Influence of Different Post Porosification Cleaning Steps on the Parameters of Porous Silicon Layer Stack

Abstract

To grow a defect-free epitaxial silicon wafer (EpiWafer) on a reorganized porous silicon layer stack, the surface must be closed, smooth and particle-free. A post-porosification cleaning step prior to reorganization should significantly reduce the density of (metallic) particles on the surface. In this paper we systematically investigate the influence of different post-porosification cleaning steps on the porous layer stack. The different cleaning steps have no significant effect on the layer thicknesses. On the other hand, the porosities change after the different cleaning steps. The change in porosity correlates very well with the oxidizing effect of the solution used: SC-1 cleaning has the strongest oxidizing effect, followed by ozone cleaning, piranha cleaning and HCl cleaning. A single HF dip has the smallest effect on porosity, showing the small influence of the native silicon oxide layer formed by aging on porosity. Except for the SC-1 cleaning, the other cleanings show no significant change in the Raman peak shift and therefore in stress compared to the as-etched sample. For the SC-1 cleaning, the increase in Raman peak shift and thus stress correlates well with the increase in porosity. After a reorganization step at 1120°C, it is observed that a higher porosity of the low porosity layer in the stack leads to larger pores.