Chemical Amplification for the Design of Sensitive Electron-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 order to meet the requirement, we have proposed "chemical amplification." In chemically amplified resist systems, an initial radiochemical event induces a cascade of subsequent chemical transformations. We have chosen "acid" as catalytic species in conjunction with acid-labile polymer matrices. Triarylsulfonium salts are convenient radiochemical acid generators. In this paper are described acid-catalyzed deprotcction to change the polarity and therefore solubility of matrix polymers and acid-catalyzed depolymerization. The negative systems include poly(p-t-butoxycarbonyloxystyrene), poly(t-butyl p-vinylbenzoate), and an alternating copolymer of α,α-dimethylbenzyl methacrylate with α-methylstyrene, which provide swelling-free negative images upon development with anisole. Selective silylation of exposed areas of these resist systems allows negative-tone development with O2 reactive ion etching (RIE). The positive systems based on polyphthalaldehyde include a thermally developable O2 RIE barrier resist utilizing poly(4-trimethylsilylphthalaldehyde) for the bilayer lithography and use of polyphthalaldehyde as a polymeric dissolution inhibitor for a novolac resin.