THE FORMATION OF ACID DIFFUSION WELLS IN ACID-CATALYZED PHOTORESISTS

This paper describes the use of two step post-exposure-bakes for impro ving the lithographic performance of the chemically amplified resist, UVIIHS(TM) from the Shipley Company. With this process, postexposure-b aking at a low temperature allows the deprotection reaction to go to c ompletion, with minimal acid diffusion into unexposed portions of the resist; and the high temperature PEB makes it possible to average out the standing waves. This study examines various two step post-exposure -bakes and provides evidence for the existence of the formation of a d iffusion well. For 250nm nominal features, conventional single bake pr ocesses yield +40nm for the isolated to grouped line bias and in exces s of -20nm for the isofocal region bias. Using a double PEB, processes were found that reduced both the isolated line to grouped line bias a nd the isofocal region bias to 0nm. Finally the kinetics of the double PEB process is studied using FTIR.