Interface Trap Profiles in 4H- and 6H-SiC MOS Capacitors with Nitrogen- and Phosphorus-Doped Gate Oxides

Abstract

We report results on the interface trap density (D _it) of 4H- and 6H-SiC metal–oxide–semiconductor (MOS) capacitors with different interface chemistries. In addition to pure dry oxidation, we studied interfaces formed by annealing thermal oxides in NO or POCl₃. The D _it profiles, determined by the C–ψ _s method, show that, although the as-oxidized 4H-SiC/SiO₂ interface has a much higher D _it profile than 6H-SiC/SiO₂, after postoxidation annealing (POA), both polytypes maintain comparable D _it near the conduction band edge for the gate oxides incorporated with nitrogen or phosphorus. Unlike most conventional C–V- or G–ω-based methods, the C–ψ _s method is not limited by the maximum probe frequency, therefore taking into account the “fast traps” detected in previous work on 4H-SiC. The results indicate that such fast traps exist near the band edge of 6H-SiC also. For both polytypes, we show that the total interface trap density (N _it) integrated from the C–ψ _s method is several times that obtained from the high–low method. The results suggest that the detected fast traps have a detrimental effect on electron transport in metal–oxide–semiconductor field-effect transistor (MOSFET) channels.