Germanium p- & n-MOSFETs fabricated with novel surface passivation (plasma-PH₃ and thin AlN) and TaN/HfO₂ gate stack

Ge-MOS devices (EOT ∼7.5 Å, J_g ∼ 10^-3 A/cm²) are fabricated on both n- & p-type Ge-substrates, using novel surface passivation and TaN/HfO₂ gate stack. Results show that the plasma-PH₃ treatment and thin AlN layer at HfO₂/Ge interface are effective to suppress the GeO formation, which is mainly formed during HfO₂ deposition, and prevent Ge out-diffusion, resulting in improved C-V characteristics for n-MOS device with extremely low leakage. Thermal stability study of TaN/HfO₂/Ge gate stack shows that low leakage with thin EOT can be obtained after post-anneal at 500 °C and degradation is observed above 600 °C. It is also observed that good Ge n⁺-p and p^--n diode characteristics are achieved by S/D activation at 500 °C and 400°C, respectively. Both p- & n-MOSFETs are fabricated by conventional self aligned process with maximum temperature of 500 °C. Compared to reported Si-MOSFETs, the mobility enhancement of 1.6X for hole and 1.8X for electron is observed with Ge-MOSFETs.