Silicon anodization in HF ethanoic solutions - Competition between pore formation and homogeneous dissolution

This work studied the morphology of p-Si anodized in ethanoic HF solutions. Parameters investigated were the anodization duration, the current density, and the HF content of the solutions. Due to the homogeneous dissolution of silicon in low concentrated HF solutions, the "apparent'' porosity obtained from mass measurements indicates a drastic change between 22 and 28 wt % HF solutions. Both the homogeneous dissolution and the pore formation are characterized by a valence slightly lower than 2. The chemical dissolution, which can attain 0.25 nm/s, is the reason for deviation from the two-electron electrodissolution. X-ray photoelectron spectroscopy measurements reveal that the anodization conditions, which lead to homogeneous dissolution, increase the O/F ratio at the surface of the sample. These compositional changes and modification of hydrogen termination are responsible for the homogeneous dissolution observed in solutions with low HF content. (C) 2002 The Electrochemical Society.