nitride capping layer 6 should be sufficiently thick to withstand further etching during subsequent processing steps next polysilicon layer 3 is etched away as by reactive ion etching using silicon nitride capping layer 6 as a self aligned hard mask the resulting structures are as shown in fig1 d and 2 d for the flash memory cell since the silicon oxide and silicon nitride layers of composite interpoly dielectric layer 8 act as an etch stop another dry e g a reactive ion etch is performed to remove the exposed portions of the ono composite dielectric layer 8 and polysilicon layer 7 poly 1 again using silicon nitride capping layer 6 as a self aligned mask etch selectivity during this process is high against silicon nitride and therefore the silicon nitride u201c capping u201d layer 6 retains sufficient thickness to prevent oxidation of the tungsten contact layer 5 during any subsequent high temperature annealing processing as may be seen from fig2 e a further technological advantage attendant the inventive process wherein silicon nitride u201c capping u201d layer 6 remains over the tungsten contact layer throughout processing is the ability to perform a high selectivity etch to remove the field oxide in a later step again the combination of silicon u201c capping u201d layer 6 and sidewall spacer layer portions 11 effectively prevents oxidation of the tungsten contact layer 5 during any high temperature processing associated therewith referring now to fig1 e and 2 e a series of light and medium dosage ion implantation steps are next performed to form active regions of differing dopant density and profile in.