Interfacial Layer Engineering for Ge MOSFET by Metal Element Doping and Characterization of Interface Density

Summary form only given. Germanium (Ge) has attracted lots of attention recently because it has 2× and 4× higher electron and hole mobilities than Si. This feature make it be a promising channel candidate for the next generation metal-oxide-semiconductor field-effect transistors (MOSFET). However, a challenging issue for Ge devices to be realized is to form a high-quality interfacial layer (IL) on Ge. C. Lu et al. proposed a potential solution to solve this issue by doping Yttrium (Y) into GeO₂ (YGO) to stabilize its network [1].In this paper, we present stabilization of IL layer with a conventional gate stack GeO_x/HfO₂/AlO_x/HfO₂/TiN (EOT~1.9 nm) on Ge by adding yttrium (Y) into GeO_x. A lowest D_it value of 7.5 × 10¹⁰ eV^-1cm^-2 was found occurred at E-E_v ~ 0.14 eV. The energy level at which the lowest value was extracted was different from the previous works in the literatures. This is because D_it and border trap distributions across the entire bandgap were determined by two-band admittance circuit model; the electrical results were measured at room temperature. We found that interface states across the entire bandgap and the dominant border traps inside the GeO IL (<; 0.5 nm) located near E-E_v of 0.31 eV were effectively eliminated by Y incorporation. Even though addition of Y can improve interface quality, however, the dielectric constant (κ) of the HfO₂ was found to be significantly degraded. A material interaction model has been proposed to explain the change in both electrical and physical properties by Y incorporation. We found non-fully oxidized Y atoms would capture nearby O atoms in Ge-O and/or Hf-O bonds. A series of XPS analyses indicated that Y doped GeO_x (YGO) could probably induce the formation of Hf-N bonds in HfO₂ during TiN deposition and degraded the κ value of HfO₂. Finally, a peak hole mobility of 908 cm²V^-1s^-for Ge pFET was achieved using YGeO IL. We keep scaling the EOT of the gate stack in order to meet the requirement of industry. Moreover, another metal has been tried and found to be able to well stabilize the IL as Y did without causing degradation of the overlying HfO₂ layer.