Characterization of the anodic polarization behavior of 4H-SiC

Accelerated stress test is the most efficient way to discover possible degradation mechanisms that the device will encounter during its lifespan. Currently, one of the major concerns about reliability is robustness against moisture. For power device, the test used to induce humidity driven-failure mechanisms is High Voltage – High Humidity High Temperature Reverse Bias (HV-H3TRB), with 85 °C, 85 % of relative humidity and 80 % of the nominal voltage which can lead to several failure mechanisms. This work is focused on the corrosion of silicon carbide (SiC) power devices. In particular, we investigate the electrochemical oxidation of SiC to establish a clear link between the degradation mechanism and the results of humidity testing. With the aim of studying the progression of the phenomenon, a conventional three-electrode electrochemical cell connected to a potentiostat was used to obtain an anodic polarization curve in an aqueous electrolyte. The polarization curves exhibit three main regions, and our samples were collected in each of them to investigate the corresponding surface evolution. The active region is the first part of the curve, where the current density increases with potential and oxidation occurs in the sample. The transition region represents a change in the behavior of the current density, as oxidation shifts from a surface-controlled regime to a diffusion-limited regime. Finally, in the passivation region, an oxide layer grows on the surface and limits the reaction. Three samples were polarized up to these three regions and then characterized by SEM and FIB to observe the surface and cross-section. The results for sample 1 (active region) show the presence of silicon oxide bumps on the surface due to the ongoing oxidation in that region. For sample 2 (transition region), they show that there is no longer any oxidizable silicon carbide surface, and for sample 3 (passivation region), they show a compact and thick silicon oxide layer, which explains the saturation region. In conclusion, in the presence of water, electrolyte, and voltage, the surface of silicon carbide can undergo electrochemical oxidation. The next step is to study how to prevent this phenomenon.