JPS61170736A - Radiation sensitive photoresist composition - Google Patents

Abstract

PURPOSE:To enable a resist soln. to be not degraded during long-term storage and an always correct film thickness to be formed on a semiconductor substrate or a mask substrate when the resist soln. is reused after storing for a long term by forming the resist compsn. consisting of a polymer, an org. solvent, and a radical inhibitor. CONSTITUTION:The resist compsn. consists of a homopolymer of a monomer represented by formula I, R1 being an alkyl group substd. by one ore more F atoms, an org. solvent, preferably, e.g., cellosolve type solvents, such as methyl cellosolve acetate, and ethyl cellosolve acetate, and alkyl acetates, and the radical inhibitor, preferably, such as phenols having a mol.wt. of <=600, in an amt. of 0.01-5wt% of the polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in Children's Business] The present invention relates to a positive radiation-sensitive resist composition. More specifically, it is a positive radiation-sensitive resist with high sensitivity and high resolution. The present invention relates to poly(fluoroalkyl α-chloroacrylate) and copolymer compositions thereof.

[Prior art]

BACKGROUND ART Conventionally, as a method for forming fine patterns for manufacturing ICs, LSIs, etc., methods using photoresists that are sensitive to ultraviolet light have been widely put into practical use. However, recently LSI
In response to the demand for higher density and higher integration, technologies using radiation with shorter wavelengths than light, such as electron beams, X-rays, and ion beams, have been developed. Resist is required.

Conventionally, methacrylate polymers have been widely used as positive radiation-sensitive resists, but they generally have the drawbacks of high sensitivity, low glass transition points, and poor heat resistance.

On the other hand, poly(fluoroalkyl α-chloroacrylate) and its copolymers proposed by Shimazaki et al. (Japanese Patent Publication No. 57-969) have extremely high sensitivity and a high glass transition point, making them useful materials as radiation-sensitive resists. It is.

[Problem that the invention seeks to solve]

The present inventors investigated the change over time of a resist solution made of poly(fluoroalkyl α-chloroacrylate) or its copolymer, and as a result, the following experimental facts were found.

That is, the above resist solution was filtered through a membrane filter under nitrogen pressure, then placed in a glass pin, sealed tightly, and stored for several weeks at room temperature.

In SO'C, the solution viscosity decreases to 1/2 to 1/10 in a few days. A resist solution with a reduced solution viscosity cannot obtain an appropriate film thickness in spin coating, and also has reduced sensitivity. Therefore, it is not possible to obtain a resist pattern with good reproducibility, and the resist pattern cannot be used as a resist.

This resist solution was reprecipitated with a non-solvent, and when the polymer powder was taken out and examined, it was found that the molecular weight had decreased.

When we investigated the cause of the decrease in molecular weight, we found that the radical source was the residual polymerization initiator in the polymer, the solvent CPOA,
Sea urchin t), ;f:9-r-1)1. Tsuka let
``We found that the backbone chain is cleaved, i.e.

Poly(fluoroalkyl α-chloroacrylate) and its copolymers have extremely unique properties compared to ordinary acrylic polymers. It is not known that ordinary acrylic polymers undergo main chain cleavage due to radical sources in solutions.

Based on this knowledge, the present inventors conducted intensive studies on a method for preserving a resist solution made of the poly(fluoroalkyl α-chloroacrylate) or its copolymer for a long period of time without changing over time, and as a result, the method of the present invention was arrived at. It is.

[Failure to solve the problem]

That is, the present invention provides a radiation-sensitive resist composition comprising poly(fluoroalkyl α-chloroacrylate), an organic solvent and a radical inhibitor, and a copolymer comprising fluoroalkyl α-chloroacrylate and other vinyl monomacaras. , a radiation-sensitive resist composition comprising an organic solvent and a radical inhibitor.

In the present invention, when a radical inhibitor is attached to a resist solution made of poly(fluoroalkyl α-chloroacrylate) or a copolymer thereof, the viscosity of the resist solution may be changed. ? It can be stored stably for a long period of time, for example, one year or more at room temperature, or two months or more at 50°C.

The radical inhibitor used in the present invention may be of any kind as long as it is stable at room temperature, but those having a molecular weight of 2 or less are preferred. That is, the resist solution is spin-coded onto the substrate and prebaked at 160° C. to 210° C., but it is preferable that the resist solution be evaporated and lost during the prebaking. If the radical inhibitor remains in the resist film after prebaking, it will precipitate into the resist film and become foreign matter, causing undesirable effects such as adversely affecting the sensitivity of the resist.

The radical inhibitor used in the present invention includes:

Stable radicals such as tri-P-nitrophenylmethyl, cyphenylpicrylhydrazyl, galpinoxyl, benzoquinone, chlorobenzoquinone, 2.5-dichlorobenzoquinone, 2.6-cyclopenzoquinone, 2.6-dimethylbenzoquinone, 2.5-dimethylbenzoquinone,
Methoxybenzoquinone, methylbenzoquinone, tetrabromobenzoquino/.

Quinones such as tetrachlorobenzoquinone, tetramethylbenzo, quinone, trichlorobenzoquinone, and trimethylbenzoquinone; naphthols such as α-naphthol, 2-nitro-1-naphthol, β-naphthol, and 1-nitro-2-naphthol;

Hydroquinone, catecholresorcin, o-t-butylphenol, 2,6-di-P-methoxyphenol, P
-ethoxyphenol-t-butyl-P-cresol,
2,6-di-monobutylphenol92,4-di-t-
Butylphenol, 3.5-di-1-butylphenol, 5-di-t-butylcatechol, 3.5-di-t
-butyl-4-hydroxybenzoic acid, 2,2'-methylenepine (6-butyl-P-cresol), etc.:y
Enols, 2゜4--, jnitrophenol, 0-nitrophenol.

m-nitrophenol, p-nitrophenol.

and the like, but the above-mentioned phenols are particularly preferred from the standpoint of stability and safety.

Of course, oxygen also has an inhibitory effect, but pressurizing organic solvents with oxygen is extremely dangerous. This is not a preferred method for two reasons, such as the limited amount that can be dissolved in the solvent.

As mentioned above, the method of the present invention was developed in view of the unique property of poly(fluoroalkyl α'-chloroacrylate) and its copolymers to undergo radical decomposition in solution, and it is possible to eliminate easily polymerizable groups in the polymer. It is essentially different from a polymerization inhibitor added for protection.

Since it does not remain in the resist film after coating, it does not relate to modification or improvement of the resist film after coating. That is, the above-mentioned decomposition of the polymer by radicals is a phenomenon observed only in a solution, and the di-2 polymer powder and the resist film after coating are stable for a long period of time.

The amount of radical inhibitor used in the present invention is from 0.01 to 5%, preferably from 0.1 to 2%, based on the weight of the polymer.
It is.

The solvent for dissolving the polymer is not particularly limited as long as it dissolves the polymer, but cellosolve acetates such as methyl cellosolve acetate and ethyl cellosolve acetate, ketones such as cyclohex f/7, n-butyl acetate, etc. Acetate esters such as acetate and 5ea-butyl acetate are preferred.

The polymer used in the present invention includes (1) a homopolymer of monomers represented by the following general formula;

CH,,C-GOOR,(I) (R, is an alkyl group in which - or more hydrogen atoms are substituted with fluorine atoms).

(2) A copolymer consisting of two or more monomers selected from the group of acrylate monomers represented by the above general formula (1).

(3) Copolymers are broadly classified into copolymers consisting of the acrylate monomer of the general formula (1) and other vinyl monomers.

As the polymer of the above (1), one in which the alkyl group (R) in formula 2 (I) is an alkyl group having one or more fluorine atoms at the 2nd or higher positions is used. Preferably it is a fluoroalkyl group having 2 to 10 carbon atoms. For example, 2.2.2-trifluoroethyl, 1-trifluoromethylethyl, hexafluoropropyl, 3,5.3-
Trifluoropropyl, 2,2,3°6.3-pentafluoropropyl + 2,2,6.3-tetrafluoropropyl, 2.2.3.5.4.4.4-hebutafluorobutyl, 2. 2.3.4.4.4-Hexafluorobutyl, 2.2.7:, 4.4.4-Hexafluoro-1-methylbutyl, 1-trifluoromethyl-1-methylethyl, 2.2 .3.3.3-pentafluoro-1,1-dimethapropyl, 2.2.5
．． Examples include, but are not limited to, 3.4.4.4-hebutafluoro-1,1-dimethylbutyl.

As the polymer in (2) above, the monomer (I) mentioned above (
It is a copolymer of 1), and there are no particular restrictions on the composition etc.

The polymer in (3) above includes a copolymer of the polymer described in (1) and one or more other vinyl monomers;
Alternatively, it is a copolymer of the polymer described in (2) above and one or more types of other vinyl monomers.

As for other vinyl monomers.

R3 CH=C-Ar (II) (R+ is a methyl group or hydrogen atom, Ar is an aromatic group)
Aromatic vinyl monomers represented by, for example, styrene, α-methylstyrene, and vinylnaphthalene.

vinylpyridine, vinyltoluene, vinylcarbazole and its aromatic ring, methoxy.

Derivatives having substituents such as alkyl having 4 or less carbon atoms.

R1 CH,=C-0-R, (■) (R is a methyl group or a hydrogen atom, R4 is an alkyl group.

aryl group or aralkyl group), such as methyl vinyl ether, ethyl vinyl ether, tn-butyl vinyl ether, etc.

A vinyl ketone monomer represented by a aryl group or an aralkyl group, such as methyl vinyl ketone.

Methyl isopropyl ketone etc.

Cyanoacrylate monomers represented by CH=C-CN (V) (R, is a hydrogen atom, a methyl group, a halogen atom, a halogenated methyl), such as acrylonitrile, methacrylonitrile, 2-
chloroacrylonitrile etc.

R1 CH, = C-C0NH, (b) (R8 is a hydrogen atom, a methyl group, a halogen atom, a halogenated methyl group, a carboxyl group) an acrylamide monomer, such as acrylamide, methacrylamide, 2-chloroacrylamide Do et al.

R9 CH, = C-C0OH (b) (R is a hydrogen atom, a methyl group, a halogen atom, a halogenated methyl group, a carboxyl group, a cyan group, an N-carboxymethyl group), an acrylic acid monomer, such as acrylic acid, methacrylic acid, 2-chloromethacrylic acid,
2-cyanoacrylic acid.

Itaconic acid, etc.
Rogenated methyl group, carboxyl group, cyano group.

An acrylic acid ester monomer represented by a carboxymethyl group (R1 is an alkyl group, an aryl group, or an aralkyl group), such as methyl acrylate.

Ethyl acrylate, isopropyl acrylate.

n-propyl acrylate, inbutyl acrylate,
n-butyl acrylate, benzyl acrylate, phenyl acrylate, methyl-α-chloroacrylate,
Ethyl α-chloroacrylate, isopropyl α-chloroacrylate, n-propyl α-chloroacrylate, isobutyl α-chloroacrylate, n-butyl α-chloroacrylate, benzyl α-chloroacrylate.

Phenyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate.

Isobutyl methacrylate, n-butyl methacrylate, benzyl methacrylate, phenyl methacrylate,
2-cyanoacrylate and derivatives having a substituent such as halogen, methoxy, or alkyl having 4 or less carbon atoms on its benzene ring.

R1□ CH, = C-C05R,, QX) (R12 is a hydrogen atom, methyl group, halogen atom, halogenated methyl group, carboxyl group t cyano group t carboxymethyl group I R11 is an alkyl group, aryl group, or aralkyl group) A thioacrylate monomer represented by, for example, methylthiomethacrylate.

Ethylthiomethacrylate etc.

IA CH, = C-ocOFt, (X) (R14 is a hydrogen atom, a methyl group, a halogen atom), a halogenated methyl group, a cyano group, and R7 is an alkyl group.

Vinyl acetate monomers represented by (aryl group, aralkyl group), such as vinyl acetate.

Examples include vinyl propionate, but are not limited to these.

In addition, in the above explanation I Rj J RA T Jl
J The alkyl group of R11 and R1° has 1 to 1 carbon atoms.
8, the aryl group refers to one having a benzene ring or naphthalene ring, and the aralkyl group refers to benzyl or haphenylethyl.

Of the above, R21R,, R,, Fl,, R,, R41
Rlo IRIf I It is preferable that R11 has a group other than a hydrogen atom, that is, one that becomes quaternary carbon after polymerization. Furthermore, among groups other than hydrogen atoms, those having a halogen atom are particularly preferred.

The proportion of these vinyl monomers in the comonomer is 50
It is preferable to make it less than wt%.

Copolymers generally improve adhesion to substrates, and copolymerization with aromatic comonomers generally improves dry etching resistance.

The molecular weight of the positive radiation-sensitive resist shown in (1), (2), and (3) above is 25 in methyl ethyl ketone.
Those having an intrinsic viscosity measured at °C of 0.3 to 3.0, preferably 0.5 to zOO are used. A higher molecular weight is generally advantageous in that sensitivity is higher.

If the viscosity is high, the viscosity of the resist solution increases, making filtration difficult. Furthermore, during pattern formation, it becomes difficult to coat the substrate and swelling occurs during shear development, which adversely affects the pattern.

Next, a method for measuring the sensitivity of the positive radiation-sensitive resist in the present invention will be described.

First, a resist solution is prepared by dissolving a polymer in a suitable solvent such as methyl cellosolve acetate, cyclohexanone, n-butyl acetate, etc., and filtering through a 0.2-0.4 .mu. membrane filter. A uniform resist film with a spin code L of 0.4 to 1.0 .mu. is formed using a spinner using this lucyst solution on a substrate. Next, a prebaking process is performed to remove the solvent and improve adhesion to the substrate.

In the case of the positive radiation-sensitive resist of the present invention, 160°C ~
It is preferable to prebake at 210°C for 15 minutes to 1 hour.

Using an electron beam exposure device, a fixed area on the substrate is exposed to light at 10 to 20 locations with a fixed current amount while changing the exposure time in a geometric progression. For each exposed part.

From the area, current amount, and exposure time, the amount of electricity per unit area (
μC/am”).

Next, the substrate is immersed in a suitable developer at a constant temperature for a certain period of time, and then immersed in a non-solvent for rinsing. After drying, post-bake the substrate. It is generally preferred that the post-bake temperature is lower than the glass transition temperature of the polymer.

Measure the film thickness of exposed and unexposed areas on the substrate using a surface roughness meter or the like. The horizontal axis is the amount of electricity (exposure amount).

Plot the film thickness of the exposed portion on the vertical axis to create a sensitivity curve. Sensitivity is defined as the point where this sensitivity curve intersects with the horizontal axis.

The film thickness before exposure is also measured, and compared with the film thickness of the unexposed part after development, the decrease is taken as the film thickness reduction.

Generally, in a positive radiation-sensitive resist, the polymer in the exposed portion undergoes main chain cleavage, resulting in a decrease in molecular weight. When this is developed, the polymer in the exposed areas dissolves at a faster rate than the polymer in the unexposed areas, thus forming a resist pattern. In this way, during development, the film thickness of the unexposed area is always
It decreases compared to before development.

The sensitivity of positive radiation-sensitive resists varies depending on the type of developer, temperature, development time, and resist film thickness.If these are not described, data on sensitivity alone is meaningless.In other words, long development times and high development temperatures are used. This increases the apparent sensitivity, but also increases the film loss.

〔Example〕

The present invention will be explained in detail in Examples below.

Example 1 2, 2.2-) IJ fluoroethyl α-chloroacrylate 200g, azobisisobutyronitrile 6.9
800 mz of t-butanol were placed in a Mitsuro flask and stirred to dissolve. After purging the inside of the flask with nitrogen, it was left standing in a 50°C water bath for 6.5 hours.

The resulting lump-like mass was dissolved in 6 tons of acetone. Pour the polymer solution into a mixture of 4 tons of methanol and 2 tons of water to reprecipitate the polymer. Determine the number of polymers that precipitate,
After washing with methanol-water 2:1, it was dried in a vacuum dryer.

186 g of polymer powder was obtained. The intrinsic viscosity at 25"C in methyl ethyl ketone was 1.00.

The following experiment was conducted using the polymer powder obtained by the above method.

(A) 620 g of polymer powder was taken and dissolved in 9380 g of methyl cellosolve acetate, filtered under nitrogen pressure using a 0.2 μ membrane filter, and pinned in 1 ton glass bottles in 1 ton portions. The resist solution was spin coded onto a chrome blank at 1000 rpm and prebaked at 200'c for 60 minutes. The resist film thickness was 5560A.

Using an electron beam exposure device, acceleration voltage 20 kV, current amount 1
An area of 0.45 x O,6- was scanned and exposed at nA while changing the exposure time sequentially.

Substrate methyl isobutyl ketone-isozolopanol 8:
The sample was immersed in developer No. 2 at 25° C. for 5 minutes with stirring, and then immersed in isopropanol for 60 seconds.

The resist film thickness of the unexposed part and the exposed part was sequentially measured, and a sensitivity curve was created. Sensitivity is 4.7μC/aI+".

The film loss in the unexposed area was 100X.

When the pinned resist solution was stored at room temperature for 20 days, the solution viscosity, which was initially 5) CP, decreased to 21 CP.

Furthermore, when the pinned resist solution was stored at 50°C for 4 days, the solution viscosity decreased to 10 cp.

(B) 620 g of polymer powder and 6.2 g of 2.6-di-t-butyl-P-cresol were dissolved in 9370 g of methyl cellosolve acetate, filtered under nitrogen pressure using a 0.2 μ membrane filter, and placed in a 1 t glass bottle. 1t per
I pinned them one by one.

When the sensitivity was measured in the same manner as in (A), the measured value agreed with the measured value in (A) within the error range.

Apply resist solution to a thickness of 11!10177) on a quartz plate.
When the ultraviolet absorption was measured with a 2 spectrophotometer using a spin code at 000/revolution, absorption of 2,6-di-t-butyl-P-cresol was confirmed.

When this quartz plate was prebaked at 200°C for 30 minutes and the ultraviolet absorption was measured again, it was found that 2,6-di-t-butyl-P
- The absorption of cresol disappeared and was consistent with the absorption of the sample obtained by prebaking the solution of (A) after spin-coding.

The resist solution packed with pins was stored at room temperature for one year, and the other pins were stored at 50°C for two months, but no change in solution viscosity was observed in either case.

Example 2 2, 2.2-t! J Fluoroethyl α-chloroacrylate 160g, Phenyl α-chloroacrylate 40g
g, azobisisobutyronitrile 3.28g, n-
5 of hexane 1600+++z was placed in a Mitsuro flask and stirred to dissolve it. After purging the inside of the flask with nitrogen, it was left standing in a water bath at 50'C for 8 hours.

After adding 1 ton of isopropanol and stirring.

The powdered polymer was washed with isopropyl alcohol. Improper Tool 4 was added to the polymer, left for 50 minutes, and then filtered. The resulting white powder was dried in a vacuum dryer to obtain 189 g of polymer powder. The intrinsic viscosity in methyl ethyl ketone at 25°C was 1.20.

The following experiment was conducted using the polymer powder obtained by the above method.

(A) 800 g of polymer powder was taken and dissolved in 9200 g of methyl cellosolve acetate, filtered under nitrogen pressure using a 0.2 μm membrane filter, and 1 ton each was pinned into 1 ton glass bottles. The resist solution was spin-coded onto a chrome blank at 2900 rpm and prebaked at 200° C. for 60 minutes. The resist film thickness was 5640X.

Using an electron beam exposure device, acceleration voltage 20 kV, current amount 1
An area of 0.45xQ, 6+mn was scanned and exposed at nA while sequentially changing the exposure time.

Substrate methyl isobutyl ketone-isopropanol 7:
The sample was immersed in developer No. 3 at 25"C for 5 minutes with stirring, and then immersed in isopropanol for 60 seconds.

The resist film thickness of the unexposed part and the exposed part was sequentially measured, and a sensitivity curve was created. The sensitivity is 6.8 μγ.

The film loss in the unexposed area was 270X.

When the pinned resist solution was stored at room temperature for 20 days, the solution viscosity, which was initially 78 cp, decreased to 33 cp.

When the still pinned resist solution was stored at 50°C for 4 days, the solution viscosity decreased to 27 cp.

(B) 800 g of polymer powder and 4.0 g of 2.6-di-t-butyl-P-cresol were dissolved in 9200 g of methyl cellosolve acetate, and filtered under nitrogen pressure using a 0.2μ membrane filter to obtain 1 t. 1 in a glass bottle
I pinned each t.

When the sensitivity was measured in the same manner as in (A), the measured value agreed with the measured value in (A) within the error range.

The resist solution was spin-coded onto a quartz plate with a thickness of 1 stroke at 2900 revolutions, and the ultraviolet absorption was measured using a spectrophotometer. Absorption of 2.6-di-t-butyl-P-cresol was confirmed. It was done.

When this quartz plate was prebaked at 200°C for 60 minutes and the absorption in the ultraviolet region was measured again, the absorption of 2,6-'-t-7'chi-P-cresol disappeared, and after spin-coding the solution (A), The absorption was consistent with that of the prebaked sample.

The resist solution packed with the pins was stored at room temperature for one year, and the other pins were stored at 50°C for two months, but no change was observed in the viscosity of the solution.

Examples 3 to 30 14 types of monomers (I to XIV
) and 5 types of radical inhibitors (A-, E) Table 9-
Stationary polymerization was carried out under the combination and conditions shown in 1.

The obtained polymer and copolymer were powdered according to Example 1 and Example 2, respectively.

A resist film was formed, and the film thickness, film reduction, and sensitivity were measured, and the results are shown in Table 1.

Structural formula of monomer % Formula % Structural formula of radical inhibitor In Table 1, AIBN, BPO and [η] refer to the following.

AIBN: Azobisisobutyronitrile BPO: Benzoyl peroxide [η]: Intrinsic viscosity [Effects of the Invention] Since the present invention is constructed as described above, the resist solution will not change in quality at all even if it is stored for a long period of time.

Therefore, even if the resist solution is stored and reused, it is possible to always form an appropriate film thickness on the semiconductor substrate or mask substrate, which is an advantage in that a good resist pattern can be obtained with good reproducibility and economically. There is.

Claims (5)

[Claims] (1) A radiation-sensitive resist composition comprising poly(fluoroalkyl α-chloroacrylate), an organic solvent, and a radical inhibitor. (2) The radiation-sensitive resist composition according to claim (1), wherein the poly(fluoroalkyl α-chloroacrylate) is poly(2,2,2-trifluoroethyl α-chloroacrylate). . (3) A radiation-sensitive resist composition comprising a copolymer of fluoroalkyl α-chloroacrylate and another vinyl monomer, an organic solvent, and a radical inhibitor. (4) The other vinyl monomer is methacrylic acid, methacrylonitrile, benzyl methacrylate or a derivative having a substituent on its benzene ring, benzyl α-chloroacrylate or a derivative having a substituent on its benzene ring,
Phenyl methacrylate or a derivative having a substituent on its benzene ring, phenyl α-chloroacrylate or a derivative having a substituent on its benzene ring, styrene or a derivative having a substituent on its benzene ring or α
- The radiation-sensitive resist composition according to claim (3), which is one selected from the group of methylstyrene or its derivatives having a substituent on a benzene ring. (5) Fluoroalkyl α-chloroacrylate is 2,
The radiation-sensitive resist composition according to claim (4), which is 2,2-trifluoroethyl α-chloroacrylate.