Lateral Diffusion of Na+ Ions from the Gate Edge into the Oxide for P+ and N+ Polycrystalline Silicon Gates

Abstract

Mobile ion contamination for p+ and n+ polysilicon gates has been studied using the triangular voltage sweep method and secondary ion mass spectroscopy. Mobile ion densities for p+ polysilicon gates are much higher than those for n+ polysilicon gates. Most of Na+ ions in the gate oxide, which are dominant of the mobile ions, diffuse laterally from the gate edge for p+ polysilicon gates but not through the polysilicon. For n+ polysilicon gates, the laterally diffusing Na+ ions are gettered more effectively than those penetrating vertically through the polysilicon.