Ultrashort pulsed laser-dicing of silicon wafers for the decollating of conventional and hybrid solar cells

In order to cut and decollate silicon for the manufacturing of solar cells and electronic components, commonly blade sawing or nanosecond-based laser processes are used. If the cut needs to be carried out with a high precision and without causing any thermal damage to the surrounding material, ultrashort pulsed laser cutting can be used to deliver a fine and small cutting kerf. The reduction of the kerf width leads to a higher yield per wafer, if single elements need to be cut out. As a result, marginal heat affected zones with minimal edge damages are attainable. Ultrashort pulsed lasers range from pico- to femtoseconds. In order to demonstrate the best pulse duration and ablation strategy for the singling of silicon wafers, the ablation threshold for pulse durations is determined using the Liu's method. Through this method, the diameter of the ablated geometry is measured, squared and plotted against the peak fluence on a logarithmic scale. With the knowledge of the ablation threshold, various influences on cutting of silicon are compared in order to create a minimal cutting kerf with reduced heat affected zone. With decreasing pulse duration, the surface of the silicon seems to be smoother and ablation is characterized by a sharp ridge. The ablation threshold of silicon depends on the temperature, so a second laser beam for pre-heating of the silicon material is coupled coaxially with the cutting beam. This arrangement is found to improve the ablation behavior of silicon.