Block copolymer selectivity: A new dry etch approach for cylindrical applications

A critical challenge for directed self-assembly of block copolymers is the selectivity between the two polymer phases. Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is one of the most studied block-copolymers to reach sub-20 nm patterns. A very high PMMA/PS selectivity (>10:1) is required to conserve a sufficient PS pattern thickness allowing pattern transfer to sublayers. In this paper, the authors propose to develop a chemistry allowing a full PMMA removal without PS consumption. It is based on CO and CO-H2 cycles allowing to get a very high etch control. The proposed etch mechanisms have been understood thanks to x-ray photoelectron spectroscopy analyses performed on blanket wafers. Finally, this new etch process has been validated on the cylindrical PS-b-PMMA patterned structure.