JP3088783B2 - Highly transparent pellicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly transparent dustproof film cover for protecting a mask or a reticle used in a photolithographic process in the manufacture of a semiconductor integrated circuit, that is, a highly transparent film having a low antireflection layer . It is about pellicles.

[0002]

2. Description of the Related Art Conventionally, a pellicle made of a thin and transparent film is fixed to a mask used in a photolithographic process in the manufacture of a semiconductor integrated circuit, and the pellicle is placed on the mask at a predetermined distance. positioned.

Therefore, even if fine dust particles adhere to the pellicle during the operation of the photolithography process, the fine particles do not form an image on the semiconductor wafer coated with the resist material. Therefore, by protecting the mask with the pellicle, short-circuit and disconnection of the semiconductor integrated circuit due to the image of the dust particles can be prevented, and the manufacturing yield of the photolithographic process is improved. Further, there is an effect that the number of times of cleaning of the mask is reduced and the life thereof is extended.

In such a pellicle, it is required that the transmittance of the light to be exposed is high in order to improve the throughput in the exposure step. For this purpose, an antireflection layer is provided on one or both sides of the transparent thin film.

When the refractive index nAR of the antireflection layer is nAR = (nC) ^1/2 with respect to the refractive index nC of the transparent thin film, the antireflection effect is maximized. The transparent thin film generally used includes a cellulose derivative, polyvinyl butyral, and the like, but since these have a refractive index of about 1.5,
The refractive index of the antireflection layer used for these transparent thin films is 1.2.
Preferably it is close to 2.

As an antireflection layer conventionally proposed, a tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene polymer is disclosed in JP-A-61-209449, and a polyfluoropolymer is disclosed in JP-A-1-100499. Although acrylates are described, the refractive index of these polymers was in the range of 1.35 to 1.37, and the antireflection effect was not sufficient.

On the other hand, a polymer having a small refractive index is disclosed in Japanese Patent Application Laid-Open No. 3-39963 as Teflon AF (trade name, refractive index 1.29) of Du Pont as a fluoropolymer having a cyclic structure in the main chain. Proposed.

This polymer is hardly soluble in a solvent, probably because of its high molecular weight.
There is a problem that it is not suitable for use in pellicles that dislike garbage because they do not pass through the filter. In addition, when a film is formed by a spin coating method or the like, there is a problem that color unevenness occurs in the thin film and light transmittance is reduced.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low- reflection layer material having a low refractive index, excellent solution permeability, and not causing color spots when a film is formed. The purpose of the present invention is to provide a pellicle having excellent permeability.

[0010]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have arrived at the present invention. That is, the present invention provides: In a pellicle having at least one antireflection layer formed on at least one surface of a transparent thin film, the low-refractive-index antireflection layer irradiates high-energy particles.
A fluoropolymer having a cyclic structure in the main chain,
And reduced viscosity at 23 ° C. of perfluorotributylamine solution of concentration 1.5 g / dl is pellicle is equal to or less than 1.0 dl / g, also,

The transparent thin film is characterized in that it is a cellulose derivative, and the transparent thin film is characterized in that it is a mixture of nitrocellulose and at least one or more cellulose derivatives. The present invention will be described in more detail.

In the present invention, the transparent thin film serving as the main body of the pellicle film includes nitrocellulose, cellulose acetate (cellulose acetate), cellulose acetate propionate (cellulose acetate / propionate), cellulose acetate butyrate (cellulose acetate / butyrate). ) Can be used.

These cellulose derivatives may be used alone. Nitrocellulose is excellent in film strength and shape retention under high humidity, but is inferior to other cellulose derivatives in light resistance. Cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate are excellent in light resistance, but have poor film strength and shape retention under high humidity, so a mixture of nitrocellulose and other cellulose derivatives other than nitrocellulose Can be preferably used.

The mixing ratio of nitrocellulose and other cellulose derivatives is determined in consideration of film strength, shape retention under high humidity, and light resistance. The content of nitrocellulose is preferably 10 to 50% by weight. And more preferably,
20 to 40% by weight. As the cellulose derivative to be used, the higher the molecular weight, the greater the shape retaining force of the thin film, and therefore, the more preferable. That is, the number average molecular weight is 30,000 or more, preferably 50,000 or more.

Of these materials, nitrocellulose is commercially available from Asahi Kasei Kogyo Co., Ltd., and cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate are commercially available from Eastman Kodak Company, and can be easily obtained. .

The fluoropolymer having a cyclic structure in the main chain used in the present invention is a copolymer containing a cyclic structure repeating unit represented by the following formula (I) .

Embedded image (However, R _{1 to} R ₂ are F or CF _3. )

Among these, a fluoropolymer containing a repeating unit having a cyclic structure in the main chain of the following formula (2) is typical.

Embedded image

[0018] These fluoropolymers, perfluoro-2,2-dimethyl-1, 3 - dioxole obtained by allowed to radical polymerization of. Also, the copolymer is
Additional perfluoro-2,2-dimethyl-1, 3 - and dioxole, obtained by copolymerization of fluorine-containing monomers such as fluoroolefin and fluorovinyl ether.

The monomers to be copolymerized include, for example, tetrafluoroethylene, perfluorovinyl ether,
Vinylidene fluoride and chlorotrifluoroethylene. Further, the polymer used in the present invention is preferably a so-called amorphous polymer having no crystal. This is because light transmission loss due to light scattering by the microcrystal does not occur.

The fluoropolymer having a cyclic structure in the main chain has a refractive index of 1.29 to 1.31, which is the refractive index of a conventional fluoropolymer such as a tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene copolymer or polyfluoroacrylate. As compared with the ratio of 1.35 to 1.37, a large antireflection effect can be obtained.

A fluoropolymer having such a cyclic structure in the main chain is available as Teflon AF (trade name) manufactured by Du Pont, but this polymer is hardly soluble in a solvent because of its high molecular weight. There is a problem in that the filter does not pass through a filter having a pore size of 0.2 μm for removing dust, so that it is not suitable for use in peculiar which dislikes dust.

Further, when a film is formed by a spin coating method or the like, there is a problem that color unevenness occurs in the thin film and the light transmittance is reduced. Accordingly, the present inventors have result of intensive studies to solve this problem, I fluoropolymer der having a cyclic structure in the main chain irradiated with high energy particles, and concentration of 1.5 g / dl perfluorotributylamine When a film formed from a butylamine solution having a reduced viscosity of 1.0 dl / g or less at 23 ° C. or less is used as a low-refractive-index antireflection layer, it has no color spots and passes through a membrane filter having a pore size of 0.2 μm, It has been found that a good antireflection film can be formed.

Here, the reduced viscosity refers to the viscosity of the solution as η [se
c], the concentration is C [g / dl], and the viscosity of the pure solvent is η ₀ [se
c], it is a quantity defined by (η−η ₀ ) / (η ₀ · C). A capillary viscometer was used for measuring the viscosity.

[0024] Such a low refractive index antireflection layer, the main
Irradiating high-energy particles such as γ-rays, electron beams, and neutron beams to fluoropolymers having a cyclic structure in the chain
Therefore, it can be easily obtained.

The above-mentioned fluoropolymer to be used as the low-refractive-index antireflection layer is formed on one or both sides of a transparent thin film of a cellulose derivative or the like to form a two-layer or three-layer structure. Alternatively, a high refractive index antireflection layer may be provided on one or both surfaces of a transparent thin film of a cellulose derivative or the like, and the fluoropolymer layer may be provided thereon to form a three to five-layer structure. The thickness of the antireflection layer is preferably 1 / (4n) (n is the refractive index of the fluororesin) of the wavelength of the light to be antireflection.

As the high refractive index anti-reflection layer, polyether sulfone, polystyrene, polyvinyl naphthalene and the like can be used. The method for producing a pellicle film having a low antireflection layer according to the present invention will be described with reference to a pellicle having an antireflection layer formed on both surfaces of a transparent thin film of a cellulose derivative mixture.

First, a method for forming a transparent thin film of a cellulose derivative mixture will be described. Nitrocellulose and other cellulose derivatives (eg, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate) are dissolved in a common good solvent at a predetermined mixing ratio. The mixing ratio is determined in consideration of film strength, shape retention under high humidity, and light resistance. The content of nitrocellulose is preferably 10 to 50% by weight, more preferably 20 to 40% by weight. It is.

Common good solvents include ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; butyl acetate, isobutyl acetate, ethyl lactate,
Esters such as cellosolve acetate; and mixed solvents of these solvents are used.

The cellulose derivative thin film is formed by a spin coating method (spin coater method). That is, the cellulose derivative solution is filtered after removing the dust, dropped on a smooth substrate such as glass or silicon, and then rotated. The thickness of the transparent thin film can be appropriately changed by changing the solution viscosity or the rotation speed of the substrate. The solvent contained in the thin film formed on the smooth substrate is volatilized on a hot plate, an oven, or the like.

Next, a method for forming a low refractive index antireflection layer will be described. For the low refractive index antireflection layer, the above-mentioned fluoropolymer having a cyclic structure in the main chain is used. The refractive index nAR of this antireflection layer is n
When AR = (nC) ^1/2 , the antireflection effect is maximized. Since the refractive index of the cellulose derivative mixture is about 1.5, nAR is preferably close to 1.22.

Creates a membrane with excellent solution filterability and no color spots
To, as a low refractive index antireflection layer, ring the backbone
Irradiation of high-energy particles such as γ-rays, electron beams, and neutrons to a fluoropolymer having a linear structure, and reduction of the irradiated polymer in a 1.5 g / dl perfluorotributylamine solution at 23 ° C. set to be the viscosity below 1.0 dl / g.

In this case , if the irradiation amount of the high-energy particles is too large, the polymer is remarkably decomposed and a uniform thin film cannot be formed. In the case of γ-rays, the irradiation amount is 10 to 400 kGy (G
y: gray = unit of absorbed dose), preferably 50 to 2
50 kGy.

Such a fluoropolymer is dissolved in a fluorinated solvent such as perfluorobenzene, perfluoro (2-butyltetrahydrofuran), trichlorotrifluoroethane or perfluorotributylamine, but the film surface is smooth and has no color spots. In order to obtain a film, a solvent having a higher boiling point is preferable. The boiling point is preferably 130 ° C. or higher,
More preferably, it is 160 ° C. or higher.

After the solution is filtered to remove dust, the solution is dropped on a transparent thin film formed on a smooth substrate, and the substrate is rotated to form an anti-reflection film. When the thickness of the anti-reflection film is
The solution concentration and the number of rotations of the substrate are determined so as to be 1 / (4n) (n is the refractive index of the fluoropolymer) of the wavelength of the light to be prevented from being reflected. The solvent contained in the formed thin film is air-dried, or heated by a hot plate, an oven, or the like to volatilize, thereby completing the formation of the two-layer film composed of the transparent thin film and the antireflection layer.

The two-layer film formed on the smooth substrate is peeled off with a double-sided tape or other metal or plastic frame. The frame and the two-layer film are set on a spin coater, and a fluororesin thin film is formed on the peeling surface side in the same manner as described above, so that a three-layer pellicle film having an antireflection layer on both surfaces of the transparent thin film body is formed. Complete.

[0036]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by this. ( Reference example ) <Preparation of sample> Teflon AF1600 and AF2400 manufactured by DuPont
(Trade name) was irradiated with gamma rays. Irradiation dose is from 0 to 2
00 kGy (Gy = gray, unit of absorbed dose).
These are dissolved in perfluorotributylamine,
A 1.5 g / dl solution was obtained.

Each of these solutions was applied to a pore having a diameter of 0.2 μm and a diameter of 1 μm.
1kg / cm by 43mm membrane filter
As a result of filtration at a pressure of ² , filtration was possible if the reduced viscosity was 1.0 dl / g or less. However, if it exceeded 1.0 dl / g, the filter was clogged and could not be filtered.

[0038]

[Table 1]

[0039]

[Table 2] Note) ×: No filtration, Δ: Low flow rate, difficult to filter, ○: Very good.

[0040] These solutions, spin coating method to a nitrocellulose membrane having a thickness of 1.3 .mu.m (rotational speed 500r
pm, rotation time 30 seconds). At this time, when the reduced viscosity was 1.0 dl / g or less, there was no color unevenness and a film having a smooth surface was formed, but when the reduced viscosity was more than 1.0 dl / g, color unevenness and surface irregularities were easily generated.

Example 1 Cellulose acetate propionate ("CAP482-" manufactured by Eastman Kodak Company)
20 ", 46 g of propionyl content, hereinafter abbreviated as CAP) 6 g, and nitrocellulose (manufactured by Asahi Kasei Corporation)
4 g of "HIG-20" nitrification degree 12.0% (hereinafter abbreviated as NC) was dissolved in ethyl acetate cellosolve to prepare a solution having a solid concentration of 7 g / dl.

For the anti-reflection film, the Teflon AF2400 manufactured by Du Pont was irradiated with 120 kGy of γ-rays and dissolved in perfluorotributylamine (Tokuyama Soda Co., Ltd., “IL-270”). 1.5g / dl
Was prepared. The reduced viscosity of this solution at 23 ° C. was 0.67 dl / g.

A silicon wafer was set on a spin coater, and the prepared CAP / NC solution was filled with a pore diameter of 0.2 μm.
And filtered through a membrane filter of 20c.
c, and then the silicon wafer is rotated at 1000 rpm.
For 45 seconds, and then the solvent was evaporated on a hot plate to form a thin film of CAP / NC having a thickness of about 1.2 μm on the silicon wafer.

Next, thereon, perfluorotributylamine solution of the γ-ray Teflon AF irradiated was filtered through a membrane filter having a pore size of 0.2μm, and the filtered
After dropping 3 cc of the liquid and rotating at 600 rpm for 30 seconds,
It was air-dried to form a two-layer film.

Further , a thin film is peeled off from the silicon wafer by attaching a frame of a metal or a plastic with a double-sided tape or the like, and the film is stuck tightly on a 120 mm × 98 mm rectangular aluminum frame. It was fixed with an adhesive. After leaving this film under high humidity for 30 minutes,
Again, the film was set on a spin coater with the CAP / NC layer side up, and the above γ-ray irradiated Teflon AF solution was
After dropping cc and rotating at 600 rpm for 30 seconds, the mixture was air-dried to form a three-layer film. The thickness of the antireflection films formed on both surfaces was 73 μm.

The thus obtained pellicle antireflection film was a good film having a smooth surface and no color spots when observed with monochromatic light from a mercury lamp. FIG. 1 shows the spectral transmittance of this three-layer film pellicle. The minimum light transmittance between 350 and 450 nm is 98%, and the average light transmittance is 9%.
It was as high as 9%. The transmittances of the mercury lamp at g-line (436 nm) and i-line (365 nm), which are bright lines, are 99.8%, and are both g-line exposure and i-line exposure, that is, g-line and i-line exposure. It can be preferably used as a common pellicle.

Example 2 Cellulose acetate butyrate (“CAB381-20” manufactured by Eastman Kodak Co., Ltd., butyryl content 37%,
6 g of nitrocellulose (manufactured by Asahi Chemical Industry Co., Ltd., “HIG-20” nitrification degree 12.0)
%, Hereinafter abbreviated as NC) was dissolved in ethyl acetate cellosolve to prepare a solution having a solid content of 7 g / dl.

A 1.6 g / dl isopropylbenzene solution of polystyrene was prepared as a material for the high refractive index antireflection layer. As the material of the low refractive index antireflection layer, the Du Pont Co. in "Teflon AF1600", gamma rays 80
What was irradiated with kGy was dissolved in perfluorotributylamine (manufactured by Tokuyama Soda Co., Ltd., “IL-270”).
A 1.5 g / dl solution was prepared. The reduced viscosity of this solution at 23 ° C. was 0.53 dl / g.

A silicon wafer was set on a spin coater, and the prepared CAB / NC solution was filled with a 0.2 μm pore diameter.
And filtered through a membrane filter of 20c.
c, and then the silicon wafer is rotated at 1000 rpm.
For 45 seconds, and then the solvent was evaporated on a hot plate to form a CAB / NC thin film having a thickness of about 1.3 μm on the silicon wafer.

Next, an isopropylbenzene solution of polystyrene was filtered thereon with a membrane filter having a pore size of 0.2 μm, and 3 cc of the filtrate was added dropwise to 500 r.
After rotating at pm for 30 seconds, it was air-dried to form a two-layer film.
Further, a perfluorotributylamine solution of Teflon AF irradiated with 80 gGy of the above-mentioned γ-ray was further coated thereon with a pore size of 0.2.
After filtration through a membrane filter of μm,
After dropping cc and rotating at 600 rpm for 30 seconds, the mixture was air-dried to form a three-layer film.

This low-refractive-index antireflection film was a good film having a smooth surface and no color spots. Further , a thin film is peeled off from the silicon wafer by attaching a frame of metal or plastic with a double-sided tape or the like, and a 120 mm × 98
The film was stretched tightly on a rectangular aluminum frame of mm, and the antireflection film side was fixed with an epoxy adhesive.

Again, this film was set on a spin coater with the CAB / NC layer side up, and a polystyrene isopropylbenzene solution and a gamma-irradiated Teflon AF solution were added in this order.
Coating was performed in the same manner as above to form a five-layer film. The film thickness of the formed high refractive index antireflection film was 63 μm, and the film thickness of the low refractive index antireflection film was 76 μm. Of this five-layer film pellicle,
The minimum light transmittance between 50 and 450 nm is 98%,
The average light transmittance was as high as 99.5%.

(Comparative Example 1) "Teflon AF1600" manufactured by Du Pont was replaced with perfluorotributylamine ("IL-IL" manufactured by Tokuyama Soda Co., Ltd.).
270 ") to prepare a 1.5 g / dl solution. The reduced viscosity of this solution at 23 ° C. was 3.4 dl.
/ G. This solution was used as an anti-reflection layer in Example 2
In the same manner as in the above, a three-layer film pellicle was formed.

When the monochromatic light from the mercury lamp was applied to the film surface and observed, streak-like color spots running radially from the center of the film were observed. Further, when the light transmittance was measured, the peak value of the light transmittance did not reach 100% probably because of scattering by spots. FIG. 2 shows the spectral light transmittance at this time.

(Comparative Example 2) "Teflon AF1600" manufactured by Du Pont Co., Ltd.
Irradiation with y-rays was performed, and dissolved in perfluorotributylamine (manufactured by Tokuyama Soda Co., Ltd., “IL-270”).
A solution of 5 g / dl was prepared. The reduced viscosity of this solution at 23 ° C. was 4.3 dl / g.

Using this solution as a solution for an antireflection layer, a three-layer film pellicle was formed in the same manner as in Example 2. Observation of the monochromatic light from the mercury lamp on the film surface revealed streak-like color spots running radially from the center of the film. Further, when the light transmittance was measured, the peak value of the light transmittance did not reach 100% probably because of scattering by spots.

[0057]

As described above, according to the present invention, the low antireflection layer
As a ring structure in the main chain irradiated with high-energy particles.
A fluoropolymer having a reduced viscosity of 1.0
By using one having a dl / g or less, the filterability of the solution is improved and a pellicle having no color spots is obtained. The pellicle having the low anti - reflection layer of the present invention has an improved minimum light transmittance near the anti-reflection wavelength and a small change in light transmittance due to interference of reflected light. The mask with the pellicle attached has an effect of improving the throughput in the exposure step.

[Brief description of the drawings]

FIG. 1 is a graph showing the spectral light transmittance of a pellicle of Example 1.

FIG. 2 is a graph showing the spectral light transmittance of the pellicle of Comparative Example 1.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-100549 (JP, A) JP-A-3-67262 (JP, A) JP-A-3-39963 (JP, A) JP-A-3-399 168642 (JP, A) JP-A-4-81756 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (3)

(57) [Claims] 1. A pellicle having one or more antireflection layers formed on at least one surface of a transparent thin film, wherein the low-refractive-index antireflection layer has a cyclic structure in its main chain irradiated with high-energy particles. a is, and pellicle, wherein the reduced viscosity at 23 ° C. of perfluorotributylamine solution of concentration 1.5 g / dl is less than 1.0 dl / g. 2. The pellicle according to claim 1, wherein the transparent thin film is a cellulose derivative. 3. The pellicle according to claim 1, wherein the transparent thin film is a mixture of nitrocellulose and at least one or more cellulose derivatives.