JPH0826165B2 - Pellicle film manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pellicle that is a protective dustproof body of a photomask and a reticle (hereinafter simply referred to as “mask”) used in a lithographic process in manufacturing a semiconductor integrated circuit. It relates to a method of manufacturing a membrane.

[Conventional technology]

In manufacturing a semiconductor integrated circuit, the step of patterning a semiconductor wafer coated with a resist material by exposure is a heavy step that affects the yield of the integrated circuit. At this time, if scratches or dust are present on the mask, which is the pattern original plate, the scratches or foreign matters are printed on the wafer together with the pattern, which may cause a short circuit or disconnection of the produced circuit. Therefore, protection of the mask and protection against dust are extremely important issues for improving productivity. In particular, in the stepper method in which the same reticle is used to repeatedly form patterns on a single wafer, scratches or defects that occur when dust is present on the reticle affect all circuits on the wafer. Dust adhesion should be avoided as much as possible.

Therefore, recently, for the purpose of protecting the mask and preventing dust, it has been proposed and implemented to cover one side or the screen of the mask with a transparent plastic thin film. At this time, by keeping the distance between the mask and the plastic thin film large enough, even if dust adheres to the plastic thin film, it is out of the focus of the optical system of the exposure apparatus, so the dust forms an image on the wafer. Not done. Furthermore, since the step of cleaning and removing the dust adhering to the mask as in the past is not necessary,
This has led to simplification of the production process and its usefulness has become clear.

As described above, the pellicle film used as the protective dustproof body of the mask needs to be transparent without absorption in the light source wavelength region of the exposure apparatus used, and to have a uniform film thickness. The reason is that if there is unevenness in the film thickness, even if the film does not have absorption, the intensity of reflection will change depending on the location within the film surface, which will cause unevenness in exposure during exposure. The less uneven the film thickness on the surface of the pellicle film, the better, and preferably 1% or less.

To date, nitrocellulose, cellulose acetate, polyethylene terephthalate, polypropylene, parylene, polymethylmethacrylate, etc. have been known as thin film materials that can be used as pellicle, and nitrocellulose is mainly used.

However, although these films can be used in the conventional near-ultraviolet region, they have poor transparency because they have absorption in the far-ultraviolet region, and are rapidly colored or deteriorated by irradiation with far-ultraviolet light, which also poses a problem in durability. There is.

On the other hand, polyvinyl acetals such as polyvinyl propional and polyvinyl butyral do not have absorption in the near and far ultraviolet regions, and therefore have excellent transparency and remarkably good durability, and are extremely excellent materials as a pellicle film. Various proposals have been made for such a pellicle film made of polyvinyl acetal.

JP-A-59-164356 has the formula: A film made of a mixture of polyvinyl butyral (where x is ≤0.13, y is ≤0.02 and z is ≤0.88) and a dispersion of colloidal silica in a silanol partial condensate aqueous solution of a lower aliphatic alcohol. This is a pellicle for projection printing, and the main part of the partial condensate is CH ₃ Si (O
H) ₃ condensation, a small portion of which is C ₂ H ₅ Si (O
H) ₃ , C ₃ H ₇ Si (OH) ₃ , And pellicles resulting from condensation with a single member selected from the group consisting of and mixtures thereof.

Further, JP-A-59-206406 discloses the following structural unit (Where x is ≦ 0.12, y is ≦ 0.02, and z is ≧ 0.88, R is methyl or ethyl, m is an integer of 1, 2 or 3, n is an integer equal to 4-m, G is - (CH _{2) P}
-Q, where p is 0, 1, 2, 3 or 4 and Q is -R ₁ , OR ₁ , when p is 1, 2, 3 or 4; Is a member selected from the group consisting of, and when p is zero, Q is R ₁ is alkyl of ₁ to 4 carbon atoms, R ₂ , R ₄ and R ₅ are selected from the group consisting of hydrogen and R ₁ , and R ₃ is 1 to It is an alkylene of 4 carbon atoms. A pellicle film for projection printing comprising a film made of a film-forming polymer having

[Problems to be solved by the invention]

However, since polyvinyl acetal has a remarkably high viscosity when made into a solution, it is more difficult to form a film than a cellulosic pellicle, and it is extremely difficult to obtain the film thickness uniformity required as a pellicle.

Therefore, an object of the present invention is to solve the problems at the time of producing the pellicle film made of the polyvinyl acetal and to produce a pellicle film having excellent film thickness uniformity, transparency, and durability. Is to provide.

[Means for solving problems]

As a result of intensive research to obtain a pellicle film composed of polyvinyl acetal having excellent film thickness uniformity, transparency, and durability, the present inventor found that an aliphatic ketone within a predetermined boiling range was used as a film forming solvent. It was discovered that a pellicle film having the above-mentioned desired properties can be obtained when used as the above, and the present invention was conceived.

That is, the method of the present invention is substantially the following general formula: (However, R ¹ is a linear or branched alkyl group having 1 to 3 carbon atoms, the content y of the vinyl acetate component is 10 mol% or less, and the degree of acetalization z / (x + y + z) is 60 mol% or more. To prepare a pellicle film made of acetal, the following general formula: And an aliphatic ketone having a boiling point in the range of 110 to 170 ° C. is used as a film forming solvent.

 The present invention will be described in detail below.

The polyvinyl acetal used in the present invention has the following general formula (I): (However, R ¹ is a linear or branched alkyl group having 1 to 3 carbon atoms.).

In order to synthesize the polyvinyl acetal represented by the general formula (I), polyvinyl alcohol and acetaldehyde, propionaldehyde, isobutyraldehyde,
Condensation reaction with n-butyraldehyde or the like can be carried out by a known method. For example, a method in which polyvinyl acetate is used as a starting material, the alcohol, acetic acid, hydrochloric acid solution or water suspension is saponified and then continuously reacted with an aldehyde under an acid catalyst such as sulfuric acid or hydrochloric acid, or polyvinyl alcohol is used. As a starting material, a method may be mentioned in which an aldehyde is added to the aqueous solution or alcohol dispersion and the reaction is carried out in the presence of an acid catalyst such as sulfuric acid or hydrochloric acid.
The method using polyvinyl alcohol as a starting material is preferable because the obtained polyvinyl acetal has good transparency and the molecular weight and the vinyl acetate component content are easily adjusted. In this case, the content of the vinyl acetate component in the polyvinyl acetal can be controlled by adjusting the content of the vinyl acetate component in the starting polyvinyl alcohol. Further, by controlling the molar ratio of polyvinyl alcohol and aldehyde, the reaction time, the reaction temperature, the amount of catalyst, etc., it is possible to obtain polyvinyl acetals having various degrees of acetalization.

The preferable range of the average molecular weight of the polyvinyl acetal used in the present invention is 10,000 or more and 200,000 or less. A pellicle film obtained from polyvinyl acetal having a molecular weight of less than 10,000 has insufficient strength. Further, polyvinyl acetal having a molecular weight of more than 200,000 has a high solution viscosity and is not preferable in forming a film.

The content of the vinyl acetate component of the polyvinyl acetal used in the present invention (represented by y in the formula (I)) is 10
It is at most mol%, more preferably at most 5 mol%. When the content of the vinyl acetate component is higher than this range, the transparency in the far ultraviolet region is reduced and the durability to long-term exposure to ultraviolet light is deteriorated.

The degree of acetalization (represented by z / (x + y + z)) of the polyvinyl acetal used in the present invention needs to be 60 mol% or more. A thin film made of polyvinyl acetal having a degree of acetalization lower than this does not have sufficient releasability from the film-forming substrate. Further, since the water content is high, irreversible elongation and cloudiness are likely to occur during dust removal by washing with water.

The film-forming solvent used in the present invention has the following general formula: And an aliphatic ketone having a boiling point in the range of 110 to 170 ° C.

When a solvent composed of an aliphatic ketone having a boiling point lower than 110 ° C. is used, it is difficult to obtain a film having a uniform film thickness because the solvent is evaporated too quickly during film formation. Further, when a solvent having a boiling point higher than 170 ° C. is used, although the uniformity of the film thickness is good,
It is very difficult to completely remove the solvent after film formation.

Examples of the aliphatic ketone satisfying the above requirements include 2-
Hexanone, 3-hexanone, 4-methyl-2-pentanone, 2,4-dimethyl-3-pentanone, 2-heptanone, 3-heptanone, 4-heptanone, 5-methyl-2
-Hexanone, 2-methyl-5-heptanone, 3-octanone, 2,6-dimethyl-4-heptanone, cyclohexanone and the like.

In the present invention, the preferable range of the polyvinyl acetal concentration of the film forming solution is 5% by weight or more and 20% by weight or less.

The pellicle film is formed by casting a film forming solution on a smooth substrate such as a silicon wafer, a glass plate, a metal plate, or a clean water surface and evaporating the solvent, or after casting, evaporating the solvent while rotating the substrate. The film can be formed by a method such as The environmental temperature during film formation is not particularly limited, but it is preferably around room temperature.

The film thickness of the popellicle film of the present invention is in the range of 0.5 to 10 μm. If the film thickness is made thinner than this, the mechanical strength of the film will decrease, and if the film thickness is made thicker than this, not only the transparency will decrease, but also the aberration of the light passing through the mask will increase, so patterning of the wafer Adversely affect.

〔Example〕

The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

Example 1 Completely saponified product of polyvinyl alcohol (average degree of polymerization: 10
00) 50g dispersed in 95% methanol 1, 36% hydrochloric acid 50m
After adding 1 and 250 g of propionaldehyde, a propionalization reaction was performed at 60 ° C. After completion of the reaction, sodium acetate was added for neutralization, and the reaction solution was poured into water, and the precipitated white solid was collected by filtration. The content of vinyl acetate component in the obtained polyvinyl propional was 0.62 mol%, and the degree of acetalization was 82 mol%.

The obtained polyvinyl propional was converted into 4-methyl-2-pentanone (boiling point 116 ° C), 3-octanone (boiling point 165 ° C) and cyclohexanone (boiling point 156 ° C) respectively.
It was dissolved at a concentration of wt% to obtain a film-forming solution.

Next, each solution was spin-coated using a silicon wafer having a diameter of 6 inches as a base material by using a spin coater to form a thin film on the silicon wafer. After vacuum drying each thin film, an aluminum frame with an outer side of 91 mm, a wall thickness of 2 mm, and a height of 5 mm is bonded to the thin film on the wafer using an epoxy adhesive, and then the thin film bonded on the aluminum frame is bonded to the wafer. The pellicle was obtained by peeling from.

The thickness of each pellicle film produced is covered over the entire surface.
91 points per 1 cm were measured by a laser multiple interference film thickness meter, and an average film thickness and a film thickness unevenness were obtained. The obtained results are summarized in Table 1.

Example 2 Completely saponified polyvinyl alcohol (average degree of polymerization: 100
0) Disperse 50g in 95% ethanol 1 and add 36% hydrochloric acid 30ml.
After adding 140 g of butyraldehyde, a butyralization reaction was carried out at 60 ° C. for 6 hours. After completion of the reaction, sodium acetate was added for neutralization, the reaction solution was poured into water, and the precipitated white solid was collected by filtration. The obtained polyvinyl butyral had a vinyl acetate content of 0.90 mol% and an acetalization degree of 79 mol%.

The obtained polyvinyl butyral was dissolved in 4-methyl-2-pentanone and cyclohexanone at a concentration of 10% by weight, and then formed into a film in the same manner as in Example 1 to obtain a pellicle film made of polyvinyl butyral. Table 1 shows the average film thickness and the uneven film thickness of the obtained pellicle film.

Example 3 Isobutyraldehyde 14 instead of butyraldehyde
Polyvinylisobutyral having a vinyl acetate component content of 0.52 mol% and an acetalization degree of 81 mol% was obtained in exactly the same manner as in Example 2 except that 0 g was added and the reaction time was 13 hours.

10% by weight of the obtained polyvinyl isobutyral was added to 4-methyl-2-pentanone and cyclohexanone, respectively.
After dissolving at a concentration of, a film was formed in the same manner as in Example 1 to obtain a pellicle film made of polyvinyl isobutyral. Table 1 shows the average film thickness and the film thickness unevenness of the obtained pellicle film.

Comparative Example 1 The polyvinyl propional obtained in Example 1 was dissolved in 3-nonanone (boiling point 190 ° C.) at a concentration of 10% by weight, and a pellicle film was formed in the same manner as in Example 1.

The obtained pellicle film had an average film thickness of 1.475 μm and an uneven film thickness of 0.85%. However, as a result of measuring the infrared absorption spectrum of this film, absorption of a strong carbonyl group attributed to 3-nonanone remaining in the film was observed, and durability under deep UV exposure was also in Example 1. It was inferior to the obtained pellicle film by about 1/10 or less. The results are shown in Table 1 for comparison.

Comparative Example 2 Polyvinyl butyral obtained in Example 2 was treated with methyl propyl ketone (boiling point 101 ° C.) and xylene (boiling point 106.2 ° C., respectively).
C.) and ethyl cellosolve (boiling point: 135.degree. C.) at a concentration of 10% by weight, and a pellicle after film formation was obtained in the same manner as in Example 1. For comparison, Table 1 shows the average film thickness and the film thickness unevenness of the obtained pellicle film.

As is clear from the above results, it is found that by producing a pellicle film from polyvinyl acetal by using a solvent composed of an aliphatic ketone having a boiling point of 110 to 170 ° C., it is possible to significantly reduce the unevenness of the film thickness of the pellicle film. On the other hand, when a film is formed using a solvent having a boiling point that is too high (Comparative Example 1), the solvent remains in the pellicle film and the durability is reduced. It is also found that when a solvent having a boiling point that is too low or a solvent other than the aliphatic ketone is used (Comparative Example 2), the film thickness unevenness of the pellicle film becomes large.

〔The invention's effect〕

As described above, by using the method for producing a pellicle film of the present invention, it is possible to obtain a pellicle film that is excellent in transparency and durability of polyvinyl acetal and is extremely excellent in film thickness uniformity. This is useful for improving the productivity of semiconductor integrated circuits by preventing the yield reduction due to the adhesion of dust.

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Claims (1)

[Claims] 1. The following general formula: (However, R ¹ is a linear or branched alkyl group having 1 to 3 carbon atoms, the content y of the vinyl acetate component is 10 mol% or less,
The degree of acetalization z / (x + y + z) is 60 mol% or more. In the method for producing a pellicle film composed of a polyvinyl acetal represented by the following formula: And a boiling point in the range of 110 to 170 ° C. is used as a film-forming solvent, the method for producing a pellicle film.