A costly step in the solar cell production of crystalline silicon solar cells is the cutting of wafers. The standard technique is the multi-wire sawing with abrasive SiC slurries. The current industrial development is to reduce cost mainly by increasing the throughput, while maintaining a high surface quality. An occasionally occurring problem is the local appearance of deep groves in parts of the wafer surface. This phenomenon, generally denoted as saw marks, can affect many wafers in a batch and reduce the yield. The problem becomes more serious, when a high throughput shall be achieved. In the paper experimental results will be presented, which lead to a physical explanation of this phenomenon. They indicate that changes of the SiC particle size distribution along the sawing channel are responsible for the occurrence of saw marks. Such a change can be caused by viscosity changes due to the temperature increase and/or the accumulation of smaller particles in the slurry from particle breakage and silicon debris. A physical model was developed to describe the observed results. It is based on the motion of the particles in the slurry and their interaction with the wire and the crystal surface. Numerical solutions of the model can predict under which slurry and sawing conditions these instabilities occur. The experimental results are compared with these predictions.

28th European Photovoltaic Solar Energy Conference and Exhibition; 927-932