JPS6368840A - Protective dustproof body for mask - Google Patents

Abstract

PURPOSE:To improve transparency, durability and mechanical strength by using a polyvinyl butyral resin contg. <=10mol% residual vinyl acetate component and having >=50mol% and <=80mol% degree of butyration as a thin transparent film. CONSTITUTION:The polyvinyl butyral resin contg. <=10mol% residual vinyl acetate component and having >=50mol% and <=80mol% degree of butyration is used for a thin transparent film-like cover body to be installed at a specified distance from the surface of a substrate of a mask for producing semiconductor integrated circuits for the purpose of providing protection and dust proofing to said surface. Such protective dust proof body has the good transparency and durability in a wide wavelength region from near UV to far UV and has the high mechanical strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protective dust-proof body for photomasks and reticles (hereinafter abbreviated as masks) used in a lithography step in the manufacture of semiconductor integrated circuits.

[Prior Art] In the manufacture of semiconductor integrated circuits, patterning of a semiconductor wafer coated with a resist material by light exposure is an important process 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 scratches or foreign matter will be printed on the wafer along with the pattern, causing short circuits and disconnections in the produced circuits.

For this reason, mask protection and dustproofing are extremely important issues in improving productivity. In particular, in the stepper type, which uses the same reticle to repeatedly form patterns on a single wafer, defects that occur when there are scratches or dirt on the reticle affect all circuits on the wafer.
Scratches or dust on the reticle (=1) must be kept to a minimum.

Recently, it has been proposed and put into practice to cover one or both sides of a mask with a transparent plastic thin film for the purpose of protecting the mask and preventing dust. At this time, by leaving a sufficiently large gap between the mask and the plastic thin film, even if dust adheres to the plastic thin film, the focus of the optical system of the exposure equipment is shifted, so the dust will not form on the wafer. Not imaged. Furthermore, since the conventional process of cleaning and removing dust adhering to the mask is no longer necessary, it also simplifies the production process, and its usefulness is becoming clear.

The performance required for a plastic thin film used for mask protection and dustproofing is to be transparent with virtually no absorption in the light source wavelength range of the exposure equipment used, and to have sufficient durability without coloring or deterioration. is. In particular, in recent years, as semiconductor circuits have become finer, the wavelength of exposure light sources has become shorter, and there is a demand for thin films that have high transparency and durability not only in the conventional near-ultraviolet region but also in the far-ultraviolet region.

Generally, the thickness of a plastic thin film is 10 μm or less, and even with such an extremely thin film thickness, it is sufficiently thick so that it will not be easily deformed or damaged when handling the protective dustproof body or when removing dust with an air can, etc. strong strength is required.

To date, the plastic thin film materials used for mask protection and dustproofing include nitrocellulose, cellulose acetate,
Polyethylene terephthalate, polypropylene, parylene, polymethyl methacrylate, etc. are known, among which 21-cellulose has been mainly used.

However, although these materials can be used in the conventional near-ultraviolet region, they all have absorption in the far-ultraviolet region and rapidly become colored or deteriorate under irradiation with far-ultraviolet light.

As described above, to date, no plastic thin film has been found that has good transparency and durability in a wide wavelength range from near ultraviolet to far ultraviolet, and has sufficient thin film strength.

[Problems to be Solved by the Invention] The present invention improves the above-mentioned drawbacks of the transparency and durability of the protective dust-proof body of a conventional mask, and improves transparency and durability in a wide wavelength range from near ultraviolet to far ultraviolet. It provides a protective dustproof body with extremely good durability and excellent mechanical strength.

[Means for Solving the Problems] The present inventors have conducted extensive studies in order to obtain a protective dustproof body for a mask that has excellent transparency, durability, and strength. the result,
Surprisingly, by using a polyvinyl butyral resin with a limited composition range, it is possible to obtain a protective dust-proof body for masks with extremely excellent transparency, durability, and strength in a wide wavelength range from near-ultraviolet to far-ultraviolet. We have discovered this and arrived at the present invention.

That is, the present invention provides a transparent thin film-like cover body installed at a certain distance from the substrate surface for the purpose of protecting and dustproofing the substrate surface of a mask for manufacturing semiconductor integrated circuits.
The content of residual vinyl acetate component is 10 mol% as a transparent thin film.
or less, and the degree of butyralization is 50 mol% or more 80
The present invention relates to a protective dust-proof body for a mask, characterized in that it uses polyvinyl butyral resin of mol % or less.

The condensation reaction of polyvinyl alcohol and butyraldehyde for synthesizing the polyvinyl butyral resin (hereinafter sometimes abbreviated as butyral resin) used in the present invention is not particularly limited, and widely known methods can be used. For example, starting from polyvinyl acetate,
After saponifying the alcohol, acetic acid, hydrochloric acid solution or aqueous suspension, it is continuously reacted with butyraldehyde under an acid catalyst such as sulfuric acid or hydrochloric acid, or using polyvinyl alcohol as a starting material. A method may be mentioned in which butyraldehyde is added to an aqueous solution or an alcohol dispersion and the mixture is reacted over an acid catalyst such as sulfuric acid or hydrochloric acid. Because the resulting butyral resin has good transparency, and the molecular weight and residual vinyl acetate content can be easily adjusted,
More preferred is a method using polyvinyl alcohol as a starting material. In this case, the content of the residual vinyl acetate component in the butyral resin can be controlled by adjusting the vinyl acetate component in the polyvinyl alcohol starting material.

Moreover, by controlling the molar ratio of polyvinyl alcohol and butyraldehyde, reaction time, reaction temperature, amount of catalyst, etc., it is possible to obtain butyral resins having various degrees of butyralization.

The content of residual vinyl acetate component in the butyral resin used in the present invention is 10 mol% or less, more preferably 5 mol%.
It is as follows. If the content of the vinyl acetate component is higher than this, the transparency in the deep ultraviolet region will decrease and the durability against long-term ultraviolet exposure will be poor.

The degree of butyralization of the butyral resin used in the present invention needs to be in the range of 50 mol% or more and 80 mol% or less. The protective dust-proof body of a mask made of butyral resin with a lower degree of butyralization has poor transparency in the deep ultraviolet region, and at the same time lacks thin film flexibility, which tends to cause defects when removing dust with an air gun. In addition, the protective dust-proof body of a mask made of butyral resin with a higher degree of butyralization has no problems with transparency and durability, but its mechanical strength is poor, and it is possible to achieve a good yield of 1q without defects such as wrinkles and sagging. difficult. In addition, it tends to spread during dust removal with an air gun or during handling.

The thickness of the protective dustproof thin film of the mask of the present invention is 0.5 to 10
It is in the μm range. Even if the film thickness is made thinner than this, it only reduces the mechanical strength of the film and is meaningless. Further, a film thicker than this not only reduces transparency but also increases aberration of light passing through the mask, which adversely affects wafer patterning.

The protective dustproof thin film is made by mixing butyral resin with a suitable volatile solvent,
For example, methanol, ethanol, methylene chloride, methyl ethyl ketone, methyl cellosolve, ethyl cellosolve,
After making a solution of dioxane, cyclohexanone, toluene, xylene, etc., it is cast onto a smooth substrate such as a silicon wafer, glass plate, metal plate, etc. to evaporate the solvent, or the solvent is poured while rotating the casting substrate. The film can be formed by evaporating the solution or spreading the solution on the surface of clean water.

It is difficult to obtain a uniform thin film with an average distribution of the butyral resin used in the present invention.

[Effects of the Invention] As described above, the protective dustproof material for masks made of polyvinyl butyral resin of the present invention has extremely good transparency and durability in a wide wavelength range from near ultraviolet to far ultraviolet, and has excellent mechanical properties. Due to its strength, it does not sag, wrinkle,
Since defects such as tears are less likely to occur and attached dust can be easily removed, it is useful for preventing a decrease in yield due to dust attached to the mask and improving the productivity of semiconductor integrated circuits.

[Examples] Hereinafter, the present invention will be explained in detail with reference to Examples.
The present invention is limited only to these examples of butyral resin 1. Dissolve OQ in 60ml of ethanol, N/1ONa
OH aqueous solution 12. ! After adding M and heating, N/10HCI
The amount was determined by adding 12.5 ml and titrating with an N/10 NaOH aqueous solution using phenolphthalein as an indicator.

(Quantification of degree of butyralization) Elemental analysis of the butyral resin was performed, and the degree of butyralization of the butyral resin was determined from the obtained C1H content and the separately determined content of the residual vinyl acetate component in the butyral resin.

(Evaluation of performance of protective dust-proof body of mask) Butyral resin was dissolved in ethyl cellosolve and spin-coated using a spin coater using a 6-inch silicon wafer as a base material to form a resin thin film with a thickness of 2 μm. Next, this thin film was fixed using an epoxy adhesive onto an aluminum frame having an outer side of 91#, a width of 2 Irun, and a height of 5#, thereby forming a protective dust-proof body for the mask.

The ultraviolet transmittance of the obtained protective dust-proof body in the range of 190 nm to 700 nm was measured using a spectrophotometer (Uv-260 manufactured by Shimadzu Corporation), and the center value of the observed etaloning maximum and minimum values was taken to determine the average transmittance of the thin film. percentage.

Next, N2 gas was sprayed onto the thin film surface from an air gun (nozzle diameter 2.0 m) installed at a distance of 1 cm from the protective dustproof thin film, and the failure pressure of the thin film was determined (10).

The UV resistance of the protective dustproof body is 10c from the protective dustproof body thin film.
A 500 W xenon-mercury lamp was installed at intervals of m, and ultraviolet light was continuously exposed for 6 hours to observe changes in the thin film.

Examples 1 to 3 After dispersing and adding 35% hydrochloric acid and butyraldehyde, a butyralization reaction was performed at 60'C. After the reaction was completed, sodium acetate was added for neutralization, and the reaction solution was poured into water, and the precipitated white solid was collected by filtration. Table 1 shows the reaction conditions, the content of residual vinyl acetate component in the obtained polyvinyl butyral resin, and the degree of butyralization.

Table 2 shows the average transmittance at 210 nm of the protective dust-proof body of the mask made from the obtained butyral resin, the breakage pressure due to the air can, and the changes after exposure to ultraviolet rays.

Comparative Example 1 Saponified polyvinyl alcohol 8B% (average degree of polymerization 10
The butyralization reaction was carried out in exactly the same manner as in Example 3 except that 00) was used. The content of residual vinyl acetate component in 1q of butyral resin was 10.8 mol%, and the degree of butyralization was 65 mol%.

Table 2 shows the performance evaluation results of the protective dustproof body made from this butyral resin.

Comparative Example 2.3 The amount of hydrochloric acid added was 20d and 40ml, the amount of butyraldehyde added was 60Q and 190Ω, and the reaction time was 2h.
A butyral resin was synthesized in the same manner as in Example 1, except that the reaction time was 3 hours. The content of residual vinyl acetate component in the obtained butyral resin was 1.3 mol% and 0.7 mol%, respectively, and the degree of butyralization was 45 mol% and 82 mol%, respectively.
Met.

Table 2 also shows the performance evaluation results of the protective dustproof body of the mask obtained from this butyral resin.

As described above, it is clear that only the butyral resin having the composition range of the present invention provides an extremely excellent protective and dustproof body for a mask that has all the necessary performances.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 show the ultraviolet transmittance curves of the protective dust-proof body of the mask obtained in Example 1.2.3, respectively. As is clear from the figure, all had extremely excellent transparency in a wide wavelength range of 190 nm to 700 nm. Patent applicant: Toyo Soda Kogyo Co., Ltd.

Claims (1)

[Claims] In a transparent thin film-like cover body installed at a certain distance from the substrate surface for the purpose of protecting and dustproofing the substrate surface of a mask for manufacturing semiconductor integrated circuits, the content of the residual vinyl acetate component as a transparent thin film is 10 mol% or less A protective dust-proof body for a mask, characterized in that it uses a polyvinyl butyral resin having a degree of butyralization of 50 mol% or more and 80 mol% or less.