JPH02272551A - Thin film for pellicle - Google Patents

Abstract

PURPOSE:To obtain an excellent light transmittance and durability even in a far IR region and to obtain characteristics to prevent the generation of static electricity by forming the thin film of a specific perfluorinated ion exchange polymer. CONSTITUTION:The thin film for a cover (pellicle) used to protect a photomask from sticking of dust in an exposing stage at the time of the formation of integrated circuits consists of the perfluorinated ion exchange polymer having a -SO3M functional group (M is H, Na, K or NR4; R is H, CH2 or C2H5). The thin film for the pellicle which has the excellent durability and light transmissivity over a 200 to 500nm wavelength range and does not generate the static electricity is obtd. in this way.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a thin film that has durability and high light transmittance in the deep ultraviolet region, and more specifically, the present invention relates to a thin film that is durable and has high light transmittance in the deep ultraviolet region. It relates to a thin film for a cover (commonly known as a pellicle) that is used to protect against the adhesion of.

(Prior Art) When dust adheres to the image surface of a photomask in a printing exposure device used to transfer an integrated circuit to a resist layer on a silicon wafer, an image of the dust is projected onto the resist layer, Hinder productivity. As a countermeasure against this problem, it is widely practiced to cover at least the image side of the photomask with a pellicle. By providing a certain gap between the image plane and the thin film of the pellicle, the projection of dust adhering to the thin film surface will not form an image on the resist layer.

For exposure, wavelength 3 is emitted from a high-pressure mercury lamp.
Near ultraviolet light in the region of 50 to 450 nm, substantially i-line (
365 nm), h-line (405 nm), or g-line (43
6 nm) is currently commonly used. The thin film of the pellicle used for this purpose is generally made of nitrocellulose.

However, in order to achieve future advances in the degree of integration of semiconductor devices, the resolution of conventional near-ultraviolet exposure has a limit, so it is necessary to
Mid-range ultraviolet rays and far ultraviolet rays of 0 nm are considered. At such short wavelengths, the chemical action of light becomes intense, so
There is a need for a thin film made of a new material that can withstand this and has good light transmittance. Examples of such products include products obtained by adding a silane compound to polyvinyl butyral resin (JP-A-59-206406), cellulose acetate, tate butyrate (JP-A-61-106243), and cyanoethyl cellulose (JP-A-61-1999). 130346), ethyl cellulose (Japanese Patent Application Laid-Open No. 62-59955), etc.

(Problems to be Solved by the Invention) Although these materials have better light transmittance than nitrocellulose at wavelengths of 350 nm or less, they still exhibit large light absorption at wavelengths of 250 nm or less. Furthermore, since the main chain skeleton is made of hydrocarbon, durability cannot be said to be sufficient, as can be seen from the comparison between bond dissociation energy and light energy.

Furthermore, electrostatic charging that attracts dust is undesirable for pellicles, but a thin film for pellicles made of a material that meets this problem has not yet been found.

An object of the present invention is to provide a thin film for a pellicle that has excellent durability and light transmittance over a wavelength range of 200 to 500 nm, and is free from static electricity.

(Means for Solving the Problems) The present inventors have focused on a fluorinated ion exchange polymer, which is unprecedented as a material for a thin film for a pellicle, and have completed the present invention.

That is, the present invention provides (1)-3o: 1M functional group (where M is 1, Na, K
or N R4, where R is H, CH, or C, R
3 membrane for pellicle consisting of a perfluorinated ion exchange polymer having 3).

(2) The thin film according to item 1 above, having a uniform thickness within the range of 0.5 to 10 μm.

(3) 90 nm over the wavelength range of 200 to 500 nm
3. The thin film according to items 1 and 2 above, which has a light transmittance of % or more.

(4) The film according to items 1 to 3 above, wherein at least one surface is coated with an antireflection coating.

(5) 95% over the wavelength range of 200 to 500 nm
5. The thin film according to item 4, which has a light transmittance of or above.

(6) The ion exchange polymer is a copolymer of tetrafluoroethylene and perfluoro(3,6-thioxer 4-methyl-7-octensulfonyl fluoride) whose sulfonyl fluoride group has been converted to the 303M functional group. The thin film according to items 1 to 5 above.

(7) The thin film according to items 1 to 6 above, wherein the ion exchange polymer has an equivalent weight within the range of 1000 to 1500.

I will provide a.

A precursor of this fluorinated polymer having a -303M functional group (where M is H, Na, K or NR4 and R is H, CH, or C2Hs), i.e. a sulfonyl fluoride (as a functional group) -3o2F) are shown in U.S. Pat. Nos. 3,282,875, 3,560,568 and 3,718,627. More particularly, such polymers can be prepared from monomers that are fluorinated or fluorinated vinyl compounds. The polymer is at least 2
monomers, at least one of which is selected from each of the two groups below.

The first group is vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl ether) and mixtures thereof.

The second group is monomers having a sulfonyl fluoride group, which is a precursor of an ion exchange group. More specifically, it is a monomer represented by the general formula %. The T group in the formula has 1 to 8 carbon atoms.
A difunctional fluorinated group consisting of , which may be branched or unbranched.

That is, it may be linear and may have one or more ether bonds. It takes a while.

Quantity is U.S. Patent No. 3.2B2.875, U.S. Patent No. 3.04
1.317, 3,718,627 and 3
．． No. 560.5613, examples of which include:

CF2 = CFOCF2CF2SO□F CF 2 = CFOCF zcF (CF 3) O
CF 2CF ZSO□FCFz=CF +0CFzC
F(CI”+)÷rOCFzCFzSOzFCF2=C
FOCFzCF(CFiOcFa)OCFzcFzso
□F A commercially easily obtained sulfonyl fluoride-containing monomer is perfluoro(3,6-thioxal 4
-methyl-7-octensulfonyl fluoride), C
F2 = CFOCFZCF (CFff) 0CF2
It is CF2SO2F. The copolymer obtained from the monomers of Group 1.2 is, for example, a polymer having the following repeating units.

゛→−−′p CP-R.

F2 5O□F In the formula, m is 3 to 15, n is 1 to 10, and P is 0, 1. or 2, at least one of X is fluorine, the rest are fluorine, chlorine or hydrogen, Y is F, CF20CFff or CF:l,
And Rf is F, C1, or 01 to C1 (1 perfluoroalkyl group).

In terms of optical properties, mechanical strength, hygroscopicity, etc., preferred copolymers that can be used in the pellicle thin film include, for example, tetrafluoroethylene and perfluoro(3,6-thioxer 4-methyl-7-octensulfonyl fluoride).
It is a copolymer of

Such copolymers can be prepared by the general polymerization methods developed for the homo- and copolymerization of fluorinated ethylene, in particular those used for tetrafluoroethylene, which are presented in the literature, but the pellicle Since it is desirable that the copolymer used as the material for the thin film has as little contamination as possible, it is preferably produced by a non-aqueous polymerization method as disclosed in, for example, US Pat. No. 3,041,317. That is, in an inert liquid such as perfluorocarbon or chlorofluorocarbon as a solvent, in the presence of a free radical initiator of perfluorocarbon peroxide or an azo compound, at a temperature of 0 to 200'C1 pressure of 1 to 20
It can be manufactured at 0 atmospheric pressure.

The pellicle is used by being set in the optical path between the light source of the exposure device and the optical lens system. Therefore, the thin film of the pellicle must have a uniform light transmittance over the area, and at the same time, it must not have a substantial effect on the deviation in the path of the exposure rays that would occur due to the refractive index of the thin film. It must be of uniform thickness. Also, its thickness is usually 0.5~
It is within the range of 10 μm. If it is less than 0.5 μm, mechanical strength tends to be insufficient. Moreover, if it exceeds 10 μm, there is a tendency for the path of the exposure light beam to shift. The preferred range is 1 to 5 μm.

It is appropriate to manufacture such a thin film of uniform thickness from a solution of the raw material copolymer by high-speed rotational casting using a spin coater. That is, it can be manufactured by adding a predetermined amount of a solution onto a rotating smooth substrate such as a silicon wafer, glass plate, metal plate, etc. and evaporating the solvent while rotating and casting the solution. For example, copolymer solid content concentration 5
When using ~10 wt% solution, spin speed is 500
~2,00Or,p,m thickness about 0.5~10p
A thin film of m is obtained. However, the conditions for spin coating to obtain the thin film of the present invention involve many influencing factors such as the fluidity of the solution, the volatility of the solvent in the solution, the temperature and humidity around the spin coater, the spin rotation speed, and the spin time. Select strictly to achieve the objectives.

The solution of the fluorinated ion exchange polymer having a sulfonic acid type or sulfonate type functional group, which is the material of the thin film of the present invention, can be manufactured according to the manufacturing method disclosed in JP-A-57-192464. can. For more details,
A fluorinated polymer having a sulfonic acid type or sulfonate type ion exchange group is made to coexist with a mixed liquid medium of water and lower alcohol in a closed pressure vessel, and the temperature is below the critical temperature of the liquid medium and at 180 to 300°C. A solution can be obtained by heating with shaking. Preferred lower alcohols are n-propanol, a mixture of methanol and n-propanol, diglyme, ethyl cellosolve, and the like.

Further, in order to obtain a solution with a concentration suitable for manufacturing a thin film using a spin coater, it is preferable that the equivalent weight of the ion exchange polymer used is 1,000 to 1,500. More preferably 1,100 to 1,400, most preferably 1,100 to 1,200.

A fluorinated polymer having a sulfonic acid type or sulfonate type ion exchange group is prepared by adding the precursor fluorinated polymer having a sulfonyl fluoride group to an aqueous solution of an alkali metal hydroxide or a water-miscible organic compound. Compound 5 can be obtained, for example, by contacting with an aqueous solution containing dimethylsulfochito to hydrolyze the sulfonyl fluoride group.

The fluorinated ion exchange polymer from which the thin film of the present invention is made has an n, refractive index of about 1.34 to 1.38. This is smaller than other thin film materials that have been proposed so far. This property gives the thin film of the present invention the characteristics of low light reflectance and low light refraction.

In addition, while the thin films for pellicles that have been proposed so far have a common tendency to exhibit significant light absorption, particularly at wavelengths of 250 nm or less, the thin film of the present invention exhibits much smaller absorption. Due to these characteristics, the thin film of the present invention has a wavelength of 90 nm at any wavelength from 200 to 500 nm.
A major feature is that it has a light transmittance of more than %.

Further, by applying an antireflection coating made of, for example, calcium fluoride, which has a lower optical refractive index than the fluorinated ion exchange polymer, to one or both sides of the thin film of the present invention by vacuum deposition or sputtering, it is possible to achieve a wavelength of 200 nm. at least 95% over ~500 nm
As described above, a light transmittance of over 99.5% can be provided.

Furthermore, the thin film of the present invention does not carry any static electricity.

This is a remarkable characteristic not seen in any of the thin films for pellicles that have been proposed up to now, and it shows its true value in the production and handling of pellicles that do not attract dust.

Furthermore, the durability of the thin film of the present invention, which consists essentially of a fluorocarbon backbone chain, particularly in the mid-ultraviolet and deep ultraviolet regions, is far superior to conventional thin films that consist of a hydrocarbon backbone main chain. Furthermore, the thin film of the present invention has a large tensile modulus and low crib property, presumably because it has ionic crosslinks inside, and therefore has excellent shape retention under tension, which is preferable as a thin film for a pellicle.

The equivalent weights stated in the text and examples are determined by titrating the free acid form of the polymer with a standard aqueous solution of sodium hydroxide.

This measurement is accurate to only about ±25 equivalent weight units.

(Example) Examples illustrating the present invention will be described below, but the present invention is not limited to these Examples.

Example 1 With stirrer 1! n-proper tool 45 in autoclave
0m1. Tetrafluoroethylene and perfluoro(3,
Add 60g of copolymer of 6-thioxer (4-methyl 7-octensulfonyl fluoride) and add 2.
After heating to 40'C for 18 hours, it was cooled to room temperature.

No undissolved polymer was observed, and the solution was clear and had a viscosity of about 13 centistokes.

After filtering this solution with a 0.2 μm porous membrane filter, approximately 10 gr was supplied to the center of an 8" diameter polished silicone wafer set in a spin coater, and the solution was rotated at approximately 50 r, p, m rotation. Immediately after spreading over the entire surface of the wafer, about 1,000 r,
The rotation was increased to p, m, and this state was continued for 60 seconds. Next, the wafer was dried in an air oven at 90° C. for 10 minutes, and then the wafer was immersed in clean water. The thin film that peeled off from the wafer was dried at room temperature until the dimensional shrinkage reached an equilibrium, yielding a transparent thin film with a thickness of approximately 1 μm. This thin film was supported with a slight tension in an appropriate frame and measured using a spectrophotometer (UV-240 manufactured by Shimadzu Corporation) at wavelengths of 190 to 50.
The light transmittance at 0 nm was measured.

The average light transmittance indicated by the center value between the maximum value and the minimum value of etaloning was 93% or more over a range of 200 to 500 nm.

Example 2 N-Propatzl 200 in a 12 autoclave with a stirrer
d, methanol 160+1, water 400 ml and 1,
has an equivalent weight of 100, and its functional group is 13O3H
Tetrafluoroethylene and perfluoro(3,6-thioxal-4-methyl-7-
Octenesulfonyl fluoride) copolymer 80gr
and heated to 220°C for 3 hours while stirring,
It was cooled to room temperature and left standing. No undissolved polymer was observed, and the liquid phase was separated into two layers. The lower density upper layer was removed, and 80 gr of triethyl phosphate was added to the lower layer, a clear solution having a viscosity of about 120 centistokes, and stirred to form a homogeneous solution. Approximately 10g of this solution was filtered through a 0.2μm porous membrane filter and supplied to the center of an 8" polished silicon wafer set in a spin coater, and the solution was rotated at approximately 50 r, p, m. Immediately after it spreads over the entire wafer, it becomes about 2.00 Or
, p, n+, and continued in this state for 60 seconds. Next, the wafer was placed in an air oven, dried at 120''C for 10 minutes, and then immersed in clean water.

The thin film that peeled off from the wafer in water was air-dried at room temperature until the dimensional shrinkage reached equilibrium, yielding a transparent thin film with a thickness of approximately 1 μm.

This thin film was supported with a slight tension in an appropriate frame, and the light transmittance was measured using a spectrophotometer.

The average light transmittance indicated by the center value between the maximum value and the minimum value of etaloning was 93% or more over a range of 200 to 500 nm.

Example 3 A fluoride-deadred lucium layer having a thickness of about 0.05 μm was applied as an antireflection layer to both sides of the thin film obtained in Example 2 by vacuum evaporation. The average light transmittance of this thin film was 95% or more over wavelengths of 200 to 500 nm.

Example 4 The thin films obtained in Examples 1.2 and 3 above were continuously exposed to light having a wavelength of 254 nm from a low-pressure mercury lamp. io,
After irradiation with ooo tv·sec/CfI, the light transmittance and infrared absorption spectrum were measured, and both thin films were unchanged from before exposure.

Example 5 The thin films obtained in Examples 1 and 2 were placed on a wafer and incubated at a temperature of 25±1° C. and a relative humidity of 70±5%.
After leaving it for 2 hours, it was bonded to an aluminum frame for mounting a printing exposure device (outer side 90III+, width 21nIn, height 5cm) using an epoxy adhesive. When this is moved to a room with a temperature of 25 ± 1°C and a relative humidity of 55 ± 5%,
A pellicle with a thin film tension was obtained.

Next, one side of the thin film was covered with an aluminum plate, and the whole was placed under a low-pressure mercury lamp (254 nm light, L, 8 mW/c+fl illuminance) for an exposure durability test. Total 5.0
After irradiation with 00 W·sec/cnl, interference fringes were observed under sodium monochromatic light, and no difference was observed between the exposed and non-exposed surfaces.

(Effects of the Invention) The thin film of the present invention has high light transmittance and durability even in the deep ultraviolet yA region, and has the property of not being charged with static electricity, so it is effective as a pellicle thin film in the production of high-density integrated circuits. It is.

[Brief explanation of drawings]

FIG. 1 is a light transmission spectrum of a thin film having a thickness of about 1 μm and containing -SO,Na groups obtained in Example 1. Figure 2 shows about 1 with -5O3H group obtained in Example 2.
It is a light transmission spectrum for a thin film with a thickness of μm. Figure 3 shows the antireflection-treated 13O obtained in Example 3.
It is a light transmission spectrum of a thin film having 3H groups. Patent applicant: Asahi Kasei Kogyo Co., Ltd. Figure 1 Figure 2 Figure 3 Procedural amendment (voluntary) Month/7, 1999

Claims (1)

[Claims] -SO_3M functional group (where M is H, Na, K or N
R_4 and R is H, CH_3 or C_2H_5)