Phosphorous passivation of the SiO2/4H–SiC interface

We describe experimental and theoretical studies to determine the effects of phosphorous as a passivating agent for the SiO2/4H–SiC interface. Annealing in a P2O5 ambient converts the SiO2 layer to PSG (phosphosilicate glass) which is known to be a polar material. Higher mobility (approximately twice the value of 30–40 cm2/V s obtained using nitrogen introduced with an anneal in nitric oxide) and lower threshold voltage are compatible with a lower interface defect density. Trap density, current–voltage and bias-temperature stress (BTS) measurements for MOS capacitors are also discussed. The BTS measurements point to the possibility of an unstable MOSFET threshold voltage caused by PSG polarization charge at the O–S interface. Theoretical considerations suggest that threefold carbon atoms at the interface can be passivated by phosphorous which leads to a lower interface trap density and a higher effective mobility for electrons in the channel. The roles of phosphorous in the passivation of correlated carbon dangling bonds, for SiC counter-doping, for interface band-tail state suppression, for Na-like impurity band formation and for substrate trap passivation are also discussed briefly.

► Phosphorous instead of nitrogen for the passivation of SiO2/4H–SiC interface.
► Results for mobility and trap density.
► Oxide stability.