JPH01179946A - Protective dustproof body for mask having improved peelability - Google Patents

Abstract

PURPOSE:To improve the peelability from a film forming base material and to easily obtain a uniform and defectless protective dustproof body for a mask by using specific polyvinyl acetal having a fluorine-contained silyl group at the side chain. CONSTITUTION:The protective dustproof body consisting of the polyvinyl acetal which is expressed by the formula I, contains the silyl-substd. vinyl alcohol component expressed by x2/x1 at >=0.05 ratio, contains <=10mol.% vinyl acetate component and has >=60mol.% rate of acetalization. In the formula I, R<1>-R<3> denotes an alkyl group of 1-10C and a group in which the hydrogen atom of at least one group thereof is partly or wholly substd. with a fluorine atom; R denotes an alkyl group of 1-3C. The peelability from the film forming base material is thereby improved and the uniform and defectless protective dustproof body for the mask is produced at a good yield.

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 lithography steps in the manufacture of semiconductor integrated circuits.

[Conventional technology]

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 pattern original, the scratches or foreign matter will be printed on the wafer along with the pattern, causing short circuits, disconnections, etc. 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 a pattern on a single wafer, if there are scratches or dust on the reticle, the defects that occur will affect all the circuits on the wafer. Also, adhesion of dust 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, the distance between the mask and the plastic thin film should be kept sufficiently large (so that even if dust adheres to the plastic thin film, it will not condense on the wafer because it will be out of focus of the optical system of the exposure equipment). Further, since the conventional process of cleaning and removing dust adhering to the mask is no longer necessary, the production process is simplified, 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, as semiconductor circuits 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.

On the other hand, in manufacturing a plastic thin film that is uniform and free from unevenness and defects, it is necessary for the plastic thin film to have high mechanical strength and sufficient peelability. The most effective means of obtaining a thin film is to cast plastic dissolved in a volatile solvent onto a smooth substrate such as a silicon wafer, glass plate, or metal plate, and after the solvent evaporates, the thin film formed on the curtain material is peeled off. However, in this case, it is extremely difficult to peel a thin film without sufficient strength and peelability from the substrate without causing defects.

To date, the plastic thin film materials used for mask protection and dustproofing include nitrocellulose, cellulose acetate,
Polyethylene terephthalate, polypropylene, parylene, 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, so they rapidly become colored or deteriorate under irradiation with far-ultraviolet light, making them unusable.

On the other hand, polyvinyl butyral and its compositions have recently been proposed as thin film materials that can be used in a wide range from near ultraviolet to far ultraviolet (US Pat. No. 4,47 to 17).
No. 2, No. 4,482.5'M.

4, No. 499.231). However, as is clear from the fact that polyvinyl butyral is mainly used as an adhesive, it exhibits strong adhesion to silicon wafers, glass plates, metal plates, etc. used as base materials when producing thin films. Since the thin film cannot be easily peeled off from these base materials, it has been extremely difficult to manufacture uniform and defect-free protective dust-proof bodies for masks with a high yield.

[Problem that the invention seeks to solve]

The present invention improves the transparency, durability, and releasability of the protective dust-proof body of a conventional mask from the film-forming base material, as described above, and can be used in a wide wavelength range from near ultraviolet to far ultraviolet. The present invention provides a protective dust-proof body for a mask that has excellent strength and productivity.

[Means for solving problems]

The inventors of the present invention have conducted intensive studies in order to obtain a protective dust-proof body for masks that can be used in the entire ultraviolet region and that can be manufactured at a high yield without causing defects such as stretching, wrinkles, and tears. As a result, by substituting the vinyl alcohol component of polyvinyl acetal with a fluorine-containing silyl group, it is possible to improve the transparency and durability of polyvinyl acetal without sacrificing its excellent transparency and durability.
The inventors have discovered that the releasability, which was a drawback, can be improved, and that a uniform and defect-free protective dustproof body for a mask can be obtained fairly easily, and the present invention has been achieved.

That is, the present invention aims to protect and prevent dust on the substrate surface of a photomask or reticle for manufacturing semiconductor integrated circuits.
A protective dust-proof body for a photomask or reticle, which is a transparent thin film-like cover installed at a certain distance from the surface of a substrate, and the transparent thin film substantially has a -pattern hole (1) (However, R in the formula ', R'', R3 are alkyl groups having 1 to 10 carbon atoms, and R1, R2, and R3 are
Both are groups in which some or all of the hydrogen atoms in one group are substituted with fluorine atoms. Moreover, R is an alkyl group having 1 to 3 carbon atoms. ), the ratio of the silyl-substituted vinyl alcohol component represented by The present invention provides a protective dustproof body for a mask with improved removability.

The fluorine-containing silyl group-substituted polyvinyl acetal represented by the above-mentioned -Momona (1) used in the present invention is the following -Momona (II) (wherein R is an alkyl group having 1 to 5 carbon atoms). )
The polyvinyl acetal shown by and the following - Monna (11
0%Formula%(2) (However, in the formula, R1, R'', R~ is an alkyl group having 1 to 10 carbon atoms, and R'', R'', R%t is a hydrogen atom of at least one of the groups. It is a group partially or entirely substituted with fluorine atoms.) It can be obtained by a condensation reaction with a fluorine-containing disilazane represented by the following.

The polyvinyl acetal represented by the above-mentioned pattern (II) is obtained by a condensation reaction between polyvinyl alcohol and an aldehyde. Examples of the aldehyde used here include acetaldehyde, propionaldehyde, isobutyraldehyde, n-butyraldehyde, and the like, and the aldehydes may be used alone or as a mixture of two or more. The condensation reaction is not particularly limited (a widely known method can be used. For example, using polyvinyl acetate as a starting material, after saponifying its alcohol, acetic acid, hydrochloric acid solution or aqueous suspension, A method of continuously reacting with an aldehyde under an acid catalyst such as sulfuric acid or hydrochloric acid, or a method using polyvinyl alcohol as a starting material, adding an aldehyde to its aqueous solution or alcohol dispersion, and reacting under an acid catalyst such as sulfuric acid or hydrochloric acid. A method using polyvinyl alcohol as a starting material is more preferable because the resulting polyvinyl acetal has good transparency and the molecular weight and vinyl acetate component content can be easily controlled. The content of vinyl acetate component in the polyvinyl alcohol starting material can be controlled by adjusting the vinyl acetate component content in the polyvinyl alcohol starting material.In addition, the molar ratio of polyvinyl alcohol and aldehyde, reaction time, reaction temperature, catalyst amount, etc. By controlling , polyvinyl acetals having various degrees of acetalization can be obtained.

The content of the vinyl acetate component in the poly and nyl acecool used in the present invention is 10 molti or less, more preferably 5 molti 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 the polyvinyl acetal used in the present invention needs to be 60 molti 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. Also, due to its high moisture content, it tends to cause irreversible sagging when removing dust by washing with water.

The condensation reaction of the polyvinyl acetal represented by the above general formula (n) and the disilazane represented by the above general formula (8) is carried out using a solvent that does not have active hydrogen and is inert to the polyvinyl acetal and disilazane, such as diethyl ether. , tetrahydrofuran, dioxane, methyl ethyl ketone, etc.

The reaction is usually carried out at a temperature of 0° C. to 150° C., preferably room temperature to 100° C., and the reaction time is preferably in the range of 30 minutes to 24 hours.

In the general formula (1), the ratio of the silyl-substituted vinyl alcohol component to the remaining vinyl alcohol component, that is, the value of "v'Xt" is preferably α05 or more.

If the value of x,/XI is smaller than this, the improvement in releasability, which is an effect of the present invention, is not sufficient.

The protective dustproof thin film of the present invention is prepared by using the polyvinyl acetal reactant obtained in the above reaction in a suitable volatile solvent, such as evaporated ethanol, methylene chloride, acetone, methyl ethyl ketone,
After making a solution of methyl isobutyl ketone, methyl selonulp, ethyl cellosolve, tetrahydrofuran, dioxane, cyclohexanone, toluene, xylene, etc., it is cast onto a smooth substrate such as a silicon wafer, glass plate, metal plate, etc., and the solvent is evaporated. Alternatively, the film can be formed by evaporating the solvent while rotating the curtain material after casting.

The thickness of the protective dustproof thin film of the mask of the present invention is α5 to 10μ
m range. Even if the film thickness is made thinner than this, it only reduces the mechanical strength of the film and is meaningless.

Also, if the film thickness is thicker than this, it will not only reduce the transparency (but also increase the aberration of the light passing through the mask,
Adversely affects wafer patterning.

The average molecular weight of the polyvinyl acetal used in the present invention is preferably in the range of 10,000 to 200,000. Thin films obtained from polyvinyl acetal with a molecular weight of less than 10,000 do not have sufficient strength. Furthermore, since polyvinyl acetal having a molecular weight exceeding 200,000 has a high solution viscosity, it is difficult to obtain a uniform and even thin film.

〔Effect of the invention〕

As described above, the protective dustproof material for a mask of the present invention, which is made of polyvinyl acetal having a fluorine-containing silyl group in the side chain, has extremely excellent transparency and durability in a wide wavelength range from near ultraviolet to far ultraviolet. (Due to the introduction of fluorine atoms, the peelability from the film-forming base material is extremely good, so it can be easily manufactured without defects such as stretching, wrinkles, and tears. It is useful for effectively preventing a decrease in yield due to adhesion and improving productivity of semiconductor 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.

Example 1 Polyvinyl butyral (number average molecular size calculated as polystyrene 27.000, vinyl acetate component content CL54 mol.
Acetalization degree 80 mol%) 15fi' was dissolved in 1,4-dioxane 200-
i ((After adding H crystal fmya 18 ri, 60
The reaction was carried out by stirring at °C for 15 hours.

After the reaction was completed, the reaction solution was poured into n-hexane, and the precipitated white solid was filtered and dried. As a result of analysis, a polymer represented by the following structural formula was obtained.

Infrared absorption spectrum of the obtained polymer, 197-NM
The results of R spectrum and elemental analysis were as follows. From the elemental analysis results, the ratio x,/Xl was α079.

Infrared absorption spectrum (σ-1): 3490i), 2956$), 2919i), 2869
i).

1465i, 1433(rL), 1379hl), 13
42 (yt).

1323-, 1238i, 1130(s), 110
5(s).

1053←), 995(θ), 968(s),
910(n).

808←), 756(6) "F'-NMR spectrum/l/ (DMSO-d, ,
OF'C4 standard) δ (ppm) -81-CF.

-116be, -122-CF', -123(-02-)2 -126 -C2- Elemental analysis value (%) c: 64.96. H:9.45. F: 2.83 The obtained condensate of polyvinyl butyral and fluorine-substituted disilazane was dissolved in ethyl cellosolve and spin-coated using a spin coater using a 6-inch silicone urethane as a base material. A thin film with a thickness of about 2 μm was formed. Next is the outer area 91 deception.

A thin film of an epoxy adhesive was used to adhere the wafer to an aluminum frame with a width of 2 wm and a height of 5 m, and then the thin film adhered to the aluminum frame was peeled off from the wafer to serve as a protective dust-proof body for the mask.

The 20 protective dust-proof bodies produced in this way were inspected for defects such as scratches, stretches, wrinkles, and tears under irradiation with a Rodan lamp, and the number of protective dust-proof bodies without any defects was expressed as a percentage. Yield.

The yield of the protective dustproof body of the manufactured mask, and 300
The average transmittance in nm is shown in Table 1.

Example 2 As disilazane (ay, aH, ca, s i (CH
The reaction was carried out in the same manner as in Example 1 except that NH62 was added, and a polymer represented by the following structural formula was obtained. From the elemental analysis results, X2/
The ratio of XH was α075.

Elemental analysis value (%) C: 6 & 19. H:9.74. F: Protective dustproof body 2 of a mask was prepared from the obtained polymer α64 in the same manner as in Example 1.
0 pieces were produced. Table 1 shows the production yield and average transmittance at 300 nm.

Comparative Example When polyvinyl butyral, which was used as a raw material in Example 1, was dissolved in ethyl cellosolve and 20 protective dust-proof bodies for masks were prepared in the same manner as in Example 1, defects such as scratches, stretching, wrinkles, and tears were observed from the wafers. No peeling was obtained at all.

Table 1 Example 1 100 91.5 Example 2
100 91.2 Comparative example 0
91.0 As shown above, it is clear that the protective dustproof material for a mask made of polyvinyl acetal having a fluorine-containing silyl group in the side chain of the present invention is an extremely excellent protective dustproof material that has all the necessary performances. be.

Claims (1)

[Claims] For the purpose of protecting the substrate surface of a photomask or reticle for manufacturing semiconductor integrated circuits and preventing dust, a transparent thin film-like cover body is installed at a certain distance from the substrate surface for the purpose of protecting the substrate surface of the photomask or reticle for manufacturing semiconductor integrated circuits. It is a protective dust-proof body, and its transparent thin film is essentially a general formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (However, in the formula, R^1, R^2, R^3 are Carbon number 1-10
is an alkyl group, and R^1, R^2, and R^3 are groups in which at least one of the hydrogen atoms is partially or entirely substituted with a fluorine atom. Moreover, R is an alkyl group having 1 to 3 carbon atoms. ), the ratio of the silyl-substituted vinyl alcohol component represented by x_2/x_1 is 0.05 or more, the content of the vinyl acetate component is 10 mol% or less, and the degree of acetalization is 60 mol% or more A protective dust-proof body for masks with improved removability, made of polyvinyl acetal.