Germanium/HfO2/TiN gate stacks for advanced nodes: influence of surface preparation on MOS capacitor characteristics

For the first time, we report electrical and physical characterization of metal-oxide-semiconductor (MOS) capacitors fabricated on 2.5μm epitaxial germanium layers grown on (100) silicon. These capacitors were made using HfO₂ as the dielectric and TiN as the metal gate electrode. We have studied the influence of the Ge surface preparation on the MOS electrical characteristics. It is demonstrated that a surface anneal step in a NH₃ ambient before the HfO₂ deposition results in significant improvements in both the equivalent oxide thickness (EOT) and the gate leakage current. We show that it is possible to achieve Ge/GeON/HfO₂/TiN gate stacks with an EOT of 0.7 nm and a leakage current of 0.84 A/cm² at -2 V gate bias. The better transport properties of Ge and these performances show the interest of Ge and GeOI for the ITRS advanced nodes.