Polystyrene-block-poly(methyl methacrylate), (PS-b-PMMA) diblock copolymer is a promising lithography alternative for nanometer scale features. The two components segregate into nanoscale domains when the polymer solution is spun on to form a thin film and annealed above the glass transition temperatures of both components. Preferential removal of PMMA domains through plasma etching to leave behind a PS mask for subsequent etching of underlying layers is the focus of this work. The quality of the PS mask is characterized by the thickness and lateral dimension of the PS structures after removal of the PMMA, as well as the smoothness of their surfaces. The effects of different plasma chemistries including O-2, Ar/O-2, Ar, CF4, and CHF3/O-2 on etch selectivity and surface/sidewall roughness for PS and PMMA have been characterized. Ar/O-2 produced the overall best results for the range of conditions studied. (C) 2008 American Vacuum Society.