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Measurements of ablation rate have traditionally been carried out only at normal incidence. However, in real-world applications ablation is often carried out at oblique angles, and it is useful to have prior knowledge of the ablation rate in this case. Detailed information about the angular dependence is also important for the development of ablation simulation tools, and can provide additional insight into the ablation mechanism. Previously we have reported on the angular dependence of direct-write ablation at 266 nm wavelength in solgel and polymer materials. In this paper we present a systematic study of angular dependence for excimer laser ablation of two polymer materials of interest for microfabrication: polycarbonate and SU8 photoresist. The results are used to improve simulation models to aid in mask design.

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Measurements of the angle-dependent ablation rates of polymers that have applications in microdevice fabrication are reported. A simple model based on Beer's law, including plume absorption, is shown to give good agreement with the experimental findings for polycarbonate and SU8, ablated using the 193 and 248 nm excimer lasers, respectively. The modeling forms a useful tool for designing masks needed to fabricate complex surface relief by ablation.

Laser micromachining by ablation is an established technique for the production of 2.5D and 3D features in a wide variety of materials. Mask projection techniques using excimer lasers have been used to fabricate microstructures on large panels where diamond turning and reflow techniques have reached their limits. We have developed 3D structuring tools based upon UV laser ablation of polymers to create large arrays of repeating micro-optical features. Synchronization of laser pulses with workpiece movement allows layer-by-layer growth of deep structures with outstanding repeatability. Here, we show recent developments in laser structuring with the combination of half-tone and binary mask techniques. Significant improvements in surface quality are demonstrated for a limited range of structures.