Changes of n-Si (111) silicon surface morphology after anodisation at different voltage conditions in dilute NH4F solutions were studied by AFM technique. The electrochemical etching was done with respect to current-voltage (I-V) characteristics. The Si surface was investigated at increasing and constant voltage conditions. The porous silicon was formed at potentials slightly anodic from the rest potential (from -0.6 V to 0.02 V). On the other hand silicon oxide formation and electropolishing occurs at higher anodic potentials. The sustained current oscillations take place in the Si electrode, at 6 V potential in dilute NH4F solution. The nature of oscillations was attributed to cyclic silicon oxide formation and its dissolution. The surface undergoes from smooth (before oscillation peak) to rough (little before top of the peak) during oscillation peak, and finally transforms to smooth at the bottom of the peak. It was confirmed by the roughness parameter.

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