JPS63163461A - Protective dust proof body for mask - Google Patents

Abstract

PURPOSE:To improve the transparency at a broad wavelength range, the durability and the mechanical strength of the titled body by using a polyvinyl isobutyral which is specified the content and the degree of acetalization of a vinylacetate component, as a transparent thin film. CONSTITUTION:The thin film of polyvinyl isobutyral which contains <=10mol.% the vinyl acetate component and has >=60mol.% the degree of acetalization, is used in a transparent thin film type cover body which is provided away from the surface of a substrate at the prescribed distance. The thin film of the protective dust proof body is formed by a method in which the polyvinyl isobutyral is dissolved to an appropriate volatile solvent such as ethanol, methylene chloride and acetone, and the obtd. solution is flowed and spreaded on the smooth substrate such as a silicon wafer, a glass plate and a metal plate, thereafter evaporating the solvent, etc. The mean mol.wt. of the polyvinyl isobutyral is preferably a range of 10,000-200,000. Thus, the titled body having the remarkably improved transparency at the broad wavelength range from a near UV ray to a far UV ray and the improved mechanical property is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of 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, the step of patterning a semiconductor wafer coated with a resist material by light exposure 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 original pattern, 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 if there are scratches or dust on the reticle affect all circuits on the wafer.
Scratches or dust adhesion on the reticle must be avoided as much as possible.

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 device 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. be. Particularly in recent years, exposure light sources have become shorter in wavelength due to the miniaturization of semiconductor circuits, and there is now a need for thin films that have high transparency and durability not only in the conventional near-ultraviolet region but also in the far-ultraviolet region. .

Furthermore, the thickness of the plastic thin film is 10 μm or less, and even with such an extremely thin film thickness, it is sufficient to prevent it from being easily deformed or damaged when handling the protective dustproof body or removing dust with an air gun, etc. Strength is required.

To date, the plastic thin film materials used for mask protection and dustproofing include nitrocellulose, cellulose acetate,
Polyethylene terephthalate, polypropylene, parylene, polyvinyl butyral, polymethyl methacrylate, and the like are known, among which nitrocellulose has been mainly used. However, although materials such as nitrocellulose can be used in the conventional near-ultraviolet region, they absorb in the far-ultraviolet region and rapidly become colored or deteriorate under irradiation with far-ultraviolet light. On the other hand, although polyvinyl butyral has good transparency in a wide wavelength range from near ultraviolet to far ultraviolet, its thin film has low strength and elastic modulus, so it easily spreads during handling or when removing dust with an air gun, etc. It had the disadvantage of being prone to wrinkles, tears, etc.

As described above, to date, no protective dustproof body for a mask 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, durability, and strength of the conventional protective dust-proof body of a mask, and makes it transparent in a wide wavelength range from near ultraviolet to far ultraviolet. The object of the present invention is to provide a protective dust-proof body for a mask, which has extremely good properties and durability, and has 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,
By using polyvinyl isobutyral, it has excellent transparency in a wide wavelength range from near ultraviolet to far ultraviolet.
The inventors have discovered that it is possible to obtain a protective dust-proof body for a mask that is durable and strong, and has 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 present invention relates to a protective dustproof body for a mask, characterized in that polyvinyl isobutyral having a vinyl acetate content of 10 mol% or less and an acetalization degree of 60 mol% or more is used as a transparent thin film.

The condensation reaction of polyvinyl alcohol and isobutyraldehyde for synthesizing polyvinyl isobutyral used in the present invention is not particularly limited, and widely known methods can be used. For example, a method using polyvinyl acetate as a starting material, saponifying its alcohol, acetic acid, hydrochloric acid solution or aqueous suspension, and then continuously reacting it with isobutyraldehyde under an acid catalyst such as sulfuric acid or hydrochloric acid, or polyvinyl alcohol An example of a method is to use isobutyraldehyde as a starting material, add isobutyraldehyde to its aqueous solution or alcohol dispersion, and react under an acid catalyst such as sulfuric acid or hydrochloric acid. A method using polyvinyl alcohol as a starting material is more preferred because the resulting polyvinyl isobutyral 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 isobutyral can be controlled by adjusting the vinyl acetate component in the polyvinyl alcohol starting material.

Further, by controlling the molar ratio of polyvinyl alcohol and isobutyraldehyde, reaction time, reaction temperature, amount of soot, etc., polyvinyl isobutyral having various degrees of acetalization can be obtained.

5 The content of the vinyl acetate component in the polyvinyl isobutyral used in the present invention is 10 mol% or less, more preferably 5 mol% or less. 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 acetalization of polyvinyl isobutyral used in the present invention needs to be 60 mol% or more. Polyvinyl isobutyral with a lower degree of acetalization has poor solubility in the solvent used for coating, and
Due to the high water content of the thin film, irreversible spreading and clouding are likely to occur when removing dust by washing with water.

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 is meaningless because it only reduces the mechanical strength of the film.

In addition, a film thicker than this not only reduces transparency but also increases aberration of light passing through the mask.
It has a negative effect on wafer patterning.

The protective dustproof thin film is prepared by dissolving polyvinyl isobutyral in a suitable volatile solvent such as ethanol, methylene chloride, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl cellosolve, ethyl cellosolve, tetrahydrofuran, dioxane, cyclohexanone, toluene, xylene, etc. , evaporate the solvent by casting onto a smooth substrate such as a silicon wafer, glass plate, or metal plate, or evaporate the solvent while rotating the substrate after casting, or spread the solution on a clean water surface. The film can be formed by a method such as spreading.

The preferred average molecular weight of polyvinyl isobutyral used in the present invention is from 10,000 to 200,000. Thin films obtained from polyvinyl isobutyral having a molecular weight of 10,000 or less do not have sufficient strength.

Furthermore, since polyvinyl isobutyral having a molecular weight of 200,000 or more has a high solution viscosity, it is difficult to obtain a uniform and even thin film.

[Effects of the Invention] As described above, the protective dustproof material for masks made of polyvinyl isobutyral 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. Because of its strength, it does not cause defects such as stretching, wrinkles, and tears. It also makes it easy to remove attached dust, which prevents a drop in yield due to dust attached to the mask and improves semiconductor manufacturing. It is useful for improving the productivity of integrated circuits.

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

(Quantification of each component in polyvinyl isobutyral) The weight percentage of the vinyl alcohol component and vinyl acetate component in polyvinyl isobutyral is determined according to JISK 6728.
The vinyl isobutyral component was calculated by subtracting the obtained fraction of the two components from 100.

(Performance evaluation of protective dust-proof body of mask) Polyvinyl isobutyral 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 thin film with a thickness of 2 μm. Next, the outer edge of this thin film was 91 mrn.

It was fixed on an aluminum frame with a width of 2 mm and a height of 5+n+n using an epoxy adhesive to serve as 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 surface of the thin film using an air gun (nozzle diameter: 2.0 mm) installed at a distance of 1 cm from the protective dustproof thin film, and the failure pressure of the thin film was determined.

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 Completely saponified polyvinyl alcohol (average degree of polymerization 110
00) 50 was dispersed in 95% ethanol 10100O,
After adding 36% hydrochloric acid and isobutyraldehyde, an isobutyralization 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 vinyl acetate component in the obtained polyvinyl isobutyral, and the degree of isobutyralization.

Table 3 shows the average transmittance at 300 nm of the protective dustproof body of the mask made from the obtained polyvinyl isobutyral, the breakage pressure by air gun, and the change after exposure to ultraviolet rays.
It was shown to.

[Brief explanation of the drawing]

FIG. 1 shows the ultraviolet transmittance curve of the protective dustproof body of the mask obtained in Example 1. As is clear from the figure, 190 nm to 70
It had extremely excellent transparency in a wide wavelength range of 0 nm.

Claims (1)

[Claims] A protective dust-proof body for a mask, which is a transparent thin film-like cover body installed at a certain distance from the substrate surface for the purpose of protecting and dust-proofing the substrate surface of a mask for manufacturing semiconductor integrated circuits, the transparent thin film comprising: The content of vinyl acetate component is 10 mol%
In the following, a protective dustproof body for a mask is made of polyvinyl isobutyral having a degree of acetalization of 60 mol% or more.