Novel Interface Trap Passivation and Channel Counter-doping for 4H-SiC MOSFETs
Type of DegreeDissertation
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4H-Silicon carbide (4H-SiC) is the most promising wide band gap semiconductor for next generation high power and high temperature metal-oxide-semiconductor field-effect transistors (MOSFETs). However, the channel mobility for as-grown oxide 4H-SiC is poor due to the high density of electronic traps near the SiO2/4H-SiC interface. Nitric oxide (NO) post oxidation anneal increased 4H-SiC MOSFET mobility and allowed for commercially available devices. However, there is a limit to the amount of nitrogen that can passivate the electronic interface traps from nitric oxide passivation due to competing nitridation and oxidation reactions. In the first part of this work, nitrogen plasma passivation, nitridation without oxidation, is explored as an alternative passivation process. Nitrogen plasma passivation is demonstrated to obtain a 50% increase in nitrogen coverage compared to standard NO. However the maximum field-effect mobility remains similar to NO. Explanations for this discrepancy are discussed. Recent publications reported that nitrogen and phosphorus both passivate interface traps and counter-dope. To further examine these observations, the effects of antimony and arsenic at the interface were studied in this work. Antimony and arsenic are both in the same periodic column as nitrogen and phosphorus, but little is known about whether antimony and arsenic passivate electronic traps. Peak mobilities using several counter-doping processes are presented (110cm2 V-1 s-1 for counter-doping combined with nitric oxide annealing). Evidence is also presented demonstrating that antimony does not passivate interface traps, thus improved field-effect mobility results from antimony are strictly from counter-doping effects.