Comparative study of the oxidation of thin porous silicon layers studied by reflectometry, spectroscopic ellipsometry and secondary ion mass spectroscopy

We present a systematic study on ultrathin porous silicon (PS) layers (40-1 20 nm) of different porosities, formed by electrochemical etching and follo wed by thermal oxidation treatment (300 degrees C and 600 degrees C) and by electrochemical oxidation. The oxidised and non-oxidised PS layers have be en analysed by spectroscopic reflectometry (SR), spectroscopic ellipsometry (SE) and secondary ion mass spectroscopy (SIMS). The SR and SE spectra wer e fitted by a multiparameter fit program and the composition and the thickn ess of the PS layers were evaluated by different optical models. PS layers, formed electrochemically in the outermost layer of a p/n(+) monocrystallin e silicon junction were successfully evaluated using a gradient porosity op tical model. The non-oxidised PS, formed in p-type silicon, can be well des cribed by a simple optical model (one-layer of two-components, silicon and voids). The spectra of the oxidised PS layers can be fitted better using an optical model with three interdependent components (crystalline-silicon, s ilicon-dioxide, voids). The SIMS results give a strong support for the opti cal model used for SR and SE. (C) 1999 Elsevier Science B.V, All rights res erved.