Ellipsometric characterization of oxidized porous silicon layer structures

Electrochemically prepared porous silicon (PS) layers were oxidized thermal ly and investigated by spectroscopic ellipsometry (SE). The SE spectra were measured in the range of 270-850 nm with a rotating polarizer ellipsometer . The PS was modelled as a mixture of void and crystalline silicon or fine- grained polycrystalline silicon with enhanced absorption due to extensive g rain-boundary regions, i.e. the complex refractive index of the layer was c alculated by Bruggeman effective medium approximation. The dielectric funct ion of the fine-grained polycrystalline silicon was taken from the work pub lished by G.E. Jellison, Jr., M.F. Chisholm, S.M. Gorbatkin, Appl. Phys. Le tt. 62 (1993) 3348. The porosity, the layer thickness and the composition o f the oxidized PS layers were determined. Oxidation at 900 degrees C was pe rformed after a stabilizing heat treatment at 320 degrees C. The oxidation at 900 degrees C for 10 min generated only a few nm silicon dioxide on sing le crystalline Si while in the case of PS with 57% porosity nearly complete oxidation was found. For PS with 68% porosity complete oxidation was obser ved. (C) 2000 Elsevier Science S.A. All rights reserved.