Abstract
Reactive ion etching of crystalline silicon, polysilicon, SiO2, and Si3N4 has been studied in a parallel plate electrode configuration, with and without magnetic confinement, in SF6 gas diluted with varying proportions of O2, N2, H2, and Ar. In order to investigate the contamination from the RF cathode, RIE studies were done with RF cathode covered with aluminum disk as well as with 0.5 cm thick circular quartz plate. The RF frequency used is 13.56 MHz and RF power density varied from 0.1 to 0.4 Wcm-2. Experimental results indicate the following: (i) significant contamination occurs on the etched surface with the aluminum covered cathode, but no detectable contamination occurs with the quartz plate covered cathode, (ii) there are etch rate maxima both for silicon and polysilicon with O2 dilution in the range 10–20 volume percent for aluminum covered cathode; these maxima are more pronounced at higher power levels, (iii) etch rates of silicon and polysilicon are much reduced with O2, N2, and especially H2 dilution in volume proportions >30% at all power levels and irrespective of cathode covers; argon dilution has the least effect on the etch rates; (iv) due to loading effect the etch rates of silicon and polysilicon are reduced significantly if the aluminum cover on the cathode is substituted by a quartz plate. Moreover, scanning electron microscopic studies of silicon and polysilicon etch profiles have shown that in SF6 gas mixtures, the RIE process is physical-chemical and not purely chemical. The degree of etch anisotropy has been found to vary from 0.5 to 0.3 depending upon argon dilution in SF6 and operating pressure. Magnetic confinement has been found to reduce anisotropy, and RF power density levels above 0.1 Wcm-2 have not been found to affect anisotropy. The highest Si:Si02 selectivity obtained with quartz cathode is 18:1 for 100% SF6 at 0.1 Wcm-2 power density level with magnetic confinement. At higher power density levels, the Si:SiO2 selectivity has been found to decrease. © 1987, The Electrochemical Society, Inc. All rights reserved.