Threshold Voltage Variability in Nanosheet GAA Transistors

Nanosheet gate-all-around (GAA) field-effect transistor (NSFET) is a potential replacement for the FinFET at advanced technology nodes owing to better control of short-channel effects and higher drive current. Due to the increased complexity of the GAA stacked structure, new forms of process variability come into the picture, which are dominant over the conventional process variability such as metal gate granularity (MGG) and line edge roughness (LER) for FinFETs. In this article, we show one such process variability called as metal thickness variation (MTV). MTV causes WF variations on the gates of the GAA sheet transistor and results in a significant V-T variability. The impact ofMTV is studied using an analytical framework. We studied three variants of NSFETs and reported variability in terms of key device design parameters such as intersheet spacing and metal thicknesses. The results presented here help in designing the process flow for a type of NSFET to minimize the V-T variability.