ACID-CATALYZED DEPROTECTION MECHANISM OF TERT-BUTYLOXYCARBONYLOXY POLYMERS IN CHEMICALLY AMPLIFIED RESISTS

A mechanism of acid-catalyzed deprotection of poly(4-tert-butyloxycarb onyloxy-styrene), PBOCST, in chemically amplified resists has been elu cidated in terms of elementary processes by means of semiempirical mol ecular orbital calculations. It is concluded that the overall deprotec tion of tert-butyloxycarbonyl (t-BOC) group proceeds stepwise; i.e., ( a) the first products are an acid carbonate and a tert-butyl cation; ( b) a phenolic compound is the secondary and final product from the aci d carbonate, which is realized by assistance with a counter anion acco mpanied by acid; (c) the counter anion also assists acid regeneration from the tert-butyl cation to produce isobutylene. The yield rate of t he phenol is proportional to the product of concentrations of the poly mer, the catalytic acid, and the counter anion. The activation energy (21 kcal/mol) calculated for the rate-determining step (a) is in good agreement with an experiment. (C) 1998 John Wiley & Sons, Inc.