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High-quality percussion drilling of silicon with a CW fiber laser

It has been shown that 30 ns FWHM duration pulses from a MOPA fiber laser (wavelength: 1064 nm) cleanly micromachines silicon with little cracking or heat-affected zone1. In this paper, we show that similar results can be achieved using a 1070 nm quasi-continuous wave laser pulsed with a 6.6 μs duration (average power: 2.8 W) in combination with coaxially delivered nitrogen assist gas. The holes are cut at a 5 kHz repetition rate with a resulting diameter on the order of 15 μm and an etch rate of up to 18 μm/pulse. Hole size is increased for longer pulses and the heat-affected zone broadens to greater than 25 μm with no assist gas. By combining low coherence microscopy with machining, we depth image the machining front and obtain in situ images during and after the drilling process showing rich cut dynamics in real time.