Effects of Sulfur Passivation on Germanium MOS Capacitors With HfON Gate Dielectric

In this letter, we study the effects of sulfur (S) passivation, using aqueous ammonium sulfide ((NH
₄
)
₂
S), on germanium (Ge) MOS capacitors with sputtered HfON as gate dielectric and TaN as metal-gate electrode. Compared with control samples, the S passivation can effectively reduce both equivalent oxide thickness and interface-state density. X-ray-photoelectron-spectroscopy analysis shows that (NH
₄
)
₂
S treatment can reduce the Ge-O bonds on Ge surface. The thermal stability of the S passivation under different postmetal-annealing temperatures was also examined, and it was found that samples with (NH
₄
)
₂
S treatment exhibit stable Ge/high-fc interface upon 550-deg C postmetal-deposition annealing, whereas interface quality degrades for those samples without S passivation.