Electrical properties of La2O3 and HfO2/La2O3 gate dielectrics for germanium metal-oxide-semiconductor devices

Germanium metal-insulator-semiconductor capacitors with La2O3 dielectrics deposited at high temperature or subjected to post deposition annealing show good electrical characteristics, especially low density of interface states D-it in the 10(11) eV(-1) cm(-2) range, which is an indication of good passivating proper-ties. However, the K value is estimated to be only about 9, while there is no,evidence for an interfacial layer. This is explained in terms of a spontaneous and strong reaction between La2O3 and Ge substrate to form a low K and leaky La-Ge-O germanate over the entire film thickness, which, however, raises concerns about gate scalability. Combining a thin (similar to 1 nm) La2O3 layer with thickef HfO2 degrades the electrical characteristics, including Dit, but improves gate leakage and equivalent oxide thickness, indicating a better potential for scaling. Identifying suitable gate dielectric stack which combines good passivating/interfacial properties with good scalability remains a challenge. (c) 2008 American Institute of Physics.