Impact of boron diffusion on oxynitrided gate oxides in 4H-SiC metal-oxide-semiconductor field-effect transistors

An alternative gate oxide configuration is proposed to enhance the SiO₂/SiC interface quality, enabling high mobility 4H-SiC lateral metal-oxide-semiconductor field-effect transistors (MOSFETs). The gate oxide is prepared by the combination of rapid thermal oxidation in N₂O ambient, boron diffusion into SiO₂, and plasma enhanced chemical vapor deposition of tetraethyl orthosilicate oxide. Capacitance-voltage (C-V) and conductance-voltage (G-V) measurements on fabricated capacitors reveal a reduction of both interface trap and near interface oxide trap densities. The fabrication of MOSFETs with very high field-effect mobility (μ_fe) values, up to 160 cm²/V s, is enabled. Several channel orientations, with respect to the wafer flat {11$2¯$0}, have been studied to check μ_fe values and isotropy. Higher μ_fe values are obtained for a channel orientation of 90°. Boron distribution is studied by secondary ion mass spectrometry (SIMS) and time of flight SIMS. We propose that the combination of boron and nitrogen induces changes in the structure of the gate oxide which are positive in terms of the SiO₂/SiC interface quality.