Direct Monte-Carlo simulation of dry e-beam etching of resist

Abstract

Novel model of e-beam interaction with PMMA, based on Direct Monte-Carlo simulation algorithm, is presented. It takes into account valence bond structure in PMMA monomers and could be easily applied for the study of e-beam-induced PMMA at higher temperatures due to various PMMA degradation pathways. The model was verified by the simulation of changes in PMMA molecular weight distribution and comparison of simulated and experimental G(S) values for e-beam irradiation of PMMA. Simulation algorithm of dry e-beam etching of resist (DEBER) is provided, including simulation of most significant processes: e-beam-induced PMMA degradation above glass transition, PMMA chain depropagation with subsequent released monomer diffusion and structure profile melting due to low PMMA viscosity at higher temperatures. Only 70% of DEBER profile depth is expected to be caused by monomer evacuation from the specimen, while the remaining 30% are supposed to be a result of PMMA swelling. Simulation of DEBER profile obtained by PMMA exposure at 160 °C in series of parallel lines was carried out. PMMA chain scissions are suggested to originate from ionization events on C–С backbone atoms and hydrogen abstraction. PMMA zip length at 160 °C was determined from the comparison of simulated and experimental profiles and comprised 3400. Experimental DEBER profiles were reproduced basing on the assumption of gaussian profile nature.