Material Characterization of Metal Germanide Gate Electrodes Formed by Fully Germanided Gate Process

The work functions and thermal stability of metal (Pt, Ni, Ta, and Er) germanide gate electrodes formed by the fully germanided (FUGE) gate process were investigated. Germanides have approximately 0.3 eV higher effective work function ( Φeff) values than silicides. The Φeff values corresponding to Si conduction and valence band edges (Ec and Ev, respectively) were realized with these germanides as well as the Si midgap (Pt3Ge2: 5.19 eV, NiGe: 5.01 eV, TaGe2: 4.70 eV, Er2Ge3: 4.05 eV). The Φeff values of germanide and silicide change linearly with the geometric mean of the electronegativities of the constituent metal and Ge(Si), which is the same as that in the case of pure metals. Low-level gate leakage current and stable Φeff values are maintained up to 400 °C for Ni germanide and up to 600 °C for Pt germanide, respectively. A W cap layer effectively improves the gate leakage current degradation, and makes Ni germanide gate electrodes sufficiently stable up to 600 °C. Fermi level pinning occurs at the germanide/HfSiON interface as in the case of the silicide/HfSiON interface. However, the Φeff values corresponding to almost Ev (>4.9 eV) were maintained with Ni and Pt germanides. In addition, a good thermal stability is maintained even on HfSiON.