Experimental analysis of a Ge-HfO2-TaN gate stack with a large amount of interface states

First, the quality of the Ge-HfO₂ interface of early MOS capacitors is studied. The characterization difficulties related to the introduction of germanium as substrate material are analyzed and can be subdivided in problems due to the initial low quality of the samples, and due to the different material properties as compared to silicon. It is concluded from measurements of CV-curves at low temperature, gated diodes, and conductance analysis, that a large number interface states prevents inversion for p-substrate capacitors and accumulation for n-substrate capacitors. The paper then briefly discusses the difficulties related to the characterization of early MOS transistors on germanium substrates. These difficulties are mainly caused by a large amount of junction leakage.