Highly selective removal of poly(methyl methacrylate) from polystyrene-block-poly(methyl methacrylate) by CO/H2 plasma etching

Abstract

The directed self-assembly lithography process using polystyrene (PS)-block-poly(methyl methacrylate) (PMMA) requires selective removal of PMMA, which is called the development process. The development process using plasma etching (dry development) without surface roughness of the line/space pattern was investigated. First, the authors focused on the chemical compositions of PMMA and PS. Using CO plasma, highly selective etching of PMMA was achieved (PMMA/PS etch selectivity >20). It was found that the PS surface roughness induced by plasma treatment depended on the thickness of the deposition layer formed on the PS surface. To suppress the PS surface roughness because of plasma treatment, the authors controlled the thickness of the deposition layer by adding H2 gas to the CO plasma. Using CO/H2 plasma, highly selective PMMA/PS etching without surface roughness was achieved. Consequently, the authors successfully achieved dry development of random lamella patterns by application of the CO/H2 plasma process.