JP3071362B2 - Synthetic quartz mask substrate for ArF excimer laser lithography and method of manufacturing the same - Google Patents

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 more particularly to a synthetic quartz mask substrate for ArF excimer laser lithography having excellent stability against irradiation with an ArF excimer laser (193 nm). It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, with the increase in integration of LSIs, in the photolithography technology for drawing an integrated circuit pattern on a wafer, a drawing technology of a sub-micron unit has been required. In order to achieve this, the wavelength of the light source for the exposure system has been shortened, so that lenses and mask substrates used in lithography steppers and catadioptric systems have excellent homogeneity and excellent UV transmission. There is a demand for a property and a strong resistance to ultraviolet irradiation. Regarding the light source wavelength, the currently mainstream I-ray (365 nm) is shifting to a high energy wavelength such as a KrF excimer laser (248 nm) or an ArF excimer laser (193 nm). In the wavelength region, quartz glass, particularly synthetic quartz glass having a low impurity content, is used as the transmission material.

As the synthetic quartz glass, a high purity silicon compound, for example, chemically synthesized and distilled from silicon tetrachloride (SiCl ₄ ) is used. As a method for producing glass, a direct flame method, a soot method comprising 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, a composition such as an OH group content and a Cl content, Structural defect types and the like largely depend on the manufacturing method. Among these manufacturing methods, a transparent synthetic quartz glass member particularly manufactured by a direct flame method or a soot method shows good transparent light transmittance up to a short-wave region of about 190 nm, and an ultraviolet laser beam, for example, KrF, XeCl (308 nm), XeBr
(282 nm), XeF (351 nm), excimer laser light such as ArF, and a fourth harmonic (250 nm) of YAG are used as transmission materials.

[0004] However, the synthetic quartz glass produced by the direct flame method contains hydrogen molecules, which have excellent transmittance stability with respect to, for example, a KrF excimer laser. However, since the synthetic quartz glass member made by the soot method, which has been transparently vitrified through a porous glass base material, hardly contains hydrogen molecules, the hydrogen molecules are removed by heat treatment. Doping is intended to produce a similar effect.

[0005] However, although the synthetic quartz glass produced by these methods has a sufficiently stable light transmittance with respect to a KrF excimer laser, it contains hydrogen molecules when irradiated with an ArF excimer laser. In some cases, this is not preferable because a large decrease in transmittance, that is, a sharp rise in absorbance is exhibited at the beginning of laser irradiation. It is believed that the absorption of light generated when this synthetic quartz glass is irradiated with ultraviolet light such as an excimer laser is due to paramagnetic defects caused by photoreaction from intrinsic defects in the quartz glass. Many light absorptions have been identified in ESR spectra, etc.
These include, for example, E 'center (Si.) And NBOHC (Si-O.).

This paramagnetic defect generally has an optical absorption band. Therefore, the absorption band which is problematic in quartz glass is, for example, 215 nm at the E 'center and 260 nm which has not yet been accurately identified. Absorption band is relatively broad and may cause strong absorption. This is a problem particularly when the material is used as a transmission material of an ArF laser. The intrinsic defect in quartz glass that causes this paramagnetic defect is as follows. For example
Structures other than SiO ₂ such as SiOH and SiCl, and Si-Si
, Si-OO-Si and other oxygen-deficient and oxygen-excess structures. For this reason, it is also known to use synthetic quartz glass produced from alkoxysilane or the like as a so-called chlorine-free raw material in which SiCl, which is a precursor of these paramagnetic defects, cannot exist, and this is used for synthetic quartz glass. It is effective for imparting appropriate laser resistance, and is suitably used for synthetic quartz glass optical members, particularly for lens systems such as steppers (see Japanese Patent Application Laid-Open No. 3-109233).

[0007] It is also known from the prior art that hydrogen molecules are effective in suppressing the paramagnetic defect. Paramagnetic defects generated by laser irradiation, such as E 'center (Si The effect that the increase of the E ′ center is suppressed when this hydrogen is bonded to Si—H to form Si—H. However, when irradiating with an ArF laser, the hydrogen molecules cause a sharp decrease in transmittance at the initial stage of laser irradiation, and further contribute to the recovery of the transmittance when the irradiation is continued. On the other hand, hydrogen molecules have been degassed by long-term heat treatment before use.

The synthetic quartz glass from which hydrogen molecules have been degassed does not exhibit the same behavior as that containing hydrogen molecules even when irradiated with ArF laser, and therefore does not have a sharp rise in absorbance at the beginning of irradiation. In this case, the transmittance gradually decreases and reaches a saturation point at a certain point, but no recovery of the transmittance is observed because no hydrogen molecule is contained. Also,
Synthetic quartz glass members produced from the fusion of a porous silica base material do not contain hydrogen molecules and therefore exhibit the same behavior, but the saturation point of the absorbance at this time depends on the synthetic quartz glass manufacturing method. Is due.

[0009]

In other words, when examining the laser resistance only for the ArF excimer laser, the synthetic quartz glass containing a large amount of hydrogen molecules (≧ 5 × 10 ¹⁸ molecules / cm ³ ) is irradiated with the ArF excimer laser. The initial (1 × 10 ⁴ shots, 100 Hz) transmittance when abruptly decreases, then recovers (1 × 10 ⁶ shots, 100 Hz), and then the transmittance gradually decreases when irradiation is continued. In a synthetic quartz glass that does not contain hydrogen molecules or has been dehydrogenated, the transmittance does not suddenly decrease 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, particularly a material that requires a long optical path length, such as a projection lens material for a stepper, and that requires excellent transmittance does not contain this hydrogen molecule or is subjected to a dehydrogenation treatment. Synthetic quartz glass is preferred.

When this is a synthetic quartz mask substrate, the thickness is thin (2 to 7 mm), which is completely different from the above-mentioned optical lens material, so that the transmittance is greatly affected only by a short optical path length. Good, but because a fine circuit pattern is printed on this mask substrate,
Very strict requirements are imposed on dimensional changes, especially warpage and shrinkage, and in order to satisfy these requirements in consideration of the specialty of the mask, the hydrogen molecule concentration that differs from the lens material application in a specific range 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, ie, a stepper type and a catadioptric type, and a more precise apparatus has been developed due to technical competition in both types. for,
Synthetic quartz glass substrates used for these materials are required to have higher energy transmittance and higher refractive index stability in addition to high surface dimensional accuracy. It is also expected to be used as a reflection substrate for processing machines and the like that use the high energy of excimer lasers in other applications. In particular, synthetic quartz glass substrates used for ArF excimer lasers are being used with laser irradiation. It is required to solve the problems related to the resulting decrease in light transmittance, dimensional accuracy, and variation in 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 has solved 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 , the distribution difference in the substrate plane is ΔH ₂ ≦ 3 × 10 ¹⁸ molecules /
cm ³ in containing no chlorine, OH group content 700~1,000ppm
Is △ OH ≦ 100 ppm in the substrate surface, is at least unidirectional stria-free, and irradiates a high energy ArF excimer laser with an absorbance K ≦ 0.008 cm ⁻¹ when irradiated with a low energy ArF excimer laser. The deviation amount of the refractive index at the time of ^performing the above is characterized by Δn ≦ 1 × 10 ⁻⁶ , and the manufacturing method is characterized in that a central quintuple pipe and a plurality of pipe-shaped nozzles The alkoxysilane and oxygen gas as the raw material gas are supplied to the center nozzle of the quartz burner provided with the gas, the oxygen gas and the third gas are supplied to the second and fourth nozzles.
Hydrogen gas is supplied between the nozzle and the fifth nozzle and between the outer shell tube and the fifth nozzle, and the alkoxysilane is flame-hydrolyzed into a synthetic quartz glass ingot, which is subjected to hot forming, slicing, and polishing steps. It is characterized in that a synthetic quartz mask substrate is manufactured.

In other words, the present inventors have found that, particularly when irradiating an ArF excimer laser, the transmittance does not suddenly decrease at the beginning of laser irradiation, the absorption saturation point after continuing 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 method of manufacturing the same, the synthetic quartz glass mask substrate for ArF excimer laser lithography was found to have a hydrogen molecule content equal to that of the synthetic quartz glass mask. 0.5-4
× 10 ¹⁸ molecules / cm ³ in the substrate plane △ H ₂ is ≦ 3 × 10 ¹⁸
molecules / cm ³ , containing no chlorine and having an OH group content of 7
In the range of 00 to 1,000 ppm, the distribution difference in the substrate surface is ΔOH ≦ 100 ppm, and at least one direction is stria-free, and the absorbance when irradiated with a low energy ArF excimer laser is K ≦
Assuming that the refractive index deviation when irradiating a high-energy ArF excimer laser at 0.008 cm ^-1 satisfies Δn ≦ 1 × 10 ⁻⁶ , this is a synthetic material for ArF excimer laser lithography having such physical properties. In addition to finding that it becomes a quartz mask substrate, in the production of such a synthetic quartz mask substrate, an alkoxysilane containing no chlorine is used as a raw material gas, and the central part is formed of a quintuple tube, A quartz burner having a plurality of pipe-shaped nozzles and an outer shell tube is used around it, and a raw material gas and oxygen are supplied to the central nozzle to flame-hydrolyze alkoxysilane into silica fine particles. After forming into a synthetic quartz glass ingot according to the flame method, through a hot forming, slicing and polishing process, a synthetic quartz glass mask substrate with the above physical properties It has led to the completion of the present invention to verify that it is obtained.

[0014]

First, according to the method of manufacturing 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. The synthetic silica glass ingot is melted and vitrified simultaneously with the deposition on the porous carrier, and then processed into a mask. The organic silicon compound used as the raw material here is silicon tetrachloride (SiCl ₄ ). , Methyltrichlorosilane (CH ₃ SiCl ₃ ), chlorine is contained in synthetic quartz glass, SiCl is involved, and the hydrogen molecule concentration is 4
Even if it is × 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 and 100 Hz is not more than 0.05 cm ⁻¹ , which is not preferable. free of atoms formula _{R n Si (oR) 4-} n (R is the same or different fatty acid monovalent hydrocarbon radical, n is an integer of 0 to 3)
Is required.

The production of a synthetic quartz glass member using this alkoxysilane is performed, for example, by the apparatus shown in FIG. FIG. 1 (a) is a longitudinal 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 cross sectional view of an oxyhydrogen flame burner used here. As shown in FIG.
In this case, the alkoxysilane as a raw material is stored in a silane storage container 1, which is accompanied by an inert gas such as argon gas or nitrogen gas supplied from a gas inlet 2, and passed through a flow meter 15 through an oxyhydrogen flame burner 12. To the central nozzle. This oxyhydrogen flame burner 12 is shown in FIG.
As shown in the figure, a quintuple pipe 19 composed of straight pipes 20 to 24 is located at the center, and a plurality of nozzles 26 surrounding the
The central nozzle 20 is supplied with alkoxysilane and oxygen gas from the oxygen gas supply pipe 7 and argon gas supplied from the gas inlet 2 to the central nozzle 20. This includes the second nozzle 2
The first and fourth nozzles 23 also receive oxygen gas from the oxygen gas supply pipes 8 and 9, and the third nozzle 22 and the fifth nozzle 24 and the hydrogen gas supply pipes 4, 5 and From 6, hydrogen gas is supplied.

The alkoxysilane is converted into fine silica particles 14 by flame hydrolysis in an oxyhydrogen flame 13 from an oxyhydrogen flame burner 12 and is melted simultaneously with the deposition on a heat resistant carrier 11 rotating at 3 to 100 rpm. Synthetic quartz glass member
It becomes 18. At this time, if the flow rate ratio between the theoretical amount of oxygen required by the raw material alkoxysilane compound and the hydrogen gas and the actual flow rate of oxygen is less than 0.7, the hydrogen molecule concentration is 4 × 10 ¹⁸ molecules / cm.
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 content of hydrogen molecules becomes 5 × 10 ¹⁷ molecules / cm ³ or less, and it is not possible to stably produce the target synthetic quartz mask. Therefore, the content may be set in the range of 0.7 to 1.0.

In this case, when the surface temperature change of the fused silica growth surface is controlled to 20 ° C. or less, the synthetic quartz glass is
The synthetic quartz glass ingot may have a hydrogen molecule content of 2 to 4 × 10 ¹⁸ molecules / cm ³ and an OH group content of 700 mm × 500 mmL and a weight of 19 kg.
At 780780 ppm, there can be no striae, which is the locus of the local displacement of the refractive index from the axial direction of the ingot and again.

In manufacturing a synthetic quartz mask substrate from the synthetic quartz glass ingot, the ingot is placed in a carbon crucible, and heated to 1,800 ° C. at 200 torr in an argon gas atmosphere in an electric melting furnace and held for 1 hour. After cooling, remove the 1,180
After heating to ℃ and holding for 2 hours, 10 ℃ to 950 ℃
Cooled at / min to make a 6 "square ingot 6" square x 360mmL, and then sliced this ingot to 6.5mm thickness with an inner peripheral blade and then mirror-finished by polishing,
A 6 ″ square × 6.3 mmt synthetic quartz mask substrate could be used, but the content of hydrogen molecules in the glass substrate was 1.5%.
４4 × 10 ¹⁸ molecules / cm ³ .

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

However, in this case, if the hydrogen molecule concentration of this compound exceeds 4 × 10 ¹⁸ molecules / cm ³ , the ArF excimer laser is irradiated with a high energy density, for example, 200 mJ / cm ² · P,
Irradiation at 100 Hz causes a decrease in transmittance and a large change in refractive index.
> 1 × 10 ^-6 and this hydrogen molecule concentration is 5 × 10
^{Since the} fluctuation of the refractive index also occurs when the molecular weight is lower than ¹⁷ molecules / cm ³ , the hydrogen molecule concentration is 2 to 4 × 10 ¹⁸ molecules / cm ^3.
it is necessary to the range of cm ^3. This is mainly caused by shrinkage of quartz glass called radiation compaction, and shrinkage of about 0.04 μm has been confirmed in the irradiated portion, 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 the transmittance in the examples show the following values. (Hydrogen content) Excitation wavelength 488 nm using Raman spectrophotometer NR 1,100 (trade name, manufactured by JASCO Corporation)
And a host counting method using a photomar R943-02 (trade name, manufactured by Hamamatsu Photonics KK) having an output of 700 mW with an Ar laser beam. This hydrogen molecule content is observed at 800 cm ^-1 in the Raman scattering spectrum at this time.
The ratio of the area intensity of the scattering band of SiO _{2 to} the scattering band observed at 4,135 to 4,140 cm ⁻¹ of hydrogen was calculated by converting the concentration into a concentration. The conversion constant was 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 transmitted laser energy (emission energy / incident energy) with ArF laser light (193 nm).

Examples 1-3, Comparative Examples 1-4 Methyltrimethoxysilane [CH ₃
Si (OCH ₃ ) ₃ ], silicon tetrachloride (SiCl ₄ ), and methyltrichlorosilane (CH ₃ SiCl ₃ ) were used together with oxygen gas, hydrogen gas and argon gas in an amount shown in Table 1. It is supplied to a hydrogen flame burner, and the silica fine particles generated by flame hydrolysis of this silane compound are deposited on a rotating heat-resistant carrier and simultaneously melted and vitrified.
19kg of synthetic quartz glass ingot was prepared.

Then, after the synthetic quartz glass ingot is cylindrically ground, it is placed in a 6 ″ square carbon crucible and placed in an electric melting furnace under argon gas at 200 torr at 1,800 ° C.
And then hold it for 1 hour to form a 6 "square x 380 mmL square ingot. Then, in order to remove the thermal strain, raise the temperature to 1,180 ° C in an annealing furnace under an air atmosphere. Hold for 2 hours, cool down to 950 ° C at a rate of 10 ° C / hour, then slice to a thickness of 6.5mmt with an inner peripheral blade and finish it to a mirror surface with a polisher to make 6 ”square x 6.3mmt synthetic quartz. A mask substrate was manufactured. Next, regarding the synthetic quartz mask substrate thus obtained, the absorbance (K), the refractive index deviation (Δn), the hydrogen molecule content and the ΔH ₂ , OH group 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 were irradiated with 1 × 10 ⁵ shots of an ArF excimer laser at an energy density of 5 or 50 mJ / cm ² -p and a frequency of 100 Hz, 193 nm 2 and 3 show 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 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 irradiating with a low energy ArF excimer laser is K ≦ 0.008 cm ⁻¹ and irradiating with a high energy ArF excimer laser. Is a refractive index deviation of Δn ≦ 1 × 10 ⁻⁶ , and is manufactured from silica fine particles obtained by flame hydrolysis of an alkoxysilane in an oxyhydrogen flame burner having a central quintuple tube. However, this mask does not cause a sharp drop in transmittance at the beginning of ArF laser irradiation, has a low absorbance saturation point after continuing irradiation, and has stable dimensional accuracy and refractive index. Is provided.

[Brief description of the drawings]

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

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

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

[Description of Signs] 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 ... flow meter 17 ... viewing window 18 ... porous glass base material 19 ... quintuple tube burner 20, 21, 22, 23, 24 ... first to first 5 nozzles 25 ... shell tube 26 ... nozzle

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masatoshi Takita 28-1, Nishifukushima, Oaza, Kushiro-mura, Nakakushiro-gun, Niigata Prefecture Shin-Etsu Chemical Co., Ltd. Synthetic Technology Research Laboratory (56) References , A) JP-A-4-228443 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16 C03C 3/06 C03B 20/00

Claims (4)

(57) [Claims] (1) a hydrogen molecule content of 0.5 to 4 × 10 ¹⁸ molecu
In les / cm ³ , the distribution difference in the substrate plane is ΔH ₂ ≦ 3 × 10 ¹⁸ molecu
In les / cm ^3, containing no chlorine, OH group content 700-1,
At 000 ppm, the distribution difference in the substrate surface is ΔOH ≦ 100 ppm, at least one-way stria-free, and the absorbance when irradiated with a low energy ArF excimer laser is K ≦ 0.008 cm ^−1.
A synthetic quartz mask substrate for ArF excimer laser lithography, wherein a 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.
4. A quartz mask substrate for ArF excimer laser lithography described in 1. above. 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 quartz burner having a central quintuple pipe and a plurality of pipe-shaped nozzles and an outer shell pipe provided around the central nozzle and the alkoxysilane and oxygen gas as raw material gases, the second nozzle and the fourth nozzle. Oxygen gas is supplied to the nozzles, hydrogen gas is supplied between the third nozzle and the fifth nozzle and between the outer shell tube and the fifth nozzle, and the alkoxysilane is flame-hydrolyzed into a synthetic quartz glass ingot. A method for producing a synthetic quartz mask substrate for ArF excimer laser lithography, comprising producing a synthetic quartz mask substrate through molding, slicing, and polishing steps.