Strain Evolution in SiGe Nanosheet Transistor Process Flow
Hung-Chun Chou, Tao Chou, Shee-Jier Chueh, Sun-Rong Jan, Bo‐Wei Huang, Chien-Te Tu, Yi‐Chun Liu, Li-Kai Wang, C. W. Liu
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{0}.\text{8}}$</tex-math> </inline-formula> Ge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{0}.\text{2}}$</tex-math> </inline-formula> and Si substrate is observed. However, the strain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{xx}}$</tex-math> </inline-formula> is gradually relaxed during the S/D recess and the inner spacer cavity formation. A large strain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{xx}}$</tex-math> </inline-formula> is obtained on the channel along the current direction after Si <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{0}.\text{6}}$</tex-math> </inline-formula> Ge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{0}.\text{4}}$</tex-math> </inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{xx}}$</tex-math> </inline-formula> until the nanowire structure is formed. Nevertheless, the scaled body thickness can enhance the channel strain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{xx}}$</tex-math> </inline-formula> substantially with the 21.2% compressive strain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{xx}}$</tex-math> </inline-formula> increase from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{t}_{\text{body}}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 5 nm to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{t}_{\text{body}}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> enhancement with 1.5% compressive strain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{xx}}$</tex-math> </inline-formula> .