A thin carbonaceous resist was grown by exposing a substrate to a beam of neutral metastable argon atoms in the presence of siloxane vapor. X-ray photoelectron spectroscopy and Auger electron spectroscopy data show that the resist was composed primarily of carbon. Near edge x-ray absorption fine structure spectra of samples exposed to metastable atoms show that carbon double bonds were formed during exposure. The deposited material was used as a resist for reactive ion etching into SiO2 and Si3N4 Lines in SiO2 were fabricated with widths as small as 20 nm, aspect ratios >2:1, and sidewalls as steep as 7:1.