Influence of the grain structure on the Fermi Level in polycrystalline silicon: a quantum size effect?.

It has been observed by several authors that MOS devices with polycrystalline Si gates behave differently depending on the doping species in polySi: the work-function difference between the silicon substrate and the gate(phips) is higher when the gates are doped with arsenic than when they are doped with phosphorus. As a function of the doping level, this difference becomes first noticeable at -10 sup (19) cm sup (-3), and then it increases for heavier doped materials - reaching 120 meV near the dopant solubility limit. We believe that the different behavior of phips can be explained by different grain textures at the polySi/SiO sub 2 interface. Our TEM analysis of the films indicates that while P-doped material consists of large (~3000 angstroms) grains, As-doped polySi preserves its as- deposited columnar structure - even after a high temperature anneal.