Lithographic tone reversal in optical exposure of polymethyl methacrylate (PMMA) resist

Tone reversal in electron beam lithography when using polymethyl methacrylate (PMMA) as a resist is well known. At low electron beam dose, chain scissioning—resulting in positive tone lithography, is observed in PMMA. However, above a certain threshold dose, electron beam exposure results in cross-linking of PMMA, enabling negative tone resist action. We describe a similar phenomenon in PMMA (containing Irgacure 379—a free radical...