High-/Ge gate stack with an extremely thin-EOT by controlling interface reaction using ultrathin AlO interlayer

Tanaka, Ryohei*; Hideshima, Iori*; Minoura, Yuya*; Yoshigoe, Akitaka ; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

It has recently been demonstrated an excellent Ge-MOSFET operation with an EOT of 0.76 nm using HfO/AlO/GeO/Ge gate stack. However, the role of AlO layer in high-/Ge stack is not well understood. In this work, we systematically investigated an effect of AlO interlayer on thermal stability and EOT scaling focusing on the Ge diffusion into an overlying HfO layer by means of X-ray photoelectron spectroscopy (XPS) and electrical characterization. It was found that ultrathin AlO interlayer effectively suppresses the metal germanate formation in the high-/Ge stack, thus obtaining good electrical properties. An EOT of 0.56 nm with significantly reduced gate leakage was successfully obtained for Pt/HfO/AlO/GeO/Ge gate stack.