Photoresist composition and process for its use

Details Photoresist composition and process for its use Photoresist composition and process for its use

1997-09-12

2001-01-23

Chu, John S. (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

C430S281100, C430S288100, C430S326000, C430S905000, C430S906000, C430S910000

Reexamination Certificate

active

06177228

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an improved lithographic photoresist composition and process for its use in the manufacture of integrated circuits.
BACKGROUND OF THE INVENTION
There is a desire in the industry for higher circuit density in microelectronic devices which are made using lithographic techniques. One method of increasing the number of components per chip is to decrease the minimum feature size on the chip, which requires higher lithographic resolution. The use of shorter wavelength radiation (e.g., ultra deep UV, e.g., 193 nm) than the currently employed mid-UV spectral range (e.g., 248-450 nm) offers the potential for higher resolution. However, with deep UV radiation, fewer photons are transferred for the same energy dose and higher exposure doses are required to achieve the same desired photochemical response. Further, current lithographic resists absorb strongly at 193 nm due to aromaticity making them unsuitable for commercial use at 193 nm.
Acrylate and methacrylate resists are known in the art. For example, Allen U.S. Pat. No. 5,071,730 discloses a resist comprising a terpolymer of methyl methacrylate, t-butyl methacrylate and metharcylic acid. Allen teaches that the t-butyl group imparts acid sensitivity, the acid group influences development rate and the methyl ester increases toughness of the film. Although this resist is suitable for some commercial uses, it is deficient in that it has low reactive ion etch resistance. Reactive ion etch resistance is desired for processing in semiconductor manufacturing. Further, excessive amounts of acid in the polymer will result in thinning in the unexposed areas during development.
Nozaki et al., J. of Photopolym. Sci. Technol., Vol. 9, 1993, 509, discloses a methacrylate resist having two acid cleavable ester groups, adamantyl and pyranyl groups. The author states that the resist develops well probably due to the high acid content of the exposed areas resulting from the cleavage of both leaving groups. However, the unexposed areas of the resist will experience substantial cracking during postexposure bake due to the large shrinkage in the exposed area with the removal of the large ester groups.
The requirements for photoresists for semiconductor manufacturing include etch resistance, clean aqueous development and compatibility with strong developers currently in use in semiconductor manufacturing. Traditional DUV resists (248 nm) combine these functions quite easily by using poly(hydroxystyrene), a phenolic resin, as the polymer of choice. This material has unacceptably high optical density for 193-nm lithography. Combining these requirements in a polymer that is nearly transparent at both 193 nm and 248 nm is a significant challenge.
It is therefore an object of the present invention to provide a radiation-sensitive (meth) acrylate resist composition which has improved sensitivity and resolution.
Other objects and advantages will become apparent from the following disclosure.
SUMMARY OF THE INVENTION
The present invention relates to a chemically-amplified, radiation-sensitive resist composition comprising a photo-sensitive acid generator and an acrylate or methacrylate polymer formed by reacting an acrylate or methacrylate monomer having (a) a photogenerated acid cleavable ester substituent and (b) a monomer having the formula
H
2
C═CRR′
where R is hydrido or methyl and R′ is a polar, non photoacid cleavable substituent having the formula
—CN   (i)
where A is a spacer group and R* is a polar
group having one or more heteroatom with a Pauling electronegativity greater than 3.00. The photoresist adheres well to the substrate and develops cleanly without thinning or residue formation. The acrylate or methacrylate polymer uniquely separates the polar functionality needed for development from the photoacid cleavable functionality to avoid excessive thinning and still achieve clean development. The present invention also relates to the use of the resist composition to make integrated circuits.
A more thorough disclosure of the present invention is presented in the detailed description which follows.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to a chemically amplified, positive tone, radiation-sensitive composition comprising (a) photo sensitive acid generator; (b) a polymer formed by the reaction of (a) an acrylate or methacrylate monomer having photogenerated acid cleavable substituent and (b) an acrylate or methacrylate monomer having a polar non photoacid cleavable substituent.
The polymer in the resist composition is the reaction product of a plurality of monomers. The first monomer H
2
C═CRR′ has a polar substituent R′ which is not cleavable in the presence of a photogenerated acid, e.g., an ester group which does not cleave in the absence of water because it does not form a stable carbonium ion. However, the polarity of the substituent R′ enhances the development of the resist without causing problems associated with excessive acid formation. Suitable polar substituents R′ have the formula:
—CN   (i)
where A is a spacer group R is hydrido or methyl, R″ and R′″ are independently hydrido, alkyl (C
1-6
) or AR* and R* is a polar organic group having a heteroatom having an electronegativity greater than 3.00. In formula (iii), the polar group R* is separated from the oxygen with a divalent spacer group A. Suitable spacer groups include divalent hydrocarbon radicals (e.g., alkylene radicals C
1-6
preferably C
2
optionally branched where preferably the carbon which is bonded to the oxygen is —CH
2
—) or divalent cyclic hydrocarbon radicals (e.g., C
3-8
). Suitable R* are mono, di, tri, tetra alkoxy e.g., lower C
1-6
alkoxy; alkyl carbonyl; (mono, di, tri, tetra alkoxy) carbonyl; (mono, di, tri, tetra alkoxy) alkyl carbonyl; alkyl carbonyloxy; (mono, di, tri, tetra alkoxy) alkyl carbonyloxy; (mono, di, tri, tetra alkoxy) carbonyloxy, alkyl dicarbonyloxy; (mono, di, tri, tetra alkoxy) dicarbonyloxy; (mono, di, tri, tetra alkoxyalkyl) dicarbonyloxy, amino; alkylamino; (mono, di, tri tetra alkoxy) alkylamino; and alkyl carbonyl amino and alkyl sulfonyl amino where each alkyl is preferably lower C
1-6
alkyl.
Other suitable polar substituents include:
cycloalkylcarbonylamino (lactams e.g., caprolactam)
cycloalkylcarbonyloxyalkyl (lactones e.g., pantolactone)
m, n independently=0, 1, 2, 3 . . .
and cycloalkyl dicarbonylalkyl (cyclic glycerin).
and sulfonylamino where R is alkyl, haloalkyl (trifluoromethyl) or cycloalkyl (camphor)
Other suitable non photoacid cleavable polar groups will be known to those skilled in the art. The polar substituent functions to improve film quality (planar coating with good adhesion), enhance thermal properties (glass transition temperature), improve solubility of resist in industry standard developers and improve development of resist while avoid thinning, cracking and swelling associated with excessive acid in the polymer. Preferred polar ester substituents for use in the present invention include methoxyethyl; methylcarbonyloxyethyl; ethoxycarbonyloxyethyl and ethoxydicarbonyloxyethyl.
Polar monomers were made generally by the slow addition of a slight excess of an acid chloride in methylene chloride solution to a cooled solution of an alcohol in methylene chloride containing a stoichiometric amount (with respect to the acid chloride) of acid scavenger (generally pyridine or triethylamine). The mixture was allowed to warm to room temperature overnight, filtered and washed sequentially with water, sodium bicarbonate and brine. Removal of the solvent and vacuum distillation from phenothiazine provided the requisite monomer in 50-90% yield.
The polymer also comprises a monomer having a photogenerated acid cleavable ester group. This monomer provides acid-sensitive esters groups pendant on the polymer backbone. The preferred acid labile pendant groups are organic ester groups which undergo a cleavage reaction in the presence of a photogenerated acid. Prefe

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