Interface state densities near the conduction band edge in N-type 4H- and 6H-SiC

We report the effect on SiO/sub 2//SiC interface state density and effective oxide charge of different Si:C ratios (0.12 to 0.55) used during the growth of n-4H and n-6H-SiC epitaxial layers. We also report the effects of post-growth re-oxidation anneals and post- metalization anneals on the interface state density for both n- and p-4H-SiC. The interface trap density near the conduction band and the effective oxide charge increase with increasing Si:C ratio for both polytypes; however, the n-4H polytype is found to have an order of magnitude higher interface trap density near the conduction band compared to n-6H-SiC. The effective oxide charge is also higher for n-4H polytype. The distribution of interface states for 4H-SiC (measured using n- and p-type material) is asymmetric, with a higher trap density near the conduction band. Post-growth re-oxidation in wet O/sub 2/ at 950/spl deg/C increases the interface trap density near the conduction for n-4H-SiC. Post-metalization annealing at 450/spl deg/C in Ar for an Al gate metal results in a reduction of the effective oxide charge from 9.5/spl times/10/sup 11/ cm/sup -2/ to 3.5/spl times/10/sup 11/ cm/sup -2/. The effective oxide charge for n-4H samples with Mo gates decreases with increasing post metalization annealing temperature. Interface state densities are not affected by the post-metalization anneals in Ar.