Fabrication of Ge Metal–Oxide–Semiconductor Capacitors with High-Quality Interface by Ultrathin SiO₂/GeO₂ Bilayer Passivation and Postmetallization Annealing Effect of Al

A novel method of electrical passivation of a Ge surface by an ultrathin SiO₂/GeO₂ bilayer is proposed as an effective method for fabricating metal–oxide–semiconductor (MOS) structures, which can be processed through the thermal etching of GeO₂ by vacuum annealing and subsequent SiO₂ deposition. We demonstrated the feasibility of this passivation technique by performing interface state density (D_it) measurements of MOS capacitors, which were fabricated using several surface preparations and subsequent gate insulating film deposition. A D_it of 4×10¹¹ cm^-2 eV^-1 was obtained at around midgap. We also investigated the effect of postmetallization annealing after Al deposition (Al-PMA). Al-PMA was found to be very effective for decreasing D_it, which was 9.4×10¹⁰ cm^-2 eV^-1 at around midgap for a capacitor with PMA at 400 °C. The role of Al as a defect terminator was discussed.