New thermally crosslinkable electron beam resists: 2. Monomethyl itaconate-methyl methacrylate copolymers

The lithographic evaluation of monomethyl itaconate (MMI) and methyl methacrylate copolymers as thermally crosslinkable electron beam resists is described. Their properties were investigated as a function of copolymer composition and primary molar mass in order to determine an optimum formulation for the preparation of high resolution resist patterns. Line and space test patterns with features < 0.5 µm have been prepared using copolymers containing 10 mol% MMI with lithographic sensitivity of ~ 80 µC cm^-2 and resist contrast of ~4 cm₂ µC^-1 when developed in a mixture of n-butyl acetate and n-hexyl acetate. In accordance with previously published results, the electron exposure dose required to first destroy the pre-crosslinked fraction of the resist has been found to be very much less than the electron exposure dose required for the preparation of high resolution resist patterns. The results obtained in this work are compared to a theory of gel degradation originally developed to describe the solubilization of lignin from plant tissue, whereby the breakdown of the gel can be modelled using the statistics for random network formation, except applied in reverse. © 1992.