JPH08220734A - Thin film for pellicle - Google Patents

Abstract

PURPOSE: To increase the elastic modulus of a film without decreasing the transmittance for light rays and to improve the durability against air blow by stretching an amorphous fluorinated polymer material. CONSTITUTION: This thin film for a pellicle consists of a stretched amorphous fluorinated polymer material. As for the amorphous fluorinated polymer, a fluorinated polymer having a cyclic structure in the main chain is preferably used. A polymer obtd. by polymn. of monomers having a fluorinated cyclic structure or a polymer having a cyclic structure in the main chain obtd. by cyclization polymn. of fluorine-contg. monomers having at least two polymerizable double bonds are used. This kind of polymer is obtd. by single polymer. of monomers such as perfluoro(arylvinylether) or copolymn. with radical polymerizable monomers such as tetrafluoroethylene. The polymer is stretched by uniaxial or biaxial stretching method. The obtd. film has high film strength against air blow and high transparency and durability for UV rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pellicle thin film having an elastic modulus increased by stretching an amorphous fluoropolymer.

[0002]

2. Description of the Related Art With the progress of miniaturization in the field of semiconductor manufacturing, the wavelength of light used for microlithography has shifted to a short wavelength. Conventionally, in microlithography using g-line and i-line as a light source, a nitrocellulose-based material has been used as a thin film for a photomask dustproof cover (pellicle) in terms of good film-forming property and thin film strength. However, in recent years, since the excimer laser having a shorter wavelength is being used, it is impossible to use a nitrocellulose-based material that is destroyed by the excimer laser.

Therefore, JP-A-3-67262 describes that a fluoropolymer having a ring structure in the main chain, which has a high transmittance not only for visible light but also for ultraviolet light, is useful. However, the pellicle thin film is usually a thin film having a thickness of 1 μm or less, and since this amorphous fluoropolymer is softer than nitrocellulose, the film is locally blown by an air blow to remove adhering foreign matters. It may stretch and leave a dot-like mark. Such traces are not preferable because they cause light scattering as well as the adhesion of foreign matter.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to newly provide a thin film for a pellicle which has an elastic modulus of the above-mentioned amorphous fluoropolymer and has resistance to air blow.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies based on the recognition of the above problems, and as a result, stretched the amorphous fluoropolymer to obtain elastic modulus without impairing light transmittance. It was found that a pellicle thin film having durability against air blow was obtained. The present invention is a pellicle thin film comprising a stretched amorphous fluorine-containing polymer.

The amorphous fluoropolymer in the present invention is preferably a fluoropolymer having a ring structure in its main chain. The fluorine-containing polymer having a ring structure in the main chain is obtained by polymerizing a monomer having a fluorine-containing ring structure, or obtained by cyclopolymerizing a fluorine-containing monomer having at least two polymerizable double bonds. The polymer having a ring structure in the main chain is exemplified in a wide range including known and well-known polymers.

Polymers having a ring structure in the main chain obtained by cyclopolymerization of a fluorine-containing monomer having at least two polymerizable double bonds are disclosed in JP-A-63-238111 and 63-238115. Are known. That is,
Homopolymerization of monomers such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether),
Alternatively, it can be obtained by copolymerizing with a radically polymerizable monomer such as tetrafluoroethylene.

A polymer having a ring structure in its main chain, which is obtained by polymerizing a monomer having a fluorine-containing ring structure, is known from Japanese Examined Patent Publication No. 63-18964. That is,
It can be obtained by homopolymerizing a monomer having a fluorine-containing ring structure such as perfluoro (2,2-dimethyl-1,3-dioxole) or by copolymerizing with a radical polymerizable monomer such as tetrafluoroethylene.

Further, perfluoro (2,2-dimethyl-
A monomer having a fluorine-containing ring structure such as 1,3-dioxole) and at least 2 such as perfluoro (allyl vinyl ether) or perfluoro (butenyl vinyl ether)
It may be a polymer obtained by copolymerizing a fluorine-containing monomer having one polymerizable double bond.

The reason why the strength of the thin film for pellicle increases by stretching is not clear, but it is probably in the film thickness direction, and molecular chains that do not contribute to the strength of the film are arranged in the direction perpendicular to the film thickness direction by stretching, It is considered that this is because the proportion of molecular chains that contribute to the strength of the membrane increases. The pellicle thin film is used as a pellicle composed of this thin film and a metal support frame such as aluminum.

As the stretching method, known methods such as uniaxial stretching and biaxial stretching are adopted. For example, as an example of uniaxial stretching, a thin film made of an amorphous fluoropolymer is formed on a substrate by a spin coating method, then peeled from the substrate, and the temperature is lower than the softening temperature (glass transition temperature) of the polymer. Both ends of the thin film are fixed to a jig and pulled at a speed of 10 to 200 mm / min. As a result, so-called necking occurs in which the central portion is constricted, and the extended portion spreads to both ends and finally the whole extends. The amorphous fluoropolymer thin film thus cold-drawn has an increased elastic modulus and improved durability against air blow.

As the biaxial stretching method, a method of simultaneously cold stretching in four or eight directions of the thin film and a vacuum forming method of stretching while suction-adhering to a convex shape or a concave shape can be applied. Vacuum forming methods include straight, drape method, match mold method, air slip method, plug assist method, pressure bubble plug assist method, vacuum snap bag method, pressure bubble snap bag method, hot plate contact pressure air method, etc. is there.

[0013]

【Example】

"Synthesis example" Perfluoro (butenyl vinyl ether) 3
0 g, 120 g of ion-exchanged water and 50 mg of ((CH ₃ ) ₂ CHOCOO) ₂ as a polymerization initiator were placed in a pressure-resistant glass autoclave having an internal volume of 200 ml. After purging the system with nitrogen three times, suspension polymerization was carried out at 40 ° C. for 22 hours. The resulting polymer was vacuum dried at 100 ° C. for 20 hours and then treated at 250 ° C. for 5 hours in a N ₂ / F ₂ mixed gas atmosphere. As a result, 26 g of a polymer was obtained (hereinafter, this polymer is referred to as polymer A).

The intrinsic viscosity [η] of the polymer A is 0.5 at 30 ° C. in perfluoro (2-butyltetrahydrofuran).
It was 8. The glass transition point of the polymer A was 108 ° C., and it was a tough and transparent glassy polymer at room temperature.
The light transmittance was 95% or higher at wavelengths of 250 to 700 nm and 90% or higher at wavelengths of 200 to 250 nm.

"Example" The polymer A of the synthesis example was dissolved in perfluorotributylamine to obtain a 6.5% solution. 500 rp using precision polished soda glass as a substrate
Spin coating was performed under the conditions of m / 10 sec and 2500 rpm / 20 sec. When dried at 180 ° C. for 1 hour, a thin film having a film thickness of 1.58 μm was obtained. When the thin film is peeled from the glass substrate, both ends of the film are pulled and stretched, the thickness becomes
It became 86 μm.

Next, the stretched film was fixed to a circular aluminum support frame having a diameter of 15 cm with an adhesive. An air gun having a nozzle diameter of 0.65 mm and a predetermined pressure was used for this, and when air blowing was performed for 20 seconds from a distance of 10 mm from the film surface, the presence or absence of dot-like marks on the film was examined. The results are shown in Table 1.

"Comparative Example" As a comparative example, an unstretched 0.86 µ film of the polymer A was subjected to the same air blow test as in the example. The results are shown in Table 1.

[0018]

[Table 1]

[0019]

Since the stretched thin film for pellicle of the present invention has high film strength against air blow, and high transparency and durability against ultraviolet light, it can be used as a thin film for pellicle not only for g-line and i-line but also for excimer laser. Is also useful.

Claims (3)

[Claims] 1. A thin film for a pellicle, comprising a stretched amorphous fluorine-containing polymer. 2. The thin film for a pellicle according to claim 1, wherein the amorphous fluoropolymer is a fluoropolymer having a ring structure in its main chain. 3. A pellicle comprising a pellicle thin film according to claim 1 and a support frame.