The influence of surface electric fields on the chemical passivation of Si-SiO2 interfaces after firing

Abstract

In this work it is demonstrated that the presence of surface electric fields during a post-deposition anneal can impact the chemical passivation of SiO2 + SiNx double layer stacks. Although the surface passivation generated in such dielectrics is well known, we demonstrate that an electric field present in the dielectric not only modifies the surface carrier concentration but can also induce a chemical change in the interface properties upon annealing. By tailoring the surface electric field in the dielectric stack prior to annealing, it is shown that the capture rates at the Si-SiO2 interface can be modified depending on the field polarity and magnitude. Planar FZ specimens are examined here. It is found that annealing in the presence of a field pointing into the Si surface, as intrinsically occurs in positively charged SiNx, increases the dielectric charge density without any substantial changes in the chemical passivation. When an opposite electric field is established by negative charge on the dielectric, the chemical passivation worsens substantially where a fourfold increase in the capture rate of minority carriers is obtained via electrical characterisation. We hypothesise that the electric field may be driving atomic hydrogen away from the interface, thus damaging the passivation.