Record 60.3 mV/dec Subthreshold Swing and >20% Performance Enhancement in Gate-All-Around Nanosheet CMOS Devices Using O₃-Based Quasi-Atomic Layer Etching Treatment Technique

To overcome the critical channel interface issues in gate-all-around (GAA) devices that are induced by germanium (Ge) residue on the nanosheet (NS) channels, a precise quasi-atomic layer etching (qALE) technique based on O3 was developed in this work. This technique has a self-limited oxidation thickness of 6.1 Å and is able to remove the residual Ge atoms. The improved interface quality leads to a 99% reduction in the interface state density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{\textit {it}}$ </tex-math></inline-formula>) and a reduction in the current density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${J} _{g}$ </tex-math></inline-formula>) of two orders of magnitude. Therefore, the GAA devices fabricated using this method achieve a record low subthreshold swing (SS) of 60.3 mV/dec, with the maximum reduction in the SS reaching up to 21% when compared with that of unprocessed devices after a two-cycle qALE treatment. Moreover, the treatment also results in an enhancement of more than 20% in the on-current (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I} _{\textit {on}}$ </tex-math></inline-formula>) and a 66.7% reduction in the off-current (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I} _{\textit {off}}$ </tex-math></inline-formula>). These results and the proposed method provide effective technical guidance for improving the interface characteristics, leakage characteristics, and performance of future mass-produced GAA NS field-effect transistors.