Polymers, resist compositions and patterning process

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

2001-09-07

2003-01-28

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, C430S907000, C430S910000, C526S242000, C526S319000

Reexamination Certificate

active

06511787

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. 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. Also, the change-over from i-line (365 nm) to shorter wavelength KrF laser (248 nm) brought about a significant innovation. 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.
For 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 10-0739, 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 which are used as the base resin for ArF 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) which is used as the base resin for KrF has a window for absorption in proximity to 160 nm, so the transmittance is somewhat improved, but far below the practical level.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel polymer having a high transmittance to vacuum ultraviolet radiation of up to 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 (126 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 polymer an acrylic resin comprising hexafluoroisopropanol units, a resist material featuring high transparency, substrate adhesion, alkali developability and acid-elimination capability is obtained.
In a first aspect, the invention provides a polymer comprising recurring units of at least one of the following general formulae (1a), (1b) and (1c).
Herein R is selected from the group consisting of hydrogen, an acid labile group, straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, acyl group, and acyl group having a fluorinated alkyl moiety, R
1
and R
2
each are a hydrogen or fluorine atom, R
3
is an acid labile group, R
4
is an adhesive group, and R
5
is a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms.
In a second aspect, the invention provides a resist composition comprising the polymer defined above.
Also provided is a chemically amplified, positive resist composition comprising (A) the polymer defined above, (B) an organic solvent, and (C) a photoacid generator. The resist composition may further include (D) a basic compound and/or (E) a dissolution inhibitor.
In a third 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 in a wavelength band of 110 to 180 nm or 1 to 30 nm through a photo mask; and optionally heat treating the exposed coating and developing it with a developer. Preferably, the high-energy radiation is an F
2
excimer laser beam, Ar
2
excimer laser beam or soft x-ray.
For improving the transmittance in proximity to 157 nm, reducing the number of carbonyl groups and/or carbon-to-carbon double bonds is contemplated to be one effective way. It was also found that introducing fluorine atoms into base polymers makes a great contribution to improved transmittance. In fact, poly(vinyl phenol) having fluorine introduced in its aromatic rings offers a transmittance nearly on a practically acceptable level. However, this base polymer was found to turn negative upon exposure to high-energy radiation as from an F
2
excimer laser, interfering with its use as a practical resist. In contrast, those polymers obtained by introducing fluorine into acrylic resins or polymers containing in their backbone an alicyclic compound originating from a norbornene derivative have been found to be suppressed in absorption and overcome the negative turning problem. Especially esters having hexafluoroisopropanol units introduced therein according to the present invention is improved in transmittance near 157 nm, substrate adhesion, and alkali developability as well as acid-elimination capability.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Polymer
According to the invention, the polymers or high molecular weight compounds are defined as comprising recurring units of at least one of the following general formulas (1a), (1b) and (1c).
Herein R is hydrogen, an acid labile group, straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, acyl group, or acyl group having a fluorinated alkyl moiety, R
1
and R
2
each are a hydrogen or fluorine atom, R
3
is an acid labile group, R
4
is an adhesive group, and R
5
is a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms.
In the recurring units of the above formulas, R is selected in order to control the dissolution rate of unexposed areas and the dissolution rate and swelling behavior of exposed areas, from among hydrogen, acid labile groups, straight, branched or cyclic alkyl or fluorinated alkyl groups of 1 to 20 carbon atoms, acyl groups, and acyl groups having a fluorinated alkyl moiety. One of these groups or a mixture of two or more of these groups may be selected as R.
The acid labile group represented by R may be any of the groups used as a blocking or protective group on phenols in prior art chemically amplified resist composition. Tertiary alkyloxycarbonyl and acetal groups are preferred. Exemplary tertiary alkyloxycarbonyl group include t-butoxycarbonyl and t-amyloxycarbonyl. Exemplary acetal groups include ethoxyethyl, ethoxypropyl, ethoxybutyl, ethoxyisobutyl, butoxyethyl, t-butoxyethyl, hexyloxyethyl, cyclohexyloxyethyl, benzyloxyethyl, benzyloxypropyl, phenethyloxyethyl, and phenethyloxypropyl. Also useful are the foregoing groups in which some or all hydrogen atoms in their alkyl moiety are substituted with fluorine atoms.
Examples of the straight, branched or cyclic C
1-20
alkyl groups represented by R and R
5
include methyl, ethyl, propyl, isopropyl, n-propyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, n-octyl, phenyl, tricyclo[5,2,1,0
2,6
]decylmethyl, tricyclo[5,2,1,0
2,6
]decanyl, adamantyl, norbornyl, methylnorbornyl and isobornyl.
The fluorinated alkyl groups correspond to the foregoing alkyl groups in which some or all of the hydrogen atoms are substituted with fluorine atoms. Illustrat

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