Conversion of Silicon Nitride Films to Anodic SiO[sub 2]

Abstract

An introduction is given to the principles underlying the anodization of pre‐existing dielectric films. In the case of amorphous silicon nitride films on a silicon substrate it is shown that conversion of the nitride film to anodic occurs by oxygen ions reacting with the nitrogen, the latter being evolved from the film as N2 or as a nitrogen oxygen compound. The process has been applied to the opening of windows in structures. Nitride films up to 1000Aå thick can be rendered soluble by a single anodization step to 350v; thicker films require a repeated anodization. The electric field applied during anodization causes a shift in surface potential of the silicon substrate. The original surface potential can be restored by a bake in forming gas at 500°C. High‐resistivity silicon tends to passivate under anodic bias; growth of an oxide film occurs only at very large current densities.