Dependence of polymer surface roughening rate on deposited energy density during plasma processing

The roughening behavior of three basic photoresist polymers (aromatic, adamantyl, adamantyl + lactone) was examined for fluorocarbon/argon plasma etch conditions. The roughening rate, defined as surface roughness introduced per depth of material etched, scales linearly with energy density deposited by the ions at the surface during processing, regardless of plasma process details. The Roughening rate after etch is uniquely determined by polymer structure and energy density. Adamantyl groups cause higher roughening rate. Addition of lactone groups increases removal rates, but leaves the roughening rate at a given energy density unaffected. We also show that sidewall roughness of etched nanostructures directly correlates to surface roughening.