Underwater laser micromachining of silicon in pressurized environment

Optical interference caused by gas bubbles in water is of prime concern in underwater laser micromachining process since it importantly affects the quality of laser-ablated surface and material removal rate. This study applied positive water pressure in the underwater laser ablation with the attempts to reduce the bubble size, minimize the optical disturbance to the laser beam in water, and promote the cut quality. A nanosecond pulse laser was used for grooving a single-crystalline silicon wafer in a pressurized water environment. The effects of water pressure and average laser power on groove width, groove depth, size of heat-affected zone, and cut surface morphology were examined and discussed together with the analysis of laser beam refraction in water. The results revealed that the higher the water pressure, the cleaner the cut surface, and smaller heat-affected zone and higher aspect ratio of groove were obtained. The ablation technique proposed in this paper could be a promising method for scribing silicon and plausibly other semiconductor materials at high removal rate with high cut quality and negligible damage.