Strain Evolution in SiGe Nanosheet Transistor Process Flow

• Published in: IEEE transactions on electron devices Vol. 71; no. 5; pp. 2907 - 2913
• Main Authors: Chou, Hung-Chun, Chou, Tao, Chueh, Shee-Jier, Jan, Sun-Rong, Huang, Bo-Wei, Tu, Chien-Te, Liu, Yi-Chun, Wang, Li-Kai, Liu, C. W.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Compressive properties; Epitaxial growth; Evolution; Finite element analysis (FEA); Finite element method; gate-all-around; Germanium; Hole mobility; Lattices; nanosheet (NS); Nanosheets; Nanowires; SiGe; Silicon; Silicon germanides; Silicon germanium; Silicon substrates; Strain; Substrates
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2024.3383409

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 Si0.8Ge0.2 and Si substrate is observed. However, the strain<inline-formula> <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> <tex-math notation="LaTeX">_{\textit {xx}} </tex-math></inline-formula> is obtained on the channel along the current direction after Si0.6Ge0.4 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<inline-formula> <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 strainxx substantially with the 21.2% compressive strain<inline-formula> <tex-math notation="LaTeX">_{\textit {xx}} </tex-math></inline-formula> increase from <inline-formula> <tex-math notation="LaTeX">{t}_{\text {body}} </tex-math></inline-formula> = 5 nm to <inline-formula> <tex-math notation="LaTeX">{t}_{\text {body}} </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 <inline-formula> <tex-math notation="LaTeX">3.6\times </tex-math></inline-formula> enhancement with 1.5% compressive strain<inline-formula> <tex-math notation="LaTeX">_{\textit {xx}} </tex-math></inline-formula>.