Low stress dicing assisted by pulsed laser for multi-layer EMS

We have developed a novel debris-free in-air laser dicing technology, which is expected to give less failure of MEMS devices and hence improves yields. Our technology combines two processes: a dicing guide fabrication and a wafer separation process. The first process is internal transformation using a nanosecond Nd:YVO4 laser with high repetition rate and/or a pulsed fiber laser with 200ns pulsewidth. The laser pulses are focused inside the MEMS wafer without surface ablation. In order to make cross-sectional internal transformation, the laser beam is scanned several times with defocusing. The laser scanning speed per each scanning is 100-700 mm/sec depending on the layer material, the machining time is much faster than the conventional blade dicing. The second process is non-contact separation by thermally-induced crack propagation using a CO₂ laser or mechanical separation by bending stress In the each separation process, the internal transformation fabricated in the first process worked well as the guide of separation, and the processed wafer was diced with low stress. This dicing technology was applied for 4-inch MEMS wafers, e.g. pressure sensors, etc., and the sensor chips were separated without mechanical damages.