A flash memory is a type of non-volatile memory device that may be programmed by hot electron injection and erased by Fowler-Nordheim tunneling. Typical flash memories include a plurality of memory cells formed on a semiconductor substrate. Each cell includes a drain region and a source region embedded in the substrate. A channel region is disposed between the drain region and the source region. The memory cell may further include a multi-layer split gate structure or word line. The split gate structure may include: a thin gate dielectric or tunnel oxide film formed on the surface of the substrate overlaying the channel region; a floating gate formed of an electroconductive film, such as polysilicon, overlaying the tunnel oxide; an intergate dielectric film overlaying the floating gate; and a control gate formed of an electroconductive film, such as polysilicon, overlaying the intergate dielectric film.
The source coupling ratio of a flash memory cell is generally used as an gauge to evaluate the programming and erasing efficiency of the cell. Increasing the source coupling ratio of the memory cell will generally result in an increase in the programming and erasing efficiency of the cell. Accordingly, to increase programming and erasing efficiency, a need exists for an embedded flash memory cell having a higher source coupling ratio, and a method of fabricating such a memory cell.