Strain Evolution in SiGe Nanosheet Transistor Process Flow
Journal
IEEE Transactions on Electron Devices
Journal Volume
71
Journal Issue
5
Date Issued
2024-01-01
Author(s)
Chou, Hung Chun
Chou, Tao
Chueh, Shee Jier
Jan, Sun Rong
Huang, Bo Wei
Tu, Chien Te
Liu, Yi Chun
Wang, Li Kai
Abstract
The step-by-step strain evolution in the channel during the SiGe nanosheet (NS) integration process flow for pFETs is demonstrated using finite element analysis (FEA). The effect of device dimensions and defective source/drain (S/D) is studied. After fin formation, the 0.77% compressive biaxial strain resulting from the lattice mismatch between Si $_{\text{0}.\text{8}}$ Ge $_{\text{0}.\text{2}}$ and Si substrate is observed. However, the strain $_{\textit{xx}}$ is gradually relaxed during the S/D recess and the inner spacer cavity formation. A large strain $_{\textit{xx}}$ is obtained on the channel along the current direction after Si $_{\text{0}.\text{6}}$ Ge $_{\text{0}.\text{4}}$ S/D regrowth, increasing from 0.21% to 1.50% for defect-free S/D epitaxy. The compressive strain along the channel remains similar for different shapes of the S/D regrowth, with small variations between every channel. Decreasing the NS width only leads to an insignificant increase in channel strain $_{\textit{xx}}$ until the nanowire structure is formed. Nevertheless, the scaled body thickness can enhance the channel strain $_{\text{xx}}$ substantially with the 21.2% compressive strain $_{\textit{xx}}$ increase from $\textit{t}_{\text{body}}$ $=$ 5 nm to $\textit{t}_{\text{body}}$ $=$ 1 nm. The defective S/D is also simulated with air gaps between the merged epitaxes, where compressive strain in the channel is totally relaxed and further turns into tensile-strained. The hole mobility is expected to have a 3.6 $\times$ enhancement with 1.5% compressive strain $_{\textit{xx}}$ .
Subjects
Epitaxial growth | Finite element analysis (FEA) | gate-all-around | Germanium | Lattices | nanosheet (NS) | SiGe | Silicon | Silicon germanium | Strain | strain | Substrates
Type
journal article