The etch rate of 4H-SiC in a SF6 helicon plasma has been investigated as a
function of pressure, rf power, bias voltage and distance between the subst
rate holder and the helicon source. Very high etch rates of 1.35 mum/min we
re achieved when this distance is minimum. Good uniformity on 2 in. SiC sub
strates and smooth etched surfaces free of micromasking have been obtained
when using a nickel mask. The selectivity SiC/Ni was found to be about 50 i
n high etch rate conditions. Via holes have been etched to a depth of 330 A
m in 4H-SiC substrates. Etch mechanisms were also studied in a parallel-pla
te capacitively coupled reactor, We have detected by laser-induced fluoresc
ence (LIF), the radicals SiF2, CF, and CF2 produced during the reactive ion
etching of SiC in a pure SF6 plasma. Spatially and temporally resolved LIF
measurements were used to distinguish between gas phase and etched surface
production of these species. Whereas CF and CF2 are primary etch products
(i.e., mainly produced at the etched surface), the SiF2 radicals are mainly
produced in the gas phase (probably by electron impact dissociation of SiF
4, the putative major etch product). We attribute this difference to the fo
rmation of a carbon-rich layer on the SiC substrate surface. The removal of
this layer, which is a rate-limiting step, produces unsaturated CFx (x = 1
,2,3) radicals. The CF2 radical represents up to 20% of the total carbon et
ch products under our conditions. (C) 2001 American Vacuum Society.