Dion, J., “MICROMACHINING OF PHOTOSENSITIVE GLASS WITH AN ARF EXCIMER LASER”, MSc in Electrical Engineering, 2008, Université de Sherbrooke, Sherbrooke, Canada. [pdf]
Glass is a technologically important material finding numerous applications in photonicsand optoelectronics. In the recent decade, we have also observed a growing interest inexploring the potential of this material for the manufacture of micro-electro-mechanicalsystems (MEMS). Conventional methods for micromachining of glass are prohibitivelyslow, and laser ablation leads to macrocracks and rough surfaces morphologies. In thatcontext, photosensitive glass ceramics, such as FoturanTM, offer significant advantages infabrication of commercial grade, optically transparent, two- and three-dimensional (2Dand 3D) microstructures. To address the problem of rapid fabrication of such microstructureswith smooth surface morphology, we have undertaken a study of micromachiningof FoturanTM with an ArF excimer laser (λ = 193nm) mask projection system. To ourknowledge, this is the shortest wavelength laser ever used for processing of FoturanTM.The applied micromachining technique consists of three major steps: 1) Irradiationwith the laser, 2) High-temperature annealing and, 3)Wet etching to remove the irradiatedand annealed glass volume. Due to the strong optical absorption at 193 nm, it wasexpected that a better control could be achieved of the machined surface morphologywhen compared to the previously reported results obtained with 266 and 355 nm lasers,or with femtosecond lasers. At the same time, the application of the excimer laser maskprojection should allow processing of relatively large dimension wafers.We have demonstrated that a one-step irradiation approach allows fabricating craterswith the maximum depth not exceeding 35 μm. Deeper craters, up to 120 μm, have beenfabricated following a series of irradiation-annealing-etching steps. We have fabricated aseries of complex 3D microstructures using special masks and a mask scanning technique.The amplitude of the surface roughness of as-fabricated microstructures was, typically,not worse than 100 nm. This is expected to be reduced to less than 10 nm by implementingpost-processing annealing. The results of this study have indicated clearly thefeasibility of the 193 nm excimer laser and the mask projection technique for rapid fabricationof 3D microstructures in photosensitive glass. The proposed method is expectedto find applications in the fabrication of, e.g., shallow microfluidic devices, or a specialtyof optoelectronic devices.
