High density MNOS transistor with ion implant into nitride layer adjacent gate electrode

Claim 1

In a metal nitride oxide semiconductor (MNOS) dual threshold memory transistor comprising: a semiconductor substrate comprising silicon of a first conductivity type; a pair of spaced source and drain diffusion regions of a second conductivity type formed in the substrate, the diffusion regions being separated by an interstitial portion of said substrate and sharing a common boundary therewith; a layer of oxide material adhered to the common boundary surface said oxide layer comprising a silicon dioxide layer having a central memory region having a thickness of less than about 4 nanometers located atop the interstitial portion and surrounding oxide regions of substantially greater thickness; a layer of silicon nitride material adhered to said oxide layer; an electrically conductive gate electrode adhered to the silicon nitride layer overlying the central memory region of the oxide layer; the improvement comprising the addition of ion implanted ions of the first conductivity type into and no deeper than the silicon nitride layer in those portions thereof adjacent to the gate electrode such that the implantation of the ions into those regions of the silicon nitride layer beneath the gate electrode is effectively blocked by the gate electrode.