An Ultralow EOT Ge MOS Device With Tetragonal HfO2 and High Quality HfxGeyO Interfacial Layer

A Ge MOS device with an ultralow equivalent oxide thickness of ~0.5 nm and acceptable leakage current of 0.5 A/cm² is presented in this paper. The superior characteristics can be attributed to a tetragonal HfO₂ with a higher k value (k ~ 31) and comparable bandgap. In addition, a Ge MOS device with tetragonal phase HfO₂ (t-HfO₂) also shows a lower leakage current and better thermal stability. The mechanisms for t-HfO₂ formation may be explained by the little Ge diffusion from Ge substrate and oxygen deficiency, which are obtained by in situ interfacial layer (IL) formation and high-k processes. The IL with k ~ 13 can be formed by in situ H₂O plasma treatment. Moreover, a Ge MOS device with the IL grown by H₂O plasma shows smaller interface trap density and hysteresis effects due to a high composition of Ge⁺⁴.