Investigation of current‐voltage characteristics of p‐type silicon during electrochemical anodization and application to doping profiling

The analysis of anodic current-potential I-V characteristics of p-type silicon in concentrated hydrofluoric acid solution shows that the mechanism at the origin of porous silicon PS formation is determined by the charge exchange at the silicon surface over a Schottky barrier formed at the interface through a thermionic emission process. In addition, a negative potential shift in the I-V characteristics is observed with increasing doping concentration which can explain the selective formation of PS towards the doping level of silicon. In fact, when a silicon wafer of different regions of doping concentration is anodized at a fixed current or potential, the dissolution current will be more important in regions of higher doping level and PS formation can only take place there. The property of selectivity is used in this work in order to determine the p-type doping impurity profiles. During anodization under galvanostatic conditions of a specific test sample presenting dopant concentration variations, it is shown that the measured anodization potential varies according to silicon doping concentration. Consequently, by converting potential values to dopant concentration, and the electrolysis time to a depth scale, a doping impurity profile can be extracted. The profile using this technique appears to be in a good agreement with the secondary ion mass spectrometry (SIMS) analysis. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)