POROSITY DEPTH PROFILING OF THIN POROUS SILICON LAYERS BY USE OF VARIABLE-ANGLE SPECTROSCOPIC ELLIPSOMETRY - A POROSITY GRADED-LAYER

Variable-angle spectroscopic ellipsometry was used to determine nondes tructively the porosity depth profile and thickness of thin porous sil icon layers produced by anodization of p(+)-doped silicon wafers. A po rosity graded-layer model is presented and used in the analysis of the material. In the porosity graded-layer model an inhomogeneous layer i s built up by several thin sublayers with the porosity changing slight ly from one sublayer to the next. Results from the ellipsometry analys is and from transmission electron microscopy reveal inhomogeneous laye rs whose porosity and thereby optical properties change with their dep th in the layers. (C) 1998 Optical Society of America.