A Long-Term Reliability of Thermal Oxides Grown on n-Type 4H-SiC Wafer

A long-term reliability of thermal oxides grown on n-type 4H-SiC(0001) wafer by dry oxidation has been investigated. In order to examine the effects of SiC wafer quality on the reliability of thermal oxides, two types of 4H-SiC epitaxial wafers with different influences, which were surface roughness and metal impurity concentration, were used. A barrier height of oxide/4H-SiC interface derived from Fowler-Nordheim plot was about 2.8 eV on the both wafers. Time-zero dielectric breakdown measurement results showed that almost thermal oxides ruptured at the field-to-breakdown (Ebd) of 10 MV/cm, and maximum Ebd was 11 MV/cm regardless of the influences of SiC wafer. However, it was indicated that the charge-to-breakdown (Qbd) of thermal oxide depended on the influences by time-dependent dielectric breakdown measurements. The Qbd value of 63% cumulative failure for the thermal oxides grown on SiC wafer with low influences was 0.16 C/cm2, which was about one order higher than that for high one. These results show that two types of oxide breakdown regimes would exist under high field region that EBD is more than 10 MV/cm, resulting in the difference of Qbd between both wafers.