Dicing of thin Si wafers with a picosecond laser ablation process and high-speed polygon scanner system

Currently, electrical semiconductor components such as LEDs, solar cells or transistors are commonly produced in a batch process. This way, many identical components can be processed in parallel on one big wafer; subsequently, each chip has to be singulated. In contrast to state-of-the-art technologies like blade sawing and nanosecond-based laser processes, laser dicing with picosecond lasers offers fundamental advantages [1]. Due to the short interaction time between laser and material, small kerf widths, marginal heat affected zones and minimal edge damaging are attainable. While a reduction of the kerf width leads to a higher yield per wafer, minimal thermal and mechanical damage increases the breaking strength of each die [2]. Though ablation processes with ultra-short pulsed lasers deliver best results in terms of quality, the production speed mostly suffers due to a missing technology to distribute the average power on the workpiece. In this paper an ablation cutting process of thin Si wafers with an ultra-short pulsed laser system (22.5W@5MHz, 5 ps, 532 nm) is investigated in order determine the most suitable process parameters. Beside a conventional Galvo scanner we use a novel high-speed polygon scanner to guide the laser beam to the wafer surface. With an in-house developed software and control system it is possible to obtain scanning speed higher than 200 m/s and thus the operation of high repetition rate lasers.