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
1999-10-07
2004-02-17
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
C430S910000, C526S270000, C526S281000, C526S282000
Reexamination Certificate
active
06692888
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new polymers and use of such polymers as a resin binder component for photoresist compositions, particularly chemically-amplified positive-acting resists that can be effectively imaged at short wavelengths such as sub-200 nm, particularly 193 nm. Polymers of the invention contain in specified molar ratios both nitrile and photoacid labile groups that have an alicyclic moiety, particularly a bridged bicyclic group or other caged group.
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. 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.
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 11th 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). See European Published Application EP915382A2. 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 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 G-line (436 nm) and I-line (365 nm) are generally unsuitable for imaging at short wavelengths such as sub-200 nm. Even shorter wavelength resists, such as those effective at 248 nm exposures, also are generally unsuitable for sub-200 nm exposures, such as 193 nm imaging.
More specifically, current photoresists can be highly opaque to extremely short exposure wavelengths such as 193 nm, thereby resulting in poorly resolved images.
Efforts to enhance transparency for short wavelength exposure can negatively impact other important performance properties such as substrate adhesion and resistance to etchants employed after development, which in turn can dramatically compromise image resolution. In particular, reducing aromatic (e.g. phenyl or substituted phenyl such as phenol) content of a resist to thereby increase transparency at sub-200 nm exposures can provide a resist that exhibits quite poor resistance to plasma etchants used to process substrate surfaces bared upon development.
It thus would be desirable to have new photoresist compositions, particularly resist compositions that can be imaged at short wavelengths such as sub-200 nm exposure wavelengths, particularly 193 nm. It would be particularly desirable to have such resist compositions that exhibit good transparency to sub-200 nm wavelengths, particularly 193 nm, as well as good resistance to plasma etchants.
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 nitrile groups and acid labile ester groups with an alicyclic moiety leaving group. The photoresist compositions of the invention can provide highly resolved relief images upon exposure to extremely short wavelengths, particularly sub-200 nm wavelengths such as 193 nm.
More particularly, polymers of the invention contain at least two distinct repeat units: 1) nitrile groups, such as may be provided upon polymerization of methacrylonitrile or acrylonitrile; and 2) photoacid labile groups that contain a tertiary ester alicyclic hydrocarbon group that 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. Additional alicyclic ester groups also will be suitable, including additional bicyclic, tricyclic and other polycyclic moieties.
Moreover, we have surprisingly found that significantly enhanced lithographic performance and plasma etch resistance can be provided where the molar ratios of those units 1) and 2) are within specified values, i.e. where the polymer contains from about 20 to 50 mole percent of nitrile units 1), and from about 30 to 60 mole percent of alicyclic units 2).
Additionally, we have found that use of a photoacid labile ester group that contains a fencyl group, particularly ethylfencyl, provides a resist system that can be deprotected at relatively lower temperatures (lower activation energy required). More particularly, it has been found that resists of the invention that contain a polymer having nitrile units and photoacid labile ester units having ethylfencyl leaving groups can provide high resolution relief images (e.g. sub-quarter micron) with post-exposure bakes (ca. 60 seconds duration) of no more than 110° C., or even no more than about 100° C. or 90° C.
Polymers of
Barclay George G.
Kavanagh Robert J.
Mao Zhibiao
Alexander John B.
Chu John S.
Corless Peter F.
Edwards & Angell LLP
Shipley Company L.L.C.
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