Analysis of electron energy distribution function in ultra-thin gate oxiden-MOSFETs using Monte Carlo simulation for direct tunneling gate current calculation

Direct tunneling (DT) current through ultra-thin gate oxide of a sub-0.1 mu m MOSFET is calculated using the semi-classical approximation. The procedu re consists in coupling the current calculation to 2D device simulation, wh ose role is to deliver the physical microscopic data necessary to the DT cu rrent estimation, i.e., the electron energy distribution at the interfaces and the potential barrier to be tunneled along the gate. We study the influ ence of drain voltage on gate current by assuming first a uniform gate oxid e layer. It is shown that the contribution of hot carriers is very small an d that the maximum of gate current density is located near the source. Then the oxide thickness fluctuations are taken into account. It is shown that high current densities run through the oxide layer in the vicinity of weak points, which is certainly related to the soft breakdown of the ultra-thin oxide layer. A correct agreement is achieved with experimental results. (C) 1999 Published by Elsevier Science B.V. All rights reserved.