Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2001-12-27
2004-08-10
Ashton, Rosemary (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S325000, C430S905000, C430S910000, C430S272100, C430S313000, C430S318000, C430S311000
Reexamination Certificate
active
06773872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the reduction of inorganic contaminants in polymers and the use of such polymers as a resin component for photoresist compositions, particularly chemically-amplified positive-acting resists. More particularly, the invention provides methods for reducing such contaminants in polymerization initiators.
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.
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 as 248 nm and 193 nm. In particular, prior resists exhibit poor resolution (if any image at all can be developed) upon exposure to these shorter wavelengths. Among other things, current photoresists can be highly opaque to extremely short exposure wavelengths such as 248 nm and 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, which in turn can dramatically compromise image resolution.
It thus would be desirable to have new photoresist compositions, particularly resist compositions that can be imaged at short wavelengths such as 248 nm and sub−200 nm wavelengths such as 193 nm. It would be particularly desirable to have such resist compositions that can provide high resolution relief images, particularly small features such as sub−0.25 &mgr;m images.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides novel methods for reducing inorganic contaminants in polymerization initiators, particularly free radical polymerization initiators, especially azo type initiators. Such initiators are commonly used as free radical sources in various polymerization procedures. However, we have found that commercial sources of azo type initiators all contain high levels of ionic metal contaminants, e.g., up to several tens of parts per million (ppm), particularly sodium (Na), iron (Fe), and calcium (Ca).
Depending on the quantity of initiator required for the polymerization reaction, we have found that these high levels of contaminants make it nearly impossible to achieve low metals levels, e.g., preferably less than about 20 ppb, in the finished polymer solution, even with further processing to remove the contamination. This is particularly true for sodium, which often is present in the highest concentration of the contaminant metals.
We have found that inorganic contaminants, such as sodium and other ionic metal contaminants, may be significantly reduced or eliminated from initiators prior to their use as free radical sources in polymerization procedures. Thus, using methods of the invention, low metals levels are achieved in the finished polymer. Consequently, inorganic contaminants in the resist resin component also are significantly reduced or eliminated, resulting in enhanced lithographic performance.
In addition, the use of polymerization initiators in accordance with the present invention, e.g., initiators which have reduced or even undetectable metals levels, provides a significant economic improvement in polymer manufacturing operations. For example, using initiators of the invention, cycle-time may be reduced by as much as about 60% to 90%, more preferably by as much as about 80% to 90%. Likewise, using initiators of the invention, available capacity may be increased by as much as about 200% to 400%, more preferably by as much as about 300% to 400%. Moreover, using polymerization initiators having such reduced or undetectable metals levels, the desired polymer can be made in a one-step procedure without requiring further processing time or equipment.
In contrast, using conventional methods which employ an unpurified polymerization initiator, the polymer typically must be purified using several intermediary steps. In that way, such methods require additional processing time and significant processing equipment capacity. This, in turn, limits the polymer production throughput. Furthermore, depending on the molecular weight of the polymer, we found the alternative conventional polymer purification processes to be quite tedious and at times impractical or even impossible to carry out with success.
We have found a variety of suitable methods for removal of such contaminants from free radical initiators. A pref
Coley Suzanne
Gronbeck Dana A.
Pandya Ashish
Truong Chi Q.
Ashton Rosemary
Corless Peter F.
Edwards & Angell LLP
Frickey Darryl P.
Lee Sin J.
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