Highly selective Si3N4 etching on Si using pulsed-microwave CH3F/O2/Ar plasma

Abstract

Abstract Highly selective Si3N4 etching on Si was achieved in a CH3F/O2/Ar plasma using pulsed-microwave plasma and time-modulation bias. The Si3N4/Si selectivity reached infinity at a peak-to-peak voltage (V pp) of 240 V. The effect of pulsed-microwave on CH3F gas dissociation for highly selective Si3N4 etching was investigated by deposited film analysis, optical emission spectroscopy, and ion current flux measurements. As the duty cycle of the pulsed-microwave was decreased, the plasma density during the pulse on period decreased and the CH/H ratio increased. The pulsed-microwave plasma produced low-dissociation radicals by providing a low plasma density. The low-dissociation radicals in the CH3F plasma formed a fluorine (F)-rich hydrofluorocarbon (HFC) layer on the Si3N4 wafer surface. The F-rich HFC layer promotes Si3N4 etching even at low ion energy, where Si etching does not proceed, and enables highly selective Si3N4 etching on Si.