Variability induced by random discrete dopants in source and drain extensions of gate-all-around nanosheet FETs: a quantum transport simulation study

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-3 nm 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 (S/D) regions continue to pose challenges. This study addresses the local variability induced by RDDs, particularly in the S/D 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 S/D extensions cause not only threshold voltage variation but also increase resistance and reduce ON-state current. GAA nanosheet FETs with a3 nm×10 nmcross-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<i>µ</i>A. Mitigation of these effects requires the use of thin, wide, and large cross-section nanosheets and short spacer lengths.