Empirical process planning for exposure controlled projection lithography
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The stereolithography (SLA) process is a rapid prototyping technique in which a solid physical model of a part is made directly from a three dimensional CAD by repeatedly exposing ultraviolet light at certain regions with a liquid photopolymer resin bath. It is based on the principle of curing (hardening) a liquid photopolymer into a specific shape. The Exposure Controlled Projection Lithography (ECPL) process is developed based on SLA as a method to fabricate precise microstructure for micro-optics’ application. In the ECPL process, ultraviolet light patterned by a dynamic mask passes through a transparent substrate to cure liquid photopolymer resin into a desired shape. The dimensions of the part can be controlled by the exposure time and functional pixels in the dynamic mask. The primary objective of this research is to increase the accuracy of the process plan for fabricating micro-optical elements using the ECPL process. A process planning method to predict the shape of a part cured by the ECPL process is available in literature and is based on solving polymerization kinetics and irradiation model. The dimensional error of the cured part resulting from using this process planning method was about 15%. The goal for this research is to modify the existing process planning method to improve the dimensional accuracy and to reduce the dimensional error within 5%.