Polymers, resist compositions and patterning process

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

2002-02-08

2004-03-23

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S242000, C526S281000, C526S282000, C526S284000, C526S317100, C526S328500, C430S270100

Reexamination Certificate

active

06710148

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, 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 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
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 (121 nm), and useful as the base resin in a resist composition. Another object is to provide a resist composition comprising the polymer, and a patterning process using the same.
It has been found that using as the base polymer a copolymer of an acrylate monomer containing fluorine at &agr;-position with a norbornene derivative, a chemically amplified resist composition having a drastically improved transparency and dry etching resistance is obtained.
In a first aspect, the invention provides a polymer comprising recurring units of the following formulae (1a) and (1c) or formulae (1a), (1b) and (1c).
Herein R
1
, R
2
, R
5
to R
7
each are hydrogen, a fluorine atom, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R
3
is a fluorine atom or a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; R
4
and R
8
each are an acid labile group, an adhesive group, hydrogen, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R
9a
, R
9b
, R
10a
and R
10b
each are hydrogen, hydroxyl, a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, (CH
2
)
e
CO
2
R
11
or (CH
2
)
e
C(R
12
)
2
(OR
11
); R
11
is an acid labile group, an adhesive group, hydrogen, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R
12
is a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; letters a to e are 0<a<1, 0≦b<1, 0<c<1, 0<a+b+c≦1, d=0 or 1, and 0≦e≦6.
In formula (1a), R
3
is preferably a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms, and most preferably a trifluoromethyl group.
In another aspect, the invention provides a resist composition comprising the polymer defined above, and more particularly, a chemically amplified, positive resist composition comprising (A) the polymer defined above, (B) an organic solvent, (C) a photoacid generator, and optionally, (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 defined above onto a substrate to form a coating; heat treating the coating and then exposing it to high-energy radiation in a wavelength band of 100 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. The high-energy radiation is typically 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 to be 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.
Heretofore, no copolymers of norbornene derivatives with acrylates have been available. Quite unexpectedly, the inventor has found that an acrylate monomer containing fluorine at &agr;-position as shown by formula (1a) can be copolymerized with a norbornene derivative and that copolymers of an acrylate monomer containing fluorinated alkyl at &agr;-position with a norbornene derivative, specifically polymers comprising recurring units of formulae (1a) and (1c) or formulae (1a), (1b) and (1c) are highly transparent to radiation near 157 nm and fully resistant to dry etching.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Polymer
According to the invention, the polymers or high molecular weight compounds are defined as comprising recurring units of the following general formulae (1a) and (1c) or formulae (1a), (1b) and (1c).
Herein R
1
, R
2
, R
5
to R
7
each are hydrogen, a fluorine atom, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R
3
is a fluorine atom or a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; R
4
and R
8
each are an acid labile group, an adhesive group, hydrogen, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R
9a
, R
9b
, R
10a
and R
10b
each are hydrogen, hydroxyl, a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms, (CH
2
)
e
CO
2
R
11
or (CH
2
)
e
C(R
12
)
2
(OR
11
); R
11
is an acid labile group, an adhesive group, hydrogen, or a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms; R
12
is a straight, branched or cyclic fluorinated alkyl group of 1 to 20 carbon atoms; letters a to e are 0<a<1, 0≦b<1, 0<c<1, 0<a+b+c≦1, d=0 or 1, and 0≦e≦6

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