Effect of partial deprotection on lithographic properties of t-butoxycarbonyloxystyrene-containing polymers

摘要

Abstract: In chemically amplified resist polymers containing t-butoxycarbonyloxystyrene (TBS), a photogenerated acid catalytically removes the t-butoxycarbonyl (TBOC) protecting groups, yielding hydroxystyrene (HS) and thereby promoting aqueous base solubility of the exposed resist. Areas of concern in the lithographic use of positive tone resist polymers containing TBS include radiation sensitivity, substrate adhesion, optical density, and the loss of mass that accompanies TBOC deprotection. One approach to optimization of the lithographic performance of TBS-containing resists is to partially deprotect the matrix polymer prior to lithographic exposure. Partial deprotection yields a polymer comprised of a mixture of TBS and HS functionalities within the same chain. An easily controlled and reproducible process has been developed that causes partial conversion of TBS to HS in any TBS-containing polymer, prior to resist solution formulation. Lithographic tests of these materials were carried out using a deep UV exposure tool ($lambda@$EQ248 nm) and a nitrobenzyl sulfonate photoacid generator. Partial deprotection of these polymers, prior to use in lithography, is shown to substantially increase the resist sensitivity and reduce film shrinkage induced by post-exposure bake. The extent of deprotection has also been found to strongly affect the optical density at 248 nm of the sulfone-containing polymers, but to have minimal effect on the optical density of the sulfone-free polymer. !11