JPH04202204A - Pellicle - Google Patents

Abstract

PURPOSE:To provide a resin which can give a pellicle excellent in transmittance, etc., and durability to i-rays of a lithographic light source by reacting a polyvinyl acetal resin of a specified composition with hydrazine monohydrate. CONSTITUTION:Polyvinyl alcohol is reacted with an aldehyde to produce a polyvinyl acetal resin represented by formula I (wherein R is 1-3 linear or branched alkyl) and having a content of vinyl acetate units, y/(x+y+z), 0.1 or below and a degree of acetalization, z/(x+y+z), of 0.6 or above. To remove an unsaturated carbonyl structure of formula II (wherein n=0 or 1-3) contained in a small amount in the main chain of this resin, it is reacted with hydrazine monohydrate. The transmittance of a methylene chloride solution of the obtained resin at 365nm is as high as 93-97%, and this resin gives a film which neither discolors nor degrades even when irradiated with i-rays.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pellicle film that is a protective dust-proof body for photomasks and reticles (hereinafter abbreviated as masks) used in lithography steps in the manufacture of semiconductor integrated circuits.
In particular, the i-line (wavelength 36
The present invention relates to a pellicle film that is compatible with lithography using a light source of 5 nm).

[Prior Art] In the manufacture of semiconductor integrated circuits, the step of patterning a semiconductor wafer coated with a resist material by exposing it to light is an important step that affects the yield of integrated circuits. At this time, if there are scratches or dust on the mask, which is the pattern original, the image of the scratch or foreign substance is transferred onto the wafer along with the pattern, causing short circuits or disconnections in the produced circuits. For this reason, mask protection and dustproofing are important issues in improving productivity, and pellicles, which are protective dustproof bodies for masks, are increasingly being used.

The material of the pellicle membrane provided in this pellicle is as follows:
Nitrocellulose, cellulose acetate, cellulose propionate, polyethylene terephthalate, polypropylene, polymethyl methacrylate, and the like are known so far. Among these, pellicles whose film material is mainly nitrocellulose are used in conventional exposure apparatuses that use g-line (wavelength 436 nm) as a light source.

[Problems to be Solved by the Invention] In recent years, as the density of semiconductor integrated circuits has increased, the wavelength of lithography light sources has become shorter. It has come to be used as a.

However, materials such as nitrocellulose mentioned above,
Although it can be used in lithography that uses light in the near-ultraviolet region such as G-line and H-line as a light source, it has light absorption properties in the deep ultraviolet region such as I-line, so it cannot be used in exposure equipment that uses I-line as a light source. Under irradiation with i-rays, coloration or deterioration occurred rapidly, and the transmittance of the pellicle membrane decreased, making it unsuitable for practical use. Therefore, for these pellicles, g
In recent years, there has been a strong desire for something that can handle not only the line or h-line but also the i-line.

The following performance is required of the pellicle membrane provided in these pellicles.

b) High transmittance without absorption in the light source wavelength range of the exposure equipment used.

(1) Even when exposed to continuous exposure light, there is no decrease in transmittance due to coloring or deterioration, and the film has sufficient durability.

In other words, a pellicle film that is compatible with the i-line is required to be transparent and durable to the i-line as well.

As a pellicle membrane capable of handling such i-rays, a pellicle membrane having a multilayer structure in which antireflection layers are provided on both sides of a conventional pellicle membrane made of nitrocellulose has been proposed (Japanese Patent Laid-Open No. 1-100549, etc.). ).

This is achieved by applying antireflection treatment to the surface of the conventional single-layer pellicle membrane made of nitrocellulose, which absorbs i-rays and has poor durability, by coating it with a fluorine-containing polymer. It aims to improve the However, this method has the problem that the production process of the pellicle film becomes complicated, resulting in a lower yield or higher cost.

It has also been proposed to use a material that is highly transparent to i-rays and has excellent durability as a material for the pellicle membrane in place of the conventional nitrocellulose.

This method has the advantage that it is not necessary to provide an antireflection layer in order to obtain durability against i-rays, and a pellicle compatible with i-rays can be manufactured at low cost using a simpler process. Several materials using polyvinyl acetal resin have been disclosed as materials for such pellicle membranes (Japanese Unexamined Patent Publication No. 1-172430, etc.). However, even with these pellicle membranes made of polyvinyl acetal resin, the transmittance decreases due to coloring and deterioration due to extremely long-term single-line irradiation, and the durability is not necessarily satisfactory. I wasn't getting anything.

That is, an object of the present invention is to provide a pellicle film that has excellent durability and is compatible with i-line.

[Means for Solving the Problems] As a result of various investigations into this problem, the present inventors found that the deterioration of the pellicle film made of the polyvinyl acetal resin due to i-ray irradiation is due to the following causes. I found out.

Polyvinyl acetal resin is usually obtained by using polyvinyl alcohol as a synthetic raw material and reacting it with the corresponding aldehyde under an acid catalyst, but this polyvinyl alcohol has a small amount of the following unsaturated carbonyl structure in its main chain. It has been reported that (e.g. C, S, Marvel).

J, A*, Chem, Soc,, 85.1710 (19
43), Jl, C1arke.

J, Polys, Sei, 1.419 (194B), etc.).

-d+-CH-CH-+-n (2)(n-
0,1,2,3) Therefore, polyvinyl acetal resin synthesized from polyvinyl alcohol containing this carbonyl structure also contains this structure, but it is this carbonyl structure that is synthesized from polyvinyl acetal resin. It has become clear from the results of various structural analyzes that this is the cause of coloring and deterioration of the pellicle film under i-ray irradiation.

For this reason, the present inventors investigated the removal of this carbonyl structure by chemical modification and came to the conclusion that it is desirable to convert the carbonyl into a hydrazonate as shown in the following formula (3). Polyvinyl acetal resin was treated with hydrazine monohydride. As a result, the resulting resin (hereinafter referred to as hydrazine-treated polyvinyl acetal resin to distinguish it from ordinary polyvinyl acetal resin that has not been treated with hydrazine monohydride) has a decreased ultraviolet absorption near 365 nm. Furthermore, they have discovered that the pellicle film made of this reduced polyvinyl acetal resin has significantly improved durability against irradiation with ultraviolet rays, especially i-rays, and have completed the present invention.

Hereinafter, the pellicle membrane of the present invention will be explained in detail.

The polyvinyl acetal resin, which is a synthetic raw material for the hydrazine-treated polyvinyl acetal resin used in the present invention, has the following general formula (1): The content rate y/ (x+y+z) is 0.1 or less, and the degree of acetalization z/ (x+y+z) is 0.6 or more.

In the formula, R is a straight chain or branched alkyl group having 1 to 3 carbon atoms, specifically a methyl group, an ethyl group, an n-propyl group or a 1so-propyl group.

The above-mentioned polyvinyl acetal resin can be obtained by a condensation reaction between polyvinyl alcohol and an aldehyde such as acetaldehyde, propionaldehyde, n-butyraldehyde, and 5ec-butyraldehyde using a known technique. For example, starting with polyvinyl acetate, it is dissolved in a solvent such as methanol, ethanol, acetic acid, etc., and a catalyst such as sulfuric acid or hydrochloric acid and an aldehyde are simultaneously added thereto.
A method of carrying out acetalization simultaneously with saponification,
Alternatively, polyvinyl alcohol is used as a starting material and dispersed in this aqueous solution, an alcohol such as methanol, ethanol, n-propyl alcohol, 1so-propyl alcohol, or a mixed solvent of these alcohols and water, and then dispersed in an acid catalyst such as sulfuric acid or hydrochloric acid. The above-described method of adding an aldehyde and causing a reaction can be mentioned.

A method using polyvinyl alcohol as a starting material is more preferred because the resulting resin has good transparency and the molecular weight and vinyl acetate component content can be easily controlled. In this case, the content of the vinyl acetate component in the polyvinyl acetal resin can be adjusted by adjusting the content of the vinyl acetate component in the polyvinyl alcohol that is the starting material. Moreover, by adjusting the reaction charge ratio of polyvinyl alcohol and aldehyde, reaction time, reaction temperature, amount of catalyst, etc., polyvinyl acetal resins having various degrees of acetalization can be obtained.

The content rate y/(x+y+z) of vinyl acetate units in the polyvinyl acetal resin represented by the above general formula (1) is 0.01 or less, more preferably 0.005 or less, and the degree of acetalization 2/(x+y+z) is 0. .6 or more. If this range is exceeded, problems may occur in pellicle membranes manufactured from such polyvinyl acetal, such as reduced peelability from the membrane base material, or irreversible stretching or clouding during dust removal by water washing. do.

The number average molecular weight (M n
) is preferably in the range of 10,000 or more to 200,00
It is less than or equal to 0. If it deviates from the above range, it is not preferable because it will affect the uniformity or strength of the obtained pellicle film.

The reaction conditions of the polyvinyl acetal resin and hydrazine monohydride for obtaining the hydrazine-treated polyvinyl acetal resin used in the present invention are shown below.

The hydrazine monohydride used in the present invention may be either anhydrous hydrazine monohydride or hydrous hydrazine monohydride.

As the reaction solvent, a system containing at least one component of an ether solvent such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and diethylene glycol dimethyl ether can be used. Particularly preferred is ethylene glycol monoethyl ether. Moreover, the reaction can also be carried out without a solvent.

There are no particular restrictions on the reaction temperature, but it can range from room temperature to 60°C.
It is more preferable to set it as °C.

As a treatment method, the polyvinyl acetal resin and hydrazine monohydride are mixed together with the above-mentioned solvent,
Or mix and dissolve without solvent for 1 hour to 1 hour.
This can be carried out by stirring for a week and then pouring the solution into water to recover the resin.

The pellicle film of the present invention is prepared by dissolving the above-mentioned hydrazine-treated polyvinyl acetal resin in an organic solvent such as cyclohexanone, ethylene glycol monoethyl ether, or acetic acid ethylene glycol monoethyl ether, and using a spin coater to coat a smooth film such as a silicon wafer. It can be produced by spin coating on a base material to form a uniform thin film with a thickness of about 1.5 μm, and then peeling this thin film from the base material.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these examples in any way.

Example 1 Completely saponified polyvinyl alcohol (PVA-110 manufactured by Kuraray Co., Ltd., average degree of polymerization 11000) 50%
Water-containing methanol [methanol:water-95:5 (wt%)
Disperse in 1500ml and add 35% hydrochloric acid 1. After adding Orr+J and 115.35 g of propionaldehyde, the mixture was heated and stirred at 55° C. for 96 hours. After the reaction was completed, the reaction solvent was removed by decantation, and the precipitated polymer was collected. This polymer was dissolved in 1.5 g of acetone, and the resulting solution was added dropwise to 811 g of water to precipitate and purify the polymer. This polymer was vacuum dried at 40°C for 48 hours,
55 g of polyvinyl propional was obtained.

Next, as an evaluation of the transparency of this polyvinylpropional, a methylene chloride solution of polyvinylpropional 1
3 wt. A rate measurement was performed. As a result, the transmittance at 365 nm was 87.8%. This spectral curve is shown in FIG.

Example 2 50 g of polyvinyl propional obtained in Example 1 was added to 300 rrl of ethylene glycol monoethyl ether.
A solution of polyvinylpropional was prepared by dissolving it in the solution, and 50 g of 80% hydrazine monohydride (water content 20%) was added to this solution, followed by stirring at room temperature for 48 hours.

After the reaction was completed, the obtained reaction solution was added dropwise to 8 g of water to precipitate a polymer. After repeatedly washing the polymer with water,
This was vacuum dried at 40° C. for 48 hours to obtain 42 g of hydrazine-treated polyvinyl propional.

Next, to evaluate the transparency of this hydrazine-treated polyvinylpropional, a methylene chloride solution (concentration 3% by weight) of hydrazine-treated polyvinylpropional was prepared, and an ultraviolet-visible spectrophotometer was used in the same manner as in Example 1. Transmittance measurements were carried out.

As a result, the transmittance at 365 nm was 95.6%,
Transparency was improved compared to polyvinylpropional before hydrazine treatment.

This transmittance curve is also shown in FIG.

Example 3 30 g of the hydrazine-treated polyvinyl propional obtained in Example 2 was dissolved in 270 g of ethylene glycol monoethyl ether to prepare a polymer solution. This solution was applied to a 6 inch diameter silicon wafer as a base material using a spin coater at 2800 rpm, and then vacuum dried.
A thin film with a thickness of 1.5 μm was formed on a silicon wafer. This thin film was peeled off from the wafer to obtain a pellicle film.

The light transmittance at 365 nm of the prepared pellicle film was measured using an ultraviolet-visible spectrometer (manufactured by Kinsei Seisakusho Co., Ltd., UV-26).
0) without inserting anything into the reference beam, it was 99.9%.

Next, this pellicle film was exposed to 365 nm monochromatic light (i-line, illuminance = 30, 41 mW) from an ultra-high pressure mercury lamp (Multilight ML-501D/B, manufactured by Ushio Electric Co., Ltd.).
/cd) for 1500 hours (corresponding to the exposure amount of 20 million shots when converted to the number of exposures on the reticle surface in an i-line stepper.Hereinafter, the i-line irradiation amount is expressed as the number of shots). . After that, when we measured the light transmittance at 365 nm in the same way as before, it was still 9.
9.9%, and no decrease in light transmittance at 365 nm was observed in this pellicle film compared to before i-ray irradiation.

Comparative Example A pellicle membrane was prepared in the same manner as in Example 1 using the conventional polyvinylpropional obtained in Example 1 and not subjected to hydrazine treatment. 365 of this pellicle membrane
The light transmittance in nm was 99.9%.

Next, this pellicle film was coated with 1
When irradiated with light, the light transmittance at 365 nm decreased to 99.0% after approximately 5 million shots were irradiated, making it unusable for practical use.

[Effects of the Invention] As explained above, the transmittance of an untreated polyvinyl acetal resin in methylene chloride solution at 365 nm is about 91.0% at most, whereas the transmittance of a polyvinyl acetal resin treated by the method of the present invention is about 91.0%. 93. for resin.
It is as high as 0% to 97.0%, and can also suppress the coloring and deterioration that occurs in conventional pellicle membranes when irradiated with i-rays. It becomes possible to provide a pellicle film having excellent durability even against

[Brief explanation of the drawing]

Figure 1 shows a methylene chloride solution (concentration 3) of hydrazine-treated polyvinylpropional and non-hydrazine-treated polyvinylpropional of the present invention.
FIG. 3 is a diagram showing an ultraviolet absorption curve of □ shows the ultraviolet absorption curve of hydrazine-treated polyvinylpropional, and ......... shows the ultraviolet absorption curve of untreated polyvinylpropional.

Claims (2)

[Claims] (1) General formula (1) below: ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (1) (However, R is a straight chain or branched alkyl group having 1 to 3 carbon atoms, and the content of vinyl acetate units y /(x+y+z) is 0.1 or less, and the degree of acetalization z/(x+y+z) is 0.6 or more.) A resin obtained by reacting a polyvinyl acetal resin represented by the following formula with hydrazine monohydride. . (2) A pellicle film made of the resin according to claim 1.