Ge MOS capacitors with thermally evaporated Hf O2 as gate dielectric

We have investigated the characteristics of thermally evaporated hafnium oxide (Hf O2) films on germanium substrates. Surface roughness of the Hf O2 film was studied by scanning electron microscopy. The presence of crystalline Ge O2 was evident from X-ray diffraction results on as-deposited films. Capacitance-voltage (C-V) and current-voltage (I-V) measurements of the as-deposited metal-oxide semiconductor (MOS) capacitors demonstrated a hysteresis of 2.3 V and leakage current density of 10 A cm2 at 1 V, respectively. Annealing of these films at two different temperatures of 500 and 550°C in N2 ambience reduced the hysteresis to 0.9 V and the leakage current density by five orders of magnitude. Observed increment of equivalent oxide thickness (EOT) after annealing indicates growth of an interfacial layer. The composition of film evaluated by X-ray photoelectron spectroscopy for annealed devices further confirms the increase of interfacial layer. Interface state density, estimated using the conductance method after 550°C annealing, was 5.1× 1012 cm-2 eV-1.