JP2001264957A - Pellicle for lithography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pellicle for lithography with a high performance pellicle membrane using an amorphous perfoluroropolymer as the material of the membrane, excellent in peelability from a substrate in the formation of the membrane, free of photogradation and decomposition due to the absorption of short-wavelength ultraviolet light even when irradiated with the light for a long the time and having a long service life and a high invariable transmittance. SOLUTION: In the pellicle for lithography consisting essentially of a pellicle membrane and a pellicle frame, the pellicle membrane stretched on the pellicle frame comprises an amorphous perfluoropolymer and the terminal groups of the perfluoropolymer have been fluorinated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pellicle for lithography, and more particularly to a pellicle for lithography used as a dust-repelling material for an exposure original (reticle) when manufacturing a semiconductor device such as an LSI or a super LSI or a liquid crystal display panel. More particularly, the present invention relates to a pellicle for lithography used in exposure requiring high resolution.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices such as LSIs and VLSIs, or liquid crystal display panels, semiconductor wafers or liquid crystal masters are irradiated with light to perform patterning. If foreign matter adheres, the foreign matter absorbs or reflects light, resulting in deformation of the transferred pattern, rough edges, and black background, resulting in size, quality, appearance, etc. However, there is a problem that the performance and 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, it is difficult to keep the exposure master clean even in the clean room. A method of mounting a pellicle that transmits light well is adopted. in this case,
Foreign matter does not directly adhere to the surface of the exposure master, but adheres to the pellicle film of the pellicle, so if the focus is focused on the pattern of the exposure master during lithography, the foreign matter on the pellicle film surface will be unrelated to transfer .

As shown in FIG. 1, for example, this pellicle is a transparent pellicle film 1 made of nitrocellulose, cellulose acetate, fluororesin or the like which normally transmits light well.
Is a pellicle frame made of aluminum, stainless steel, polyethylene, etc. (hereinafter simply referred to as a frame)
A good solvent for the pellicle film is applied to the upper end surface of the pellicle film 2, and the pellicle film 1 is adhered and air-dried and adhered (see Japanese Patent Application Laid-Open No. 58-219023). Bonded with an adhesive such as fluororesin (US Pat. No. 4,861,402, JP-B-63-27707),
An adhesive layer 3 made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, or the like is provided on a lower end surface of the frame 2,
Further, a protective sheet (separator) for protecting the adhesive layer 3
4 is attached.

[0005]

In recent years, the resolution of lithography has been gradually increased, and in order to realize the resolution, light having a gradually shorter wavelength has been used as a light source. Specifically, the g-line (436)
nm) or i-ray (365 nm) from the KrF excimer laser (2
48 nm) and ArF excimer laser (193 nm). Generally, when the wavelength is shortened as described above, the light energy is increased, and accordingly, the material used for lithography causes a great light deterioration. In particular, since the pellicle film is made of an organic material,
As the wavelength of light becomes shorter, this effect increases at an accelerated rate.

[0006] The photoreaction basically starts only after light is absorbed. As the wavelength of light becomes shorter in recent years, an amorphous perfluoropolymer having no absorption even in a short wavelength ultraviolet region is used for a pellicle film. The basic skeleton of the amorphous perfluoropolymer does not contain unsaturated bonds or the like, and has a fluorine atom having a high electronegativity, so that it does not absorb short-wavelength ultraviolet light. However, since an ester group (-COO-, the same applies hereinafter) is present at a part of the terminal of the polymer structure and absorbs ultraviolet light, light degradation has been a problem when using short-wavelength ultraviolet light. As the film deteriorates, there arises a problem that the film thickness decreases and the transmittance decreases. In addition, radical scission of the polymer chain,
Recombination is caused and the refractive index of the polymer changes.
Such changes in transmittance and refractive index cause uneven illuminance on a wafer to be exposed, and adversely affect lithography.

Generally, a pellicle film is obtained by applying a polymer solution onto a substrate such as silicon, drying the film, and then peeling the film to obtain a single film. At this time, if an ester group is present at the terminal of the polymer structure, there are problems such as difficulty in peeling off the film, wrinkling, and extension of the film itself beyond the stretching limit. The present invention has been made to solve such a problem, and uses an amorphous perfluoropolymer as a material of a pellicle film, has excellent peelability from a substrate during film formation, and has a short wavelength ultraviolet light. Provided is a pellicle for lithography having a high-performance pellicle film having a long life without absorbing, deteriorating or decomposing even if irradiated for a long time, and having a high transmittance and no change. Is an issue.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on the photodegradation of the pellicle film against short-wavelength ultraviolet light, and as a result, have found that amorphous perfluoropolymers, especially cyclic perfluoroether groups, The fluorine-containing polymer obtained by reacting a fluorine gas with the fluorine monomer polymer having the terminal group is fluorinated by KrF excimer laser, ArF
The absorption of short-wavelength ultraviolet light such as excimer laser decreases, and when irradiated with light having a wavelength of substantially 300 nm or less, a pellicle film with almost no light deterioration, that is, a decrease in film thickness and a decrease in transmittance is obtained. The present inventors have found that the present invention can be performed, and scrutinized various conditions to complete the present invention.

That is, a pellicle for lithography of the present invention is a pellicle comprising at least a pellicle film and a pellicle frame, wherein the pellicle film stretched on the pellicle frame is made of an amorphous perfluoropolymer, and the terminal group of the polymer is Is fluorinated. This amorphous perfluoropolymer having a terminal group fluorinated has a cyclic perfluoroether group represented by the following chemical formula (Formula 2). Further, the content of the ester group (—COO—) in the terminal group is desirably 3 mol% or less of the whole terminal group.

[0010]

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[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As an amorphous perfluoropolymer having a fluorinated terminal group used in the pellicle membrane of the present invention, for example, b in the above-mentioned formula (Formula 2) is replaced by b = CYTOP CTX S type (made by Asahi Glass Co., Ltd., trade name) with 0 is used. Further, those manufactured by the following method can also be used. For example, as an amorphous perfluoropolymer used as a raw material, A type, E type, M type, or Cytop 69 of Cytop CTX represented by the following chemical formula (Chem. 3) (all manufactured by Asahi Glass Co., Ltd., trade names) And dissolving them in a good solvent such as a fluorine solvent, and then performing fluorination treatment, thereby fluorinating the terminal groups of the polymer and reducing the ester group content in the terminal groups to 3 mol% or less. The resulting amorphous perfluoropolymer is obtained. Further, the same fluorination treatment as described above for the S-type of Cytop CTX whose terminal group has already been fluorinated to further reduce the ester group content can also be suitably used.

[0012]

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Specifically, for example, a method of introducing a mixed gas of fluorine into a raw material polymer solution by bubbling can be mentioned. If the reaction temperature at this time exceeds 200 ° C., the polymer main chain may be cut off. If the reaction temperature is lower than 0 ° C., the reaction rate is reduced.
The range of ° C. is preferred. As the fluorine mixed gas, a mixture of fluorine and an inert gas (such as nitrogen or argon) may be used. At this time, if the content of fluorine in the mixed gas is less than 1% by volume, the reaction rate becomes slow, while
If the content exceeds 90% by volume, the polymer main chain may be broken. Therefore, the content of fluorine in the mixed gas is preferably in the range of 1 to 90% by volume.

The reaction may be terminated when the content of the ester group at the terminal of the polymer becomes 3 mol% or less with respect to the entire terminal group. When the content of the ester group in the terminal group is 3 mol% or less of the whole terminal group, if it exceeds 3 mol%, peeling of the film from the substrate at the time of forming the pellicle film becomes difficult, and wrinkles occur. This is because in addition to the fact that the film itself is stretched beyond the stretching limit, the absorption of the irradiated ultraviolet light increases, and photodeterioration occurs.

A pellicle film processed using the thus obtained polymer having a reduced ester group content in the terminal group can be easily peeled off from the substrate, and the dimensional stability can be improved. A good pellicle film without deformation can be obtained. The pellicle produced using this pellicle film is Kr
A pellicle film that makes full use of the inherent properties of amorphous perfluoropolymer, such as transparency, film strength, and light resistance, to short wavelength ultraviolet light such as F excimer laser and ArF excimer laser is obtained. As a result, it is possible to manufacture a high-performance pellicle having a long life and a small change in transmittance.

Next, a method for quantifying the degree of fluorination of the polymer terminal group and evaluation of characteristics as a pellicle film will be described. [Quantification of Fluorination Degree of Terminal Group] The quantification of the degree of fluorination of the terminal group was carried out by converting an ester group into a carboxyl group, reacting with hexamethyldisilazane, and quantifying the silicon fixed to the polymer. . Specifically, a lithium aluminum hydride (LiAl
H ₄ ) was added and reacted in a methanol dry ice refrigerant bath adjusted to −68 ° C. to convert an ester group to a carboxyl group, and then an excess amount of hexamethyldisilazane was added.
The mixture was heated at 100 ° C. for 72 hours in a pressure vessel to completely silylate the carboxyl groups. After the reaction, the solution was heated at 200 ° C. for 2 hours.
Heat drying was performed for 4 hours to remove unreacted hexamethyldisilazane. After drying, the polymer was subjected to atomic absorption analysis to determine the silicon content. Taking into account the molecular weight of the polymer, the content of the ester group terminal relative to the entire terminal group was calculated from the silicon content.

[Evaluation of Peeling Property] The peeling property was evaluated by the following method. The polymer solution was applied on a mirror-polished silicon substrate having a diameter of 200 mm and a thickness of 0.6 mm using a spin coater to form a 0.8 μm-thick pellicle film. Next, a fluorine-based resin adhesive is applied to an aluminum alloy frame having an inner diameter of 180 mm, and the applied surface is adhered to a pellicle film on the substrate, and the frame is lifted from the substrate at room temperature of 23 ° C. and 90% humidity. The pellicle film was peeled off. The state of the film was observed using a condenser lamp in a dark room. Those with good releasability peel off smoothly from the substrate with little resistance. Those with poor peelability exceeded the elongation limit of the material during peeling, and it was observed that the film was whitened and clouded under a condensing lamp. Further, if the film has poor releasability, the film may be wrinkled or, in extreme cases, the film may not be peeled from the silicon substrate.

[Evaluation of Light Fastness] The light fastness was evaluated by the following method. The polymer solution was applied on a mirror-polished silicon substrate having a diameter of 200 mm and a thickness of 0.6 mm using a spin coater to form a 0.8 μm-thick pellicle film. Next, a fluorine-based resin adhesive is applied to the aluminum alloy frame, and the pellicle film is adhered to the pellicle film on the substrate on the coated surface, and the pellicle film is lifted from the substrate by lifting the frame under an atmosphere of room temperature 23 ° C. and 90% humidity. The film was peeled off to form a single film. KrF excimer laser light, ArF
Excimer laser light was irradiated in the air, the film thickness and transmittance before and after the irradiation were measured, and the amount of change due to the irradiation was calculated to examine the effect of the irradiation. Irradiation conditions are KrF excimer laser and ArF excimer laser, both of which have a pulse intensity of 1 mJ / cm ² , a frequency of 400 Hz, and a cumulative irradiation energy of 30,000 J / cm ² .

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples 1 to 3 and Comparative Examples 1 to 3, but the present invention is not limited to these Examples. (Example 1) Cytop CTX S type (described above) was replaced with a fluorine-based solvent CT-Solv. 180 (trade name, manufactured by Asahi Glass Co., Ltd.)
And a solution having a concentration of 9% was prepared. When the fluorination degree of the terminal group was quantified in this solution as it was, the silicon content after the silylation was 1.0 ppm. This corresponds to a content of 0.3 mol% in terms of ester groups. This solution is applied on a silicon substrate to form a film,
When peeled, the peelability was good. When the peeled film was observed under a condenser lamp, no white clouding or wrinkles were observed. When this film was irradiated with excimer laser light at a cumulative irradiation energy of 30,000 J / cm ² , the rate of decrease in film thickness was 0.2% in the case of a KrF excimer laser.
%, And 0.7% in the case of an ArF excimer laser, indicating excellent light resistance. These results are shown in Examples 2 and 3 below.
The results are shown in Table 1 together with the results of Comparative Examples 1 to 3.

Example 2 Cytop CTX S type (described above) was replaced with a fluorinated solvent CT-Solv. 180 (described above) to prepare a solution having a concentration of 9%. This solution was placed in a nickel container, and a fluorine-containing solution containing 30% by volume of fluorine was added.
A nitrogen mixed gas was introduced by bubbling at 120 ° C. for 100 hours to sufficiently perform fluorination. After the completion of the reaction, the inside of the vessel was replaced with nitrogen gas, and the solution was taken out. When the fluorination degree of the terminal group of this solution was quantified, the silicon content after silylation was 0.07 ppm, which is the detection limit. This corresponds to a content of not more than 0.02 mol% in terms of ester groups. This solution was coated on a substrate to form a film, and the film was peeled off. The peelability was good. When this film was observed under a condensing lamp, no white haze or wrinkles were observed.
When this film was irradiated with excimer laser light at a cumulative irradiation energy of 30,000 J / cm ² , the rate of decrease in film thickness was extremely light-resistant: zero in the case of a KrF excimer laser and 0.3% in the case of an ArF excimer laser. It was excellent.

Example 3 CYTOP CTX type E (described above) was replaced with a fluorine-based solvent CT-Solv. 180 (described above) to prepare a solution having a concentration of 9%. This solution was placed in a nickel container, and a fluorine-containing solution containing 30% by volume of fluorine was added.
Nitrogen mixed gas was introduced by bubbling at 120 ° C. for 100 hours to perform fluorination treatment. After the completion of the reaction, the inside of the vessel was replaced with nitrogen gas, and the solution was taken out. When the degree of fluorination of the terminal group of this solution was quantified, the silicon content after silylation was 7.0 ppm. This corresponds to a content of 2.0 mol% in terms of ester groups. When this solution was applied on a substrate to form a film and peeled, peeling was possible although there was some resistance.When the peeled film was observed under a condensing lamp, white clouding and wrinkles were not observed. Was. When this film was irradiated with an excimer laser beam at a cumulative irradiation energy of 30,000 J / cm ² , the film thickness reduction rate was 0.5% in the case of a KrF excimer laser.
%, And 3.4% in the case of an ArF excimer laser, indicating excellent light resistance.

COMPARATIVE EXAMPLE 1 Cytop CTX E type (described above) was replaced with a fluorine-based solvent CT-Solv. 180 (described above) to prepare a solution having a concentration of 9%. When the fluorination degree of the terminal group was quantified in this solution as it was, the silicon content after the silylation was 198 ppm. This corresponds to a content of 57 mol% in terms of ester groups. When this solution was applied on a substrate to form a film, the film could not be peeled off at all, and thus the light resistance could not be evaluated.

(Comparative Example 2) A type of CYTOP CTX (described above) was prepared using a fluorinated solvent CT-Solv. 180 (described above) to prepare a solution having a concentration of 9%. This solution was placed in a nickel container, and a fluorine-nitrogen mixed gas containing 0.5% by volume of fluorine was introduced by bubbling at 23 ° C. for 100 hours to perform a fluorination treatment. After the completion of the reaction, the inside of the vessel was replaced with nitrogen gas, and the solution was taken out. When the fluorination degree of the terminal group of this solution was quantified, the silicon content after silylation was 23 ppm. This corresponds to a content of 6.5 mol% in terms of ester groups. When this solution was applied on a substrate to form a film, and the film was peeled off, the peelability was poor and the film could be peeled off for a time, but the film was in an extended state. Also, the light resistance could not be evaluated.

(Comparative Example 3) A type of Cytop CTX (described above) was converted to a fluorinated solvent CT-Solv. 180 (described above) to prepare a solution having a concentration of 9%. This solution was placed in a nickel container, and a fluorine-nitrogen mixed gas containing 0.5% by volume of fluorine was introduced by bubbling at 50 ° C. for 100 hours to perform a fluorination treatment. After the completion of the reaction, the inside of the vessel was replaced with nitrogen gas, and the solution was taken out. When the fluorination degree of the terminal group of this solution was quantified, the silicon content after silylation was 13 ppm. This corresponds to a content of 3.7 mol% in terms of ester groups. When this solution was applied on a substrate to form a film and peeled, the film was peeled, but there was resistance, but peeling was possible.When the film after peeling was observed under a condensing lamp, white clouding and wrinkles were not observed. Was. When this film was irradiated with excimer laser light at a cumulative irradiation energy of 30,000 J / cm ² , the film thickness reduction rate was 1.3% in the case of a KrF excimer laser, but was 9% in the case of an ArF excimer laser. 0.5%, which was not at a practical level.

[0025]

[Table 1]

[0026]

As described in detail above, the terminal group of the amorphous perfluoropolymer, particularly the fluorine-containing monomer polymer having a cyclic perfluoroether group, is fluorinated as the material of the pellicle film, The polymer whose ester group content is suppressed can be easily peeled off from the substrate, and a pellicle film having good dimensional stability and no deformation can be obtained. Further, the pellicle manufactured using this pellicle film has little light deterioration even when irradiated with short-wavelength ultraviolet light such as a KrF excimer laser or an ArF excimer laser for a long time. It had excellent light resistance, long life and high performance.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view showing the structure of a pellicle.

[Explanation of symbols]

 1. Pellicle membrane; Frame, 3. 3. an adhesive layer; Protection sheet.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shu Kashida 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Gunma Office F-term (reference) 2H095 BC33 4J100 AE72P CA01 CA21 CA31 HA21 HB03 HC05 HE14 JA39

Claims (3)

[Claims] 1. A pellicle comprising at least a pellicle film and a pellicle frame, wherein the pellicle film stretched over the pellicle frame is made of an amorphous perfluoropolymer, and a terminal group of the polymer is fluorinated. Characteristic pellicle for lithography. 2. The pellicle for lithography according to claim 1, wherein the amorphous perfluoropolymer is a fluoropolymer having a cyclic perfluoroether group represented by the following chemical formula (1). Embedded image 3. The amorphous perfluoropolymer, wherein the content of an ester group (—COO—) in the terminal group is as follows:
The pellicle for lithography according to claim 1, wherein the pellicle is 3 mol% or less of the entire terminal groups.