Origin of trap assisted tunnelling in ammonia annealed SiC trench MOSFETs
J Berens and MV Mistry and D Waldhor and A Shluger and G Pobegen and T Grasser, MICROELECTRONICS RELIABILITY, 139, 114789 (2022).
The interface between silicon carbide (SiC) and silicon dioxide (SiO2) is of considerable importance for the performance and reliability of 4H-SiC (trench) metal oxide semiconductor field effect transistors (MOSFETs) and various different post oxidation anneals (POAs) have been used to optimize its quality. Whereas nitric oxide (NO) POA leads to very reliable and well performing MOSFETs, ammonia (NH3) can further improve the device performance, however, at the cost of the gate oxide (GOX) reliability, e.g. leading to trap assisted tunneling (TAT). We investigate the origin of TAT and GOX leakage in differently annealed gate oxides experimentally, using 4H-SiC trench MOSFETs, and theoretically, using Density Functional Theory (DFT) simulations. Our findings reinforce the view that the NO anneal for SiC devices results in the best overall quality as devices annealed in NH3 and nitrogen N2 show higher oxide charge density and leakage currents. DFT simulations demonstrate that, contrary to what has often been assumed so far, NH3 annealing leads to the formation of additional hydrogen related defects, which open leakage paths in the oxide otherwise not present in NO treated oxides.
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