JPH11109101A - Optical member for laser beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical member for laser beam in which the optical homogeneity is not degraded or degradation of the image-forming performance is small even under irradiation of the UV laser beam such as KrF by forming the optical member of high-purity transparent synthetic quartz glass containing hydrogen molecule, and specifying the mean hydrogen molecule concentration in the glass, the ratio of the maximum hydrogen molecule concentration to the minimum molecule concentration in the glass, and the content of OH group. SOLUTION: An optical member for laser beam to be used for the laser beam of the UV ray wavelength range of 190-400 nm is formed of high-purity transparent synthetic quartz glass containing hydrogen molecule. The mean hydrogen molecule concentration in the glass is >=1×10<17> molecules/cm<3> , and the ratio of the maximum hydrogen molecule concentration to the minimum molecule concentration in the glass is 1.0-2.2, and the OH group content is <=500 ppm. If the mean hydrogen molecule concentration is <=5×10<16> molecules/cm<3> , the reduction effect o the optical damage is not sufficiently demonstrated, and the transmissivity is degraded, and the refractive index is increased in the laser beam irradiation. The OH group concentration is preferably <=300 ppm, more preferably, <=100 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lens, a window member,
The present invention relates to a mirror, a prism, a filter, an etalon plate, and other optical systems for laser light, and more particularly to an optical system member for laser light used in the ultraviolet wavelength region of 190 to 400 nm, particularly an optical system member for a photolithography apparatus.

[0002]

2. Description of the Related Art With the recent increase in the degree of integration of LSIs, optical lithography techniques for drawing an integrated circuit pattern on a wafer also require a drawing technique in sub-micron units. Lenses and mask substrates used in lithography steppers and catadioptric optical systems are required to have excellent homogeneity, excellent ultraviolet transmittance, and strong resistance to ultraviolet irradiation.

[0003] Quartz glass is a transparent material over a wide wavelength range from near infrared to vacuum ultraviolet.
Synthetic quartz glass, which has a particularly small amount of impurities, has been used as an optical system member for a photolithography apparatus or a substrate material for a photomask because of its extremely small thermal expansion coefficient and excellent dimensional stability.

[0004]

However, in the lithography technology, the wavelength of the light source has been shortened in recent years with the miniaturization and high integration of LSI, and the KrF (248
190 nm to 400 n such as ArF (193 nm).
The use of laser light in the ultraviolet wavelength range of m has been put to practical use or studied. When these laser beams are irradiated on quartz glass for a long time, the glass is damaged, and there is a problem that the transmittance is reduced, the absolute refractive index is increased, and fluorescence is generated.

The cause of the decrease in transmittance during laser irradiation is NB
It is generally thought to be due to the generation of a 260 nm absorption band called OHC and a 215 nm absorption band called E 'center. Although various studies have been made as a method for solving these absorption problems, it is known that hydrogen molecules may be contained in quartz glass in some form. For example, JP-A-3-1
No. 09233 discloses that hydrogen molecules are contained in an amount of 5 × 10 ¹⁶ molecules / cm ³ or more in order to impart laser resistance in an ultraviolet wavelength region of 190 to 400 nm.

Although the action of hydrogen molecules in glass is not clear, it is considered that the defects generated during laser irradiation are repaired. As a result of examining the influence of the hydrogen molecule concentration, the concentration was found to be 5 × 10 ¹⁶ molecules / cm. If it is ³ or more, KrF
Excimer laser at 400 mJ / cm ² · pulse, 1
2 when 5 × 10 ⁵ shots are irradiated under the condition of 00 Hz
The decrease in the transmittance at 48 nm is 0.2% or less, which is a practically acceptable level.

However, also contain 5 × 10 ¹⁶ molecules / cm ³ or more hydrogen, that is the uniformity of the transmittance and refractive index, at the time of laser irradiation degradation, a problem that the imaging performance is degraded I understand.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem. Quartz glass which does not cause a decrease in transmittance and a deterioration in imaging performance even when irradiated with a laser in the ultraviolet wavelength region of 190 to 400 nm. Is provided.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is an optical member for laser light used for laser light in the ultraviolet wavelength region of 190 to 400 nm, comprising hydrogen. It is formed of high purity transparent synthetic quartz glass containing molecules, and the average hydrogen molecule concentration in the glass is 1 ×
The ratio of the highest concentration of hydrogen molecules to the lowest concentration of hydrogen molecules in the glass is at least 10 ¹⁷ molecules / cm ³ , and the OH group content is at most 500 ppm. An optical member for laser light is provided.

That is, the average hydrogen molecule concentration is 5 × 10 ¹⁶
When the molecular weight is not more than the molecule / cm ³ , the effect of reducing optical damage is not sufficiently exhibited, and a decrease in transmittance and an increase in refractive index occur during laser irradiation. Even if the hydrogen molecule concentration is 5 × 10 ¹⁶ molecules / cm ³ or more, if the concentration has a distribution,
Variations occur in the effect of reducing optical damage, and problems such as deterioration of imaging performance due to deterioration of homogeneity occur. .2.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows KrF according to hydrogen concentration.
Absorption coefficient change Δk at a wavelength of 214 nm after laser irradiation
The horizontal axis represents the hydrogen concentration, and the vertical axis represents the absorption coefficient change Δk. That is, Δk [1 / cm] is equal to Kr
F laser (100mJ / cm ² · Pulse, 100H
z) is the change in the absorptance at a wavelength of 214 nm before and after irradiating 3.6 × 10 ⁵ shots.

The hydrogen concentration C _H2 was measured by a Raman scattering method. That is, wave number 800c for SiO ₂
The ratio was calculated from the ratio of the enhanced I ₈₀₀ of the Raman band at m ⁻¹ and the intensity I ₄₁₃₅ of the Raman band at ₄₁₃₅ cm ⁻¹ for the hydrogen molecules contained in the synthetic quartz using the following equation (Zh):
urnal Prikladnoi Spektros
Ropii vol. 46, No. 6, pp. 146-64. 987-9
91, 1987).

[0013]

C _H2 [molecule / cm ³ ] = 12200 × (I ₄₁₃₅₎
/ I ₈₀₀ )

The size of the area where the measurement is performed is about 1 mm square.

[0015] As can be understood from FIG. 1, also contain 10 ¹⁹ (molecules / cm ³⁾ levels of hydrogen molecules, the hydrogen concentration is varied, also varied absorption rate changes. That is, even if the transmittance is not significantly reduced, the uniformity is reduced, and the imaging performance is deteriorated.

In the present invention, the ratio of the highest concentration of hydrogen molecules to the lowest concentration of hydrogen molecules in the glass is in the range of 1.0 to 2.2.

At the same time, the OH group concentration of the optical member according to the present invention is at most 500 ppm, more preferably at most 300 ppm, particularly preferably at most 100 ppm. In other words, when an OH group is contained, it is cleaved by laser irradiation to generate NBOHC, and the transmittance at a wavelength near 260 nm is reduced.
m or less.

[0018]

EXAMPLE Transparent quartz glass (size: 20 × 20 × 1) having different maximum hydrogen molecule concentration and minimum hydrogen molecule concentration shown in Table 1
5mm ³ ) and prepare a KrF laser (energy density:
400mJ / cm ² · Pulse, frequency: 100H
z) was irradiated for 3.0 hours. The refractive index distribution before and after the irradiation was measured by Zygo Mrak III System manufactured by Canon Inc.
m (light source: He-Ne laser, wavelength 633 nm). Examples 1 to 6 are Examples and Examples 7 to 9 are Comparative Examples. Table 2 shows the results. 248 nm wavelength before and after irradiation
The transmittance and the distribution in the plane are measured by U
It was measured at -3210. Table 3 shows the results. In addition,
The hydrogen molecule concentration was measured in the same manner as shown in the graph of FIG.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

In Example 7, since the maximum / minimum ratio of the hydrogen molecule concentration is large, the homogeneity of the transmittance before and after the irradiation of the KrF laser light is remarkably reduced. Example 8 is an example in which the content of the hydrogen molecule concentration is small, and the transmittance before and after irradiation with the KrF laser light is remarkably reduced. Further, Example 9 is an example in which the content of the OH group is large, the transmittance is significantly reduced by KrF laser beam irradiation, and the transmittance uniformity is also significantly reduced.

[0023]

According to the present invention, an optical member for laser light can be obtained in which the optical homogeneity does not deteriorate and the imaging performance does not decrease much even when irradiated with ultraviolet laser light such as KrF.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in absorption coefficient at a wavelength of 214 nm after KrF laser irradiation with respect to a hydrogen concentration.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akio Masui 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Inside the Central Research Laboratory of Asahi Glass Co., Ltd. (72) Inventor Shuhei Yoshizawa 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Inside the corporation

Claims (1)

[Claims] 1. An optical member for laser light used for laser light in an ultraviolet wavelength range of 190 to 400 nm, which is made of high-purity transparent synthetic quartz glass containing hydrogen molecules, and has an average hydrogen molecule content in the glass. Concentration is 1 × 10 ¹⁷ molecules / cm ³
As described above, the ratio between the highest hydrogen molecule concentration and the lowest molecule concentration in the glass is 1.0 to 2.2, and the OH group content is 5%.
An optical member for laser light, characterized in that the content is not more than 00 ppm.