Polymers, resist compositions and patterning process

Details Polymers, resist compositions and patterning process Polymers, resist compositions and patterning process

2001-09-07

2003-12-09

Ashton, Rosemary (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

C430S326000, C526S346000, C526S341000, C526S242000

Reexamination Certificate

active

06660447

ABSTRACT:

This invention relates to polymers useful as the base resin in chemical amplification resist compositions suited for microfabrication. It also relates to chemical amplification resist compositions comprising the polymers, and a patterning process using the same.
BACKGROUND OF THE INVENTION
In the drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The rapid advance toward finer pattern rules is grounded on the development of a projection lens with an increased NA, a resist material with improved performance, and exposure light of a shorter wavelength. In particular, the change-over from i-line (365 nm) to shorter wavelength KrF laser (248 nm) brought about a significant innovation, promising a possibility of commercial manufacture of devices on 0.10 micron rule. To the demand for a resist material with a higher resolution and sensitivity, acid-catalyzed chemical amplification positive working resist materials are effective as disclosed in U.S. Pat. Nos. 4,491,628 and 5,310,619 (JP-B 2-27660 and JP-A 63-27829). They now become predominant resist materials especially adapted for deep UV lithography.
Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.3 micron process, went through the 0.25 micron rule, and currently entered the mass production phase on the 0.18 micron rule. Engineers have started investigation on the 0.15 micron rule, with the trend toward a finer pattern rule being accelerated. With a wavelength reduction from KrF to ArF laser (193 nm), it is expected to enable miniaturization of the design rule to 0.13 &mgr;m or less. Since conventionally used novolac resins and poly(vinyl phenol) resins have very strong absorption in proximity to 193 nm, they cannot be used as the base resin for resists. To ensure transparency and dry etching resistance, some engineers investigated acrylic and alicyclic (typically cycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198.
With respect to F
2
excimer laser (157 nm) which is expected to enable further miniaturization to 0.10 &mgr;m or less, more difficulty arises in insuring transparency because it was found that acrylic resins are not transmissive to light at all and those cycloolefin resins having carbonyl bonds have strong absorption. It was also found that poly(vinyl phenol) is somewhat improved in transmittance near 160 nm, but far below the practical level. It was found that reducing carbonyl and carbon-to-carbon double bonds is essential for insuring a transmittance.
Under the circumstances, there is a need for a resist composition which performs well upon exposure to radiation having a wavelength below 180 nm.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel polymer having a high transmittance to vacuum ultraviolet radiation below 300 nm, especially F
2
excimer laser beam (157 nm), Kr
2
excimer laser beam (146 nm), KrAr excimer laser beam (134 nm) and Ar
2
excimer laser beam (121 nm), and useful as the base resin in a chemical amplification resist composition. Another object is to provide a chemical amplification resist composition comprising the polymer, and a patterning process using the same.
It has been found that using as the base resin a polymer having fluorinated vinyl phenol units copolymerized with acrylonitrile units, a resist material featuring high transparency and etching resistance is obtained.
The invention is predicated on the finding below. Phenolic polymers exhibit superior etching resistance and alkali solubility to acrylic polymers. Among others, halogenated, especially fluorinated phenolic polymers have significant transmittance-improving effects, affording a practically acceptable transmittance. Polyacrylonitrile is relatively transparent to wavelengths in the F
2
region and has higher etching resistance than acrylic polymers. Then copolymerization of fluorinated hydroxystyrene with polyacrylonitrile can improve transparency without sacrificing etching resistance.
In one aspect, the invention provides a polymer comprising recurring units of the following general formula (1).
Herein R
1
, R
2
, R
3
and R
5
each are independently hydrogen, fluorine, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, R
4
is an acid labile group, letters a, b and c are numbers satisfying 0≦a<5, 0≦b<5, 0<a+b<5 and 0<c<5, and m and n are positive numbers.
In another aspect, the invention provides a resist composition comprising the polymer. In a preferred embodiment, the invention provides a chemically amplified, positive resist composition comprising (A) the polymer, (B) an organic solvent, and (C) a photoacid generator. In further preferred embodiments, the resist composition further includes (D) a basic compound and/or (E) a dissolution inhibitor.
In a further aspect, the invention provides a process for forming a resist pattern comprising the steps of applying the resist composition onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation having a wavelength of up to 300 nm or electron beam through a photo mask; and optionally heat treating the exposed coating and developing it with a developer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Polymer
According to the invention, the polymer or high molecular weight compound is defined as comprising recurring units of the following general formula (1).
Herein R
1
, R
2
, R
3
and R
5
each are independently hydrogen, fluorine, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms. R
4
is an acid labile group.
The straight, branched or cyclic alkyl groups represented by R
1
, R
2
, R
3
and R
5
are those of 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, and more preferably 1 to 10 carbon atoms, including methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-octyl. The fluorinated alkyl groups correspond to the foregoing alkyl groups in which some or all of the hydrogen atoms are replaced by fluorine atoms and include, for example, trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl, and 1,1,2,2,3,3,3-heptafluoropropyl.
The acid labile group represented by R
4
is selected from a variety of such groups, preferably from among the groups of the following formulas (2) and (3), tertiary alkyl groups with 4 to 40 carbon atoms of the following formula (4), trialkylsilyl groups whose alkyl groups each have 1 to 6 carbon atoms, and oxoalkyl groups of 4 to 20 carbon atoms.
In formula (2), R
6
is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms or a group of formula (4). Exemplary tertiary alkyl groups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and 2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl, triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and 5-methyl-5-oxooxoran-4-yl. Letter “a” is an integer of 0 to 6.
In formula (3), R
7
and R
8
are independently hydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl and n-octyl. R
9
is a monovalent hydrocarbon group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may have a hetero atom (e.g., oxygen atom), for example, straight, branched or cyclic alkyl groups, and such groups in which some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino or alkylamino groups. Illustrative examples of the substituted alkyl groups are given below.
A pair of R
7
and R
8
, a pair of R
7
and R
9
, or a pair of R
8
and

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