Variability Induced by Random Discrete Dopants in Source and Drain Extensions of Gate-all-around Nanosheet FETs: A Quantum Transport Simulation Study.

Abstract

Gate-all-around (GAA) nanosheet field-effect transistors (FETs) have significantly advanced nanoscale device technology by mitigating short-channel effects. These GAA structures are becoming essential in sub-3nm technology and are evolving into complementary FETs. Despite the reduction in variability achieved by multi-gate structures, random discrete dopants (RDDs) in source and drain regions continue to pose challenges. This study addresses the local variability induced by RDDs, particularly in the source and drain extensions in GAA nanosheet FETs. Through statistical quantum transport simulations under a ballistic approximation, we investigate parameters such as spacer length, channel width, and channel thickness. The results show that RDDs in the source and drain extensions cause not only threshold voltage variation but also increase resistance and reduce ON-state current. GAA nanosheet FETs with a 3 nm×10 nm cross-sectional channel and 5 nm spacer length exhibit 10% reduction in ON-state current compared to the ideal device, along with a standard deviation (variability) of 0.35 µA. Mitigation of these effects requires the use of thin, wide, and large cross-section nanosheets and short spacer lengths.