Chemical amplification for the design of sensitive E-beam and X-ray resist systems

Abstract

Electron-beam and X-ray lithographic technologies are capable of resolving sub-half-micrometer features and thus could support future ULSI fabrication. However, the economical operation of these high resolution technologies in the production environments demands extremely high resist sensitivity. In this paper are described acid-catalyzed deprotection reactions to change the polarity and therefore the solubility of matrix polymers and acid-catalyzed depolymerization for the design of positive resist systems. The negative-working systems based on the polarity change include poly(p-t-butoxycarbonyloxystyrene) (PBOCST) poly(t-butylp-vinylbenzoate), and an alternating copolymer of α,α-dimethylbenzyl methacrylate (DMBZMA) with α-methylstyrene (MST), which provide swelling-free negative images upon development with anisole. Selective silylation of exposed areas of these resist systems allows negative-tone development with oxygen reactive ion etching (RIE). The positive-working systems based on acid-catalyzed depolymerization of polyphthalaldehyde (PPA) derivatives include self-and thermal developments, a thermally developable oxygen RIE barrier resist utilizing poly(4-trimethylsilylphthalaldehyde) (PSPA) for the bilayer lithography and the use of PPA as a dissolution inhibitor for a novolac resin.