Device performance degradation to hot-carrier injection at energies below the Si-SiO2energy barrier

Device performance degradation due to hot-carriers having energies below the Si-SiO
2
energy barrier are examined. For a test device with L
eff
= 0.3 µm and T
ox
5 nm, transconductance degradation and/or threshold voltage shift have been detected at a drain voltage of 2.5 V, which is lower than the Si-SiO
2
energy barrier(∼ 3.2 eV). In particular, transconductance degradation, rather than threshold voltage shift, is more noticeable. No sharp cut-off is shown near a drain voltage of 3 V. This transconductance degradation is mainly due to an interface state increase caused by drain avalanche hot-carrier injection. It was also found that the time, τ, that it takes for
G_{m} or V_{th}
to degrade a certain degree, can be expressed as
\tau \propto (1/V_{D})
for a V
D
range of greater than 2.5 V. This degradation occurs in the same way as for long channel devices at V
D
> 3 V. Thus, hot carrier-related device degradation may be one of the most stringent problems in submicron MOS FETs, even after the power supply voltage is reduced.