JPH11322352A - Synthetic quartz glass optical member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the formation of reducing type defects and prevent the transmissivity from deteriorating due to the irradiation with ultraviolet ray laser beams by heat-treating a synthetic quartz glass with a specific hydrogen molecule content at a temperature according to the OH group concentration in the synthetic quartz glass in an atmosphere under a specified hydrogen gas pressure. SOLUTION: A synthetic quartz glass with <5×10<16> molecules/cm<3> content of hydrogen molecules is heat-treated at a temperature TC ( deg.C) defined by the formula TC=370+1.55 [COH] [COH] is the OH group concentration (ppm) in the synthetic quartz glass} according to the OH group concentration in the synthetic quartz glass in an atmosphere under 0.5-30 atm, preferably about 5-30 atm hydrogen gas pressure. Thereby, the content of the hydrogen molecules is increased to >=5×10<16> molecules/cm<3> to produce a synthetic quartz glass optical member at <=100 ppm OH group concentration suitable to applications for irradiating ultraviolet ray laser beams in a wavelength region of 165-185 nm wavelength λ without substantially containing reducing type defects.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
More specifically, the present invention relates to an optical member of a device using ultraviolet light of not more than m and a method of manufacturing the same, and more particularly to an excimer laser (XeC
l: 308 nm, KrF: 248 nm, ArF: 193
synthetic silica glass used as optical components such as lenses, prisms, and window materials used by irradiating vacuum ultraviolet light or ultraviolet light with a low-pressure mercury lamp (185 nm), an excimer lamp (Xe-Xe: 172 nm), or the like. The present invention relates to an optical member and a method for manufacturing the same.

[0002]

2. Description of the Related Art Synthetic quartz glass is a transparent material over a wide wavelength range from the near-infrared region to the vacuum ultraviolet region, has a very small thermal expansion coefficient, and has excellent dimensional stability. Since it has characteristics such as high purity and almost no metal impurities, it has been mainly used as an optical member of an optical device using a conventional g-line or i-line as a light source.

In recent years, with the increasing 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 conventional g-line (436 nm) and i-line (365)
nm) and a KrF excimer laser beam (248 n
m) or ArF excimer laser light (193 nm) is about to be used.

[0004] Low-pressure mercury lamps (185 nm) and excimer lamps (Xe-Xe: 172 nm) have been used for photo-CVD equipment, ozone generators, ashing and etching of silicon wafers, or to be applied to the above applications in the future. Although the development is proceeding, it is necessary to use the synthetic quartz glass also for the gas sealing tube of the lamp used for these and the optical element used by irradiating light of these wavelengths.

[0005] The quartz glass material used for these optical systems is required to have a light transmittance at a wavelength ranging from the ultraviolet region to the vacuum ultraviolet region, and has a high light resistance at a used wavelength (transmittance after light irradiation). Is not reduced).
In particular, regarding light resistance, for example, 248 nm before and after irradiating 1 × 10 ⁶ shots of KrF excimer laser light under the conditions of 400 mJ / cm ² · Pulse and 100 Hz.
It is desired that the transmittance decrease is 0.1% / cm or less and the 214 nm transmittance decrease is 1.0% / cm or less.

[0006] In the conventionally used synthetic quartz glass,
For example, KrF excimer laser light (wavelength 248 nm) or A
Irradiation with high-energy light such as rF excimer laser light (wavelength 193 nm) generates a new absorption band in the ultraviolet region, and has a problem as an optical member when constructing an optical system using the excimer laser light as a light source. . That is, when the laser light is irradiated for a long time, an absorption band of about 215 nm called so-called E 'center and an absorption band of about 260 nm called NBOHC (non-crosslinked oxygen radical) are generated.

[0007] This absorption band is formed by a glass structure in quartz glass, an oxygen deficiency defect such as {Si-Si}, {Si-OO-Si}, and an intrinsic defect due to an oxygen-excess defect. It is thought to be caused by the occurrence of paramagnetic defects, which causes a decrease in transmittance, an increase in absolute refractive index, a change in refractive index distribution, and fluorescence.

[0008]

As a method for solving these problems, various methods have been studied.
It is known that hydrogen molecules may be contained in quartz glass in some form. For example, Japanese Unexamined Patent Publication No. 3-88742 discloses that a synthetic quartz glass contains 5 × 10 ¹⁶ hydrogen molecules / c.
A method is disclosed in which the transmittance is reduced by ultraviolet laser light irradiation by containing at least m ^{3 and at} least 100 ppm of an OH group.

As a means for containing hydrogen molecules in quartz glass, there is known a method of diffusing and containing hydrogen molecules in quartz glass by subjecting quartz glass to heat treatment in a hydrogen-containing atmosphere. For example, JP-A-6-16652
For example, when hydrogen doping is performed at a high temperature of about 800 to 1000 ° C., reduction defects due to hydrogen are generated in quartz glass.
There is disclosed a technique in which hydrogen molecules are contained in quartz glass at 1 × 10 ¹⁷ molecules / cm ³ or more by maintaining the temperature in a low temperature range of −600 ° C. Here, it is described that it is particularly preferable to perform hydrogen doping under a high pressure of 50 atm or more.

In this method, it is necessary to perform a hydrogen-containing treatment at a low temperature in order to suppress the generation of reduced defects. However, since the diffusion rate of hydrogen molecules is low, a concentration distribution of hydrogen molecules easily occurs inside the sample. When the concentration distribution of the hydrogen molecules is present, the light resistance varies within the sample according to the distribution, and the refractive index distribution and the like fluctuate.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems. As a result, when the quartz glass containing hydrogen molecules is heated, the treatment temperature and the OH group in the quartz glass are increased. It has been found that reduced defects may be generated depending on the content, and the critical temperature at which the reduced defects are not generated is closely related to the OH group concentration in the quartz glass. That is, when the quartz glass containing hydrogen molecules is heated at a high temperature, it is a precursor of the defect.
Reduced defects such as Si-Si≡ and ≡Si-H are generated,
Light resistance deteriorates. The OH group has an action of suppressing the generation of these reduced defects, and as the OH group content in the quartz glass increases, substantially no reduced defects are generated even at a high temperature, and the light resistance is excellent. An optical member can be obtained.

On the other hand, the OH group content in the quartz glass is also related to the transmittance at a wavelength λ of 165 to 185 nm. As the OH group content increases, the transmittance in this wavelength region decreases, and the red at the absorption edge is reduced. A shift occurs. This shift of the absorption edge has no problem with optical members used in the wavelength range of λ ≧ 185 nm, such as a KrF excimer laser and an ArF excimer laser, but an excimer lamp (Xe-Xe: 172n)
This is a problem for optical members used in the wavelength range of λ <185 nm, such as m). That is, it is necessary to adjust the OH group content in the synthetic quartz glass according to the wavelength range used.

Accordingly, the present invention is a method for producing a synthetic quartz glass optical member used by irradiating a laser beam in the ultraviolet wavelength range, wherein the content of hydrogen molecules is 5 × 10 ¹⁶ molecules /
The synthetic quartz glass is less than cm ^3, hydrogen gas 0.1
Heat treatment at a temperature of not more than the temperature T _c (° C.) given by Equation 1 according to the OH group concentration in the synthetic quartz glass in an atmosphere of 30 atm and containing hydrogen molecules at 5 × 10 ¹⁶ molecules / cm ³ or more A method for manufacturing a synthetic quartz glass optical member, comprising the step of: _{T c = 370 + 1.55 [C} OH] In Equation 1, however the formula 1 [C _OH] is the concentration of OH groups in the quartz glass: represents a (ppm is the weight displayed the same herein).

In the present invention, the wavelength λ is 165 to 185 n.
a synthetic quartz glass optical member used by irradiating light in a wavelength range in the range of m, wherein the OH group concentration is 100 ppm
Hereinafter, there is provided a synthetic quartz glass optical member characterized in that the content of hydrogen molecules is 5 × 10 ¹⁶ molecules / cm ³ or more and substantially does not contain reduced defects.

The term “reduction type defect” used herein means ≡ in quartz glass.
Si—Si≡ bond and ≡Si—H bond,
"Substantially not containing these reduced defects" has the following meaning. That is, for {Si-Si},
The absorbance α at 163 nm in the vacuum ultraviolet region is α ≦ 1 × 10
⁻² (cm ⁻¹ ) (below the detection limit).
The intensity I ₂₂₅₀ detected by the scattering peak at 50 cm ⁻¹ is
The value of I ₂₂₅₀ / I ₈₀₀ divided by the intensity I ₈₀₀ of the scattering peak at ₈₀₀ cm ⁻¹ indicating the Si—O— bond is I ₂₂₅₀ / I ₈₀₀ ≦ 1.
× 10 ^-4 (below the detection limit).

Further, 5 × 10 ¹⁶ hydrogen molecules are contained in quartz glass.
In order to contain hydrogen molecules / cm ³ or more, the pressure of the hydrogen gas during hydrogen doping should be set to 0.1 in consideration of the equilibrium content of hydrogen molecules.
The pressure may be at least 1 atm, but in order to introduce sufficient hydrogen into the quartz glass in a short time, it is preferable to carry out at 5 atm or more. On the other hand, when the pressure exceeds 30 atm, reduction type defects may be generated. In this case, the pressure may be a partial pressure. That is, the atmosphere may be a mixed atmosphere of hydrogen and another gas, for example, an inert gas such as helium, argon, or nitrogen, and the partial pressure of hydrogen may be 0.1 to 30 atm.

Further, since the synthetic quartz glass according to the present invention is used as a stepper lens or other optical members, it is necessary to perform various heat treatments such as homogenization, molding, and annealing to give necessary optical characteristics as optical members. However, these heat treatments may be performed before or after the hydrogen-containing step. However, since these heat treatments require a high temperature of 800 to 1500 ° C., even if hydrogen is contained in the hydrogen-containing step at 5 × 10 ¹⁶ molecules / cm ³ or more, the subsequent heat treatment reduces the hydrogen molecule content. When heat treatment is performed after the hydrogen-containing step, the heat treatment is preferably performed in an atmosphere of hydrogen gas at 0.1 to 30 atm. However, in this case, since there is a problem that the furnace for the heat treatment needs to have an explosion-proof structure, it is more preferable to perform the hydrogen-containing step after the heat treatment.

On the other hand, 5 × 10 ¹⁶ molecules / cm ^{3 of} hydrogen molecules
If it is necessary to perform a heat treatment at a temperature T (° C.) after the above content, the synthetic quartz glass to be subjected to the heat treatment may include:
OH group concentration [C _OH ] _c calculated in advance by Equation 2
By containing an OH group of (ppm) or more, generation of reduced defects during heat treatment can be suppressed. [C _OH ] _c = (T-370) /1.55 ... Equation 2

Among the synthetic quartz glass optical members having a content of hydrogen molecules of 1 × 10 ¹⁷ molecules / cm ³ or more and containing substantially no reduced defects, produced by the method of the present invention,
Those having an H group concentration of 100 ppm or less are particularly 185 nm.
It has high transmittance in the wavelength range of ≧ λ ≧ 165 nm, and is suitable as an optical member used by irradiating light in such a wavelength range. When the OH group concentration exceeds 100 ppm, 185
The transmittance at nm ≧ λ ≧ 165 nm tends to decrease.

[0020]

[Example] Table 1 shows that there is substantially no reduced defect and the content of hydrogen molecules is less than 5 × 10 ¹⁶ molecules / cm ^3.
Quartz glass having different OH group concentrations (size:
30 mmφ × 10 mm) was prepared, and hydrogen doping was performed under the conditions shown in Table 1. Table 1 shows the equation 1 under each condition.
By appending the T _c (℃). Examples 1 to 9 are Examples and Examples 10 to 10
Reference numeral 15 is a comparative example. The following evaluations were performed on the obtained synthetic quartz glass.

(Evaluation 1) Raman spectroscopy was carried out, and the intensity I ₄₁₆₀ detected by the scattering peak at ₄₁₆₀ cm ⁻¹ in the laser Raman spectrum was 800 c showing ΔSi—O— bond.
value I ₄₁₆₀ / I divided by the intensity I ₈₀₀ of the scattering peak at m ⁻¹
Estimated hydrogen molecule concentration from ₈₀₀ (VSKhotimchenko, e
t.al., Z.Prikladnoi Spektroskopii, 46 (6), 987-997,19
86). (Evaluation 2) Vacuum ultraviolet spectroscopy (V manufactured by Acton Research Co., Ltd.)
TMS-502) and absorbance at ₁₆₃ nm (α ₁₆₃ )
, The {Si-Si} concentration was evaluated.

(Evaluation 3) Raman spectroscopy was performed, and the intensity I ₂₂₅₀ detected by a scattering peak at 2250 cm ^{−1 in} the laser Raman spectrum was determined to be 800c indicating a ≡Si—O— bond.
The value of I ₂₂₅₀ / I divided by the intensity I ₈₀₀ of the scattering peak at m ⁻¹
_{From 800} , the ΔSi—H concentration was evaluated. (Evaluation 4) KrF laser (LPX manufactured by Lambda Physique)
-100) Light with an energy density of 400 mJ / cm ² · P
Irradiation was performed perpendicular to a 30 mmφ surface under the conditions of ulse and a frequency of 100 Hz. Immediately after irradiating 1 × 10 ⁶ shots of KrF laser light, the transmittance at 214 nm was measured with a spectrophotometer (U-3210 manufactured by Hitachi, Ltd.).
m per m (ΔT ₂₁₄
(% / Cm)). (Evaluation 5) Vacuum ultraviolet spectrometer (VT manufactured by Acton Research Co., Ltd.)
MS-502) was used to measure the spectral transmittance at 140 nm to 210 nm.

Table 2 shows the results of the above evaluations 1-4. N
D indicates that it is below the detection limit. By this evaluation,
The quartz glass optical member according to the manufacturing method of the present invention is subjected to a heat treatment to contain a high concentration of hydrogen molecules, or is subjected to a heat treatment in a state of containing hydrogen molecules, and thus has a reduced defect. Does not substantially contain
It can be seen that the transmittance does not decrease much even when irradiated with ultraviolet laser light. Regarding Evaluation 5, the results of Example 2 and Example 5 are shown in FIG. From this result, in particular, the optical member having an OH group content of 100 ppm is 185 nm ≧ λ ≧ 165 n
It can be seen that the optical member has a high transmittance at m, and is suitable for use by irradiating ultraviolet rays in such a wavelength range.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

According to the present invention, a synthetic quartz glass optical member having a small decrease in transmittance due to irradiation with high energy light such as excimer laser light can be obtained. 185 nm ≧ λ
An optical member having a high transmittance at ≧ 165 nm and suitable for use by irradiating with ultraviolet rays in such a wavelength range can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the spectral transmittance of a synthetic quartz glass optical member according to an example of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noriaki Shimohira 1150 Hazawacho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Asahi Glass Co., Ltd.

Claims (3)

[Claims] 1. A method of manufacturing a synthetic quartz glass optical member used by irradiating a laser beam in an ultraviolet wavelength range, wherein the content of hydrogen molecules is less than 5 × 10 ¹⁶ molecules / cm ^3. Is heated at a temperature not higher than the temperature T _c (° C.) given by the equation 1 according to the OH group concentration in the synthetic quartz glass in an atmosphere of hydrogen gas at 0.1 to 30 atm to reduce hydrogen molecules to 5 ×. A method for producing a synthetic quartz glass optical member, comprising a step of containing 10 ¹⁶ molecules / cm ³ or more. T _c = 370 + 1.55 [C _OH ] Expression 1 In Expression 1, [C _OH ] represents the OH group concentration (ppm) in the quartz glass. 2. A method for producing a synthetic quartz glass optical member which is used by irradiating a laser beam in an ultraviolet wavelength range, wherein a synthetic quartz glass containing hydrogen molecules of 5 × 10 ¹⁶ molecules / cm ³ or more is heated to a temperature T. (° C.), and the synthetic quartz glass subjected to the heat treatment has an OH group concentration [C _OH ] _c (ppm) or more calculated by the formula 2 below.
A method for producing a synthetic quartz glass optical member, comprising a base. [C _OH ] _c = (T-370) /1.55 ... Equation 2 3. A synthetic quartz glass optical member used by irradiating light having a wavelength λ in the range of 165 to 185 nm, wherein the OH group concentration is 100 ppm or less and the content of hydrogen molecules is 5 ×. A synthetic quartz glass optical member characterized in that it has 10 ¹⁶ molecules / cm ³ or more and does not substantially contain reduced defects.