Product Code: ICA10_M905

On the Percussion Drilling of Si using a 20W MOPA Based Yb Fiber Laser
Authors:
Kun Li, Institute for Manufacturing, University of Cambridge; Cambridge Great Britain
William O'Neill, Institute for Manufacturing, University of Cambridge; Cambridge Great Britain
Jack Gabzdyl, Spi Lasers; Southampton Great Britain
Presented at ICALEO 2010

A study on the nanosecond fiber laser interaction with silicon was performed experimentally for the generation of percussion drilled holes. Single pulse ablation experiments were carried out on single crystalline 650µm thick silicon wafers. Changes of the mass removal mechanism were investigated by varying laser fluence up to 45 J/cm2 and pulse duration from 50 ns to 200 ns. Hole width and depth were measured and surface morphology were studied using scanning electron microscopy (SEM) and optical interferometric profilometry (Veeco NT3300). High speed photography was also used to examine laser generated plasma expansion rates.
The material removal rate was found to be influenced greatly by the pulse energy, full pulse duration and pulse peak power. A single pulse ablation depth of 4.42 µm was achieved using a 200 ns pulse of 8.86 J/cm2, giving the maximum measured machining efficiency of 31.86 µm per mJ. Holes drilled with an increased fluence but fixed pulse length were demonstrated to be deeper, cleaner, but less efficient than those produced at a lower fluence. The increased peak power in this case led to high levels of plasma and vapour interactions which resulted in increased vapor expansion rates and high pressure expulsion of liquid silicon resulting in cleaner hole formation. The experimental findings show that for a given energy, a longer, lower peak power pulse is more desirable that a high peak power short pulse for efficient drilling.