Substituted norbornene fluoroacrylate copolymers and use...

Details Substituted norbornene fluoroacrylate copolymers and use... Substituted norbornene fluoroacrylate copolymers and use...

2001-01-26

2003-04-15

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

C430S313000, C430S317000, C430S318000, C430S323000, C430S326000, C430S907000, C430S910000, C526S281000

Reexamination Certificate

active

06548219

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to the fields of polymer chemistry, lithography, and semiconductor fabrication. More specifically, the invention relates to novel alicyclic polymers, particularly substituted norbornene fluoroacrylate copolymers, which are useful in lithographic photoresist compositions, particularly chemical amplification photoresist compositions including ultraviolet, electron-beam, and x-ray photoresists.
BACKGROUND
There is a desire in the industry for higher circuit density in microelectronic devices 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. This has been accomplished over the past twenty years by reducing the wavelength of the imaging radiation from the visible (436 nm) down through the ultraviolet (365 mn) to the deep ultraviolet (DUV) at 248 nm. Development of commercial lithographic processes using ultra-deep ultraviolet radiation, particularly 193 nm, is now becoming of interest. See, for example, Allen et al. (1995), “Resolution and Etch Resistance of a Family of 193 nm Positive Resists,”
J. Photopolym. Sci. and Tech.
8(4):623-636, and Abe et al. (1995), “Study of ArF Resist Material in Terms of Transparency and Dry Etch Resistance,”
J. Photopolym. Sci. and Tech.
8(4):637-642. The resists proposed for use with 193 nm imaging radiation do not appear suitable for use with 157 nm radiation due to their poor transparency at the 157 nm wavelength.
Certain attempts have been made to develop 157 nm resists, for example using heavily fluorinated materials such as polytetrafluoroethylene (e.g., Teflon AF®; see Endert et al. (1999)
Proc. SPIE
-
Int. Soc. Opt. Eng,
3618:413-417) or hydridosilsesquioxanes (see U.S. Pat. No. 6,087,064 to Lin et al.). These materials do not, however, have the requisite reactivity or solubility characteristics. The challenge in developing chemically amplified resists for 157 nm lithography is in achieving suitable transparency in polymers that have acid-labile functionalities and developed with industry standard developers in either exposed or unexposed areas depending on whether the resist is positive or negative.
Polymers prepared from trifluoromethyl-substituted acrylates have been described. See, for example, Ito et al. (1981), “Methyl Alpha-Trifluoromethylacrylate, an E-Beam and UV Resist,”
IBM Technical Disclosure Bulletin
24(4):991, Ito et al. (1982)
Macromolecules
15:915-920 which describes preparation of poly(methyl&agr;-trifluoromethylacrylate) and poly(&agr;-trifluoromethylacrylonitrile) from their respective monomers, and Ito et al. (1987), “Anionic Polymerization of &agr;-(Trifluoromethyl)Acrylate,” in
Recent Advances in Anionic Polymerization
, T. E. Hogen-Esch and J. Smid, Eds. (Elsevier Science Publishing Co., Inc.), which describes an anionic polymerization method for preparing polymers of trifluoromethylacrylate. Willson et al.,
Polymer Engineering and Science
23(18):1000-1003, also discuss poly(methyl &agr;-trifluoromethylacrylate) and use thereof in a positive electron beam resist. However, none of these references discloses the utility of trifluoromethyl-substituted acrylate polymers in chemical amplification resists.
Alicyclic polymers have also attracted a great deal of attention for their potential utility in advanced microelectronics technologies. The interest stems from their low dielectric constants and low UV absorption. Polymers of alicyclic monomers such as norbornene are typically prepared by metal-mediated addition or ring-opening metathesis polymerization (ROMP), which suffers from the drawbacks of high cost and possible metal contamination. Alternatively, the electron-rich norbornene monomers can be radically copolymerized with electron-deficient maleic anhydride to produce alternating copolymers, which have been heavily evaluated as 193 nm (ArF excimer laser) resist polymers. The norbornene-maleic anhydride co- and terpolymers can be readily prepared and tend to offer high performance lithographic imaging. However, these polymers tend to exhibit relatively high absorption at 157 nm. Furthermore, the maleic anhydride unit is of low functionality and therefore limits functionalization of such copolymers to only the norbornene monomer unit. It has been difficult to identify electron-deficient monomers that undergo radical copolymerization with norbornene derivatives. Such monomers have now been identified, and this invention now provides novel polymers that are synthesized by radical copolymerization of substituted norbornene derivatives—e.g., hexafluoroisopropanol-substituted norbornene—with comonomers such as &agr;-trifluoromethylacrylic acid and derivatives thereof. The polymers provide a versatile foundation for designing chemical amplification resist systems, particularly deep UV resist systems (e.g., 157 nm, 193 nm and 248 nm resists) that combine high UV transparency, aqueous base development, good dry etch resistance, and chemical amplification imaging capability.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the invention to address the above-described need in the art by providing novel substituted norbornene fluoroacrylate copolymers suitable for use in lithographic photoresist compositions.
It is another object of the invention to provide a lithographic photoresist composition containing a substituted norbornene fluoroacrylate copolymer.
It is still another object of the invention to provide such a composition wherein the substituted norbornene fluoroacrylate copolymer is transparent to deep ultraviolet radiation, i.e., radiation having a wavelength less than about 250 nm.
It is yet another object of the invention to provide such a composition wherein the substituted norbornene fluoroacrylate copolymer is a copolymer of a norbornene monomer substituted with a fluorine-containing moiety and a fluorinated methacrylic acid, a fluorinated methacrylonitrile or a fluorinated methacrylate.
It is still another object of the invention to provide a method for generating a resist image on a substrate using a photoresist composition as described herein.
It is a further object of the invention to provide a method for forming a patterned structure on a substrate by transferring the aforementioned resist image to the underlying substrate material, e.g., by etching.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect, then, the present invention relates to a substituted norbornene fluoroacrylate copolymer prepared by copolymerization of a first monomer having the structure
wherein m is zero or 1, r is zero or 1, L is a linking group, R
1
is linear or branched fluoroalkyl, R
2
is linear or branched alkyl or fluoroalkyl, and R
3
is hydrogen, alkyl (preferably lower alkyl), —C(O)R, —CH
2
—C(O)OR, C(O)OR, or SiR
3
wherein R is alkyl, preferably lower alkyl, and at least one additional monomer having the structure (II)
wherein R
4
is —COOH, —CN, an amide, an acid-inert ester, or an acid-cleavable functionality. The polymer may serve as either the base-soluble component of an unexposed resist or as an acid-labile material that releases acid following irradiation.
In another aspect, the invention relates to a lithographic photoresist composition comprising a substituted norbornene fluoroacrylate copolymer as described above and a photosensitive acid generator (also referred to herein as a “photoacid generator,” a “PAG,” or a “radiation-sensitive acid generator”).
The present invention also relates to the use of the resist composition in a lithography method. The process involves the steps of (a) coating a substrate (e.g., a ceramic, metal or semiconductor substrate) with a film comprising a radiation-sensitive acid generator and a copolymer as provided herein; (b) exposing the fi

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