JPH11305426A - Radiation-sensitive composition and production of photomask using the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a problem of deterioration in a chemically amplifying resist pattern on chromium oxide is solved and a photomask having high resolution can be produced in high throughput. SOLUTION: This radiation-sensitive compsn. described below is applied on a photomask substrate, irradiated with electron bemas, baked and developed with an alkali soln. The radiation-sensitive compsn. contains at least an alkali soluble resin, a medium having the reactivity to change its solubility with an alkali soln. by the reaction using an acid as a catalyst, and an acid precursor comprising an ester of a compd. having two or more phenolic hydroxyl groups and camphorsulfonic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an acid in a pattern latent image forming portion of a resist coating film by irradiation with a pattern of an electron beam. The present invention relates to a method for manufacturing a photomask in which solubility in a developing solution is changed and a resist pattern is revealed by a process of using an alkaline aqueous solution as a developing solution.

[0002]

2. Description of the Related Art In recent years, with the increase in integration and speed of semiconductor integrated circuits, the demand for processing dimensions of resist has been reduced from quarter microns to 0.2 microns or less. Currently, as a quarter-micron microfabrication technology,
A KrF excimer laser exposure apparatus has been introduced in a mass production process. Further, at a stage where a processing dimension of 0.2 μm or less is required, the lithography technology uses Kr.
A super-resolution exposure method combining an F exposure apparatus and a phase shift mask is considered promising.

The processing accuracy of these exposure techniques depends on the processing accuracy of a photomask that plays a role of a negative in a printing circuit. Therefore, it is important to obtain a mask pattern having a rectangular cross-sectional shape and high dimensional accuracy. In addition, the super-resolution exposure method using a phase shift mask requires quarter-micron level fine processing in photomasks in order to achieve a resolution below the exposure wavelength. Development is becoming essential.

[0004] As a lithography technique for manufacturing a photomask, a technique of exposing with an electron beam lithography apparatus excellent in fine workability is generally used. However, currently available mask electron beam resists cannot manufacture KrF exposure masks that require high precision and resolution at high throughput, and use an organic solvent as a developing solution. There is a problem that it is difficult to change to the considered process. Therefore, a high-resolution and high-sensitivity electron beam resist using an industrially advantageous alkaline aqueous solution as a developing solution is demanded.

As a resist material capable of improving the throughput of mask production, for example, a composition containing a highly reactive medium in the presence of an acid catalyst and an acid precursor which generates an acid upon irradiation with active actinic radiation, see US Pat. No. 3,779,778. Japanese Patent Publication No. Hei 2-27660,
The composition described in JP-A-2-25850 is known. This type of resist is characterized by the fact that the acid generated in the pattern latent image forming area by irradiation with these radiations catalytically reacts with a highly reactive medium by the heat treatment in the next step, so that high sensitivity can be easily obtained. There is.

The chemical change of the medium may increase or decrease the solubility of the latent image forming portion in the aqueous alkaline solution. For example, as a medium for increasing the solubility, a compound or a polymer containing a protective group (acetal group, t-butoxycarbonyl group, etc.) which is deprotected (separated) by an acid catalyst is disclosed. In the resist containing such a medium, the exposed portion is melted by development, and the unexposed portion remains, so that a positive pattern can be revealed. In order to control the alkali solubility of a highly reactive medium with an acid catalyst, the composition of the positive resist should be alkali-soluble such as a novolak resin, an acrylic resin, or a copolymer of styrene and acrylic acid, if necessary. Resin is added. On the other hand, compounds having an epoxy group, a methoxymethyl group, and a methylol group are known as a medium for reducing the solubility in an aqueous alkali solution. In a resist containing such a medium, a cross-linking reaction occurs in an exposed portion, and alkali solubility is reduced, so that a negative pattern can appear.

Examples of the acid precursor include diaryliodonium salts, triarylsulfonium salts, trialkylsulfonium salts, esters of a compound having a plurality of phenolic hydroxyl groups with alkylsulfonic acid, and sulfonic acid esters of N-hydroxyimide. No.

[0008]

The resist material containing a highly reactive medium under the acid catalyst and an acid precursor which generates an acid upon irradiation with actinic radiation is coated on a quartz substrate of a photomask. When applied on chromium oxide and processed into a pattern, the positive resist pattern has a skirted shape,
It has been found that the negative pattern has a bite shape. A similar phenomenon occurs even on a silicon wafer substrate, in which an oxide film (SiO ₂ ), an aluminum film, a nitride film (TiN,
It is known that this occurs when a resist pattern is formed on a film such as Si ₃ N ₄ ).

It is considered that such deterioration of the pattern shape is caused by the fact that the acid generated by the irradiation of the radiation reacts with the film before reacting with the medium, so that the necessary acid catalysis, which should originally occur, does not occur. ing. Therefore, in the mass production process, when using the resist material of the above-mentioned conventional example, a method of performing oxygen plasma treatment on the film surface to suppress the reaction with acid, avoiding direct contact between the film and the resist layer,
A method for forming an intermediate layer has been proposed. However, there is a problem that such a method leads to an increase in the number of process steps and an increase in cost. Also, as an improvement of the resist material, in order to avoid the acid concentration decrease phenomenon due to the coating,
There is a method of increasing the concentration of the acid precursor in advance. However, the acid precursor of the above-mentioned conventional example has a drawback that when it is contained in a resist at a high concentration, resolution and developability are reduced.

An object of the present invention is to solve the problem of an abnormal cross-sectional shape of a resist pattern on a coating highly reactive to an acid catalyst, such as chromium oxide of a photomask, to achieve high resolution and dimensional control. An object of the present invention is to provide a method for obtaining a resist pattern having excellent properties at high sensitivity.

[0011]

Means for Solving the Problems The present inventors have found that when a sulfonic acid ester compound having a specific structure is used as an acid precursor, a small amount of the sulfonic acid ester compound is effective for improving a pattern shape on a coating film. The inventors have found that a pattern can be formed with high sensitivity, and have completed the present invention. Although the details of this specific phenomenon are not clear, it is considered that the phenomenon occurred due to the number of hydroxyl groups in the acid precursor structure and the size of the molecule of camphorsulfonic acid.

That is, the present invention comprises a medium having a reactivity to change the solubility in an aqueous alkali solution by an acid-catalyzed reaction, and an ester of a compound having two or more phenolic hydroxyl groups and camphorsulfonic acid. This is achieved by a radiation-sensitive composition comprising at least an acid precursor. The radiation-sensitive composition of the present invention comprises, in addition to the chromium oxide film, Al, Zr, Si, Ta, W, T
Even when an oxide film such as i or Mo or a nitride film is used as a film, excellent characteristics can be exhibited.

In the present invention, an acid precursor comprising an ester of a compound having two or more phenolic hydroxyl groups and camphorsulfonic acid, a medium having a reactivity to change solubility in an aqueous alkali solution by a reaction catalyzed by an acid. The body need not be a different component. For example, if a phenolic hydroxyl group is a component of a reactive medium that changes its solubility in an aqueous alkali solution by a reaction catalyzed by an acid, part of the phenolic hydroxyl group can be converted to an ester with camphorsulfonic acid. It functions as the acid precursor of the invention.

Examples of the acid precursor compound comprising an ester of camphorsulfonic acid with the compound having two or more phenolic hydroxyl groups of the present invention include catechol, resorcinol, pyrogallol, phloroglucinol, 1,2,2
4-benzenetriol, dihydroxynaphthalene, dihydroxyacetophenone, dihydroxybenzoic acid, trihydroxybenzoic acid, dihydroxybenzophenone,
Dihydroxyphenylacetic acid, dihydroxyphenyl glycol, 4-[(4-hydroxyphenyl) methyl]-
1,2,3-benzenetriol, 4-phenylmethyl-1,3-benzenediol, 4,6-bis [(3,5
-Dimethyl-4-hydroxyphenyl) methyl] -1,
2,3-benzenetriol, 4,6-bis [(4-hydroxyphenyl) methyl] -1,3-benzenediol, 4,4 '-[(3,4-dihydroxyphenyl) methylene] bis [2-methyl [Phenol]] and esters of camphorsulfonic acid.
Further, an ester of a polycondensate obtained by reacting these phenols with aldehydes or ketones and camphorsulfonic acid can also be used.

The camphorsulfonic acid ester used in the acid precursor of the present invention does not have to convert all the hydroxyl groups of the compound containing two or more phenolic hydroxyl groups into esters.
A hydroxyl group may be left. By leaving the hydroxyl group, the solubility of the reactive medium in an aqueous alkaline solution can be controlled. The camphorsulfonic acid esters may be used alone as an acid precursor, or may be various diaryliodonium salts, triarylsulfonium salts, trialkylsulfonium salts, compounds containing a plurality of phenolic hydroxyl groups, and alkylsulfonic acids. Ester of
It can also be used in combination with an acid precursor such as a sulfonate of N-hydroxyimide.

The amount of the acid precursor to be added is based on 100 parts by weight of a reactive medium which changes the solubility in an aqueous alkali solution by an acid-catalyzed reaction. Is preferably 1 to 30 parts by weight with respect to 100 parts by weight of the total amount of When the addition amount is 1 to 30 parts by weight, sufficient sensitivity to actinic radiation and a good pattern shape are provided. If the addition amount is less than 1 part by weight, the effect of the present invention cannot be obtained. If the addition amount is more than 30 parts by weight, the thermal diffusion of the acid and the solubility in the solvent decrease, the pattern shape deteriorates, and the resolution becomes poor. This leads to a decrease, which is not preferable.

Examples of the medium for increasing the solubility in an aqueous alkali solution used in the present invention include alkali-soluble phenol resins such as polyvinyl phenol, bisphenols, trisphenol alkanes, and the like.
Hydroxyl groups such as trinuclear phenols and tetrakisphenols are converted to acetal groups, ketal groups, t-butyl groups, t-butyl groups.
Compounds protected with an acid-decomposable group such as a butoxycarbonyl group are exemplified. Further, a compound in which a carboxyl group such as a copolymer of polyacrylic acid or styrene and acrylic acid is protected with the above-mentioned acid-decomposable group is desirable. Compounds in which hydroxyl groups and carboxyl groups are partially or wholly protected with the above-mentioned acid-decomposable group can regenerate the hydroxyl groups and carboxyl groups by the acid generated from the acid precursor during heat treatment after exposure or standing at room temperature to reduce alkali solubility. Can be increased.

As the medium having reduced solubility in an aqueous alkali solution, for example, a compound having an epoxy group, a methoxymethyl group or a methylol group is desirable. These compounds crosslink the reactive medium itself by polymerization and condensation with an acid catalyst, and reduce alkali solubility.

In the resist of the present invention, an alkali-soluble resin can be used if necessary in order to control the alkali-solubility of a medium having high reactivity with an acid catalyst. As the alkali-soluble resin, for example, novolak resin,
Examples include a copolymer of acrylic acid and styrene, a polymer of hydroxystyrene, polyvinyl phenol, polyvinyl alkyl ether, and a styrene-maleic anhydride copolymer.

The radiation-sensitive composition of the present invention includes, for example, a surfactant for preventing striation (uneven coating) and improving developability, a storage stabilizer for a resist solution, and an unexposed acid catalyst. A basic compound for suppressing diffusion to the part, an ion dissociable compound such as onium halide, and a humectant such as tetraethylene glycol can be added as necessary.

[0021]

Next, specific examples and comparative examples of the present invention will be described. It should be noted that these examples are merely examples under suitable specific conditions within the scope of the present invention, and the present invention is not limited only to these examples.

(Synthesis example 1 of camphorsulfonic acid ester) 1.5 g of phloroglucinol is dissolved in 100 ml of tetrahydrofuran. To this is added 10 g of camphorsulfonyl chloride, 0.1 g of 4-dimethylaminopyridine is added, and the mixture is reacted at room temperature for 1 day. Thereafter, a solution obtained by diluting 5 g of triethylamine with 10 ml of tetrahydrofuran is added dropwise to this solution, and the mixture is stirred at room temperature. After reacting at room temperature for one day, the deposited precipitate is removed by filtration. The filtrate is concentrated, and the concentrated solution is added to an aqueous hydrochloric acid solution to precipitate a product. This product is filtered, washed with water several times, and dried in vacuum. yield:
1.5 g (Synthesis example 2 of camphorsulfonic acid ester) Pyrogallol: 1.5 g in 100 ml of tetrahydrofuran
Dissolve. This includes camphorsulfonyl chloride:
10 g were added and further 4-dimethylaminopyridine:
Add 0.1 g and react at room temperature for 1 day. Then, 5 g of triethylamine was added to this solution in tetrahydrofuran:
Stir at room temperature while dropping the solution diluted in 10 ml. After reacting at room temperature for one day, the deposited precipitate is removed by filtration. The filtrate is concentrated, and the concentrated solution is added to an aqueous hydrochloric acid solution to precipitate a product. After washing with filtered water, vacuum drying was performed to obtain camphorsulfonic acid ester.

(Synthesis example 3 of camphorsulfonic acid ester) Tetrahydrofuran: 4-[(4
-Hydroxyphenyl) methyl] -1,2,3-benzenetriol: 0.8 g. To this is added 10 g of camphorsulfonyl chloride, 0.1 g of 4-dimethylaminopyridine is added, and the mixture is reacted at room temperature for 1 day. Thereafter, a solution obtained by diluting 5 g of triethylamine with 10 ml of tetrahydrofuran is added dropwise to this solution, and the mixture is stirred at room temperature. After reacting at room temperature for one day, the deposited precipitate is removed by filtration. The filtrate is concentrated, and the concentrated solution is added to an aqueous hydrochloric acid solution to precipitate a product. After washing with filtered water, vacuum drying was performed to obtain camphorsulfonic acid ester.

(Example 1) m, p-cresol novolak resin: 92 parts by weight, poly (p-vinylphenol) having acid-decomposable terahydropyranyl group (weight average molecular weight: 2000) (tetrahydropyranyl group) Substitution rate: 0.1
95): 8 parts by weight, camphorsulfonic acid ester of Synthesis Example 1 as an acid precursor: 4 parts by weight was dissolved in 2-heptanone to prepare a solution having a solid concentration of about 15% by weight.
This was filtered using a Teflon membrane filter having a pore size of 0.2 μm to obtain a resist solution. For comparison,
In the above composition, 4 parts by weight of a trisubstituted ester of pyrogallol and methanesulfonic acid were dissolved in 2-heptanone in place of the camphorsulfonic acid ester added as an acid precursor to form a resist having a solid content of about 15% by weight. It was mixed to obtain a comparative sample solution.

Photomask blanks (H) in which a light-shielding film having a two-layer structure of a chromium film and a chromium oxide film are provided on a quartz substrate
The above-mentioned resist was dropped on OYA Co., Ltd.), spin-coated, and heat-treated at 90 ° C. for 5 minutes to obtain a resist film having a thickness of 0.4 μm. The substrate is irradiated with an electron beam by an electron beam lithography system (acceleration voltage of the electron beam is 30 kV) by changing the irradiation amount in a stepwise manner, and then heat-treated at 100 ° C. for 5 minutes. Accelerated reactions to increase solubility. After the above heat treatment, an aqueous solution containing 2.38% by weight of tetramethylammonium hydroxide was immersed for 100 seconds in a developing solution, and the residual film thickness of the irradiated portion was measured. Electron beam sensitivity characteristics were determined from the relationship between the residual film thickness and the amount of electron beam irradiation.

FIG. 1 shows the electron beam characteristics of the system obtained using the camphorsulfonic acid ester of the present example as an acid precursor, and the trisubstituted ester of pyrogallol and methanesulfonic acid for comparison. This shows that of the system used as the generator. According to the sensitivity curve of the present invention, a high sensitivity of 2.0 μC / cm ² was obtained, and a high contrast was obtained without film loss. On the contrary,
The sensitivity characteristic of the comparative sample was 3.0 μC / cm ^2, which was lower than that of the resist of the present invention.

Electron beam writing apparatus (acceleration voltage of electron beam is 50
Using kV), a 0.8 μm line and space pattern was drawn on a photomask blank coated with a resist solution for comparison with the present invention. Resists of the invention, the irradiation amount of 4.0μC / cm ^2, the resist proportional compare, after drawing respectively dose of 6.0μC / cm ^2, 1
A heat treatment at 00 ° C. for 5 minutes promoted a reaction for increasing the solubility of the latent image portion in an aqueous alkaline solution. After the heat treatment, an aqueous solution containing 2.38% by weight of tetramethylammonium hydroxide was immersed in the developing solution for 100 seconds to obtain a resist pattern. The resist pattern of the present invention had a rectangular cross section and a line width of 0.8 μm as designed.
On the other hand, in the resist pattern of the comparative sample, the cross section had a skirted shape, and resist scum was observed in the space.

Next, using the developing pattern as a mask, CH ₂ C
Dry etching of the chromium two-layer film was performed by reactive ion etching with a mixed gas of l ₂ and O ₂ . The resist was removed with 2-heptanone, and the etched shape of the chromium film was confirmed with an electron microscope. As a result, a pattern having a vertical cross-sectional shape was confirmed.

Example 2 Electron beam sensitivity characteristics were determined in the same manner as in Example 1 except that the camphorsulfonic acid ester of Synthesis Example 2 was used in place of the camphorsulfonic acid ester of Synthesis Example 1 as the acid precursor. Was. As a result, 2.5 μ
High sensitivity of C / cm ^2, no loss of film, and high sensitivity characteristics were obtained.

(Example 3) The electron beam sensitivity was changed in the same manner as in Example 1 except that the camphorsulfonic acid ester of Synthesis Example 3 was used instead of the camphorsulfonic acid ester of Synthesis Example 1 as the acid precursor. I asked. As a result, 2.0
High sensitivity of μC / cm ² and no film loss resulted in high contrast sensitivity characteristics.

Example 4 90 parts by weight of m, p-cresol novolak resin, 10 parts by weight of methylolmelamine and 4 parts by weight of camphorsulfonic acid ester of Synthesis Example 1 as an acid precursor were dissolved in cyclohexanone. After preparing a solution having a solid content of about 15% by weight, the solution was adjusted to a pore size of 0.1%.
The solution was filtered using a 2 μm Teflon membrane filter to obtain a resist solution. For comparison, in the above composition, triphenylsulfonium trifluoromethanesulfonate: 4 parts by weight was dissolved in cyclohexanone in place of camphorsulfonic acid ester added as an acid generator, and a resist having a solid content of about 15% by weight was used. Was prepared to obtain a comparative sample solution.

Hereinafter, a pattern was formed according to the method of Example 1. As a result, the resist pattern of the present invention had a rectangular cross section and a line width of 0.8 μm as designed. On the other hand, in the comparative resist pattern, the resist pattern bites into the interface of the coating film, and a rectangular resist pattern could not be obtained.

In the above embodiment, the method using an electron beam as the actinic radiation has been described, but the present invention is not limited to this. Similar effects can be obtained by using ultraviolet rays, X-rays or the like for forming a latent image. Further, in the above embodiment, a method using a photomask blank having a two-layer structure of a chromium film and a chromium oxide film as the resist-coated substrate was described, but the present invention is not limited to this. Al, Zr, Si, Ta,
Similar effects can be obtained by using an oxide film or a nitride film of W, Ti, Mo or the like.

[0034]

According to the present invention, a resist pattern having high sensitivity, high resolution and excellent dimensional accuracy can be formed on a film having high reactivity to an acid catalyst in an electron beam resist, and an alkali Since it can be developed with an aqueous solution, it is suitably used as a resist for fine processing in photomask production.

[Brief description of the drawings]

FIG. 1 is a graph showing electron beams of a radiation-sensitive composition of Example 1 of the present invention and a conventional example.

[Explanation of symbols]

1. Sensitivity characteristics of the resist composition of the present invention, 2. Sensitivity characteristics of a conventional resist composition.

Claims (7)

[Claims] An acid precursor comprising an ester of a compound having two or more phenolic hydroxyl groups and a camphorsulfonic acid, comprising: a medium having a reactivity that changes solubility in an aqueous alkali solution by a reaction catalyzed by an acid; A radiation-sensitive composition comprising at least: 2. The radiation-sensitive composition according to claim 1, wherein
A radiation-sensitive composition, wherein the reactivity that changes solubility in an aqueous alkali solution by a reaction using an acid as a catalyst is a reaction that increases solubility. 3. The radiation-sensitive composition according to claim 1, wherein
A radiation-sensitive composition, wherein the reactivity that changes solubility in an aqueous alkali solution by a reaction using an acid as a catalyst is a reaction that decreases the solubility. 4. A photolithographic mask substrate comprising:
An alkali-soluble resin and (b) a medium having a reaction to change solubility in an aqueous alkali solution by a reaction catalyzed by an acid, and (c) an acid comprising an ester of a compound having two or more phenolic hydroxyl groups and camphorsulfonic acid. An electron beam positive resist containing at least a precursor is applied, and after heat treatment, a predetermined pattern is drawn on the coating film using an electron beam, and thereafter, a resist pattern is formed by the predetermined development medium. Method of manufacturing a photomask. 5. The method of manufacturing a photomask according to claim 4, wherein the developing medium is an aqueous alkaline developer. 6. A process according to claim 1, wherein the coating film is exposed to a predetermined pattern using actinic radiation, and then the coating film is heat-treated in order to promote an acid-catalyzed reaction of the latent image portion of the pattern. A method for forming a pattern, comprising: 7. The method of manufacturing a photomask according to claim 4, wherein after forming the resist pattern, the light-shielding film or the shifter film is processed by dry etching using the resist pattern as a mask. Production method.