Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2001-04-03
2004-12-07
Kelly, Cynthia H. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S325000, C430S330000, C430S331000, C430S311000, C430S328000, C430S270100, C430S905000, C430S910000
Reexamination Certificate
active
06828083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new photoresists, particularly photoresists that can crosslink after a development step, typically through thermal treatment. Resists of the invention are particularly useful to provide thermal flow coverage of semiconductor contact holes.
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.
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 photo-initiators 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).
Microelectronic devices frequently have multiple metal interconnection or conductive layers that are each separated by interposed insulating (dielectric) layers. The multiple conductive layers are connected using contact hole or via holes through the dielectric layers. See, generally, S. Sze, VLSI Technology (2
nd
ed., New York, McGraw-Hill, 1988), for a discussion of semiconductor device fabrication techniques.
SUMMARY OF THE INVENTION
I have now found improved compositions and methods for the fabrication of microelectronic devices. In particular, compositions and methods of the invention provide for a controlled flow of resist into device contact (via) holes during a post-exposure, post-development hard-bake step.
Resists of the invention are positive-acting and contain one or more components that are preferably substantially stable (i.e. no substantial crosslinking) during: 1) soft-bake, pre-exposure thermal treatment to remove solvent carrier of the applied resist, and 2) post-exposure, pre-development thermal treatment to promote or enhance the acid-promoted reaction in exposed regions (typically a de-blocking reaction). However, resists of the invention will crosslink during a post-development more stringent thermal treatment (thermal flow hard-bake step). By such selective crosslinking, the thermal flow rate of the applied resist into the contact holes can be controlled to within a desired range.
I have found that the use of such a thermal flow hard-bake when processing a contact hole resist can enable obtaining smaller critical dimensions than possible without post-development hard-bake processing. The hard bake (e.g. at least about 120° C., more typically at least about 130° C. or 140° C., suitably from about 130° C. to about 140° C. to about 180° C. or about 190° C.) allows the resist to flow after development. However, in the absence of post-development crosslinking, the hard bake can produce too fast of a flow rate, which can limit resolution of formed features.
One preferred resist for use in accordance with the invention contains a photoactive component (typically a photoacid generator) and a resin with acetal and/or ketal moieties. The term “acetal” as used herein is inclusive of both acetal and ketal moieties, unless otherwise indicated. During a stringent post-development thermal flow hard-bake step, the resin can crosslink, typically by a transacetalation reaction. The hard-bake thermal treatment will cause flow of the resist as desired into a contact hole feature over which the resist has been applied, while the resist crosslinking will restrict the resist flow rate to a desired rate. At resist flow, the resist resin typically is above its Tg.
Suitable resist components that contain acetal groups that will react (crosslink) during a post-development hard-bake can be provided by a variety of routes. For instance, a vinyl ether (e.g. t-butyl vinyl ether) can be reacted with a hydroxy moiety such as phenolic —OH group to provide an acetal that will undergo reaction (particularly transacetalation) during a post-development hard-bake. Thus a polymer or copolymer containing phenolic units, such as a poly(vinylphenol) polymer or compolymer, can be reacted with a vinyl ether to provide the thermally reactive acetal moieties.
A variety of other resist systems can be employed in accordance with the invention provided one or more components of the resist can undergo crosslinking during a stringent hardbake step, but remain substantially stable (i.e. no substantial crosslinking) during prior thermal processing (i.e. pre-exposure soft bake and post-exposure, pre-development bake). For example, resists can employed that contain a resin that can contains ester groups (e.g. t-butyl ester groups) that can undergo crosslinking, such as by a transacetalation reaction.
Resists of the invention will typically contain separate components or functionalities that will be photoacid-labile and will be reactive upon exposure and any post-exposure, pre-development thermal treatment. Preferred photoacid-labile groups include acetal groups that are more reactive to photoacid-induced deblocking than the moieties that will crosslink during a post-development, hard-bake step. For instance, a resist resin can be employed that has both primary or second acetal groups and a tertiary acetal, or a primary acetal and a second or tertiary acetal. Without being bound by theory, the more branched acetal (i.e. secondary or tertiary) will more preferentially undergo transacetalization (crosslinking) at hard-bake temperatures, relative to a less substituted (i.e. primary or secondary) acetal, which less-substituted acetals will more preferentially de-block in the presence of photoacid after exposure and prior to development. See Scheme 1 below.
Resists of the invention also may contain a thermal acid generator, which is substantially stable to temperatures of a soft-bake step or a post-exposure, pre-development heat treatment, but can be activated to generate acid during more stringent temperatures of a post-development hard-bake step. The thermally generated acid then can promote crosslinking between resist component(s). However, in at least certain
Corless Peter F.
Edwards & Angell LLP
Frickey Darryl P.
Kelly Cynthia H.
Lee Sin J.
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