Mobile ion contamination of p+ and n+ polysilicon gates was studied by using the triangular voltage sweep method and secondary ion mass spectroscopy. The mobile ion densities for p+ polysilicon were much higher than those for n+ polysilicon. Most of the Na+ ions in the gate oxide, which predominated over mobile ions, diffused laterally from the gate edge in the case of p+ polysilicon; rather than through the polysilicon. In the case of n+ polysilicon, the laterally diffusing Na+ ions were gettered more effectively than were those which penetrated vertically through the polysilicon.

H.Tanaka, I.Aikawa, T.Ajioka: Journal of the Electrochemical Society, 1990, 137[2], 644-7