Germanium-on-Si MOSFETS with HFO 2 gate dielectric
Abstract
We have studied ultrathin HfO 2 gate dielectrics grown by ultrahigh vacuum reactive atomic-beam deposition and ultraviolet ozone radiation on Ge substrates. We have achieved t eq ∼11Å and 6 orders of magnitude lower leakage current compared to SiO 2. We have found that surface nitridation reduces interfacial layer formation, leakage current and hysteresis. The mobility of p- and n-MOSFETs on Ge substrates with ultrathin HfO 2 gate dielectrics was studied for various thicknesses of HfO 2. A strong reduction of electron and hole channel mobility was found with decreasing gate dielectric thickness, suggesting additional degradation factors at ultrathin gate dielectric thickness. Germanium-on-Si n-MOSFETs were fabricated by selective epitaxial growth (SEG) of Ge on small Si active areas by ultra high vacuum-chemical vapor deposition (UHV-CVD). The film was then capped by a HfO 2 gate dielectric and a TaN metal gate. The Ge-on-Si nMOSFETs had an I on/I off ratio of ∼ 10 6.