Metal contamination of silicon wafers in diamond wire sawing processes depending on the sawing parameters

Multi wire sawing of silicon ingots is still the standard process for the production of silicon wafers for solar cells. The diamond wire sawing (DWS) technique is increasingly becoming the dominant wafering technique for mono- and multicrystalline silicon bricks. In DWS a steel core wire with a coating layer of nickel is often used to fix the diamonds on the wire. Parts of the nickel coating are abraded during the wafering process and are found in the silicon kerf, may be dissolved in the cooling medium or may diffuse into the wafer surface and bulk, possibly reducing the carrier lifetime. In this contribution, the effect of different parameters during DWS processes on the metal contamination of silicon wafers and kerf is investigated. The effect of metallic impurities on the conversion efficiency of PERC solar cells is shown.