Predeposition plasma nitridation process applied to Ge substrates to passivate interfaces between crystalline-Ge substrates and Hf-based high-K dielectrics

Abstract

Interfaces between crystalline-Si and high-K Hf-based oxide gate dielectrics have a lower-K interfacial transition region (ITR), generally 0.6–0.8nm SiON, which prevents reactions between Si and Hf precursors used in film deposition. These ITRs contribute ∼0.35nm to the equivalent oxide thickness limiting aggressive scaling. This article addresses Hf-based high-K gate dielectrics for devices on crystalline Ge substrates. The band gaps of GeO2 and Ge3N4 are reduced with respect to their Si counterparts, and as such may contribute to increased levels of interfacial defect states. A novel processing sequence is presented for (i) depositing HfO2 and Hf Si oxynitrides (HFSiON) onto N-passivated Ge(111) and Ge(100), and subsequently (ii) removing Ge–N interfacial bonding during 800°C thermal annealing in Ar. Near edge x-ray absorption spectroscopy and medium energy ion scattering measurements have confirmed that the interfacial nitrogen is indeed removed. However, there are reactions between the Ge substrate and deposited high-K dielectrics, as deposited and after annealing to 600–800°C, Ge–O bonding into the high-K gate stacks which result in increased levels of conduction band edge defect states that incorporate these Ge atoms.