JPH01201664A - Method for reforming synthetic quartz glass - Google Patents

Abstract

PURPOSE:To prevent the performance of synthetic quartz glass from being deteriorated, and also, to recover the performance of synthetic quartz glass changed in quality by spattering, etc., by executing a heat treatment in a hydrogen gas atmosphere. CONSTITUTION:Synthetic quartz glass is brought to heat treatment in a hydrogen atmosphere. That is, the synthetic quartz glass whose spectro-optical quality is changed by spattering or plasma etching and the projection of an excimer laser can be recovered completely to its original state for its practical use by a method for bringing it to heat treatment in a hydrogen atmosphere, and also, can be reformed so that the change of its spectro-optical quality is not generated, even if spattering or plasma etching and the projection of the excimer laser are executed thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for modifying synthetic quartz glass, particularly synthetic quartz glass used as a substrate for a photomask for VLSI.

[Prior Art] In recent years, the degree of integration of semiconductor devices, particularly VLSIs, has increased, and the circuit patterns thereof have rapidly become finer.

For this reason, during the manufacturing of VLSIs, the wavelength of light sources is becoming shorter and the illumination intensity is increasing. Furthermore, synthetic silica glass, which exhibits good performance in the ultraviolet region, has become an important material not only for photomasks but also for optical components such as lenses and mirrors in the optical systems of exposure equipment.

This is because synthetic quartz glass is obtained by hydrolyzing silicon tetrachloride in an oxyhydrogen flame, and is resistant to ultraviolet rays and has good translucency in a wide ultraviolet range, as shown by solid line 1 in Figure 1. This is because the material exhibits a transmittance curve, and such characteristics are hardly affected by manufacturing conditions.

On the other hand, in recent years, the wavelength of the exposure source has been shortened from the g-line (436n+++) of high-pressure mercury lamps to the i-line (365r+m) in the development of exposure technology that corresponds to the high integration of VLSIs.
Furthermore, in recent years, excimer lasers have attracted attention as a light source for semiconductor device manufacturing, and a stepper using KrF (24.8nI11) as a light source has also been prototyped.

Furthermore, excimer laser-A r F (193n+o
) is also being studied as an exposure source.

[Problems to be solved by the invention] However, excimer lasers have a shorter wavelength and much higher energy density than conventional light sources such as mercury lamps, so they are difficult to use for parts of the optical system of steppers. It is thought that there is a possibility of causing damage.

Furthermore, as shown in Figure 1, synthetic silica glass is transparent and has good UV transmittance, but it generates charged particle beams, electron beams, X-rays, etc. during sputtering and plasma etching during the photomask manufacturing process. It has been found that some materials exhibit reduced transmittance performance in the ultraviolet region when exposed to harsh environments.

Broken line 2 in Figure 2 is a typical example of performance deterioration, approximately 21
In some cases, absorption bands are formed at 0 nm (A) and about 260 nm (B).

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

When we measure the fluorescence spectrum of synthetic silica glass in which an absorption band has appeared in this way, we find that it is about 650 nm as shown in Figure 2.
A fluorescent band with a peak is observed. In addition, a fluorescent inspection lamp (manufactured by Tokyo Kogaku Kikai Co., Ltd., FI-31S, Hg
When irradiated with a lamp (main wavelength: 254 nm, electric cuff, 2 W), red fluorescence was observed visually.

In this way, when synthetic silica glass whose absorption performance has deteriorated due to sputtering or plasma etching is used for a VLSI photomask substrate, the red fluorescence itself is not harmful, but the i-line (365 nm) is used as a light source. When used, since the tail of the absorption band (B) in FIG. 1 extends to around 350 nm, there is a risk of a decrease in transmittance and a possibility of insufficient exposure.

Moreover, excimer laser light (K r F, 248nn+
) is used as an exposure source, the decrease in transmittance becomes very large, and it becomes impossible to obtain a good transferred pattern due to insufficient exposure.

Changes in ultraviolet absorption rate caused by sputtering and plasma etching of synthetic silica glass,
The phenomenon of red fluorescence occurs when excimer laser is applied to synthetic quartz glass.
It also occurs when exposed to light.

KrF (248n+o) or ArF (19
When synthetic quartz glass is irradiated with 3 nm), red fluorescence is visually observed from the irradiated area. The ultraviolet transmittance of the synthetic quartz glass that has become fluorescent when irradiated with an excimer laser shows the broken LA2 curve in FIG.
In addition, the fluorescence spectrum shown in FIG. 2 is shown. Fluorescence can also be visually observed using a fluorescent inspection lamp.

Synthetic silica glass, which is altered in quality by irradiation with excimer laser light, cannot be used not only as an excimer stepper but also as a component material for optical systems that use excimer laser light.

In an attempt to modify synthetic quartz glass that has been altered by sputtering, plasma etching, and irradiation with excimer laser light, the optical performance of synthetic quartz glass whose absorption performance has decreased is temporarily restored by heat treatment at approximately 1000°C in air. and return to normal.

That is, after heat treatment, the ultraviolet transmittance returns to the solid line 1 in Figure 1, and the fluorescence spectrum also returns to about 6 in Figure 2.
The peak at 50 nm disappears. At the same time, fluorescence is no longer recognized by the fluorescent inspection lamp.

However, when a material whose optical performance has been restored through heat treatment is sputtered, plasma etched, or irradiated with excimer laser again, the phenomena of ultraviolet absorption and red fluorescence that existed before heat treatment reappear, and mere heat treatment cannot improve the fundamental performance. It turned out that there was no recovery.

Theoretical elucidation of the mechanism of performance deterioration of synthetic silica glass caused by sputtering, plasma etching, or excimer laser irradiation, including phenomena caused by heat treatment, will have to wait for future research, but both of them are caused by absorption and fluorescence. Because these spectroscopic properties agree, it seems likely that some kind of color center is generated by charged particle beams, electron beams, X-rays, and high-energy ultraviolet rays due to structural defects inherent in silica glass. It is inferred.

Therefore, it is necessary to develop a synthetic quartz glass material that does not cause performance deterioration such as changes in ultraviolet transmittance due to sputtering, plasma etching, and excimer laser light irradiation, and to develop a modification method that restores the performance of synthetic quartz glass that has undergone alteration. development is needed.

[Means for Solving the Problem] Therefore, the present inventors further conducted experiments on the heat treatment effect, and as a result of intensive research mainly on the influence of the atmosphere, the performance of synthetic silica glass improved when heat treatment was performed in a hydrogen gas atmosphere. The present invention was completed based on the discovery that it is possible to prevent the deterioration and also restore the performance of synthetic quartz glass that has been altered by sputtering, plasma etching, and irradiation with excimer laser light.

[Operation of the Invention] According to the present invention, synthetic quartz glass whose performance has been degraded by sputtering, plasma etching, and irradiation with excimer laser light can be restored by heat treatment in a hydrogen gas atmosphere. Even if sputtering, plasma etching, and excimer laser light irradiation are performed again thereafter, the properties can be modified so that no deterioration in performance occurs.

In addition, by preheating in a hydrogen gas atmosphere,
It can be modified so that performance does not deteriorate even when sputtering or plasma etching is performed.

Heat treatment in a hydrogen gas atmosphere has a similar effect on synthetic quartz glass whose performance has deteriorated due to excimer laser light irradiation, and heat treatment in a hydrogen gas atmosphere in advance can also prevent performance deterioration. be able to.

[Example] Example 1 Synthetic quartz glass photomask substrate (5
A total of five 30 mm square plates, one square each, were cut out from the five sheets (inch square, 2 and 3 arm thickness).

These were heat-treated under the following conditions.

Furnace normal temperature: 1500℃, soaking zone 1000℃ approximately 300m
m Furnace core tube: Transparent quartz glass tube, inner diameter 70+++m Processing conditions Temperature increase: 5℃/win Maximum temperature and holding time: 900℃, 1 hour temperature decrease
:1℃/+5in-300 up to 300℃
Furnace cooled from ℃.

Gas composition and flow rate: H2 100%, 600w1/
After confirming that the ultraviolet transmittance and fluorescence characteristics had recovered after the sin heat treatment, sputtering and plasma etching were performed again under the same conditions as at the beginning. Thereafter, ultraviolet transmittance and fluorescence characteristics were examined, but no deterioration in performance was observed in any of the five sheets.

Example 2 Two 30 mm square plates were cut out from five 5-inch square photomask substrates made of synthetic quartz glass, and after sputtering and plasma etching were performed on each of the five plates in a conventional manner, transmission was performed. When the rate and fluorescence characteristics were measured, it was found that 5
Deterioration in performance was observed in three of the sheets.

Next, heat all 10 sheets including the remaining 5, and set the maximum temperature to 8.
After heat treatment was performed under the same conditions as in Example 1 except that the temperature was 00°C, sputtering and plasma etching were performed. Thereafter, the transmittance and fluorescence characteristics were examined, and no deterioration in performance was observed for all 10 sheets.Example 3 Excimer laser - A r F (193 nm, 100 Hz)
) was irradiated for 2 minutes at an energy density of 45 mJ/alf, and red fluorescence was visually observed during irradiation, resulting in decreased performance. /
Heat treatment was carried out under the same conditions as in Example 1 except that the thickness was 3 m1n.

These were irradiated with excimer laser under the same conditions as before heat treatment, but no red fluorescence was visually observed and no decrease in transmittance performance was observed. Irradiation energy is 800mJ/cn
The same thing happened when I raised it to f. Furthermore, 10100O/a
When the temperature was raised to +, slight red fluorescence was observed during irradiation, but no performance deterioration due to a decrease in transmittance was observed. 20
At 00 mJ/a#, red fluorescence was clearly visible,
Transmittance performance also decreased. The above irradiation results are summarized in Table 1.

Table 1 Example 4 The sample after the test of Example 3 was changed to He/H gas composition.
Heat treatment was carried out under the same conditions as in Example 3 except that = 1/20.

The irradiation results of A r F (193nn+, 100Hz) are shown in Table 2.

Table 2 Example 5 From the same synthetic quartz glass material, l0XIOX30 (
Cut out two samples of m + *), and one of them was heated with ArF (19
3 nm, 100 Hz), and as the energy density was increased, red fluorescence was emitted at 2000 mJ/a#.

Next, both of them were heat-treated together with the unirradiated ones under the same conditions as in Example 3 except that the maximum temperature was 900°C.
A r F (193 nm, 1oOHz) was irradiated. Those irradiated before heat treatment and those not irradiated showed exactly the same behavior. The irradiation results are shown in Table 3.Table 3 Comparative Example 1 6011IIIlφX30mm from the same material as Example 5
Two cylindrical samples of t were cut out. One was heat treated according to Example 5. In addition, the cooling rate of the other side was set to 5℃/+ni
The heat treatment was carried out in accordance with Example 5 except that n was used.

The amount of strain before and after heat treatment was measured for both samples.

The amount of strain was measured at four points located 3 mm from the circumference of two arbitrary perpendicular diameters on the circular surface.

The results are shown in Table-4.

Table 4 As shown in Table 4, at a cooling rate of 1°C/min, the strain amount was less than lnm7cm at all measurement points, but
The annealing effect was insufficient at a temperature decreasing rate of 5°C/min.

Example 6 Synthetic silica glass was irradiated with excimer laser (KrF (248 nm, 20) 1z) at an energy density of 65 mJ/cJ for 2 minutes, and red fluorescence was visually observed during the irradiation, and a decrease in transmittance performance was also observed. l0XIOX30 (mm)
A sample of KrF (248
20 Hz). The results are shown in Table-5.

Table 5 Example 10 The test of Example 6 was completed using ArF (193 nm,
100Hz) and heat treated under the conditions of Example 3.
- and then irradiated again with ArF (193 nm, 10011z). The results are shown in Table-6.

Table 6 Example 8 The gas composition of the sample after the test of Example 7 was changed to He/H2.
Heat treatment was performed according to Example 3 except that A = 5/20.
rF (193nm, 100Hz), 10100O/
Although irradiation was carried out for 2 minutes at an energy density of cr#, no red fluorescence was observed and no deterioration in performance was observed.
At 00 mJ/Cii, red fluorescence was observed and the performance decreased.

[Effects of the Invention] As described in detail above, synthetic silica glass whose spectroscopic properties have been altered by sputtering, plasma etching, and excimer laser irradiation can be practically completely cured by heat treatment in a hydrogen atmosphere. It can be restored to its original state quickly, and it can be modified so that no change in spectroscopic properties occurs even after subsequent sputtering, plasma etching, and excimer laser irradiation.

In addition, by pre-treating unused synthetic quartz glass using the method of the present invention, good synthetic quartz glass that does not change its spectroscopic properties even when subjected to sputtering, plasma etching, and excimer laser irradiation can be obtained. Obtainable.

[Brief explanation of the drawing]

FIG. 1 shows the ultraviolet transmittance, and FIG. 2 shows the fluorescence spectrum. Patent applicant Nippon Quartz Glass Co., Ltd. Yamaguchi Nippon Quartz Co., Ltd.

Claims (7)

[Claims] (1) A method for modifying synthetic quartz glass, which comprises heat-treating synthetic quartz glass in a hydrogen atmosphere. (2) A method for modifying synthetic quartz glass according to claim 1, in which heat treatment is performed in an atmosphere containing hydrogen and He. (3) The method for modifying synthetic quartz glass according to claim 1, wherein the temperature is raised at 5° C./min, the maximum temperature is 900° C., and the temperature is lowered at a rate of 1° C./min or less. (4) The method for modifying synthetic quartz glass according to claim 1, wherein the synthetic quartz glass is a substrate for a photomask. (5) The method for modifying synthetic quartz glass according to claim 1, wherein the synthetic quartz glass is a substrate for a photomask that has been altered by sputtering or plasma etching. (6) The method for modifying synthetic quartz glass according to claim 1, wherein the synthetic quartz glass has been altered by excimer laser irradiation. (7) The method for modifying synthetic quartz glass according to claim 2, wherein the mixing ratio of hydrogen and He is 20:5.