Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-10-08
2002-12-10
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
C430S905000, C430S910000
Reexamination Certificate
active
06492086
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new polymers that contain repeat units of phenol and photoacid-labile esters that contain a tertiary ester alicyclic hydrocarbon group. Polymers of the invention are particularly useful as a component of chemically-amplified positive-acting resists.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble.
In general, photoresist compositions comprise at least a resin binder component and a photoactive agent. Photoresist compositions are described in Deforest,
Photoresist Materials and Processes
, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau,
Semiconductor Lithography, Principles, Practices and Materials
, Plenum Press, New York, ch. 2 and 4, both incorporated herein by reference for their teaching of photoresist compositions and methods of making and using the same.
More recently, chemically-amplified-type resists have been increasingly employed, particularly for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain “blocking” groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is formed, e.g., carboxyl or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer. See also R. D. Allen et al.,
Proceedings of SPIE
, 2724:334-343 (1996); and P. Trefonas et al.
Proceedings of the
11
th
International Conference on Photopolymers
(
Soc. Of Plastics Engineers
), pp 44-58 (Oct. 6, 1997).
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of about 250 nm or less, or even about 200 nm or less, such as wavelengths of about 248 nm (provided by KrF laser) or 193 nm (provided by an ArF exposure tool). Use of such short exposure wavelengths can enable formation of smaller features. Accordingly, a photoresist that yields well-resolved images upon 248 nm or 193 nm exposure could enable formation of extremely small (e.g. sub-0.25 &mgr;m) features that respond to constant industry demands for smaller dimension circuit patterns, e.g. to provide greater circuit density and enhanced device performance.
However, many current photoresists are generally designed for imaging at relatively higher wavelengths, such as I-line (365 nm) and G-line (436 nm) exposures and are generally unsuitable for imaging at short wavelengths such 248 nm. In particular, prior resists exhibit poor resolution (if any image at all can be developed) upon exposure to these shorter wavelengths.
Additionally, many photoresists will not provide images of sufficient resolution required for many high performance applications. For instance, coating layers of current photoresists often have excessive loss of unexposed areas in developer solutions (known as “UFTL” or unexposed film thickness loss), thereby significantly compromising resolution of the developed resist image. For example, high UFTL, particularly in thin film resist applications, can result in low contrast images with rounded or angular profiles Many current photoresists also may exhibit relatively poor resistance to etchants employed after development, which also can dramatically compromise resolution of the feature transferred to the patterned substrate.
It thus would be desirable to have new photoresist compositions, particularly resist compositions that can be imaged at short wavelengths such as 248 nm. It would be particularly desirable to have such resist compositions that can provide high resolution relief images.
SUMMARY OF THE INVENTION
We have now found novel polymers and photoresist compositions that comprise the polymers as a resin binder component. Polymers of the invention contain repeat units of both 1) phenolic groups and 2) acid labile ester groups that contain a tertiary ester alicyclic hydrocarbon group that has a molecular volume of at least about 125 cubic angstroms (Å
3
), and preferably has two or more fused or bridged rings. Preferred tertiary ester groups include optionally substituted fencyl groups, particularly ethyl fencyl; optionally substituted alkyl adamantyl, particularly a methyladamantyl leaving group (where the ester oxygen is linked to the tertiary carbon of the methyladamantyl moiety); optionally substituted tricyclo decanyl; and optionally substituted pinanyl. The photoresist compositions of the invention can provide highly resolved relief images upon exposure to short wavelengths, including sub-300 nm and sub-250 nm wavelengths such as248 nm.
Moreover, we have surprisingly found that significantly enhanced lithographic performance and reduced UFTL can be provided by resists of the invention. See, for instance, the results of Example 11 which follows.
It also has been surprisingly found that polymers of the invention exhibit surprisingly enhanced contrast between exposed and unexposed regions of a resist coating layer, and significantly enhanced resolution, e.g. relative to a comparable phenolic/alkylester copolymer that does not contain alicyclic groups (e.g. a phenolic/t-butyl acrylate copolymer).
Without being bound by theory, it is believed that the relatively bulky alicyclic groups can effectively “shield” adjacent phenolic groups from interaction with and dissolution by aqueous alkaline developer. Hence, in unexposed coating layer regions, the resist has a relatively low dissolution in alkaline developer. However, in exposed regions, the alicyclic group is removed to provide a polar —COO
−
moiety, and the phenolic groups are “de-shielded”, to thereby together provide a relatively high dissolution rate in alkaline developer. Consequently, significant solubility differentials between exposed and unexposed resist areas can be realized.
Preferably, particularly to provide reduced UFTL, polymers of the invention will contain a major portion of phenolic units. More specifically, preferred polymers
Barclay George G.
Mao Zhibiao
Pandya Ashish
Teng Gary Ganghui
Yueh Wang
Chu John S.
Corless Peter F.
Edwards & Angell LLP
Frickey Darryl P.
Shipley Company L.L.C.
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