The impact of light on the copper outplating from aqueous 0.5% HF solutions on 10-20 Ohm cm (100) silicon wafers is investigated. Illumination is found to drastically increase the copper deposition. A model based on the semiconductor properties of the silicon substrate which describes the copper plating onto silicon is proposed. It is found that the copper deposition onto these silicon surfaces is limited by the minority carrier supply at the wafer surface.