Characterization of the semi-insulating properties of Al2O3 and AlHfO3.5 for power devices

Physical and electrical characterization of alumina and hafnium aluminates gate dielectrics were carried out to investigate their semi-insulating characteristics as passivating layer for power devices. The deposited films were annealed in pure nitrogen to simulate the thermal budget during a conventional CMOS processing. C-V measurements were performed having as a result a high-frequency behavior of the flat band voltage (V_FB) being increased from about -0.8V for Al₂O₃ to values greater than or equal to zero for AlHfO_3.5. On the other hand, the leakage phenomenon was modeled with a simplified electrical model using a leakage admittance YC whose influence was predominant at the accumulation region. Using X-ray reflectometry (XRR), the average thickness obtained was 15.5nm and a leakage process was inferred to occur for AlHfO_3.5 due to the observed phase separation and crystallization that occurs after annealing in pure N₂.