Laser micromachining by ablation is a well established technique used for the production of 2.5D and 3D features in a
wide variety of materials. The fabrication of stepped, multi-level, structures can be achieved using a number of binary
mask projection techniques using excimer lasers. Alternatively, direct-writing of complex 2.5D features can easily be
achieved with solid-state lasers. Excimer laser ablation using half-tone masks allows almost continuous surface relief
and the generation of features with low surface roughness. We have developed techniques to create large arrays of
repeating micro-optical structures on polymer substrates. Here, we show our recent developments in laser structuring
with the combination of half-tone and binary mask techniques.
Pulsed UV laser machining is an established method for production of 2.5D and 3D features in a wide variety of materials. In addition to direct laser patterning by ablation, exposure of photoresist using pulsed lasers can eliminate the need for large area contact photomasks. Half-tone machining, either by ablation or exposure, allows the production of high quality shallow features where the surface roughness from other laser machining techniques would be unacceptable. Such features could be used as anti-reflection surfaces for mobile display devices. Features produced by lithography typically exhibit low surface roughness but have more complex fabrication processes. Here, the surface roughness of shallow features produced by half-tone lithography and half-tone ablation is investigated for a photoresist. Similar surface profiles are achieved for each technique and roughness levels are comparable for both.
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.
Laser micromachining has great potential as a MEMS (micro-electro-mechanical systems) fabrication technique because of its materials flexibility and 3D capabilities. The machining of deep polymer structures with complex, well-defined surface profiles is particularly relevant to microfluidics and micro-optics, and in this paper we review recent work on the use of projection ablation methods to fabricate structures and devices aimed at these application areas. In particular we focus on two excimer laser micromachining techniques that are capable of both 3D structuring and large-area machining: synchronous image scanning (SIS) and workpiece dragging with half-tone masks. The methods used in mask design are reviewed, and experimental results are presented for test structures fabricated in polycarbonate. Both techniques are shown to be capable of producing accurately dimensioned structures that are significantly deeper than the focal depth of the projection optics and virtually free from fabrication artifacts such as the steps normally associated with multiple-mask processes.
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.
Pulsed laser sources are widely used for the micro-processing of materials from the structuring and patterning of surfaces to the direct machining of devices. This paper discusses laser micro-processing techniques for the fabrication of microstructures with high accuracy and precision. Techniques discussed include laser mask projection techniques and direct beam micromachining using galvo-scanners and high precision motion stages, with a variety of different lasers. Examples of the application of these techniques to the manufacture of MEMS and MOEMS devices are discussed.
An efficient simulation method has recently been developed for multi-pulse ablation processes. This is based on pulse-by-pulse propagation of the machined surface according to one of several phenomenological models for the laser-material interaction. The technique allows quantitative predictions to be made about the surface shapes of complex machined parts, given only a minimal set of input data for parameter calibration. In the case of direct-write machining of polymers or glasses with ns-duration pulses, this data set can typically be limited to the surface profiles of a small number of standard test patterns. The use of phenomenological models for the laser-material interaction, calibrated by experimental feedback, allows fast simulation, and can achieve a high degree of accuracy for certain combinations of material, laser and geometry. In this paper, the capabilities and limitations of the approach are discussed, and recent results are presented for structures machined in SU8 photoresist.