Atomic layer etching in HBr/He/Ar/O2 plasmas

Atomic layer etching of Si is reported in a radio frequency (RF) pulsed-power inductively coupled (ICP) plasma, with periodic injections of HBr into a continuous He/Ar carrier gas flow, sometimes with trace added O2. Several pulsing schemes were investigated, with HBr injection simultaneous with or alternating with ICP power. The product removal step was induced by applying RF power to the substrate, in sync with ICP power. Etching and dosing were monitored with optical emission spectroscopy. Little or no chemically enhanced ion-assisted etching was observed unless there was some overlap between HBr in the chamber and ICP power. This indicates that HBr dissociative chemisorption deposits much less Br on Si, compared with that from Br created by dissociation of HBr in the ICP. Chemically assisted etching rates nearly saturate at 2.0 nm/cycle as a function of increasing HBr-containing ICP dose at −75 VDC substrate self-bias. The coupled effects of O2 addition and substrate self-bias DC voltage on the etching rate were also explored. Etching slowed or stopped with increasing O2 addition. As bias power was increased, more O2 could be added before etching stopped.