Polymers, resist compositions and patterning process

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

2003-04-04

2004-09-14

Thornton, Yvette C. (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

C430S907000, C430S322000, C430S330000, C526S242000

Reexamination Certificate

active

06790591

ABSTRACT:

This invention relates to polymers useful as the base resin in resist compositions suited for microfabrication. It also relates to resist compositions, especially 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, chemical amplification positive working resist materials which are catalyzed by acids generated upon light exposure 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 excimer laser (248 nm) brought about a significant innovation. Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.30 micron process, passed 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 0.10 micron rule or less, with the trend toward a finer pattern rule being accelerated.
For ArF excimer 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 polyvinylphenol 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
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. Since carbonyl groups and carbon-to-carbon double bonds have absorption in proximity to 157 nm as mentioned above, reducing the number of such units is considered to be one effective way for improving transmittance.
It was recently found that introducing fluorine atoms into base polymers makes a great contribution to an improvement in transmittance at 157 nm. It was reported, for example, in Proc. SPIE Vol. 4345 p273 (2001), “Polymer design for 157 nm chemically amplified resists” that in resist compositions comprising a copolymer of tert-butyl &agr;-trifluoromethylacrylate with 5-(2-hydroxy-2,2-bistrifluoromethyl)ethyl-2-norbornene and a copolymer of tert-butyl &agr;-trifluoromethylacrylate with 4-(hydroxy-bistrifluoromethyl)methylstyrene, the absorbance of the polymer at 157 nm is improved to about 3. However, these resins are still insufficient in transparency because it is believed that an absorbance of 2 or less is necessary to form a rectangular pattern at a film thickness of at least 2,000 Å through F
2
exposure.
In this regard, a highly transparent resin having an absorbance of up to 1 is described in Proc. SPIE Vol. 4690 p76 (2002), “Synthesis of novel fluoropolymers for 157 nm photoresists by cyclo-polymerization.” This polymer has not only high transparency, but also good substrate adherence. Since alcoholic groups are used as soluble groups, however, this resin has the drawback of a low dissolution rate in over-exposed areas where acid-eliminatable groups have been eliminated.
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
(157 nm), Kr
2
(146 nm), KrAr (134 nm) and Ar
2
(126 nm) laser beams, and useful as the base resin in a resist composition. Another object is to provide a resist composition, and especially a chemical amplification resist composition, comprising the polymer, and a patterning process using the same.
It has been found that by substituting carboxylate, in part, for alcoholic hydroxyl groups on the aforementioned highly transparent polymer, the dissolution rate in over-exposed areas of a polymer film can be improved while minimizing a lowering of transparency.
In a first aspect, the present invention provides a polymer comprising recurring units of the following general formulae (1a) and (1b) and having a weight average molecular weight of 1,000 to 500,000.
Herein R
1
is fluorine or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, R
2a
and R
2b
each are hydrogen or —R
3
—CO
2
R
4
, and at least one of R
2a
and R
1b
contains —R
3
—CO
2
R
4
, wherein R
3
is a straight, branched or cyclic alkylene or fluorinated alkylene group of 1 to 10 carbon atoms, and R
4
is hydrogen, an acid labile group, an adhesive group or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms.
In a second aspect, the present invention provides a resist composition comprising the polymer, and preferably a chemically amplified positive resist composition comprising (A) the polymer, (B) an organic solvent, (C) a photoacid generator, and optionally, (D) a basic compound and/or (E) a dissolution inhibitor.
In a third aspect, the present invention provides a process for forming a resist pattern comprising the steps of applying the resist composition onto a substrate to form a film; heat treating the film and then exposing it to high-energy radiation in a wavelength band of 100 to 180 nm or 1 to 30 nm through a photomask; and optionally heat treating the exposed film and developing it with a developer. The resist film on the substrate preferably has a thickness of at least 0.2 &mgr;m. The high-energy radiation is typically a F
2
or Ar
2
laser beam or soft x-ray.


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Toriumi, M. et al., “Fluoropolymer-based resists for a single-resist process of 157 nm lithography”, Nov./Dec. 2002, Journal of Vacuum Science Technology B 20(6), p. 2909-2912.*
Synthesis of Novel, Fluoropolymer for 157 nm Photoresists Kodama, Shun-ichi et al. SPIE 2002 vol. 4690 pp 76-83.*
Ito, Hiroshi et al. SPIE 2001 vol. 4345 pp. 273-284.

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