Performance Degradation in p-Type Nanosheet FETs: Role of S/D Doping, Stress, Inner Spacer Interface Traps

In this work, fully titled Performance Degradation Mechanisms in p-Type Nanosheet FETs: Role of Source/DrainDoping, Stress, and Inner Spacer Interface Traps, GTS scientist Lee-Chi Hung and co-authors investigate the main performance degradation mechanisms in 2 nm-node p-type nanosheet FETs with embedded SiGe S/D epitaxy.

Using the subband Boltzmann transport equation implemented in GTS NDS, together with mechanical stress simulations in GTS VSP, the study examines three scaling-related nonidealities: insufficient doping in the lightly doped first epitaxial layer (L1), stress relaxation during the merging of the epitaxial growth fronts, and interface traps at the Si/SiN inner-spacer interfaces.

The results identify a transition from gate-controlled to injection-limited transport when the L1 doping falls below 5×10^19 cm^-3. In the injection-limited regime, the effects of stress relaxation and interface traps become significantly stronger because carrier injection is no longer effectively controlled by the gate.

The study also shows that calibrated drift-diffusion simulations reproduce the gate-controlled regime well, but overestimate the current once transport becomes injection-limited. Nonequilibrium transport modeling is therefore important for accurate device optimization at the 2 nm node and beyond.