Formation and High Frequency CV-Measurements of Aluminum / Aluminum Nitride / 6H Silicon Carbide Structures

Undoped single crystalline aluminum nitride films were grown by metal organic chemical vapor deposition (MOCVD) at 1200 °C. The precursors used were trimethylaluminium (TMA) and ammonia (NH3) in a hydrogen carrier flow, at a pressure of 10 Torr. Silicon carbide substrates of the 4H or the 6H polytype with an epilayer on the silicon face, were used to grow the 200 nm thick A1N films. Aluminum was evaporated and subsequently patterned to form MIS capacitors for high frequency (400 kHz) capacitance voltage measurements at room temperature. It was possible to measure the structure and characterize accumulation, depletion and deep depletion. However, it was not possible to invert the low doped SiC epilayer at room temperature. From an independent optical thickness measurement the relative dielectric constant of aluminum nitride was calculated to be 8.4. The films were stressed up to 50 Volts (2.5 MV/cm) without breakdown or excessive leakage currents. These results indicate the possibility to replace silicon dioxide with aluminum nitride in SiC field effect transistors.