Free carrier density enhancement of 4H-SiC Si-face MOSFET by Ba diffusion process and NO passivation

Abstract

Field effect mobility was improved in a 4H-SiC (0001) metal-oxide-semiconductor field-effect transistor with Ba diffusion into the gate oxide and NO passivation. The Ba diffusion process caused Ba interface passivation, which suppressed oxide surface roughening. Free carrier mobility and free carrier density were evaluated through Hall effect measurements using the Van der Pauw technique at room temperature. Passivation by Ba or NO was found to have no effect on free carrier mobility but contributed to increased free carrier density. A free carrier ratio of up to 70% was achieved through combined Ba diffusion and NO passivation.

Outlook for Dielectric/SiC Interfaces for Future Generation MOSFETs

“…It was observed by high-low C-V that the density of interface traps (DIT) was reduced by the Ba passivation, and the temperature dependence of the µFE showed minimal coulomb scattering effects. A recent report has shown that the free carrier density is increased with this Ba Silicon Carbide MOSFETs and Special Materials passivation process [18], which agrees with the previous findings of lower DIT levels. However, the gate oxide and threshold reliability have been shown to worsen if these are used with a SiO2 dielectric.…”

“…The present state-of-the-art MOS interface for SiC power devices consists of thermally grown SiO2 with a nitric oxide (NO) post-anneal on Si-face (0001) 4H-SiC (tilted off-axis ~4° in the [11][12][13][14][15][16][17][18][19][20] direction). This provides a stable nitrogen passivation layer [1] and good dielectric reliability [2], but with a remaining high density of interface traps (DIT) near the conduction band, about two orders of magnitude higher than for Si MOS devices.…”