The improvement of Mo/4H-SiC Schottky diodes via a P2O5 surface passivation treatment

Abstract

Molybdenum (Mo)/4H-silicon carbide (SiC) Schottky barrier diodes have been fabricated with a phosphorus pentoxide (P${}_2$ O${}_5$ ) surface passivation treatment performed on the SiC surface prior to metallization. Compared to the untreated diodes, the P${}_2$ O${}_5$ -treated diodes were found to have a lower Schottky barrier height by 0.11 eV and a lower leakage current by two to three orders of magnitude. Physical characterization of the P${}_2$ O${}_5$ -treated Mo/SiC interfaces revealed that there are two primary causes for the improvement in electrical performance. First, transmission electron microscopy imaging showed that nanopits filled with silicon dioxide had formed at the surface after the P${}_2$ O${}_5$ treatment that terminates potential leakage paths. Second, secondary ion mass spectroscopy revealed a high concentration of phosphorus atoms near the interface. While only a fraction of these are active, a small increase in doping at the interface is responsible for the reduction in barrier height. Comparisons were made between the P${}_2$ O${}_5$ pretreatment and oxygen (O${}_2$ ) and nitrous oxide (N${}_2$ O) pretreatments that do not form the same nanopits and do not reduce leakage current. X-ray photoelectron spectroscopy shows that SiC beneath the deposited P${}_2$ O${}_5$ oxide retains a Si-rich interface unlike the N${}_2$ O and O${}_2$ treatments that consume SiC and trap carbon at the interface. Finally, after annealing, the Mo/SiC interface forms almost no silicide, leaving the enhancement to the subsurface in place, explaining why the P${}_2$ O${}_5$ treatment has had no effect on nickel- or titanium-SiC contacts.