Methods of forming nonvolatile integrated circuit memory devices having high capacitive coupling ratios

Abstract

Methods of forming nonvolatile integrated circuit memory devices having high capacitive coupling ratios include the steps of forming a tunneling oxide layer on a face of a semiconductor substrate and then forming a forming a first conductive layer (e.g., doped polysilicon) on the tunneling oxide layer. A floating gate electrode mask is then patterned on the first conductive layer so as to expose a portion the first conductive layer. A second conductive layer is then patterned on the exposed portion of the first conductive layer and on sidewalls of the floating gate electrode mask, to define a concave or U-shaped floating gate electrode having conductive sidewall extensions. The sidewall extensions increase the effective area of the floating gate electrode and increase the capacitance coupling ratio which enables programming and erasing at reduced voltage levels. A first electrically insulating layer is then formed on the U-shaped floating gate electrode, opposite the tunneling oxide layer. A control gate is then formed on the first electrically insulating layer, opposite the U-shaped floating gate electrode.