JP2001072428A - Synthetic quartz glass and its evaluation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and quantitatively carry out an evaluation by irradiating synthetic quartz glass with ultraviolet rays in a specific wavelength region, determining the ratio of the fluorescent emission intensity to the produced scattered light intensity and evaluating the fluorescent emission intensity from the resultant ratio. SOLUTION: A synthetic quartz glass used for light in a wavelength region ranging from the ultraviolet region to the vacuum ulttaviolet region is irradiated with ultraviolet rays in a wavelength region of 150-400 nm to determine the ratio R of the fluorescent emission intensity to the scattered light intensity produced from the synthetic quartz glass by the ultraviolet irradiation. When the R is <=0.01, preferably <=0.001, the synthetic quartz glass is evaluated as suitable for an optical member. Furthermore, the OH group concentration in the synthetic quartz glass is <=500 ppm from the viewpoint of suppressing the red fluorescent emission and the total concentration of alkali metals, alkaline earth metals and transition metals is <=5 ppb from the viewpoint of suppressing the green fluorescent emission and yellow fluorescent emission. The oxygen excessive type defects are not contained at all from the viewpoint of suppressing the red fluorescent emission and the oxygen deficient type defects are substantially uncontained from the viewpoint of suppressing the blue fluorescent emission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a synthetic quartz glass and a method for evaluating the same. In particular, the present invention relates to a synthetic quartz glass used as an optical member of a device using ultraviolet light in a wavelength range of 150 to 400 nm as a light source, and a method for evaluating the same.

[0002]

2. Description of the Related Art Synthetic quartz glass is a transparent material in a wide wavelength range from the near-infrared region to the vacuum ultraviolet region, has a very small thermal expansion coefficient, has excellent dimensional stability, and has almost no metallic impurities. It has features such as high purity without containing. Therefore, synthetic quartz glass has been mainly used as an optical member of an optical device using a conventional g-line (wavelength: 436 nm) and i-line (wavelength: 365 nm) 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. Is being promoted. For example, KrF excimer laser (wavelength 248 nm), ArF
There excimer laser while (wavelength 193 nm) is used, even more in the future is about to be used F ₂ laser (wavelength 157 nm) is. Synthetic quartz glass used as an optical member of an apparatus using short-wavelength ultraviolet light as an exposure light source is required to have low fluorescence emission intensity upon irradiation with ultraviolet light.

However, regarding the fluorescence emission intensity, an evaluation method for visually determining the fluorescence in a dark room (JP-A-1-18996).
54) has been proposed, but this method has a problem of lack of quantitativeness. An evaluation method for determining the red fluorescence intensity having a peak at 650 nm from the intensity of an absorption band having a peak at 260 nm by irradiating X-rays (JP-A-7-4324)
Although 9) has been proposed, this method has a problem that only the intensity of the fluorescence having a peak at 650 nm can be evaluated, and the intensity of the fluorescence having a peak at another wavelength cannot be evaluated.

[0005]

An object of the present invention is to determine whether or not the fluorescence emitted when a synthetic quartz glass is irradiated with ultraviolet rays (in particular, ultraviolet rays in a wavelength range of 150 to 400 nm) is sufficiently suppressed. It is an object of the present invention to provide a method for evaluating synthetic quartz glass that can be easily and quantitatively determined under conditions close to those in which quartz glass is actually used. Another object of the present invention is to provide a synthetic quartz glass in which fluorescence emission upon irradiation with ultraviolet rays (particularly, ultraviolet rays in a wavelength range of 150 to 400 nm) is suppressed.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for evaluating synthetic quartz glass used for light in a wavelength range from the ultraviolet region to the vacuum ultraviolet region.
The present invention provides an evaluation method for synthetic quartz glass in which ultraviolet light in a wavelength region of nm is irradiated, a ratio of a fluorescence emission intensity to a scattered light intensity generated from the synthetic quartz glass by the ultraviolet irradiation is determined, and the fluorescence emission intensity is evaluated from the ratio. The present invention also provides
The present invention provides a synthetic quartz glass having a ratio of fluorescence emission intensity to scattered light intensity (hereinafter, simply referred to as intensity ratio R) of 0.01 or less in the above evaluation method.

For example, when synthetic quartz glass is used as a material for a lens of a semiconductor exposure apparatus, when fluorescence is generated in the synthetic quartz glass, the resist is exposed and the dimensional accuracy (resolution) of the obtained fine pattern is reduced. However, if the intensity ratio R is 0.01 or less, the fluorescence emission intensity generated from the synthetic quartz glass is sufficiently small, and the problem does not occur. In particular, the intensity ratio R is preferably 0.001 or less. The synthetic quartz glass of the present invention is preferably
Fluorescence emission upon irradiation with ultraviolet light in the wavelength range of 00 nm is suppressed, and it is suitable as an optical member of a device that uses ultraviolet light in the wavelength range of 150 to 400 nm as a light source.

As the ultraviolet light in the wavelength range of 150 to 400 nm, an excimer laser (XeCl: 308n) is used.
m, KrF: 248 nm, ArF: 193 nm), F ₂
Laser (157nm), low pressure mercury lamp (185n)
m), an excimer lamp (XeXe: 172 nm), a deuterium lamp and the like, which can be selected according to the application. Examples of the optical member to which the synthetic quartz glass of the present invention is applied include a lens, a prism, a window material, and a photomask.

The OH group concentration of the synthetic quartz glass of the present invention is:
From the viewpoint of suppressing red fluorescence emission (fluorescence emission centering on 650 nm), the content is preferably 500 ppm or less. Further, green fluorescent light and yellow fluorescent light (500
From the viewpoint of suppressing fluorescence emission centering on the wavelength of about 600 nm, alkali metals (particularly Na), alkaline earth metals (particularly Mg, Ca) and transition metals (particularly Fe, Cr, V, Mn) in the synthetic quartz glass of the present invention. , Cu, Ni) (total concentration of impurities) is preferably 5 ppb or less.

From the viewpoint of suppressing red fluorescence emission, the synthetic quartz glass of the present invention preferably does not substantially contain oxygen-excess type defects, and emits blue fluorescence emission (fluorescence emission mainly at 288 nm and 458 nm). From the viewpoint of suppression, it is preferable that oxygen-deficient defects are not substantially contained.

The oxygen-deficient defect means a {Si-Si} bond, and the concentration of the defect is determined from the absorption intensity at 163 nm (Phys. Rev., B38, 127).
72 (1988)). Oxygen-excess type defects are ≡Si—O
-O-Si} bond, and the concentration of the defect is obtained by synthesizing synthetic quartz glass (10 mm thick) with 100% hydrogen gas, 1 atm,
Heat treatment was performed at 900 ° C. for 24 hours to increase the OH group concentration, that is, {Si—O—O—Si} + H ₂ → ₂ }.
Determined from SiOH.

The term "substantially free from oxygen-deficient defects" means that the concentration is lower than the detection limit concentration by the above method, that is, 5 × 10 ^16.
Less than the number of defects / cm ³ and containing substantially no oxygen-excess type defects are below the detection limit concentration by the above method, that is, 2 × 1
0 ¹⁷ pieces / cm ³ .

[0013]

The present invention will be described more specifically with reference to the following examples.
The present invention is not limited to these.

According to a known method, silicon tetrachloride is hydrolyzed in an oxyhydrogen flame to produce a synthetic quartz glass, and OH group concentration, oxygen deficiency type defect concentration and oxygen excess type defect concentration shown in Table 1 are prepared. did.

The OH group concentration was measured by an infrared spectrophotometer, and the OH group concentration was determined from the absorption peak at a wavelength of 2.7 μm (Cer. Bull., 55 (5), 524).
(1976)). The impurity concentration was analyzed by ICP-Mass. The total concentration of impurities in Examples 1 to 9 is all below the detection limit (3 ppb or less), and the impurity concentrations (ppb) in Examples 10 to 11 are as shown in Table 2. The concentration of oxygen-deficient defects was determined from the absorption intensity at 163 nm (Phys. Rev., B38, 12772 (198).
8)). The concentration of oxygen-excess type defects is determined by the synthetic quartz glass (1
0 mm thickness) with 100% hydrogen gas, 1 atm, 900 ° C,
Heat treatment was performed for 24 hours, and the value was determined from the increased OH group concentration.

From the obtained synthetic quartz glass, 30 mm × 4
A sample for evaluation of 0 mm x 10 mm was cut out and 30 mm x
Two surfaces of 40 mm and two surfaces of 40 mm × 10 mm were mirror-polished. For this sample, a multi-channel photodiode was set on a 40 mm × 10 mm surface, and 30
KrF excimer laser (energy density 100 mJ / cm ² / pulss)
e, frequency 300 Hz), and measure the center wavelength of the strongest fluorescence emission from the sample (fluorescence emission center wavelength), the fluorescence emission intensity at this wavelength, and the scattered light intensity.
The ratio of the fluorescence emission intensity to the scattered light intensity (intensity ratio R) was determined. FIG. 1 is a schematic diagram showing the evaluation method. Table 3 shows the results.

In Examples 7 to 9, the intensity ratio R exceeds 0.01, the fluorescence intensity is relatively high, and depends on the sensitivity characteristics of the resist.
The intensity ratio of Examples 1 to 6 and Examples 10 to 11 is 0.01 or less, the fluorescence intensity is sufficiently small, and the resolution is hardly affected. In particular, the intensity ratio of Examples 1, 2, 3, and 10 was 0.001 or less, which is an extremely good result.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

According to the evaluation method of the present invention, the synthetic quartz glass is used to determine whether or not the fluorescent light emission caused by irradiation with ultraviolet rays (particularly, ultraviolet rays having a wavelength in the range of 150 to 400 nm) is sufficiently suppressed. Can be easily and quantitatively determined under conditions close to those actually used. Further, according to the present invention, it is possible to easily obtain a synthetic quartz glass in which fluorescence is suppressed even when irradiated with ultraviolet rays in a wavelength range of 150 to 400 nm.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a method for evaluating fluorescence emission intensity.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Noriaki Shimohira 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Asahi Glass Co., Ltd. 4G014 AH15 4G062 AA04 BB02 CC06 MM02

Claims (3)

[Claims] 1. A method for evaluating a synthetic quartz glass used for light in a wavelength range from an ultraviolet region to a vacuum ultraviolet region, comprising irradiating the synthetic quartz glass with ultraviolet light having a wavelength range of 150 to 400 nm. A method for evaluating a synthetic quartz glass in which a ratio of a fluorescence emission intensity to a scattered light intensity generated from a synthetic quartz glass is obtained by using the ratio, and the fluorescence emission intensity is evaluated from the ratio. 2. The synthetic quartz glass according to claim 1, wherein the ratio of the fluorescence emission intensity to the scattered light intensity is 0.01 or less. 3. The synthetic quartz glass has an OH group concentration of 500 p.
The synthetic quartz glass according to claim 2, which is not more than pm, the total concentration of alkali metal, alkaline earth metal and transition metal is not more than 5 ppb, and is substantially free of oxygen-deficient defects and oxygen-excess defects.