JP2764207B2 - Water-soluble synthetic quartz glass for ultraviolet region and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to synthetic quartz glass, particularly optical components such as windows, mirrors, and prisms of precision optical systems used in the ultraviolet region.
The present invention relates to a water-containing synthetic quartz glass used for a photomask substrate for an VLSI and the like and a method for manufacturing the same.

[Related Art] In recent years, the degree of integration of semiconductor devices, particularly, VLSIs has increased, and the circuit patterns thereof have been rapidly miniaturized.
For this reason, the wavelength of the light source has been shortened and the illuminance has been increased at the time of manufacturing the VLSI.

In addition, hydrated synthetic quartz glass exhibiting good performance in the ultraviolet region has been occupying an important position as a material for optical components such as lenses and mirrors in an optical system of an exposure apparatus (stepper) as well as a photomask.

Aqueous synthetic quartz glass is obtained by supplying high purity silicon tetrachloride with oxygen and hydrogen gas as carriers and supplying it to a Bernoulli furnace, and performing a hydrolysis reaction in an oxyhydrogen flame. It is like.

SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl This water-containing synthetic quartz glass has good translucency in a wide ultraviolet region, shows a transmittance curve as shown by the solid line 1 in FIG. 1, and is presumed to be due to the hydroxyl group contained. However, it is resistant to ultraviolet rays, and since such characteristics are hardly affected by the manufacturing conditions, it has come to be used as an optical member as described above.

On the other hand, recently, in the development of exposure technology corresponding to the high integration of VLSI, the g-line (436 nm)
Exposure sources have been shortened to 65 nm), and excimer lasers have also attracted attention as light sources for semiconductor device manufacturing.
A stepper using KrF (248 nm) as a light source has also been prototyped.

In addition, research is being conducted on an excimer laser using ArF (193 nm) as an exposure source.

However, since the excimer laser has a shorter wavelength and a much higher energy density than a conventional light source such as a mercury lamp, there is a possibility that the excimer laser may damage optical components of the stepper.

Synthetic quartz glass is transparent and has good ultraviolet transmission performance as shown in FIG. 1, but it generates charged particle beams such as sputtering and plasma etching, electron beams, X-rays, etc. during the photomask manufacturing process. It has been found that when exposed to a harsh environment, the transmittance performance in the ultraviolet region is reduced.

The dashed line 2 in FIG. 1 is a typical example of performance degradation,
Some absorption bands have peaks at 0 nm (A) and about 260 nm (B).

The broken line 2 in FIG. 1 shows only an example having a typical minimum value, and the intensity of the absorption peak varies depending on the sample.

When the fluorescence spectrum of the synthetic quartz glass having such an absorption band is measured, a fluorescence band having a peak at about 650 nm is recognized. In addition, a fluorescent inspection lamp (manufactured by Tokyo Kogaku Kikai Co., Ltd., FI-31S, Hg lamp, main wavelength 254 nm, power 7.
2W), red fluorescence was visually observed.

In this way, synthetic quartz glass whose quality has deteriorated due to
When used for LSI photomask substrates, the red fluorescence itself is less harmful, but when i-line (365 nm) is used as the light source,
Since the bottom of the absorption band (B) in FIG. 1 extends to around 350 nm, there is a possibility that the transmittance may decrease, and the exposure may be insufficient.

Furthermore, when excimer laser light (KrF, 248 nm) is used as an exposure source, the transmittance is greatly reduced, and a satisfactory transfer pattern cannot be obtained due to insufficient exposure.

Such a change in ultraviolet transmission performance and a phenomenon of red fluorescence caused by sputtering or plasma etching of synthetic quartz glass also occur when synthetic quartz glass is irradiated with excimer laser light.

In other words, KrF (248 nm) or ArF (193 nm) with a certain intensity or higher
Irradiates the synthetic quartz glass with red fluorescence from the irradiated part. The ultraviolet transmittance of the synthetic quartz glass which emits fluorescence by irradiation of the excimer laser shows a curve of a broken line 2 in FIG. 1 similarly to the synthetic quartz glass altered by the above-mentioned sputtering, and shows a red fluorescence spectrum. . In addition, fluorescence is visually observed with a fluorescent inspection lamp.

Synthetic quartz glass that changes its quality when irradiated with excimer laser light, as well as excimer steppers,
It cannot be used as a component material for optical systems using excimer laser light.

Optical properties are temporarily recovered by heat treatment of synthetic quartz glass with reduced UV transmission performance at about 1000 ° C in air in order to modify synthetic quartz glass that has been altered by sputtering, plasma etching, or irradiation of excimer laser light. ,Return to the original. That is, after the heat treatment, the ultraviolet transmittance is restored to the solid line 1 in FIG. 1, and the peak at about 650 nm disappears also in the fluorescence spectrum.

 At the same time, no fluorescence is observed by the fluorescent test lamp.

However, when the optical performance is recovered by the heat treatment, if it is again subjected to sputtering, plasma etching, or excimer laser irradiation, the phenomenon of ultraviolet absorption and red fluorescence before the heat treatment reappears. No recovery.

The present inventors have proposed a method for modifying a synthetic quartz glass which has undergone deterioration, as disclosed in Japanese Patent Application No. 63-27038 (JP-A-1-20166).
4) As proposed. In this method, the heat treatment is performed in a hydrogen gas atmosphere.

The phenomenon of the performance degradation of the synthetic quartz glass caused by sputtering, plasma etching, or excimer laser irradiation, including the phenomenon due to such heat treatment, is apparently completely the same, and therefore it is considered that the cause is also the same. The theoretical elucidation of the mechanism of performance degradation of synthetic quartz glass must be awaited in future studies, but both have the same spectroscopic properties of absorption and fluorescence. It is presumed that some kind of color center is generated by charged particle beams, electron beams, X-rays, and high-energy ultraviolet rays.

The spectroscopic properties of silica glass such as absorption and fluorescence are often explained by its structural defects. The complete structure of the silica glass is a random network of {Si-O-Si}, and the rest are structural defects.

A typical defect in synthetic quartz glass is ≡Si—OH.
However, the binding energy of OH is as large as 110.6 Kcal / mol, which is extremely stable, and has an absorption in the infrared region, but has no adverse effect on spectroscopy such as specific transmission performance in the ultraviolet region. .

In oxygen-deficient silica glass, {Si-Si} or ≡
It is said that Si ·· Si≡, ie, a defect, Oxygen Vacancy (OV) easily occurs, and this defect becomes a precursor to easily induce {Si · (E ′ center).

On the other hand, the oxygen-excess type silica glass is
Si≡, that is, a defect, Peroxy Linkage (PL) is likely to be formed, and this becomes a precursor, {Si-OO- (Peroxy Linkage)
Radical: PR) is said to be induced. And
It is considered that the red fluorescence is due to the emission around 650 nm (red wavelength) by PR.

Furthermore, there is a quantitative relationship between the performance degradation of synthetic quartz glass caused by sputtering and plasma etching and excimer laser irradiation, and 45 mJ / cm ² of Ar
Those that do not emit red fluorescence when irradiated with F (193 nm) or KrF (248 nm) excimer laser of 70 mJ / cm ² or more do not emit red fluorescence even under normal conditions of sputtering or plasma etching. The present inventors have found that the transmittance does not decrease, and a method for inspecting a photomask substrate by irradiating an excimer laser for each lot is disclosed in Japanese Patent Application No. 63-15158 (Japanese Patent Application No. 1-189654). Filed as

Therefore, there is a need to develop a synthetic quartz glass material that does not cause a decrease in performance such as a change in ultraviolet transmittance due to sputtering, plasma etching, or irradiation with excimer laser light.

On the other hand, precision optical systems, especially excimer steppers for the production of VLSI, which have recently been put into practical use, have strict requirements for optical homogeneity in addition to resistance to excimer laser light. That is, a highly homogeneous material without striae in three directions is required.

In general, in an optical system, if there is only one direction of the optical path, such as a window material, it is sufficient if there is no striae in that direction and it is optically uniform. However, in a prism or a corner cube, the optical path is one direction. Because it is not only a thing without striae in three directions is required.

Synthetic quartz glass, which is produced by purifying silica glass by vapor phase hydrolysis of silicon tetrachloride and depositing it as a transparent glass, undergoes the above-described chemical production reaction process.

Therefore, the properties of the product glass depend on temperature, gas composition (O ₂ , H ₂ , H ₂ O, HCl) and reaction conditions. In fact, when the temperature or the gas flow rate changes suddenly, striae (discontinuous distribution of the refractive index) parallel to the deposition surface are generated. In order to prevent the occurrence of striae, it is necessary to keep the gas flow rate or the like constant without fluctuating. Furthermore, since the temperature and gas composition are not uniform and are distributed in the flame, any change in the position or shape of the glass deposition surface exposed to the flame will affect the distribution of the flame. In response, the temperature of the deposition surface and the composition of the gas also change, causing striae.

It is theoretically possible to obtain glass with less striae by suppressing the above-mentioned fluctuation factors as much as possible, but in addition to the raw materials, combustible hydrogen gas and combustible oxygen gas are used. When used, although the cause is not clear, striae of unknown cause may be caused by factors that make it difficult to control the fluctuation of the flame.

Conventionally, in order to obtain a substantially striae-free block, a part with less striae was searched for and selectively cut out from an ingot with less striae.However, the man-hour and the low yield resulted in problems. there were.

As described above, water-based synthetic quartz glass for precision optical system members using excimer lasers and for photomask substrates has high spectroscopic quality, such as excimer laser resistance and transmittance at 200 nm, and pulse. Must have a high degree of homogeneity with virtually no logic.

[Problems to be Solved by the Invention] As described above, water-containing synthetic quartz glass manufactured by a conventional manufacturing method has drawbacks in terms of spectroscopy and homogeneity. It is an object of the present invention to provide a hydrated synthetic quartz glass free from these drawbacks and a method for producing the same.

[Means for Solving the Problems] In view of the above, the present inventors changed various manufacturing conditions and determined which factor in which manufacturing process and how much the limit value of the energy ray for generating red fluorescence (“threshold value”). Was investigated to determine the effect. As a result, the ratio of hydrogen gas to oxygen gas (H ₂
/ O ₂ ) was found to be correlated with this “threshold”. The result is shown in FIG.

The first invention is to improve the “threshold” by increasing the H ₂ / O ₂ ratio and increasing the excess of hydrogen. However, as can be seen from the figure, when the H ₂ / O ₂ ratio is increased, the transmittance of the manufactured water-containing synthetic quartz glass at 200 nm decreases. As an extreme example, an example of the transmittance when the H ₂ / O ₂ ratio is set to 2.6 is shown by the one-dot chain line 3 in FIG.
Near m, a decrease in transmittance that could be called an absorption band was observed.

In other words, the transmittance at 200 nm of the “threshold” of red fluorescence is inversely related to the transmittance at 200 nm. To obtain a synthetic silica glass with a “threshold” of high red fluorescence, the transmittance at 200 nm is high. Must be sacrificed.

When used in the region of 230 nm or more, the decrease in transmittance at 200 nm is not harmful, but it cannot be said that a fundamental solution has been obtained.

The second invention is that the silicon tetrachloride as a raw material of the hydrated synthetic quartz glass is accompanied by an inert gas not involved in the reaction for forming a hydrated synthetic quartz glass as a carrier gas, and is hydrolyzed in an oxyhydrogen flame. The problem of lowering the transmittance at 200 nm was solved.

The third invention is to hydrolyze high-purity silicon tetrachloride in an oxyhydrogen flame in which the ratio of hydrogen gas to oxygen gas (H ₂ / O ₂ ) is in excess of stoichiometric hydrogen. Threshold of red fluorescence generation energy ray of water-based synthetic quartz glass for ultraviolet region which prevents excess oxygen which causes red emission at 650 nm and improves the threshold of energy ray for red fluorescence generation It is a value improvement method.

[Effects of the Invention] According to the first aspect of the present invention, the excess of hydrogen in the synthetic quartz glass is suppressed by increasing the amount of hydrogen.
ical induction was prevented, and as a result, the "threshold" for generating 650 nm red fluorescence was improved.

According to the second invention, by performing the hydrolysis reaction of silicon tetrachloride in an atmosphere of an inert gas, a stoichiometric silica glass free from excess and deficiency of oxygen can be produced. Without lowering the transmittance of
The "threshold" of red fluorescence generation by high energy beam irradiation such as excimer laser can be dramatically improved.

Also, by supplying an inert gas to the center of the flame to lower the temperature of the center of the flame, the temperature distribution in the flame cross section is made uniform, preventing overheating of the flame center, and Is suppressed by suppressing the fluctuation of the silica glass, and the striae is prevented from being generated in the deposited silica glass, thereby making it possible to manufacture a glass ingot having substantially no striae.

As the inert gas, for example, nitrogen, argon, helium, neon, or a mixture of two or more thereof is used.

Example Comparative Example and Example of First Invention According to a conventional method, oxygen gas was used as a carrier gas.
Lot was prototyped.

Then, the quartz glass burners shown in FIG. 4 were set on the top of the Bernoulli furnace shown in FIG. 3, and various gases in the amounts shown in Table 1 were supplied from the burners.

At that time, the gas amount of the central tube, the double tube, and the triple tube was fixed, the H ₂ / O ₂ ratio was changed to a desired value according to the other gas amounts, and the furnace temperature was set to 1400. Controlled at ± 10 ° C.

An excimer laser (KrF, 20
FIG. 2 shows the results obtained by rearranging the “threshold value” of red fluorescence by irradiation and the transmittance at 200 nm with respect to the H ₂ / O ₂ ratio.

When the H ₂ / O ₂ ratio is set to 2.2 to 2.3, it does not deteriorate due to sputtering or plasma etching and emits red fluorescence, and is 200 mJ / cm for excimer laser KrF (248 nm).
Withstands energy densities of ² .

However, the transmittance (at a thickness of 10 mm) at 200 nm was about 86%. This is converted to an absorption coefficient of 2.4 × 10 ⁻² cm ⁻¹ , which is insufficient for a photomask or the like. Also,
Regarding striae, 2 to 10 striae were observed for a layer thickness of 100 mm.

Example 1 of the Second Invention Two lots were prepared under the same conditions as the above-mentioned Example of the first invention, except that argon gas was used as the carrier gas.

At that time, the H ₂ / O ₂ ratio was 2.0 for one lot and 1 for the other lot.
The lot was performed as 2.3.

As a result, the "threshold" of excimer laser (KrF)
Was 500 mJ / cm ² or more.

The transmittance (thickness: 10 mm) at 200 nm was 89% or more (absorption coefficient: 0.92 × 10 ⁻² cm ⁻¹ ).

Regarding striae, none of them had a thickness of 300 mm.

Example 2 of Second Invention Three lots were prepared under the same conditions as Example 1 of the second invention except that nitrogen gas was used as the carrier gas.

At that time, for the H ₂ / O ₂ ratio, the lot was 1.8 for each,
2.0 and 2.3 were implemented.

The result was the same as Example 1 of the second invention, and no substantial difference was found between the results of the two examples.

Nitrogen gas produced NOx at high temperatures and could react with silicon to produce Si-N defects that could cause lattice defects, but as a result, no adverse effects were found.

[Effect of the Invention] Thus, as discussed in detail, the present invention has improved "Threshold" red fluorescent generated by the ratio of hydrogen and oxygen gas (H ₂ / O ₂₎ and hydrogen excess Things.

In addition, silicon tetrachloride, which is a raw material of hydrated synthetic quartz glass, is accompanied by an inert gas not involved in the reaction for forming hydrated synthetic quartz glass as a carrier gas, and is hydrolyzed in an oxyhydrogen flame to increase the transmittance at 200 nm. Solved the problem of decline.

The water-containing synthetic quartz glass of the present invention has stable spectroscopic properties, does not deteriorate by sputtering, plasma etching, or irradiation of excimer laser, and does not generate red fluorescence. It is useful as a member or a substrate for a photomask.

In addition, the fluctuation of the flame during the production, the non-uniformity of the supply of the raw material and the non-uniformity of the temperature are improved by using the inert gas as the carrier gas, and the occurrence of striae is prevented. Therefore, since any portion of the non-striated ingot is cut out, the trouble of searching for a non-striated portion from the ingot as in the related art is omitted.

[Brief description of the drawings]

FIG. 1 is a diagram showing the ultraviolet transmittance, FIG. 2 is a diagram showing the relationship between the ratio of hydrogen to oxygen gas (H ₂ / O ₂ ), the “threshold value” and the transmittance at 200 nm, and FIG. FIG. 4 is a schematic view of a Bernoulli furnace, and FIG. 4 is a cross-sectional view of a tip portion of a burner made of quartz glass.

Continuation of the front page (72) Inventor Naoyoshi Kansugi 4555-38 Oita, Shinnanyo-shi, Yamaguchi Prefecture Yamaguchi Nippon Quartz Co., Ltd. Shinnanyo Plant (56) References JP-A-55-144243 (JP, A) -208150 (JP, A) JP-B-53-42335 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03F 1/00-1/16 C03B 8/04 C03B 8/14 C03B 20/00 C03B 37/018

Claims (13)

(57) [Claims] 1. A hydrated synthetic quartz glass obtained by hydrolyzing high-purity silicon tetrachloride in an oxyhydrogen flame, wherein the ratio of hydrogen gas to oxygen gas (H ₂ / O ₂ ) is stoichiometrically required. Hydrous synthetic quartz glass for the ultraviolet region synthesized with an excess amount of hydrogen. 2. The water-soluble synthetic quartz glass for ultraviolet region according to claim 1, wherein the ratio of hydrogen gas to oxygen gas (H ₂ / O ₂ ) is 2.2 to 2.3. 3. An aqueous synthetic quartz glass obtained by hydrolyzing high-purity silicon tetrachloride in an oxyhydrogen flame, wherein the hydrolysis reaction of the silicon tetrachloride is performed in a flame containing an inert gas, and the wavelength is 200 nm. UV synthetic quartz glass having an internal absorption coefficient of 1 × 10 ^-2 cm ^-1 or less. 4. The water-soluble synthetic quartz glass for ultraviolet region according to claim 3, wherein striae are not observed in any of the three directions. 5. The water-based synthetic quartz glass for ultraviolet region according to claim 1, wherein the water-based synthetic quartz glass is used for optical equipment. 6. The water-based synthetic quartz glass for an ultraviolet region according to claim 1, wherein the water-based synthetic quartz glass is a substrate for a photomask. 7. In the step of producing water-containing synthetic quartz glass by hydrolyzing silicon tetrachloride in an oxyhydrogen flame, the ratio of hydrogen gas to oxygen gas supplied to the burner is determined to be higher than the stoichiometric amount of hydrogen gas. A method for producing water-based synthetic quartz glass for use in the ultraviolet region, characterized in that a hydrolysis reaction is performed. 8. The method of claim 7, wherein the ratio (H ₂ / O ₂ ) of hydrogen gas to oxygen gas is 2.2 to 3, and the water content synthetic quartz glass for ultraviolet region is manufactured. 9. A process for producing water-containing synthetic quartz glass by hydrolyzing silicon tetrachloride in an oxyhydrogen flame, wherein the raw material silicon tetrachloride is accompanied by an inert gas as a carrier gas. Production method of water synthetic quartz glass for area. 10. The method for producing water-based synthetic quartz glass for ultraviolet region according to claim 9, wherein the accompanying inert gas is supplied to the center of the flame. 11. The method for producing water-containing synthetic quartz glass for ultraviolet region according to claim 9, wherein the inert gas is argon. 12. The method for producing water-containing synthetic quartz glass for ultraviolet region according to claim 9, wherein the inert gas is nitrogen. 13. A hydrolytic reaction of high-purity silicon tetrachloride in an oxyhydrogen flame in which the ratio of hydrogen gas to oxygen gas (H ₂ / O ₂ ) is in excess of stoichiometric hydrogen. ,
Prevents the residual excess oxygen that causes 650 nm red emission and raises the threshold of the energy line for generating red fluorescence. Threshold improvement method.