Accurate Evaluation of Electro-Thermal Performance in Silicon Nanosheet Field-Effect Transistors with Schemes for Controlling Parasitic Bottom Transistors.

The electro-thermal performance of silicon nanosheet field-effect transistors (NSFETs) with various parasitic bottom transistor ( tr pbt )-controlling schemes is evaluated. Conventional punch-through stopper, trench inner-spacer (TIS), and bottom oxide (BOX) schemes were investigated from single-device to circuit-level evaluations to avoid overestimating heat's impact on performance. For single-device evaluations, the TIS scheme maintains the device temperature 59.6 and 50.4 K lower than the BOX scheme for n/pFETs, respectively, due to the low thermal conductivity of BOX. However, when the over-etched S/D recess depth ( T SD ) exceeds 2 nm in the TIS scheme, the RC delay becomes larger than that of the BOX scheme due to increased gate capacitance ( C gg ) as the T SD increases. A higher TIS height prevents the C gg increase and exhibits the best electro-thermal performance at single-device operation. Circuit-level evaluations are conducted with ring oscillators using 3D mixed-mode simulation. Although TIS and BOX schemes have similar oscillation frequencies, the TIS scheme has a slightly lower device temperature. This thermal superiority of the TIS scheme becomes more pronounced as the load capacitance ( C L ) increases. As C L increases from 1 to 10 fF, the temperature difference between TIS and BOX schemes widens from 1.5 to 4.8 K. Therefore, the TIS scheme is most suitable for controlling tr pbt and improving electro-thermal performance in sub-3 nm node NSFETs.