High quality laser micromachining of silicon: A crystallographic comparison of process results achieved with state-of-the-art tripled Nd:YAG and IR lasers

The ability to cut, scribe, and drill holes and slots in silicon material is of great interest for many applications in the microelectronics and semiconductor industry. We investigated the use of a Q-switched frequency-tripled Nd:YAG laser for rapid micromachining of silicon and compared the results to results achieved with a pulsed fiber laser operating near 1060nm. Cutting, drilling, marking and surface ablation were performed by direct writing using a high-speed x-y galvano-mechanical beam positioner equipped with a telecentric lens focusing system and a high precision x-y-z stage. This paper focuses on circular and linear cutting experiments on "thick" silicon wafers, i.e. wafers with a thickness of 440 ?m and above. The sample morphology was studied by scanning electron microscopy; the results indicate 8-10 times larger surface roughness on the IR processed samples. We also applied X-ray double-crystal topography to analyse the defects and local strain induced by the two laser processes. The topographs show remarkable differences between the cuts generated by the UV laser and the cuts produced by the IR laser. Our data reveals the capabilities and limitations of both laser types for micromachining in different silicon wafers and helps the user select a laser for a specific process. The results demonstrate the advantages of the short-wavelength laser for damage-free micromachining of silicon.