Experimental Demonstration of TreeFETs Combining Stacked Nanosheets and Low Doping Interbridges by Epitaxy and Wet Etching

A novel TreeFET architecture as a combination of stacked nanosheets and additional fin interbridges between nanosheets can enhance I _ON per footprint. The straight sidewalls of interbridges requires {110} sidewalls, which can be fabricated using n ⁺ Ge/Ge _0.95 Si _0.05 /Ge epitaxial layers with co-optimization of wet etching. The TreeFET with {110} interbridges has I _ON per footprint of $870~\mu \text{A}/\mu \text{m}$ at V _OV =V _DS =0.5V (2.1X of the referenced 3 stacked nanosheets). To minimize the impurity scattering in the interbridges, the 400 °C annealing is used to drive phosphorus in interbridges into the nanosheets, while the low source/drain resistance is still maintained. The increasing I _ON down to 77 K indicates that the phonon scattering dominates, and the impurity scattering is minimized in the interbridge channels.