Product Code: ICAL07_M1303

Characteristics of High-Aspect Ratio Nanosecond Laser Ablation of Silicon at 355nm Wavelength
Sedao, National Centre for Laser Applications, Nui; Galway Ireland
Alan Conneely, Ncla; Galway Ireland
Gerard O'Connor, NCLA; Galway Ireland
Thomas Glynn, Ncla; Galway Ireland
Presented at ICALEO 2007

We report on pulsed laser ablation for dicing/scribing monocrystalline silicon with a frequency tripped DPSS Q-switched nanosecond laser (355nm, AVIA, Coherent). Using a Galvanometer scanhead, a laser beam (repetition rate 30 kHz, 140µJ per pulse) was focused down to a 30µm diameter spot on silicon wafer and scanned in single-line mode. A series of slots were machined by applying different number of laser scan passes and the cross-section and the side-wall of the slots were examined using optical and scanning electron microscopes. The laser machining throughput was evaluated by measuring the slot depth and the results show as the slot deepens with repetitive scans the effective ablation rate slowed down and maximum depth of 500µm was achieved (aspect ratio 17 approximately). The debris generation and transport is known to be critical in optimising throughput of laser ablative processes. Study of the debris reveals that instead of being removed from the slot part of the debris generated from laser ablation re-deposits in the slot and on the side-walls and forms a recast layer. The formation of such features narrow the open space inside the slots, which made laser beam delivery and debris transport more difficult.

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