JPH0831723A - Synthetic quartz mask substrate for arf excimer laser lithography and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a synthetic quartz mask substrate for ArF excimer laser lithography having excellent stability to the irradiation of an ArF excimer laser and manufacture thereof. CONSTITUTION:The synthetic quartz mask substrate for excimer laser lithography has hydrogen molecule content of 0.5-4X10<18> molecules/cm<3> and contains no chlorine, has OH group content of 700-1000ppm and is free of unidirectional stria, has absorbance of K<=0.008cm<-1> at a time when an ArF excimer laser having low energy is applied, and has the quantity of the deviation of a refractive index of DELTAn<=1X10<-6> at a time when an ArF laser having high energy is applied. The manufacture is produced from synthetic quartz glass manufactured from silica fine particles obtained by flame-hydrolyzing alkoxy silane in the oxyhydrogen flame burner of a quintuple tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic quartz mask substrate for ArF excimer laser lithography, and particularly to a synthetic quartz mask substrate for ArF excimer laser lithography having excellent stability against irradiation with ArF excimer laser (193 nm). The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, with the high integration of LSIs, a submicron unit drawing technique is required in the optical lithography technique for drawing an integrated circuit pattern on a wafer. In order to do so, the wavelength of the light source of the exposure system is being shortened, so the lens and mask substrate used for the stepper for lithography and the catadioptric optical system have excellent homogeneity and excellent transmission of ultraviolet rays. And strong resistance to UV irradiation are required. Regarding the wavelength of this light source, the I-line (365 nm), which is currently the mainstream, is shifting to a wavelength with high energy such as KrF excimer laser (248 nm) or ArF excimer laser (193 nm). In the wavelength region, quartz glass is used as the transmissive material, and in particular synthetic quartz glass with a low content of impurities is used.

It is said that this synthetic quartz glass is usually made of a highly pure silicon compound, such as silicon tetrachloride (SiCl ₄ ), which is chemically synthesized and distilled. As a method for producing glass, a direct flame method, a soot method consisting of melting a porous silica base material, a plasma method, a sol-gel method and the like are known, and the physical properties of the glass, for example, the composition such as the OH group content and the Cl content, Structural defect species are largely due to their manufacturing method. Among these production methods, the transparent synthetic quartz glass member produced by the direct flame method or the soot method in particular exhibits excellent transparent light transmittance up to a short wave region of about 190 nm, and has an ultraviolet laser beam such as KrF, XeCl (308nm), XeBr
(282 nm), XeF (351 nm), ArF and other excimer laser lights, and YAG fourth harmonics (250 nm) are used as transmission materials.

However, the synthetic quartz glass produced by the direct flame method contains hydrogen molecules, and the hydrogen molecules contained in the synthetic quartz glass have excellent transmittance stability against, for example, a KrF excimer laser. It is known that, since almost no hydrogen molecules are contained in the synthetic quartz glass member made by the soot method, which is transparent vitrified through the porous glass base material, hydrogen molecules are not contained during the heat treatment. Doped to produce the same effect.

However, although the synthetic quartz glass produced by these methods has a sufficiently stable optical transparency to the KrF excimer laser, it contains the hydrogen molecules when irradiated with the ArF excimer laser. In some cases, it is not preferable because it shows a large decrease in transmittance at the initial stage of laser irradiation, that is, a sharp rise in absorbance. It is considered that the absorption of light generated when the synthetic quartz glass is irradiated with ultraviolet rays such as excimer laser is mainly due to the paramagnetic defect generated by the photoreaction from the intrinsic defect in the quartz glass. Many light absorptions due to have been identified by ESR spectra,
This includes, for example, E'center (Si.) And NBOHC (Si-O.).

This paramagnetic defect generally has an optical absorption band. Therefore, the absorption band in question in quartz glass is, for example, 215 nm at the E'center and 260 nm which has not yet been accurately identified. The absorption band of is relatively broad and may cause strong absorption, which is a problem especially when used as a transmission material for ArF laser. However, the intrinsic defect in quartz glass that causes the paramagnetic defect is For example
Structures other than SiO ₂ , such as SiOH and SiCl, or Si-Si
, Si-OO-Si, etc. have oxygen deficiency and oxygen excess structure. Therefore, it is also known to use a synthetic quartz glass produced from alkoxysilane or the like as a so-called chlorine-free raw material in which SiCl that is a precursor of these paramagnetic defects cannot exist, and this is a synthetic quartz glass. It is effective for giving appropriate laser resistance and is suitably used for a synthetic quartz glass optical member, particularly for a lens system such as a stepper (see JP-A-3-109233).

It is also known from this prior example that hydrogen molecules are effective as a substance that suppresses this paramagnetic defect, and the paramagnetic defect generated by laser irradiation, such as E'center (Si). The effect of suppressing the increase of E'center is provided when this hydrogen is bonded to.) To form Si-H. However, when irradiated with ArF laser, this hydrogen molecule causes a rapid decrease in transmittance at the beginning of laser irradiation, and since it contributes to recovering the transmittance when irradiation is continued, a synthetic quartz glass member containing hydrogen is involved. On the other hand, hydrogen molecules have been degassed by heat treatment for a long time before use.

This synthetic quartz glass degassed with hydrogen molecules does not show the same behavior as when it contains hydrogen molecules even when irradiated with ArF laser, and therefore, there is no rapid rise in absorbance at the beginning of irradiation, Although the transmittance gradually decreases and reaches the saturation point at a certain point, the recovery of the transmittance is not seen because it does not contain hydrogen molecules. Also,
The synthetic quartz glass member produced by melting the porous silica base material does not contain hydrogen molecules, and thus exhibits the same behavior, but the saturation point of the absorbance at this time is different from that in the method for producing synthetic quartz glass. It is due.

[0009]

In other words, when the laser resistance is limited to the ArF excimer laser, the synthetic quartz glass containing a large number of hydrogen molecules (≧ 5 × 10 ¹⁸ molecules / cm ³ ) is irradiated with the ArF excimer laser. The initial transmittance (1 × 10 ⁴ shots, 100Hz) dropped sharply, and then it recovered (1 × 10 ⁶ shots, 100Hz), and when the irradiation was continued, the transmittance gradually decreased. Then, the synthetic quartz glass that does not contain hydrogen molecules or is dehydrogenated does not cause a rapid decrease in transmittance at the initial stage of laser irradiation, but gradually decreases and then saturates at a constant value. Therefore, an optical member for an ArF excimer laser, in particular, a material that requires a long optical path length such as a projection lens material for a stepper and needs excellent transparency does not contain this hydrogen molecule or is dehydrogenated. Synthetic quartz glass is preferred.

In the case of a synthetic quartz mask substrate, which is completely different from the above-mentioned optical lens material, the thickness is thin (2 to 7 mm), and therefore the transmittance is affected only by the short optical path length. It is good because there is no gap, but since a fine circuit pattern is printed on this mask substrate,
Extremely strict requirements are imposed on dimensional changes, especially warpage and shrinkage, and in order to satisfy these requirements in consideration of the peculiarities of the mask, the hydrogen molecule concentration in a specific range different from the lens material application It is known that the problem can be solved by defining the range (see Japanese Patent Application No. 5-190143).

However, recently, there are two types of excimer laser lithography, a stepper system and a catadioptric system. Due to technical competition between these two systems, a more accurate device has been developed. for,
The synthetic quartz glass substrates used for these are required to have higher energy transmittance as well as stability of refractive index in addition to high surface dimensional accuracy. Since it is expected to be used as a reflection substrate for processing machines and the like that use high energy of excimer lasers for other purposes, synthetic quartz glass substrates used for ArF excimer lasers are accompanied by laser irradiation. It is required to solve the problems associated with the decrease in light transmittance, dimensional accuracy, and fluctuations in the refractive index.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a synthetic quartz mask substrate for ArF excimer laser lithography and a method of manufacturing the same, which solves the above problems.
This synthetic quartz mask substrate for ArF excimer laser lithography has a hydrogen molecule content of 0.5 to 4 × 10 ¹⁸ molecules /
cm ³ , distribution difference in the plane of the substrate is ΔH ₂ ≦ 3 × 10 ¹⁸ molecules /
cm ³ in containing no chlorine, OH group content 700~1,000ppm
The substrate surface distribution difference is ΔOH ≦ 100ppm, it is free of striae in at least one direction, and when the low energy ArF excimer laser is irradiated, the absorbance is K ≦ 0.008cm ⁻¹ and the high energy ArF excimer laser is irradiated. The refractive index deviation amount in this case is Δn ≦ 1 × 10 ⁻⁶ , and this manufacturing method uses a central quintuple tube and a plurality of pipe-shaped nozzles and an outer shell tube around the quintuple tube. Alkoxysilane and oxygen gas as the raw material gas are provided in the center nozzle of the quartz burner provided with, and oxygen gas is provided in the second and fourth nozzles,
Hydrogen gas was supplied between the nozzle and the fifth nozzle and between the outer shell tube and the fifth nozzle to flame-hydrolyze the alkoxysilane into a synthetic quartz glass ingot, which was subjected to hot molding, slicing and polishing steps. It is characterized in that a synthetic quartz mask substrate is manufactured.

That is, the present inventors do not cause a sudden decrease in transmittance at the initial stage of laser irradiation, particularly when the ArF excimer laser is irradiated, and the absorption saturation point after irradiation is low and the dimensional accuracy is low. As a result of various studies to develop a synthetic quartz glass mask substrate for lithography having a stable refractive index and a manufacturing method thereof, the synthetic quartz glass mask substrate for ArF excimer laser lithography has a hydrogen molecule content of 0.5 ~ 4
× 10 ¹⁸ molecules / cm ³ in the substrate plane △ H ₂ is ≦ 3 × 10 ¹⁸
molecules / cm ³ , no chlorine, OH group content 7
In the case of 00 to 1,000 ppm, the difference in the in-plane distribution of the substrate is ΔOH ≦ 100 ppm, the striation is free in at least one direction, and the absorbance when irradiated with a low energy ArF excimer laser is K ≦.
Assuming that the refractive index deviation amount when irradiated with a high-energy ArF excimer laser at 0.008 cm ⁻¹ is Δn ≦ 1 × 10 ⁻⁶ , this product has such physical properties as a composition for ArF excimer laser lithography. In addition to finding that it will be a quartz mask substrate, in the production of such a synthetic quartz mask substrate, it is decided to use chlorine-free alkoxysilane as a raw material gas, which has a quintuple tube at the center. A quartz burner with multiple pipe-shaped nozzles and an outer shell tube is used around it, and the raw material gas and oxygen are supplied to this central nozzle to flame-hydrolyze the alkoxysilane into silica fine particles. A synthetic quartz glass mask substrate having the above-mentioned physical properties after being made into a synthetic quartz glass ingot according to the flame method and then undergoing hot forming, slicing and polishing steps. It has led to the completion of the present invention to verify that it is obtained.

[0014]

First, according to the method for producing a synthetic quartz mask substrate for ArF excimer laser lithography according to the present invention, alkoxysilane is flame-hydrolyzed by an oxyhydrogen flame to generate silica fine particles, which are rotated at 3 to 100 rpm. A synthetic quartz glass ingot is formed by melting and vitrifying it on a crystalline carrier at the same time as it is processed into a mask. The organosilicon compound used as the raw material here is silicon tetrachloride (SiCl ₄ ). , Methyltrichlorosilane (CH ₃ SiCl ₃ ), chlorine is contained in the synthetic quartz glass and SiCl is involved, and the hydrogen molecule concentration is 4
Even with × 10 ¹⁸ molecules / cm ³ , the decrease in transmittance at the initial stage of ArF laser irradiation is large, and the absorbance at 50 mJ / cm ² · P, 100 Hz is 0.05 cm ⁻¹ or more, which is not preferable. Chemical formula containing no atoms R _n Si (OR) _4-n (R is the same or different fatty acid monovalent hydrocarbon group, n is an integer of 0 to 3)
It is necessary to use an alkoxysilane represented by

The production of the synthetic quartz glass member using the alkoxysilane is carried out, for example, by the apparatus shown in FIG. FIG. 1 (a) is a vertical sectional view of an apparatus for producing synthetic quartz glass by flame hydrolysis of an alkoxysilane with an oxyhydrogen flame, and FIG. 1 (b) is a horizontal sectional view of an oxyhydrogen flame burner used here. As shown, this Figure 1 (a)
In the above, the alkoxysilane as a raw material is stored in the silane storage container 1, which is entrained by an inert gas such as argon gas or nitrogen gas supplied from the gas inlet 2, and passes through the flow meter 15 and the oxyhydrogen flame burner 12 Is supplied to the central nozzle of the. This oxyhydrogen flame burner 12 is shown in Fig. 1 (b).
As shown in FIG. 5, a quintuple pipe 19 composed of straight pipes 20 to 24 is located in the center, and a plurality of nozzles 26 surrounding the quintuple pipe 19 are provided.
And a structure having an outer shell tube 25 on the outside thereof, the central nozzle 20 is supplied with alkoxysilane, oxygen gas from the oxygen gas supply tube 7 and argon gas supplied from the gas inlet 2. This is the second nozzle 2
1. Oxygen gas is also supplied to the first and fourth nozzles 23 from the oxygen gas supply pipes 8 and 9, and the hydrogen gas supply pipes 4, 5, and 5 are provided between the third nozzle 22, the fifth nozzle 24 and the outer shell pipe 25. Hydrogen gas is supplied from 6.

This alkoxysilane is subjected to flame hydrolysis in the oxyhydrogen flame 13 from the oxyhydrogen flame burner 12 to form silica fine particles 14, which are melted at the same time as being deposited on the heat-resistant carrier 11 rotating at 3 to 100 rpm. Synthetic quartz glass member
Will be 18. At this time, when the flow rate ratio between the theoretical amount of oxygen and the actual flow rate of oxygen required by the raw material alkoxysilane compound and hydrogen gas is less than 0.7, the hydrogen molecule concentration is 4 × 10 ¹⁸ molecules / cm 3.
³ Beyond high, in a normal heat treatment process remains at a high concentration difficult hydrogen gas escapes at the center, increase the absorption of laser radiation early, not preferred because cause decrease in transmittance, and this ratio 1.0 If it exceeds, the hydrogen molecule content will be 5 × 10 ¹⁷ molecules / cm ³ or less, and the intended synthetic quartz mask cannot be stably manufactured. Therefore, this should be set in the range of 0.7 to 1.0.

Further, in this case, if the surface temperature change of the fused silica growth surface is controlled to 20 ° C. or less, the synthetic quartz glass is
An ingot with a diameter of mmφ × 500 mmL and a weight of 19 kg can be obtained. This synthetic quartz glass ingot has a hydrogen molecule content of 2 to 4 × 10 ¹⁸ molecules / cm ³ and an OH group content of 700.
At ˜780 ppm, there can be no striae, which is the locus of local displacement of the refractive index from the axial direction of the ingot.

The production of a synthetic quartz mask substrate from this synthetic quartz glass ingot was carried out by placing the ingot in a carbon crucible and heating it to 1,800 ° C. under an argon gas atmosphere at 200 torr in an electric melting furnace and holding it for 1 hour. After cooling, remove the strain in an annealing furnace in an atmosphere of 1,180 for strain relief.
After raising the temperature to ℃ and holding it for 2 hours, 10 ℃ to 950 ℃
It was cooled at a rate of 1 minute / minute to make a 6 "square ingot 6" square x 360mmL, and then this ingot was sliced to a thickness of 6.5mm with an inner peripheral blade and then mirror-finished by polishing.
A synthetic quartz mask substrate of 6 "square x 6.3 mmt could be used, but the hydrogen molecule content in this glass substrate was 1.5.
-4 × 10 ¹⁸ molecules / cm ³ .

Next, three 20 × 75 × 6.3 mmt glass plates were cut out from this synthetic quartz mask substrate as samples,
When the hydrogen molecule concentration was confirmed in consideration of the distribution of each in-plane substrate, it was found that these were within the range of 2 to 4 × 10 ¹⁸ molecules / cm ³ , and the ArF excimer laser had an energy density of 50 mJ / cm ² · P. When irradiated under the conditions of 100 Hz and 1 × 10 ⁶ shots, the absorbance at the initial stage of irradiation was 0.008 cm ⁻¹ , and the variation in the absorbance was 0.0005 cm ⁻¹ or less.

However, in this case, when the hydrogen molecule concentration of this product exceeds 4 × 10 ¹⁸ molecules / cm ³ , the ArF excimer laser has a high energy density, for example, 200 mJ / cm ² · P,
Irradiation at 100 Hz causes a decrease in transmittance and a large fluctuation in the refractive index.
> 1 × 10 ^-6 , and this hydrogen molecule concentration is 5 × 10
Even if it is lower than ¹⁷ molecules / cm ³ , the refractive index fluctuation similarly occurs, so that the hydrogen molecule concentration is 2 to 4 × 10 ¹⁸ molecules / cm ^3.
It is required to be in the cm ³ range. This is mainly caused by the contraction of quartz glass called radiation compaction, and it is confirmed that the irradiated part contracts by about 0.04 μm, which is considered to be caused by the hydrogen concentration.

[0021]

EXAMPLES Examples of the present invention and comparative examples will now be described.
The hydrogen molecule content and transmittance in the examples show the following values. (Hydrogen molecule content) Raman spectrophotometer NR 1,100 [trade name of JASCO Corporation], excitation wavelength 488 nm
Was carried out by a host counting method using Photomar R943-02 [trade name of Hamamatsu Photonics KK] having an output of 700 mW with Ar laser light. The hydrogen molecule content is observed at 800 cm ^-1 in the Raman scattering spectrum at this time.
The area intensity ratio of the scattering band of SiO _{2 and} the scattering band observed at 4,135 to 4,140 cm ⁻¹ of hydrogen was converted into concentration, and the conversion constant was the reference value 4,135 cm ⁻¹ / 800 cm ⁻¹ × 1.22 × Ten
²¹ was used. (Transmittance) The transmittance measurement is a value calculated from the amount of laser energy transmission (amount of emitted energy / amount of incident energy) of ArF laser light (193 nm).

Examples 1 to 3, Comparative Examples 1 to 4 Methyltrimethoxysilane [CH ₃ as a raw material silane compound
Si (OCH ₃ ) ₃ ], silicon tetrachloride (SiCl ₄ ), and methyltrichlorosilane (CH ₃ SiCl ₃ ) are used together with oxygen gas, hydrogen gas and argon gas in the amounts shown in Table 1. It is supplied to a hydrogen flame burner, and the silica fine particles produced by flame hydrolysis of this silane compound are deposited on a rotating heat-resistant carrier and, at the same time, fused and vitrified, 150 mmφ × 500 mmL
A synthetic quartz glass ingot of 19 kg was produced.

Then, this synthetic quartz glass ingot was cylindrically ground and then placed in a 6 "square carbon crucible and placed in an electric melting furnace under an argon gas of 200 torr at 1,800 ° C.
After heating to 1 hour and holding for 1 hour to form a 6 ”square × 380 mmL square ingot, the temperature was raised to 1,180 ° C in an annealing furnace in an air atmosphere to remove the thermal strain at this time. Hold for 2 hours, cool to 950 ° C at a cooling rate of 10 ° C / hour, then slice into 6.5mmt thick with an inner peripheral blade and polish to a mirror surface with a polishing machine, 6 "square x 6.3mmt synthetic quartz A mask substrate was produced. Next, regarding the synthetic quartz mask substrate thus obtained, the absorbance (K), the refractive index deviation amount (Δn), the hydrogen molecule content and the ΔH ₂ , OH group when the excimer laser was irradiated on the substrate. When the content and ΔOH were examined, the results shown in Table 1 were obtained. Also,
When the synthetic quartz mask substrates obtained in Examples 2 and 3 and Comparative Example 2 above were irradiated with ArF excimer laser at an energy density of 5 or 50 mJ / cm ² -p at a frequency of 100 Hz for 1 × 10 ⁵ shots, 193 nm. Changes in absorbance at
It was shown to.

[0024]

[Table 1]

[0025]

The present invention relates to a synthetic quartz mask substrate for ArF excimer laser lithography and a method for producing the same. The synthetic quartz mask substrate has a hydrogen molecule content of 0.5 to 4 × 10 ¹⁸ molecules / cm ³ and contains chlorine. Does not contain
When the OH group content is 700 to 1,000 ppm, the striae are free in at least one direction, and the absorbance when irradiated with a low-energy ArF excimer laser is K ≦ 0.008 cm ^-1 and when irradiated with a high-energy ArF excimer laser. The refractive index deviation amount of Δn ≦ 1 × 10 ⁻⁶ is used. This manufacturing method is made from silica fine particles obtained by flame hydrolysis of alkoxysilane in an oxyhydrogen flame burner with a central quintuple tube. However, this mask does not show a sharp decrease in transmittance in the early stage of ArF laser irradiation, has a low absorbance saturation point after irradiation, and has stable dimensional accuracy and refractive index. The advantage is that

[Brief description of drawings]

FIG. 1 (a) is a vertical sectional view of an apparatus for producing synthetic quartz glass from alkoxysilane by the method of the present invention, and FIG. 1 (b) is a horizontal sectional view of an oxyhydrogen flame burner used therein. .

2] ArF excimer laser on synthetic quartz mask substrate with energy density of 50 mJ / cm ² -p and frequency of 100 Hz, 1 × 10 ⁵
FIG. 3 is a diagram showing the relationship between the number of shots when shot is irradiated and the change in absorbance at a wavelength of 193 nm.

FIG. 3: ArF excimer laser on synthetic quartz mask substrate with energy density of 5 mJ / cm ² -p and frequency of 100 Hz, 1 × 10 ⁵
FIG. 3 is a diagram showing the relationship between the number of shots when shot is irradiated and the change in absorbance at a wavelength of 193 nm.

[Explanation of symbols]

 1 ... Alkoxysilane storage container 2 ... Gas inlet 3 ... Inert gas inlet 4, 5, 6 ... Hydrogen gas supply pipe 7, 8, 9 ... Oxygen gas supply pipe 10 ... Refractory brick 11 ... Heat-resistant carrier 12 ... Oxyhydrogen flame Burner 13 ... Oxyhydrogen flame 14 ... Silica fine particles 15 ... Flowmeter 17 ... Peephole 18 ... Porous glass base material 19 ... Five-tube burner 20, 21, 22, 23, 24 ... 1st-5th nozzle 25 ... Outside Shell tube 26 ... Nozzle

Front page continuation (72) Inventor Masatoshi Takita 28, Nishi-Fukushima, Kubiki-mura, Nakabuki-gun, Niigata Prefecture 1 Shin-Etsu Chemical Co., Ltd.

Claims (4)

[Claims] 1. A hydrogen molecule content of 0.5 to 4 × 10 ¹⁸ molecu
The distribution difference in the substrate plane is les / cm ³ △ H ₂ ≦ 3 × 10 ¹⁸ molecu
les / cm ³ , chlorine-free, OH group content 700 ~ 1,
At 000 ppm, the difference in the in-plane distribution of the substrate is ΔOH ≦ 100 ppm, and at least one direction is free of striae, and the absorbance when irradiated with a low energy ArF excimer laser is K ≦ 0.008 cm ^−1.
The synthetic quartz mask substrate for ArF excimer laser lithography, wherein the refractive index deviation amount when irradiated with a high energy ArF excimer laser is Δn ≦ 1 × 10 ⁻⁶ . 2. The ArF excimer laser has a low energy density of 50 mJ / cm ² · P or less and a frequency of 100 Hz.
The quartz mask substrate for ArF excimer laser lithography described in 1. 3. The synthetic quartz mask substrate for ArF excimer laser lithography according to claim 1, wherein the ArF excimer laser has a high energy density of 200 mJ / cm ² · P and a frequency of 100 Hz. 4. A central nozzle of a quartz burner having a central quintuple tube and a plurality of pipe-shaped nozzles and an outer shell tube around the central quintuple tube, an alkoxysilane and oxygen gas as a source gas, a second nozzle and a fourth nozzle. Oxygen gas was supplied to the nozzles, and hydrogen gas was supplied between the third nozzle and the fifth nozzle and between the outer shell tube and the fifth nozzle to flame-hydrolyze the alkoxysilane into a synthetic quartz glass ingot, which was hot-pressed. A method of manufacturing a synthetic quartz mask substrate for ArF excimer laser lithography, which comprises manufacturing a synthetic quartz mask substrate through molding, slicing, and polishing steps.