Three- and four-membered ring structures) Raman spectroscopy (Ramonor T manufactured by Jobin Ybon)
64000 cold air light source: argon ion laser (wavelength 51
4.5 nm)) and a scattering peak intensity I ₁ of 495 cm ⁻¹ and 605 cm ⁻¹ in the laser Raman spectrum.
The scattering peak intensity I ₂ of ^-1 to obtain the intensity ratio I ₁ / I ₀ and I ₂ / I ₀ of the scattering peak intensity I ₀ of 440 cm ^-1. The smaller the value of the intensity ratio I ₁ / I ₀ and the value of the intensity ratio I ₂ / I ₀ , the better.

Note that each scattering peak intensity I₁, I_Two, I₀
Is as follows. 495cm^-1Scattered pi
And 605cm^-1For each scattering peak
Perform curve fitting with one Lorentz function
So that the least square error with the real spectrum is minimized.
An approximation was made to determine the coefficients for each function. 440cm ^-1of
For the scattering peak, by combining three Gaussian functions,
Also 495cm^-1Scattering peak of 605cm^-1Scattered pi
And 440cm^-1(Excluding the scattering peak of
Curve) by a quadratic function
Perform fitting and find the least square error with the real spectrum.
The coefficient of each function was determined by approximation so as to be the minimum.
Using the function obtained above, the intensity of each scattering peak
I asked.

(Evaluation 6) Xe_TwoExcimer lamp (center wave
Length 172 nm, Ushio's UER20-172)
0mW / cm^Two3mm and 10mm thickness test
The sample was irradiated for a total of 500 hours. Irradiation on two samples
Before and after irradiation for 10 hours (1.08 kJ / cm ^Two),
After irradiation for 500 hours (54 kJ / cm^Two15)
The 7.6 nm transmittance is measured by a vacuum ultraviolet spectrophotometer, and the formula is used.
The internal transmittance of 157.6 nm was determined according to (4), and irradiation was performed.
Change amount ΔT of internal transmittance at 157.6 nm before and after
₁₅₇Was calculated according to equation (5). ΔT₁₅₇Is small
It is stable and excellent in vacuum ultraviolet ray transmittance. T₁₅₇(% / Cm) = exp (−ln (T₁/ T_Two) /0.7) × 100 (4) ΔT₁₅₇= T₁₅₇(After irradiation) -T₁₅₇(Before irradiation) (5)

(Evaluation 7) F ₂ laser (center wavelength: 157.
6 nm, 1 mJ of Lambda Physique LPX240)
/ Mm ² / pulse 3mm thickness and 1 thickness
A 0 mm sample was irradiated with a total of 2 × 10 ⁷ pulses. 2 × 10 ⁶ before and 2 × 10 ⁶ pulse irradiation for 2 samples
^The transmittance of 157.6 nm after the irradiation of ⁷ pulses was measured with a vacuum ultraviolet spectrophotometer, and 157.6 n was measured according to the above formula (4).
m internal transmittance was obtained, and a change amount ΔT ₁₅₇ of the internal transmittance at 157.6 nm before and after irradiation was calculated according to the above equation (5). The smaller ΔT ₁₅₇ is, the more stable and excellent the vacuum ultraviolet ray transmittance is.

Table 2 shows the results of the evaluations 1 to 5, and Table 3 shows the results of the evaluations 6 and 7. Examples 1 to 4 and Example 1
3, Example 14 is a comparative example, and others are examples.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

The synthetic quartz glass of the present invention is excellent in vacuum ultraviolet ray transmission and exhibits the vacuum ultraviolet ray transmission in a stable manner, and particularly has a stable light transmittance at a wavelength of 157.6 nm. .

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinya Kikukawa 1150 Hazawacho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in the Central Research Laboratory, Asahi Glass Co., Ltd. 4G062 AA04 BB02 CC07 GE02 JJ05 JJ06 MM02 MM35 NN01 NN16 5F071 AA04 FF07

Claims (6)

[Claims] A synthetic quartz glass used for an optical member of an optical device using an F ₂ laser as a light source has a wavelength of 157.
The variation of the internal transmittance at 157.6 nm during irradiation of a total of 20 kJ / cm ^{2 of} an F ₂ laser having an internal transmittance at 6 nm of 88% / cm or more and an energy density of 1 mJ / cm ² / pulse or less is ± Synthetic quartz glass of not more than 4% / cm. 2. F_TwoOptical part of optical device using laser as light source
In the synthetic quartz glass used for the material, the wavelength 157.
The internal transmittance at 6 nm is 88% / cm or more.
And illuminance 50mW / cm^TwoThe following Xe_TwoExcimara
Pump light is 20kJ / cm in total ^Two157 during irradiation
Synthesis with 6 nm internal transmittance variation of ± 5% / cm or less
Quartz glass. 3. The synthetic quartz glass has an OH group content of 2 pp.
3. The synthetic quartz glass according to claim 1, wherein the synthetic quartz glass has a molecular weight of m or less and does not substantially contain oxygen-deficient defects. 4. The synthetic quartz glass according to claim 3, wherein the OH groups in the synthetic quartz glass are present in a state of hydrogen bonding. 5. 495c in laser Raman spectrum
scattering peak intensity I ₂ of the scattering peak intensity I ₁ and 606 cm ^-1 in m ^-1 is, I ₁ / I ₀ ≦ 0.59 respectively scattering peak intensity I ₀ of 440 cm ^-1, I ₂ / I ₀ ≦
The synthetic quartz glass according to any one of claims 1 to 4, wherein the ratio is 0.15. 6. The synthetic quartz glass according to claim 1, wherein the chlorine content is 10 ppm or less and the fluorine content is 10 ppm or more.