Si wafers unpredictable inhomogeneities and their crucial role in porous Si fabrication

Porous Silicon (PSi) is a remarkably versatile material, whose structural reproducibility is highly sensitive to substrate properties and fabrication parameters. This study demonstrates that persistent inconsistencies in PSi fabrication originate not from experimental errors, but from undetected nanoscale substrate inhomogeneities that elude standard metrology. We identify these features as small-scale inhomogeneities occurring at densities as high as 8 × 108 cm-2, representing a nine-orders-of-magnitude increase over the industrial defect standards. Scanning Electron Microscopy and Kelvin Probe Force Microscopy (KPFM) were employed to probe these fluctuations, establishing a detection threshold for both defect density and charge carriers concentration fluctuations and confirming that such defects remain hidden to high-end surface metrology while critically impacting electrochemical etching. We propose that the observed morphology distortions probably result from a localized modulation of the depletion region and a consequent redirection of the tunneling current. Our results highlight how these unpredictable inhomogeneities dictate the local transition from ordered vertical growth to stochastic branched structures. Furthermore, we propose Electrochemical NanoLithography (ENL) as a high-sensitivity diagnostic tool to map these defects, enabling the efficient selection of optimal and homogeneous wafers. By ensuring substrate consistency, this approach significantly enhances the reliability of experimental data and paves the way for the successful transition of PSi technologies from laboratory research to large-scale industrial applications.