High rate and highly selective SiO2 etching employing inductively coupled plasma and discussion on reaction kinetics

Abstract

High rate and highly selective SiO2/Si etching employing a C4F8+H2 mixture was achieved in the diffusive region of an inductively coupled plasma where electrons in its diffusive region were not so energetic. It was considered that hydrogen fluoride formed by hydrogen introduced to scavenge fluorine (F) radicals was not dissociated in the region and was exhausted outside. The carbon-rich film was deposited selectively on the Si surface, thereby providing high selectivity. The thick film, in particular, deposited selectively onto the bottom of holes below 1 μm and exposure of C4F8+30% H2 for as-etched holes at floating potential showed that polymer films conformed to the inner surfaces of holes. Hence, this selective deposition was ascribed to the accumulation of the resputtered polymer on the bottom films. Appearance mass spectroscopy measurements of fluorocarbon radicals for some discharge conditions showed that the CF1 radical played a major role in the polymer film deposition, while the CF2 radical might not contribute to the polymer deposition and a sticking probability of the CF1 radical was reduced considerably in the presence of hydrogen. A simulated etching experiment using a capillary plate mask made it clear that the carbon-rich polymer film was deposited on the Si bottom surface in the presence of hydrogen at a high CF1/CF2 radical density ratio. Accordingly, CF1 radicals whose surface loss is suppressed in the presence of hydrogen were likely to arrive at a deep bottom surface, forming a carbon-rich polymer by scavenging fluorine from CF1 radicals with hydrogen.