Process Modeling and In-Situ Monitoring of Photopolymerization for Exposure Controlled Projection Lithography

Abstract

One of the main challenges in additive manufacturing is to ensure the consistent production of accurate and precise parts. Investigation of real-time monitoring and closed-loop feedback control for these processes is an area with great potential for discovery and innovation. These capabilities can vastly improve the quality and efficiency of production, and make additive manufacturing a lucrative option in a wide range of applications. Among the burgeoning field of additive manufacturing, stereolithography has proven to be an effective process to create a variety of products. However, the process lacks the resolution to manufacture small parts with a high degree of accuracy and precision. In order to meet the demand of modern technology, in which the use of micro-and nano-scale products is becoming more and more ubiquitous, a method of in-situ measurement and control for micro-stereolithography is being developed. Exposure controlled projection lithography (ECPL) is a micro-stereolithography process in which UV light is projected by a dynamic mask through a transparent substrate onto photopolymer resin to grow features from the substrate surface. The interferometric curing monitoring (ICM) system monitors the ECPL fabrication in real time, using the principles of interference optics to measure small changes in the dimensions of the cured part. Additionally, ECPL has been simulated using COMSOL software to characterize the reaction kinetics. The work presented in this thesis models the curing process based the simulation and based on information from the ICM system, and compares these results to develop a more complete understanding of the optical properties of ECPL. This could be used to establish a more accurate model to estimate the dimensions of the cured part in real time, which could then be used in a feedback-controlled system to fabricate more accurate and precise parts using ECPL.