JP3126188B2 - Quartz glass substrate for photomask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass substrate for a photomask.

[0002]

BACKGROUND ART quartz glass, it is transparent material over a wide range of wavelengths from the near infrared to vacuum ultraviolet region, and that the thermal expansion coefficient and excellent extremely small dimensional stability, is et to chemical For excellent durability,
It is most suitable and widely used as a photomask substrate material used in an LSI photolithography process and the like.

On the other hand, recent advances in the integration density of LSIs have been remarkable, and there has been a great demand and expectation for the miniaturization of the processing technology. In the future, as the degree of integration of the DRAM, when the rather have migrated to 16M~64M,
For even photo lithography technology, a shorter wavelength and the practical use of the phase shift method of exposure wavelength it has become an issue of urgent.

[0004] Against this background, for the practical use of the phase shift method, there is a demand for a more sophisticated and higher quality photomask than ever before. that is, from a relatively low temperature region only process such patterning by wet / dry etching using a formation and photoresist chromium film is the light-shielding film by spatter method, it has been caused a need to adopt a higher temperature process .

[0005] Further, it is predicted that excimer laser exposure will be put to practical use in the future to shorten the exposure wavelength. However, in the case of a conventional quartz glass substrate, structural defects induced by excimer laser irradiation are expected. Wavelength 230 accompanying
An increase in absorption in the range of up to 300 nm causes a decrease in exposure dose, and furthermore, there is a problem that fluorescent emission based on these structural defects exposes the resist as stray light and hinders formation of a sharp mask pattern.

[0006] In addition, with the super-miniaturization of mask pattern, are necessary to have produced a sufficient consideration also optical homogeneity of the substrate material.

[0007]

The object of the present invention is to solve the above is to solve the problems described above, useful in the practical use of shorter wavelength of the phase shift method and the exposure wavelength, the photo mask for the quartz glass base
Is in providing board .

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a halogen content of 10%.
What is provided is a quartz glass substrate for a photomask, wherein the OH content is 100 ppm or less, the total content of heavy metals and alkali metals is 1 ppm or less, and the annealing point is 1150 ° C. or more. It is.

[0009] In a quartz glass substrate for a photomask of the present invention, the outer diameter (circular case of its diameter, in the case of a rectangular length of the short side) of the base plate when the is D, the plane center of the substrate
It is preferable that the fluctuation range of the refractive index in a region surrounded by a circle having a center and a radius of 0.4 × D is 3 × 10 ⁻⁶ or less.

[0010] In a quartz glass substrate for a photo mask of the present invention, before and after the plasma etching process, an increase in extinction coefficient in the wavelength range of 230 to 300 nm 0.0
It is preferably not more than 05 cm ^-1 .

In the quartz glass substrate for a photomask according to the present invention, a KrF excimer laser of 248 nm is irradiated at an irradiation intensity of 200 mJ / cm ² · pulse × 200 Hz to a cumulative irradiation amount of 100,000 J / cm ² . It is preferable that the increase in the extinction coefficient is 0.005 cm ^-1 or less.
Good .

In the present invention, the amount of halogen contained in the quartz glass substrate for a photomask is 10 ppm or less . When the halogen in excess of this is contained, the heat resistance is lowered. Further, OH content, 100 ppm Ri der less, preferably Ru der below 50 ppm. 100pp
When containing OH content of greater than m, like heat resistance is lowered and a halogen. The total content of heavy metals and alkali metals is 1 ppm or less . 1pp
If the content exceeds m is to cod also a decrease in the spectral transmittance in a short wavelength region. The annealing point is a temperature at which the viscosity of the glass shows 10 ¹³ poise, which is 1150 ° C. or more . If the annealing point is higher than this temperature, about 1000 ° C is used as the process temperature for photomask fabrication.
I can .

Normally, a photomask is used under the condition that the effective area is about 80% at the center of the substrate.
At least in such a range, it is preferable that the variation width of the in-plane refractive index is 3 × 10 ⁻⁶ or less. Exceeding such a variation width is not preferable because it becomes difficult to form a sharp pattern when the line width of the mask pattern is reduced.

Further, before and after the plasma etching process, an increase in the extinction coefficient in the wavelength range of 230~300nm is 0.
It is preferably at most 005 cm ⁻¹ . Here, the extinction coefficient α is represented by the following equation when the transmitted light amount is I, the incident light amount is I _O , the reflectance is R, and the thickness of the glass substrate is t (cm).
The value to be defined. I / I _O = (1−R) ² · exp (−α · t) Here, if the increase in the extinction coefficient is 0.005 cm ⁻¹ or less, it is a general size of a photomask substrate. 6
025 (6 inch square, 0.25 inch plate thickness), the decrease in transmittance is about 0.3%, and the accompanying fluorescence emission is about 100,000 to 1 / 100,000 of the incident light amount. Thus, there is no practical problem.

In addition, regarding excimer laser resistance,
248nm KrF excimer laser at 200mJ / c
100,000 J with irradiation intensity of m ² · pulse × 200 Hz
It is preferable that the increase in the extinction coefficient after irradiation to the cumulative irradiation amount of / cm ² is 0.005 cm ⁻¹ or less.

Generally, the lifetime of a photomask is estimated to be about 100,000 J / cm ² as a cumulative irradiation dose. Was although I, if an increase of 0.005 cm ^-1 or less absorption coefficient, even after 100,000 J / cm ² irradiation, the change in transmittance, there is about 0.3% as described above Also, since the fluorescence emission is about 1 / 100,000 to 1 / 100,000 of the incident light amount, there is no practical problem.

The method of manufacturing such a quartz glass substrate is not particularly limited as long as the above items are satisfied. For example, quartz glass fine particles obtained by heating and hydrolyzing a glass-forming raw material are previously deposited on a substrate.・ After heating and maintaining the grown porous quartz glass body in an atmosphere with a low partial pressure of water vapor for a certain period of time in a temperature range not higher than the temperature at which the vitreous quartz is vitrified, the temperature is raised to the vitrification temperature and heated to clear vitrification to form quartz. It can be made by a method of forming a glass body.

The glass forming raw material used is not particularly limited as long as it is a gasizable raw material.
iCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , Si (CH
₃ ) chlorides such as Cl ₃ , SiF ₄ , SiHF ₃ , SiH
₂ F ₂ fluorides such as, SiBr _4, SiHBr ₃ and the like bromides, halogenated silicon compounds of the iodide or the like of SiI ₄ is preferable in view of workability and cost. The porous quartz glass body is formed by hydrolyzing these glass forming raw materials in an ordinary oxyhydrogen flame and depositing them on a substrate.

[0019] The thus obtained porous quartz glass body, one after being held for a certain time heating under low water vapor partial pressure atmosphere had a quartz glass and transparent glass is heated to a transparent vitrification temperature Become. That is, for example, porous stone
The English glass body is pre-mounted in an electric furnace whose atmosphere can be controlled, and then heated at a constant heating rate. Then, after reaching a predetermined temperature, dry gas is introduced into the atmosphere, and the porous quartz
By replacing the atmosphere in contact with the glass body, the partial pressure of water vapor in the atmosphere is reduced to a predetermined value or less. The water vapor partial pressure is preferably 0.002 mmHg or less. If it exceeds this, it is not preferable because it is difficult to reduce the OH content in the finally obtained quartz glass.

The heating temperature range is 800
The temperature is preferably in the range of 1250 ° C., and at a temperature lower than this temperature range, a substantial effect is not obtained. At a temperature higher than this temperature range, vitrification of the surface of the porous quartz glass body progresses. It is not preferable because the inside of the quartz glass body cannot be replaced with a desired low steam partial pressure atmosphere. Further, this be a temperature range, as the method of heat treatment, rather it may also be held at a constant temperature, also but it may also be treated while warming the temperature range within a predetermined time. The holding time in this temperature range depends on the holding temperature and cannot be specified unconditionally, but is preferably about 1 to 30 hours, and when it is shorter, there is no substantial effect. Since the effect does not change even when applied for a long time, it is not preferable to take production efficiency into consideration.

As the drying gas, nitrogen, helium, argon or the like can be usually used, but is not necessarily limited to these gases as long as it can be used as the drying gas. Then, after such heat treatment, the porous quartz glass body is transparent.
The temperature is raised to a light vitrification temperature to form a transparent vitrification. Transparent
As the light vitrification temperature, it is preferable to adopt from a range of 1350 to 1500 ° C. In addition, heat treatment and transparency <br/> vitrification process, I also performed in separate heating devices <br/> Iga, in that case, prevent moisture and absorption Chakusu Rukoto during transport It is preferable to take measures such as doing. Therefore ,
It is preferable to perform pressurization heat treatment and vitrification at the same facility.

The quartz glass body thus obtained is heated to a temperature equal to or higher than the softening point and formed into a desired shape to produce a quartz glass block. The temperature range of the forming process is 165
It is preferable to select from the range of 0 to 1800 ° C. 1
At a temperature lower than 650 ° C., the viscosity of quartz glass is high, so that its own weight is not substantially deformed, and cristobalite, which is a crystal phase of SiO ₂ , grows and so-called devitrification occurs. In this case, sublimation of SiO ₂ cannot be ignored, which is not preferable.
The direction in which the quartz glass body undergoes its own weight deformation is not particularly limited, but is preferably the same as the growth direction of the porous quartz glass body. The glass block thus obtained is ground and sliced, and then polished to obtain a glass substrate.
Note that the sliced substrate may be heat-treated in a hydrogen atmosphere as needed to improve the transmittance.

The quartz glass obtained through the above steps has an OH content of 100 ppm in the quartz glass.
Follows it, the variation width of the OH content of the glass is quartz glass having excellent and uniformity within ± 5 ppm and have you in most areas. In addition, the quartz glass of the present invention can be used as a raw material for forming a glass, since a high-purity synthetic raw material can be used as a glass forming raw material, and since there is no impurity from a crucible or the like because it does not go through a melting step, a heavy metal element such as iron or nickel is used. And sodium,
The total amount of impurities of alkali metal elements such as potassium is 1 ppm
It has an extremely high purity as described below, and has little fluorescence emission and solarization with respect to ultraviolet rays such as a KrF laser and an ArF laser, and has excellent ultraviolet resistance.

Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

[0025]

EXAMPLES Example 1 By a known method, a porous quartz glass body having a diameter of 35 cm and a length of 100 cm formed by heating and hydrolyzing SiCl ₄ in an oxyhydrogen flame can control the atmosphere at room temperature. Installed in the furnace. Then, after replacing the atmosphere in the electric furnace with a nitrogen gas having a dew point of -70 ° C, the temperature was raised to 1000 ° C at a rate of 500 ° C / hr while flowing a nitrogen gas having a dew point of -70 ° C. Subsequently, the heating rate was set to 50 ° C./hr,
The temperature was raised to 250 ° C. and maintained at that temperature for 10 hours.
The heat-treated porous quartz glass body thus obtained is placed in an upper part of an electric furnace controlled at a maximum furnace temperature of 1450 ° C. for transparent vitrification, and the furnace has a dew point temperature of −70 ° C.
After the helium gas was replaced with the helium gas, the glass was passed through the highest temperature range while being lowered at a speed of 80 cm / hr to perform vitrification.

The transparent quartz glass thus obtained is placed in an electric furnace having a carbon heating element and has a softening point of 175 or more.
It is heated to 0 ° C and deformed under its own weight, 170 mm × 170
It was formed into a block shape of mm × 400 mm . From the central part in the longitudinal direction of the quartz glass block thus obtained,
Cut out 170 mm × 170 mm × silica glass block of 57 mm, about its center 140mmφ the results of evaluation of the refractive index distribution by precision interferometer (ZygoIV)
Table 1 shows the homogeneity (Δn) . In addition, the amount of OH and its
Distribution width of 170 mm × 170 mm × 400mm silica glass block, from right next to the place of part of the evaluation of the refractive index distribution by JASCO Corporation simple FTIR device cut the glass plate of 2mm thickness of 3700 cm ^-1 Quantified by absorption. After Cl content that alkali fusion quartz glass obtained was determined by ion chromatography I method. In addition, the annealing point was set at a sample size of 2.4 mm × 5.
Cut out a sample of mm × 60mm, span 52mm
And was measured by a beam bending method. Table 1 shows the results
Shown in As can be seen from Table 1, according to the present embodiment,
Quartz glass suitable for use as a mask was obtained.

Example 2 A sample of 10 mm × 10 mm × 30 mm was cut out from a glass block prepared in the same manner as in Example 1 . Then , after heat-treating in a 100% hydrogen atmosphere for 14 hours, the opposing surfaces of 10 mm × 10 mm are mirror-polished, and a KrF excimer laser is irradiated with 200 mJ / cm ² · p.
ulse, total irradiation amount of 100,000 J / c at 200Hz
After irradiation until reaching m ² , the transmittance in the range of 230 to 300 nm was measured. As compared with the transmittance before irradiation, the transmittance was reduced by 0.5%. From this value, the increase in the extinction coefficient was estimated to be 0.002 cm ^-1 .

Example 3 A sample of 10 mm × 10 mm × 30 mm was cut out from a glass block prepared in the same manner as in Example 1.
Was. Then , after heat treatment for 14 hours in a 100% hydrogen atmosphere, all six surfaces were mirror-polished and dry-etched for 5 minutes. The dry etching process uses a dry etcher (S-600) manufactured by Tokyo Ohka, an atmosphere of 0.35 torr in an oxygen / carbon tetrachloride atmosphere, and an input power of 2
00W. 230-3 before and after plasma etching
When the transmittance at 00 nm was compared, the transmittance was 0.8%.
Had decreased. The increase in absorption coefficient is estimated to be 0.003
cm ^-1 .

Comparative Example A quartz glass block was manufactured in the same manner as in Example 1 except that the heat treatment at 1250 ° C. was not performed. Its center 1
40 mm φ refractive index distribution, OH content and its distribution width, C
Table 1 shows the l content.

[0030]

[Table 1]

[0031]

As described above, the quartz glass substrate for a photomask of the present invention has a high annealing point and excellent heat resistance, so that it can be used in a high-temperature process and before and after plasma etching. increase in absorption light coefficient in the short wavelength side at small, it has excellent characteristics substantially no fluorescence emission.

Also, it has a feature of excellent optical homogeneity. It also has excellent features as a photomask substrate that can use a KrF excimer laser.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-139779 (JP, A) JP-A-5-139778 (JP, A) JP-A-5-139776 (JP, A) JP-A-5-139776 139775 (JP, A) JP-A-5-24856 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 3/06 G03F 1/14

Claims (4)

(57) [Claims] 1. A halogen content of 10 ppm or less, an OH content of 100 ppm or less, a total content of heavy metals and alkali metals of 1 ppm or less, and a slow cooling point of 115 ppm.
A quartz glass substrate for a photomask, which has a temperature of 0 ° C. or higher. Wherein when the outside diameter (in the case of circular the diameter, if the rectangle length of the short side) of the base plate is D, plane within the center of the substrate
The quartz glass substrate for a photomask according to claim 1, wherein the fluctuation range of the refractive index in a region surrounded by a circle having a radius of 0.4 x D around the center is 3 x ^10-6 or less. 3. flop plasma etching wavelength 230 before and after
0.005c increase in extinction coefficient in the range of ~ 300nm
The quartz glass substrate for a photomask according to claim 1 , wherein the quartz glass substrate is at most m ⁻¹ . 4. A 2 a KrF excimer laser of 2 48nm
The increase in the extinction coefficient after irradiating to a cumulative irradiation amount of 100,000 J / cm ² at an irradiation intensity of 00 mJ / cm ² · pulse × 200 Hz is 0.005 cm ^-1 or less .
4. The quartz glass substrate for a photomask according to 2 or 3 .