Study of AlN/SiO2 as dielectric layer for SiC MOS structures

Silicon dioxide (SiO₂) has shown to be performance limited for SiC application at high temperature and high electric fields due to its low dielectric constant. Aluminium Nitride (AlN) could be a valuable alternative thanks to its high dielectric constant and good thermo-mechanical matching with SiC. A study on an MOS capacitor has been performed in order to evaluate the AlN capability as a gate and passivation dielectric layer for SiC devices. Direct deposition of AlN layers on the semiconductor has resulted in a very high leakage current and unstable C-V characteristics due to interface and bulk charges. In a second phase, we have fabricated an MNOS (or MIS) SiC-SiO₂-AlN capacitor on p-type 6H-SiC substrates. In this case, the extracted fixed charge and interface trap densities are in the range of the values obtained with SiC-SiO₂ structures. C-V characteristics exhibit low hysteresis unlike the SiC-SiO₂-Si ₃N₄ structure. Low leakage current is measured and this proposed dielectric layer could support high electric field