The electrochemical etching of (100) n-type Si was investigated in dilute HF solutions containing copper. Two anodic current regimes were observed : one, as expected, dependent on the HF concentration and the other one on the Cu concentration. The enhancement of the anodic current in the Cu concentration dependent regime is related to an increase of the chemical etching of silicon associated to reactions involving OH (or H2O) species. The etching of Si, influenced by the metal, occurs concomitantly to the reduction of Cu ions, Rutherford backscattering from Cu deposits obtained in the anodic regime revealed the existence of oxygen at the Cu/Si.