Design for Variability: Counter-Doped Source/Drain Epitaxy Pockets in Gate-All-Around FET
Jaehyuk Lim, Donghwan Han, Sangwoo Seon, Hyoung Won Baac, Changhwan Shin
Abstract
One of the obstacles in the evolution from the fin-shaped field-effect transistor (FinFET) to the gate-all-around field-effect transistor (GAAFET) is the etching-depth variation. In the process step for etching the source/drain (S/D) regions, the variation makes the over-etching inevitable to avoid the fatal issue that under-etched region may induces (e.g., two adjacent gates can be connected in the following processes). However, the over-etching goes with the degradation of device performance, especially OFF-state performance. To ease the degradation, a counter-doped pocket was suggested in this work. The process parameters for the pocket such as the over-etching depth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {ov}}$ </tex-math></inline-formula> ), the pocket epitaxy thickness ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {EPI}}$ </tex-math></inline-formula> ), and the pocket doping concentration ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\text {pocket}}$ </tex-math></inline-formula> ) were explored. Subsequently, the device performance was evaluated with respect to OFF-state leakage current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ) and threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> ) variation. It was confirmed that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> decreased, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> variation was suppressed with optimized process parameters. By analyzing the total doping concentration at substrate, it also turned out that the GAAFET with the pocket can give advantageous impact on the feasibility.