Peculiar Current Instabilities & Failure Mechanism in Vertically Stacked Nanosheet ggN-FET

The behavior of gate grounded vertically stacked nanosheet N-FET (ggNFET) under ESD stress is investigated in this work. Single Fin (3-Sheet) ggNFET devices exhibit multiple instability points in the TLP-IV characteristic around the snapback region. Each of these instabilities was found to be arising due to non-uniform sheet turn-on and was independent of the presence of body contact. However, this instability was more severe, with a decreased body distance from the source. Furthermore, the sequence of turn-on was found to be dependent on the TLP current ramp rate. A 24-Fin (72 Sheet) ggNFET was simulated to reproduce the current filament like behavior. These 24- Fin simulations revealed a more severe low-current instability due to both non-uniform sheet turn-on and non-uniform Fin turn-on. For a smaller body to source contact distance, this non-uniform turn-on was seen to result in an early failure of the device.

Automated summary

This study investigates the behavior of gate grounded vertically stacked nanosheet N-FET under ESD stress and finds that instability caused by non-uniform sheet turn-on becomes more severe with decreased body distance from the source. The sequence of turn-on is also influenced by the TLP current ramp rate, and non-uniform turn-on can lead to early failure of the device, especially with a smaller body to source contact distance.