Microstructure and thermal stability of HfO2 gate dielectric deposited on Ge(100)

We report on physical and electrical characterization of ultrathin (3–10nm) high-κHfO2 gate stacks deposited on Ge(100) by atomic-layer deposition. It is observed that uniform films of HfO2 can be deposited on Ge without significant interfacial growth. The lack of an interlayer enables quasiepitaxial growth of HfO2 on the Ge surface after wet chemical treatment whereas a nitrided interface (grown by thermal oxynitridation in ammonia) results in an amorphous HfO2. The stacks exhibit surprisingly good thermal stability, up to temperatures only 150°C below the melting point of Ge. In terms of electrical properties, HfO2 on Ge shows significantly reduced (up to 4 decades) gate leakage currents in the ultrathin regime of equivalent electrical thickness down to ∼1.4nm due to the high-dielectric constant of ∼23. Nitrided interface is observed to be important for good insulating properties of the stack.