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

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 N 2 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.