JP2000258895A - Pellicle for lithography with improved light resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pellicle for lithography consisting of a pellicle film which has a long life without deterioration or decomposition by light even when the film is irradiated for a long time with vacuum UV rays of short wavelength and which has high transmissivity for light and high performance without changes, by treating the pellicle film with fluorine gas to form a fluorinated layer on the film surface. SOLUTION: A pellicle film comprising an amorphous perfluoropolymer is treated with fluorine gas to form a fluorinated layer on the film surface. By forming a fluorinated layer of high density on the surface of the pellicle film, the fluorinated layer of high density causes recombination of opened bonds due to the radical reaction even under the conditions that the film absorbs light to produce radicals and deterioration is accelerated. Thus, deterioration of the film can be suppressed to an extremely low level. The fluorine atom content on the film surface is preferably at least >=60 mol.%. However, when the content exceeds 80 mol.%, the film strength may decrease, so the fluorine atom content is especially preferably controlled to 60 to 80 mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pellicle for lithography, and more particularly to a pellicle for lithography used in vacuum ultraviolet light exposure at a wavelength of 200 nm or less, which is used in exposure requiring high resolution.

[0002]

2. Description of the Related Art Conventionally, when a semiconductor device such as an LSI or a super LSI or a liquid crystal display panel is manufactured, a semiconductor wafer or a substrate for a liquid crystal is irradiated with light to perform patterning. If dust adheres to the substrate, the dust absorbs or bends the light, causing the transferred pattern to be deformed, the edges to be rough, and the white background to become black. Therefore, there has been a problem that dimensions, appearance, quality, and the like are impaired, and the performance and manufacturing yield of semiconductor devices and liquid crystal display panels are reduced.

[0003] For this reason, these operations are usually performed in a clean room. However, even in this clean room, it is difficult to keep the exposed substrate clean at all times. A method of attaching a pellicle to be made has been performed. In this case, the dust does not directly adhere to the surface of the exposed substrate, but adheres to the pellicle film. Therefore, if the focus is focused on the pattern of the exposed substrate during lithography, the dust on the pellicle becomes independent of transfer. There is.

As shown in FIG. 1, a transparent pellicle film 1 made of nitrocellulose, cellulose acetate, fluororesin, or the like, which allows light to pass therethrough, is provided on a pellicle frame 2 made of aluminum, stainless steel, or the like. A good solvent for the film is applied, and the pellicle film is adhered by air drying after adhesion (Japanese Patent Laid-Open No. 58-21902).
No. 3) and bonded with an adhesive such as acrylic resin, epoxy resin or fluororesin (US Pat. No. 486140).
No. 2, JP-B-63-27707, JP-A-7-27707
In the lower part of the pellicle frame 2, a polybutene resin, a polyvinyl acetate resin, an acrylic resin,
An adhesive made of a silicone resin or the like and a release layer 4 (separator) for protecting the adhesive layer 3 are adhered to each other.

[0005]

However, in recent years,
The resolution of lithography is gradually increasing,
In order to realize the resolution, light having a short wavelength is gradually used as a light source. In particular,
From ultraviolet light (g line (436 nm), I line (365 nm)) to far ultraviolet light (KrF excimer laser (248n
m)), and in the near future, vacuum ultraviolet light (A
An rF excimer laser (193 nm) will be used. As the wavelength becomes shorter, the photon energy becomes larger, and the material used for lithography causes greater light degradation. In particular, since the material of the pellicle film is an organic substance, its influence increases at an accelerated rate as the wavelength becomes shorter.

Incidentally, the photoreaction basically starts only after light is absorbed. Resin used for pellicle membrane,
For example, a fluororesin originally does not contain a double bond in its basic skeleton, and has a fluorine atom having a high electronegativity, so that it does not originally have absorption in the far ultraviolet region. However, there is a possibility that an ester group derived from the reaction initiator may be present at the terminal of the polymer, and it is difficult for the actual resin to complete the polymerization reaction completely. The possibility of existence cannot be denied. These functional groups absorb ultraviolet light and can be a starting point of a photodegradation reaction.

[0007] Then, when the optical deterioration of the film proceeds, there arises a problem that the film thickness is reduced and the transmittance is reduced. In addition, cleavage and recombination of the polymer chain by radicals are caused,
The refractive index of the polymer changes. Such changes in transmittance and refractive index cause uneven illuminance on the wafer to be exposed, and adversely affect lithography. Further, since the pellicle film is a very thin film, it causes interference with light serving as a light source for lithography. Therefore, at the time of manufacturing the pellicle, the film thickness is controlled so as to maximize the transmittance by calculating light interference. However, when the film thickness changes due to light irradiation, interference deviates, causing a problem that transmittance decreases and illuminance unevenness occurs on the wafer.

As a result of analyzing the surface of the film after the light irradiation, it was found that a concave portion was formed in the portion irradiated with the light. on the other hand,
Despite the light irradiation in the atmosphere where oxygen and the like are present, the chemical analysis of the light-irradiated portion has not altered the portion. That is, it is considered that the photodeterioration in this case is due to the fact that the polymer chains constituting the pellicle film are cut by the light irradiation, and the resulting low molecular weight is evaporated to reduce the film thickness.

The present invention has been made in view of the above-mentioned problems, and the pellicle film is made of an amorphous perfluoropolymer. It is a main object of the present invention to provide a pellicle for lithography comprising a high-performance pellicle film which has a long life and does not change and has a high light transmittance without being worn or decomposed.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the invention described in claim 1 of the present invention provides an amorphous pellicle film used for lithography. A pellicle for lithography using a perfluoropolymer, wherein the pellicle film is treated with a fluorine gas to form a fluorinated layer on the surface.

As described above, in a pellicle for lithography using an amorphous perfluoropolymer as the material of the pellicle film used for lithography, the pellicle film is treated with fluorine gas to form a fluorinated layer on the surface. A pellicle for lithography that is made of a pellicle film that has no light degradation even after long-time light irradiation, that is, a pellicle film that is excellent in light resistance without a change in film thickness or light transmittance and has a long life and high performance. Can be.

In this case, as described in claim 2, the pellicle for lithography can be used for vacuum ultraviolet light exposure of 200 nm or less.

As described above, the pellicle for lithography can be used to produce ultraviolet light having a large photon energy of 200 nm or less,
For example, even when used for vacuum ultraviolet light exposure such as ArF excimer laser, the thickness change of the pellicle film,
A pellicle for lithography comprising a long-lived and high-performance pellicle film without reduction in light transmittance and generation of cracks can be obtained.

In this case, it is preferable that the fluorine atom content on the surface of the pellicle film treated with the fluorine gas is 60 mol% or more.

As described above, when the fluorine atom content on the surface of the pellicle film treated with the fluorine gas is 60 mol% or more, ultraviolet light having a large photon energy of 200 nm or less, for example, a vacuum such as an ArF excimer laser. A pellicle for lithography consisting of a long-life, high-performance pellicle film that does not change the thickness of the pellicle film, reduces light transmittance, and does not crack even if used for ultraviolet light exposure. Can be. However, if the fluorine atom content is larger than 80 mol%, the film strength may be reduced. Therefore, it is particularly preferable that the content be in the range of 60 to 80 mol%.

The invention according to a fourth aspect of the present invention is characterized in that the pellicle film has a reduction rate of 0.5% or less when irradiated with a laser beam of 20,000 J / cm ^2. .

As described above, in the present invention, for example, ArF
Even when the light is irradiated at 20000 J / cm ² by an excimer laser, the rate of decrease in the thickness of the pellicle film is 0.1%.
It can be 5% or less, and even if exposed to a short wavelength such as vacuum ultraviolet light, the pellicle film is formed of a long-life and high-performance pellicle film without a decrease in light transmittance or cracking of the pellicle film. It can be a pellicle for lithography.

According to a fifth aspect of the present invention, there is provided a method for manufacturing a pellicle for lithography comprising attaching a pellicle film made of an amorphous perfluoropolymer to a pellicle frame. A method for producing a pellicle for lithography, comprising: forming a pellicle film made of a polymer, treating the film with a fluorine gas, and forming a fluorinated layer on the surface of the film.

As described above, in the method of manufacturing a pellicle for lithography in which a pellicle film made of an amorphous perfluoropolymer is attached to a pellicle frame, the pellicle film is made of a pellicle film made of an amorphous perfluoropolymer. After the film is formed, if the film is treated with fluorine gas to form a fluorinated layer on the film surface, the pellicle film thickness change and light transmittance even when exposed to a short wavelength such as vacuum ultraviolet light It is possible to easily produce a pellicle for lithography comprising a high-performance pellicle film having a long life and no reduction in cracks and generation of cracks.

In this case, it is preferable that the pellicle film is treated with fluorine gas so that the fluorine atom content on the surface of the pellicle film is 60 mol% or more.

As described above, if a pellicle for lithography is manufactured by treating the pellicle film with fluorine gas so that the fluorine atom content on the surface becomes 60 mol% or more, the pellicle film is exposed to a short wavelength such as vacuum ultraviolet light. However, a change in the thickness of the pellicle film, a decrease in light transmittance, and the generation of cracks are reliably suppressed, and a pellicle for lithography comprising a pellicle film having a long life and high performance can be easily and reliably manufactured.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, if a pellicle film made of an amorphous perfluoropolymer is treated with a fluorine gas to form a fluorinated layer on the surface, For example, it has been found that even if the pellicle film is irradiated with vacuum ultraviolet light of 200 nm or less such as an ArF excimer laser, the pellicle film hardly undergoes photodegradation, that is, it is possible to obtain a pellicle film without a decrease in the thickness or transmittance of the pellicle film. The present invention was completed by examining various conditions.

Hereinafter, the pellicle film of the pellicle for lithography of the present invention will be described in detail. The material of the pellicle film of the pellicle for lithography of the present invention is an amorphous perfluoropolymer, and these are commercially available, for example, as Cytop (manufactured by Asahi Glass Co., Ltd.).

The fluorine-based resin such as an amorphous perfluoropolymer is easily thinned, has excellent transmittance, and has excellent characteristics not absorbing in the ultraviolet region. However, even when such a fluorine-based resin is used, when light irradiation is performed by short-wavelength laser light such as vacuum ultraviolet light, problems such as a decrease in film thickness and a decrease in transmittance due to light degradation occur. As a result of various studies to solve this problem, it was found that under irradiation with an ArF excimer laser, the polymer chain was cut by radicals generated by the absorption of light by the fluororesin, and the low molecular weight molecules were evaporated. It has been found that the change and the transmittance change are the major causes.

Therefore, as a result of various studies on methods for protecting the surface of the fluororesin film, if the surface of the film is fluorinated using fluorine gas, the film surface of the fluororesin can be extremely easily and at low cost. It has been found that a pellicle film having a high concentration fluorinated layer can be obtained. As a result, the above-described object is achieved in which a pellicle for lithography is formed of a pellicle film having little photodeterioration even when irradiated with ArF excimer laser light having a large photon energy for a long time, that is, having a small change in film thickness and transmittance due to light irradiation. Was.

The mechanism of suppressing the photodeterioration of the pellicle film, which became apparent during the process of completing the present invention, will be described. Generally, photodeterioration of a polymer is caused by radical absorption when light is absorbed and molecules are excited. Although this occurs as a reaction, when this radical reaction occurs, the chemical bond is homogenously cleaved. Then, the generated radical propagates in the molecule, and cleavage of the polymer chain proceeds.

However, in the case of a fluorine-based resin, the fluorine atom which is the main constituent atom has a very high electronegativity, so that even if the polymer molecule is cleaved by a radical reaction, the fluorine atom has a large electronegativity. As a result, the rate at which the broken bonds are recombined increases, and the lowering of the molecular weight of the polymer is suppressed much lower than predicted from light absorption, and light degradation is suppressed. As a result, the influence on the transmittance and the refractive index of the film is also suppressed.

That is, if a high-concentration fluorinated layer is provided on the surface of the pellicle film, the high-concentration fluorinated layer is free from radicals even under conditions in which the film absorbs light to generate radicals and deterioration proceeds. Since the reaction causes the recombination of the bond that has been cleaved, the deterioration of the film can be kept very small.

In this case, the content of fluorine atoms on the surface of the film can be easily calculated by measuring by X-ray photoelectron spectroscopy (XPS). That is, X-ray photoelectron spectroscopy is the most suitable measurement method for obtaining information on the surface because it measures photoelectrons from several hundred square meters on the surface.
The 1s and O1s spectra are measured, the sensitivity of each measurement is corrected, and the fluorine atom content can be easily calculated from the integrated area ratio of the spectra.

The higher the fluorine atom content present on the surface of the pellicle film, the more easily the effect of recombining the cleaved bond is obtained. It is desirable that the content is at least 60 mol% or more. However, if it exceeds 80 mol%, the film strength may be reduced, so that the fluorine atom content is particularly preferably in the range of 60 to 80 mol%.
If the fluorine atom content on the film surface is 60 mol% or more, for example, even if the irradiation amount of the ArF excimer laser reaches 20,000 J / cm ² , the film thickness reduction rate is 0.5%.
% Or less.

Next, a method for manufacturing a pellicle film of a pellicle for lithography of the present invention will be described. First, a solution of an amorphous perfluoropolymer is dropped on a substrate, for example, a silicon substrate, formed into a thin film using a spin coater, and then dried by heating to evaporate the solvent to form a pellicle film on the silicon substrate.

Then, the pellicle film on the silicon substrate is
A temporary frame made of a material that is not eroded by fluorine, such as a pellicle film of a pellicle for lithography of the present invention, which is attached to a temporary frame made of nickel and then treated with fluorine gas to form a fluorinated layer on the surface of the pellicle film. Is obtained. In this case, the treatment with fluorine gas may be performed by any method.For example, a pellicle film is placed in a reactor made of a material such as nickel that is not eroded by fluorine gas, and the treatment is performed by introducing fluorine gas into the pellicle film. It does not matter. Further, the treatment of the fluorine gas may be performed as a mixed gas of fluorine and an inert gas such as nitrogen or argon.

[0033]

The present invention will be described below with reference to examples and comparative examples.

Here, the determination of fluorine atoms on the surface of the pellicle film of the present invention is performed by the above-mentioned X-ray photoelectron spectroscopy (XPS).
This was performed using The evaluation of the light resistance of the pellicle film
This was performed as follows.

[Evaluation of Light Resistance] The film was irradiated with ArF excimer laser light (wavelength: 193 nm) in the air, and the film thickness and transmittance before and after the irradiation were measured. After that, calculate the amount of change,
The effects of irradiation were investigated. The irradiation conditions of the ArF excimer laser were an intensity of 1 mJ / cm ² / pulse and a pulse frequency of 400 Hz.

(Example) Cytop CTX-S (Asahi Glass Co., Ltd.) which is an amorphous perfluoropolymer as a film material
Manufactured by Fluorinated Solvent CT-solv. 180 (manufactured by Asahi Glass Co., Ltd.) to prepare a 5% concentration solution. Next, this solution was dropped on a surface-polished silicon substrate having a diameter of 200 mm and a thickness of 1.2 mm, and the substrate was rotated using a spin coater to form a 1 μm-thick permeable film. Thereafter, the substrate was dried at 200 ° C. for 15 minutes to form a pellicle film on the substrate. Then, a temporary nickel frame was attached to the film on the substrate, and the entire frame was peeled off from the silicon substrate to obtain a single film.

Next, after introducing the CYTOP film attached to the nickel temporary frame into the nickel reaction vessel and evacuating it, the volume ratio of fluorine gas to nitrogen gas was reduced to 1: 9. The mixed gas mixture was introduced into the reaction vessel. The reaction was carried out at room temperature for 24 hours to fluorinate the film. After completion of the reaction, the inside of the container was replaced with nitrogen gas, and a sample was taken out. XPS measurement was performed on the fluorine atom content on the surface of the fluorinated pellicle film in this manner, and the results are shown in Table 1.

The light fastness was evaluated by irradiating an ArF excimer laser at a dose of 5000 J / cm ² and 10,000 J / c.
The test was performed at m ² and 20,000 J / cm ² , and the results are shown in Table 2.

(Comparative Example) A CYTOP film attached to a nickel temporary frame obtained under the same conditions as in the example was
Without forming a fluorinated layer, the content of fluorine atoms on the surface of the pellicle film and the light resistance were measured. Tables 1 and 2 show the results.
It was shown to.

[0040]

[Table 1]

[0041]

[Table 2]

As is clear from the above results, the content of carbon atoms and oxygen atoms on the surface of the pellicle film was 6 mol% and 3 m
ol%. On the other hand, the fluorine content increased by 9 mol%. From this experimental result, it was proved that a high concentration fluorinated layer was formed on the surface of the pellicle film by fluorination.

[0043] With respect to light fastness, in the case of performing the fluorination of the pellicle film, a film thickness reduction rate is 0.1% after the ArF excimer laser irradiation of 5000 J / cm ^2, also 10000 J / cm ² at 0 .2% and 2000
Since it was 0.4% even at 0 J / cm ² , it was found that there was little light deterioration, and it was extremely excellent. In addition, even when irradiation with an ArF excimer laser having a large photon energy is performed,
The pellicle membrane did not have any appearance defects such as reduced permeability and cracks.

On the other hand, when the pellicle film was not fluorinated, the reduction rate of the film thickness after the irradiation of 5000 J / cm ² ArF excimer laser was 0.2%, and 1%.
0.4% at 0000 J / cm ² and 20,000 J
/ Cm ² , the film thickness reduction rate was as large as 1.0%, indicating that the photodegradation was so severe that it could not be adapted to irradiation with a short wavelength exposure light source, for example, vacuum ultraviolet light.

From the above, when a fluorinated layer having a high concentration is formed on the surface of the pellicle film, the reduction rate of the film thickness due to the irradiation of short wavelength light such as ArF excimer laser is small, and the light deterioration is small. This proved that the high-concentration fluorinated layer on the film surface suppressed photodegradation due to laser irradiation.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention. Within the technical scope of

For example, in the present invention, not only a perfluoroether group-containing fluoromonomer polymer but also a linear perfluoroether group-containing monomer polymer may be used as the amorphous perfluoropolymer.

[0048]

According to the present invention, when the material of the pellicle film is an amorphous perfluoropolymer, in particular, a fluorine-containing monomer polymer having a perfluoroether group, the surface of the film is fluorinated and fluorinated at a high concentration. If a layer is formed, light degradation of the pellicle film due to a short-wavelength exposure light source during lithography, particularly an ArF excimer laser, is suppressed, so that a decrease in film thickness and transmittance and generation of cracks hardly occur,
A pellicle for lithography comprising a long-life and high-performance pellicle film can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration example of a pellicle film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pellicle film, 2 ... Pellicle frame, 3 ... Adhesive layer, 4 ... Release layer.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shu Kashida 2-13-1 Isobe, Annaka-shi, Gunma F-term in Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory 2H095 BC33 BC35

Claims (6)

[Claims] 1. A pellicle for lithography using an amorphous perfluoropolymer as a material of a pellicle film used for lithography, wherein the pellicle film is treated with fluorine gas to form a fluorinated layer on the surface. Pellicle for lithography, characterized in that: 2. The pellicle for lithography according to claim 1, wherein
2. The pellicle for lithography according to claim 1, wherein the pellicle is used for vacuum ultraviolet light exposure of 0 nm or less. 3. The pellicle for lithography according to claim 1, wherein the fluorine atom content on the surface of the pellicle film treated with the fluorine gas is 60 mol% or more. 4. The pellicle film according to claim 1, wherein the pellicle film has a thickness reduction rate of 0.5% or less when irradiated with a laser beam of 20,000 J / cm ^2. A pellicle for lithography according to 1. 5. A method for manufacturing a pellicle for lithography comprising attaching a pellicle film made of an amorphous perfluoropolymer to a pellicle frame, wherein the pellicle film is formed after forming a pellicle film made of an amorphous perfluoropolymer. ,
A method for producing a pellicle for lithography, characterized in that the film is produced by forming a fluorinated layer on the film surface by treating with a fluorine gas. 6. The method for producing a pellicle for lithography according to claim 5, wherein the fluorine atom content on the surface of the pellicle film treated with the fluorine gas is 60 mol% or more.