Simulation of current transients through ultrathin gate oxides during plasma etching

Monte Carlo simulations of electron tunneling through a 3 nm gate oxide during etching of dense patterns of gate electrodes in uniform high-density plasmas reveal two current transients, which occur: (a) when the open area clears, and (b) when the polysilicon lines just become disconnected at the bottom of trenches. The first charging transient is fast (controlled by charging) and may be followed by a steady-state current which lasts until the lines get disconnected. The second charging transient lasts longer; the magnitude of the tunneling current generally decreases as the sloped polysilicon sidewalls become straighter. Most of the damage occurs at the edge gate when the open areas are covered by field oxide; however, the edge gate suffers no damage when the 3 nm oxide extends into the open areas.