MICROSTRUCTURAL CONTROL OF POROUS SILICON BY ELECTROCHEMICAL ETCHING IN MIXED HCL HF SOLUTIONS/

The role of hydrochloric acid in the fabrication of porous silicon was investigated with atomic force microscopy (AFM) and spectroscopic ell ipsometry. The study was focused on surface morphology, in terms of ro ughness and power spectral density (PSD), and layer microstructure and quality in terms of thickness, porosity, interface sharpness and laye r homogeneity. The results show that HCl can be used as an additional component in the standard hydrofluoric acid-based etching solution in order to affect different properties of porous silicon layers such as volume porosity, thickness and pore size. In addition, HCl/HF mixtures can be used to obtain samples with sharper porous silicon/silicon int erfaces and less in depth inhomogeneities as compared with porous sili con samples having similar volume porosities and thicknesses and manuf actured in conventional solutions containing HF only. Whereas large va riations in both thickness and volume porosity can be obtained by conv entional solutions, the HCl/HF interplay yield large variations in one of the mentioned parameters only. (C) 1998 Elsevier Science B.V. All rights reserved.