Plasma passivation of near-interface oxide traps and voltage stability in SiC MOS capacitors

Abstract

Near-interface oxide traps severely affect the voltage stability of silicon carbide metal-oxide-semiconductor devices. In this work, electron cyclotron resonance microwave nitrogen plasma and electron cyclotron resonance microwave nitrogen-hydrogen-mixed plasma were used to passivate near-interface oxide traps in silicon carbide metal-oxide-semiconductor capacitors. An improved low-temperature midgap voltage drift method was proposed to evaluate the voltage stability of silicon carbide metal-oxide-semiconductor capacitors. Results showed that the effect of passivating near-interface oxide traps and voltage stability could be improved by increasing the nitrogen passivation time. However, excessive nitrogen passivation created deep-level interface traps that degraded the interface quality, and a small amount of hydrogen could passivate the deep-level traps produced by the excess nitrogen. As a result, the samples subjected to the passivation process with the nitrogen-hydrogen-mixed plasma had a smaller flat-band voltage drift and more stable carbide metal-oxide-semiconductor capacitors than the samples subjected to nitrogen plasma. However, the excessive introduction of hydrogen also produced additional defects, consequently making the stability of the metal-oxide-semiconductor devices sensitive to the time of the passivation process by nitrogen-hydrogen-mixed plasma. Therefore, the suitable time of mixed plasma passivation is crucial to the improvement of the stability of devices.