Improvement of plasma etching durability of positive working resist by copolymerization, blending, and crosslinking

The plasma etching durability of O2 and CCl4 was investigated for copolymer and polymer blend of poly(methyl methacrylate) (PMMA) and poly(α‐methylstyrene) (PMSt) as a function of MSt content. Further, the effects of crosslinking on plasma etching were studied by incorporating N‐methylolated methacrylamide into the copolymer as a crosslinkable site during prebaking. The plasma‐etching resistance of PMMA was largely improved by incorporating or adding only a small amount of MSt. Especially in the case of the CCl4 plasma etching, the copolymer and the polymer blend with 10 mol% of MSt showed etching resistance as great as that of PMSt homopolymer. Stabilization of the polymers against the plasma etching can be explained by the sponge effect, the energy migration followed by the quenching by the phenyl ring. The polymer blend offered similar etching resistance as the copolymer, indicating an effective occurrence of the energy migration between the polymer chains. Etching resistance was also improved by crosslinking, also due to the enhancement of the sponge effect.