Density of interface states, electron traps, and hole traps as a function of the nitrogen density in SiO2 on SiC

Abstract

Nitridation of the SiO2/SiC interface yields a reduction in interface state density, immunity to electron injection, as well as increased hole trapping. It is shown that the accumulation of nitrogen at the oxide/semiconductor interface is solely responsible for these three effects. The evolution of the density of interface states, electron traps, and hole traps is measured in metal-oxide-semiconductor capacitors as a function of the nitrogen content which is varied by adjusting the gate oxide NO annealing time. A rate equation is derived to model the change in the interface state density, observed at various energy levels, in terms of nitrogen binding cross-sections. While the generation of acceptor interface states upon electron injection is suppressed after minimum N incorporation, the density of oxide hole traps appears to scale linearly with the amount of nitrogen. The origin and the properties of the N-induced hole traps resembles those of the defects responsible for enhanced negative bias temperature instability observed in nitrided silicon devices. It is proposed that the binding of nitrogen is not exclusively driven by the passivation of defects at the semiconductor surface but also results in the formation of a silicon oxynitride layer redefining the interface.