Nitrogen incorporation and interface trap reduction in silicon dioxide/4H-silicon carbide

Silicon carbide is a wide band gap semiconductor whose properties make it an ideal material for high power applications. Silicon carbide thermally oxidizes to form SiO₂, which is used as a gate insulator in MOSFETs; however, MOSFETs produced from the 4H-SiC polytype exhibit much lower channel mobilities than expected. A large density of interface traps produced by carbon clusters and located near the conduction band has been proposed as the source of the poor mobility. The nitridation of the SiO₂/4H-SiC interface using NO and NH₃ has been shown to reduce this interface trap density and improve the channel mobility. In this work, the kinetics of nitrogen incorporation using NO and NH₃ are compared, and the relationship between nitrogen content and interface trap density are discussed.; The nitridation of SiO₂/4H-SiC in NO at temperatures from 1050–1175°C incorporates ∼1014 cm−2 of nitrogen at the interface. Oxygen formed during the thermal decomposition of NO oxidizes the substrate and removes carbon and nitrogen from the interface. When the nitridation and oxidation reactions reach equilibrium, the nitrogen content saturates independently of temperature. The nitridation of SiO ₂/4H-SiC in NH; at temperatures from 1050–1175°C incorporates ∼10 16 cm−2 uniformly throughout the oxide bulk. During nitridation, oxygen is removed from the oxide, and the stoichiometry of the film is changed significantly.; The nitridation of SiO₂/4H-SiC in NO reduces the interface trap density near the conduction band by a factor of 10, but the trap density remains high. The complete passivation of these particular traps occurs at a nitrogen content of ≈2.5 × 1014 cm−2 , regardless of the annealing conditions. The data are consistent with a model of the interface in which the traps near the conduction band are produced by large carbon clusters with a near-continuum of energy levels. The passivation of these traps with nitrogen then proceeds by the dissolution of these carbon clusters by the removal of passivated carbon atoms.