Deep etching of silicon carbide for micromachining applications: Etch rates and etch mechanisms

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 substrate holder and the helicon source. Very high etch rates of 1.35 mum/min were achieved when this distance is minimum. Good uniformity on 2 in. SiC substrates 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 in high etch rate conditions. Via holes have been etched to a depth of 330 Am in 4H-SiC substrates. Etch mechanisms were also studied in a parallel-plate capacitively coupled reactor, We have detected by laser-induced fluorescence (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 SiF4, the putative major etch product). We attribute this difference to the formation 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 etch products under our conditions. (C) 2001 American Vacuum Society.