A better understanding of substrate enhanced gate current in VLSI MOSFET'sand flash cells - Part II: Physical analysis

In this work different physical mechanisms that could lead to the direct pr oportionality between I-G and I-B highlighted in Part I as the signature of substrate enhanced electron injection (SEEI), are analyzed in detail. By m eans of experiments and simulations rye substantiate the current interpreta tion of SEEI in terms of an impact ionization feedback process and attribut e a quantitatively negligible role to both drain avalanche hot electron inj ection and substrate electrons generated by the photons emitted by channel hot electrons. These experiments reconcile the current explanation of SEEI with the well k nown phenomenon of photon assisted minority carrier injection in the substr ate, whose presence is clearly detectable in our devices, but whose impact on the gate current is estimated to be orders of magnitude smaller than tha t of impact ionization feedback.