Comparative electrical performance and failure analysis of air-annealed ruthenium Schottky contacts on 6H-SiC and 4H-SiC

Abstract

Thin films of ruthenium (Ru) on 6-hexagonal silicon carbide (6H-SiC) and 4-hexagonal silicon carbide (4H-SiC) were analysed by Rutherford backscattering spectroscopy (RBS) at various annealing temperatures in the air-ambient. RBS analysis indicated Ru oxidation at a temperature of 400 °C and commencement of diffusion of Ru into SiC at a temperature of 500 °C for both Ru–4H-SiC and Ru–6H-SiC. X-ray diffraction analysis of samples annealed in air at 600 °C showed evidence of formation of ruthenium silicide in both 4H and 6H-SiC. Silicide formation in 4H-SiC and Ru oxidation in 6H-SiC were also confirmed by Raman analysis. Both samples of Ru–6H-SiC and Ru–4H-SiC Schottky barrier diodes (SBD) showed excellent rectification behaviour and linear capacitance-voltage characteristics up to an annealing temperature of 600 °C for 6H-SiC and 300 °C for 4H-SiC . The Ru–6H-SiC and Ru–4H-SiC SBDs degraded after annealing at 700 °C and 400 °C, respectively as evidenced by the appearance of infinite series resistance. The degradation of Ru–6H-SiC may be attributed to the inter-diffusion of Ru and Si at the Schottky-substrate interface, while the oxidation of Ru which led to the formation of of non-conducting and gaseous oxide compounds is the likely cause of Ru–4H-SiC SBDs device failure.