Chapter 4
Copolymer Approach to Design of Sensitive Deep-UV Resist Systems with High Thermal Stability and Dry Etch Resistance 1
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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 13, 2017 | http://pubs.acs.org Publication Date: October 31, 1989 | doi: 10.1021/bk-1989-0412.ch004
Hiroshi Ito , Mitsuru Ueda , and Mayumi Ebina 1
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IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099 Department of Polymer Chemistry, Yamagata University, Yonezawa, Yamagata 992, Japan 2
A sensitive deep UV resist was designed by copolymerizing α,α-dimethylbenzyl methacrylate with α-methylstyrene by radical initiation. The electron-rich α-methylstyrene lacks self-propagation and tends to undergo alternating copolymerization with electron-poor monomers such as methacrylates, especially at high feed ratios. Intramolecular anhydride formation that occurs upon heating of certain polymethacrylates and poly(methacrylic acid) is suppressed in such alternating copolymers. Thus, a high glass transition temperature of 210°C is observed for the 1:1 copolymer after deesterification. When mixed with an "onium salt" photochemical acid generator, the dimethylbenzyl ester moiety provides a high resist sensitivity and acid-catalyzed polarity changes. The methacrylate units incorporated in the polymer chain give excellent UV transmission, while the α-methylstyrene units provide good dry etch resistance and high thermal stability.
A s the trend toward the higher circuit density in microelectronic devices continues, there has been an increasing interest in lithographic technologies utilizing short wavelength radiations such as electron beam, X-ray, and deep U V (
