Reactive Ion Etching in SF 6 Gas Mixtures

Abstract

Reactive ion etching of crystalline silicon, polysilicon, , and has been studied in a parallel plate electrode configuration, with and without magnetic confinement, in gas diluted with varying proportions of , , , 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 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 , , and especially 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 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 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 selectivity obtained with quartz cathode is 18:1 for 100% at 0.1 Wcm−2 power density level with magnetic confinement. At higher power density levels, the selectivity has been found to decrease.