Comparison of laser and O 2 plasma etching of diamond-like carbon films

Abstract

Hard hydrogenated amorphous carbon (a-C:H) films with a mass density ranging from 1.7 to 2.4 g cm −3 were deposited on Si substrates from benzene in an r.f. glow discharge plasma. The etching of these films by an O 2 r.f. plasma and by 20 ns pulses of the KrF excimer laser was studied, and a correlation of etch rates with film properties was established. The etch rate in an O 2 plasma was found to depend on the hydrogen state in a network structure, the minimum of mass removal rate being achieved for films with the highest content of unbound hydrogen. Thermal effects dominate in the case of laser processing, the etch rate decreasing with increasing film density presumably because of the higher thermal diffusivity of denser films. Two laser-etching mechanisms were identified: the first which is based on carbon oxidation occurs at low laser fluences and provides etch rates of up to 50 Å pulse −1; the second is the direct ablation which starts at higher fluences E ⩾ 200–500 mJ cm −2 and results in etch rates above 100 nm pulse −1. Micron-sized patterns in a-C:H films were produced by laser-assisted chemical etching.