Reduction of Process Variations for Sub-5-nm Node Fin and Nanosheet FETs Using Novel Process Scheme
Jun-Sik Yoon, Seunghwan Lee, Junjong Lee, Jinsu Jeong, Hyeok Yun, Rock‐Hyun Baek
Abstract
Process (systematic) variations of sub-5-nm node fin field-effect transistors (FinFETs) and nanosheet field-effect transistors (NSFETs) were investigated thoroughly using fully calibrated TCAD. All the process parameters consisting of front-endas well as middle-of-line structure were independently randomized within feasible process conditions. A novel process scheme called source/drain patterning (SDP), having a superior performance by decreasing outer fringing capacitance through the downsized source/drain (S/D) epi, has also been analyzed for the variability study. SDP FinFETs have smaller variations of threshold voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ), OFF-state currents (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ), and effective currents (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ) than conventional ones because the subfin leakage is effectively controlled by bottom oxide (BO) beneath the source/drain instead of high punch through-stopper doping. The Spearman's correlation results between process parameters, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> , and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> , showed that the process parameters affecting the short-channel effects vary IOFF and Ieff greatly. Especially, the most critical one was the fin width (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fin</sub> ) for FinFETs. SDP NSFETs have the smallest variations of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> , I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> , and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> . The BO blocks the bottom leakage completely, and the variations of nanosheet(NS)thickness(TNS)are much smaller than those of Wfin due to the different process flows: epitaxial growth for TNS versus patterning for Wfin. Therefore, NSFETs are promising to reducethe variations of Vth, IOFF, and Ieff in the sub-5-nm node.