Chapter 2
The Annealing Concept for Environmental Stabilization of Chemical Amplification Resists
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Hiroshi Ito, Greg Breyta, Donald C. Hofer, and R. Sooriyakumaran IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099
The postexposure bake delay problem of chemical amplification resists, which manifests itself as a line width change and/or T-top/skin formation, is primarily caused by surface contamination by airborne basic substances. This paper describes our annealing concept to solve this serious problem, which is based on reduction of the resistfilmfree volume by carrying out postapply bake above its glass transition temperature. As the diffusivity of small molecules is an exponential function of the free volume, this approach dramtically reduces contaminant absorption and provides excellent environmental stabilization. Use of meta-isomer resins to lower glass trnsition temperatures for better annealing is describedfirstto prove the validity of our annealing concept. In addition, a new positive resist named ESCAP is proposed, which is processed at unconventionally high temperatures to achieve good annealing and contamination resistance. The chemical amplification concept proposed in 1982 (7,2) has become the predominant foundation for the design of advanced resist systems for lithographic imaging as the minimum feature size of semiconductor devices shrinks to
