Highly selective dry etching of polystyrene-poly(methyl methacrylate) block copolymer by gas pulsing carbon monoxide-based plasmas

We propose a very selective PMMA removal method from poly(styrene-block-methyl methacrylate) (PS-b-PMMA) copolymer using gas pulsing cyclic etching. Flow ratio of hydrogen (H₂) added to carbon monoxide (CO) plasma was periodically changed to control etch and deposition processes on PS. By controlling the process time of each etch and deposition step, full PMMA removal including etching of the neutral layer was demonstrated at 28 nm pitch, while PS thickness remained intact. This is more than 10 times higher etch selectivity than conventional continuous plasma etch processes using standard oxygen (O₂), CO–H₂ and CO–O_2-based chemistries. (paper)