Defect states in HfO ₂ on deposited on Ge(1 1 1) and Ge(1 0 0) substrates

There is considerable interest in the direct bonding between Si and Ge substrates and high-K nano-crystalline transition metal elemental and complex oxides. Implicit in this is the elimination of lower-K interfacial transition regions (ITRs) in gate stacks which limit device down-scaling of advanced devices to meet roadmap targets. A novel approach is presented in this article for (i) deposition of HfO ₂ onto N-passivated Ge(1 1 1) and Ge(1 0 0) substrates, a process that also prevents subcutaneous oxidation of the Ge substrate during the deposition of nano-crystalline HfO ₂ and non-crystalline Hf Si oxynitride dielectrics as well, and (ii) the effective removal of Ge-N, during an 800 °C rapid thermal annealing. Removal of Ge-N bonding has been confirmed by X-ray absorption N K ₁ spectra (XAS). However, even though X-ray photoelectron spectroscopy (XPS) studies has indicated no detectable Ge-O bonding at the Ge-dielectric interfaces as-deposited, a significant amount of Ge-O bonding throughout the entire HfO ₂ film is detected by XPS and XAS after the 800 °C anneal. Current-voltage measurements indicate significantly higher leakage for HfO ₂ films on Ge(1 1 1) compared with Ge(1 0 0). These correlate with differences in band edge defect state densities obtained from spectroscopic measurements, and are consistent with a more columnar, bonding morphology for direct bonding of HfO ₂ on Ge(1 1 1) than for Ge(1 0 0).