A Better Understanding of Substrate Enhanced Gate Current in VLSI MOSFET's and Flash Cells - Part II: Physical Analysis

In this work different physical mechanisms that could lead to the direct proportionality between la and IB highlighted in Part I as the signature of substrate enhanced electron injection (SEEI), are analyzed in detail. By means of experiments and simulations we substantiate the current interpretation of SEEI in terms of an impact ionization feedback process and attribute a quantitatively negligible role to both drain avalanche hot electron injection and substrate electrons generated by the photons emitted by channel hot electrons. These experiments reconcile the current explanation of SEEI with the well known phenomenon of photon assisted minority carrier injection in the substrate, whose presence is clearly detectable in our devices, but whose impact on the gate current is estimated to be orders of magnitude smaller than that of impact ionization feedback.