Browsing by Subject "exposure controlled projection lithography"
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Item Experimental Implementation and Investigation of Real-Time Metrology for Exposure Controlled Projection Lithography(University of Texas at Austin, 2016) Zhao, Xiayun; Wang, Jenny M.; Zhao, Changxuan; Jariwala, Amit; Rosen, David W.Exposure Controlled Projection Lithography (ECPL) is a stereolithography based process, curing photopolymer parts on a stationary substrate. To improve the process accuracy with closed-loop control, an in-situ interferometric curing monitoring and measurement (ICM&M) system was developed to infer the output of cured height. The previously reported ICM&M method incorporated a sensor model and online parameter estimation algorithms based on instantaneous frequency. In this paper, to validate the ICM&M method, an application program was created in MATLAB to integrate the ECPL and ICM&M systems and to acquire and analyze interferograms online. Given the limited computing power, the interferogram analysis is performed offline. Experiments were performed curing square samples by varying exposure time and intensity. They show that the ICM&M can provide a cost-effective metrology for cured heights with excellent accuracy and reliability, and decent capability of estimating lateral dimensions. The offline ICM&M is a convincing demonstration and benchmark for the real-time ICM&M metrology.Item Process Modeling and In-Situ Monitoring of Photopolymerization for Exposure Controlled Projection Lithography (ECPL)(University of Texas at Austin, 2017) Wang, J.; Zhao, C.; Zhang, Y.; Jariwala, A.; Rosen, D.Exposure controlled projection lithography (ECPL) is an additive manufacturing process in which photopolymer resin is used to fabricate three-dimensional features. During this process, UV curing radiation, controlled by a dynamic mask, is projected through a transparent substrate onto the resin. COMSOL software has been used to model the photopolymerization reaction kinetics, predicting the cured part geometry based on certain process parameters. Additionally, an Interferometric Curing Monitoring (ICM) system has been implemented to acquire real-time information about the optical properties of the cured part. Potential sources of error with the real-time monitoring system were investigated. Additionally, refractive index and degree of conversion changes were modeled throughout the reaction. Measured and simulated results were compared to understand the ICM signal with the reaction kinetics. These comparisons were used to validate the simulation model and identify system level errors that must be reconciled to improve the accuracy and precision of the ECPL process.Item Real Time Monitoring of Exposure Controlled Projection Lithography with Time-Varying Scanning Points(University of Texas at Austin, 2016) Zhao, Changxuan; Jariwala, Amit S.; Rosen, David W.Exposure Controlled Projection Lithography (ECPL) is a stereolithographic process in which photopolymer resin is used to fabricate lens shaped features. During this process, a dynamic mask projects radiation patterns through a transparent substrate onto the photopolymer resin to grow features from the substrate surface. We present a novel method to monitor the photopolymerization process in real-time with higher spatial resolution in a plane perpendicular to the polymerization growth. A Spatial Light Modulator (SLM) was incorporated into our Interferometric Cure Monitoring (ICM) system, which periodically moves the positions of the scanning points onto the curing area to estimate the cured part height. This time-varying scanning strategy avoids interference caused by points too close to one another and enables higher spatial resolution than fixed scan patterns. This time-varying multi-point monitoring approach is experimentally validated to measure the cured part height and the lateral dimensions of the cured part at the substrate level.Item Real-Time Process Measurement and Feedback Control for Exposure Controlled Projection Lithography(University of Texas at Austin, 2017) Zhao, Xiayun; Rosen, David W.The Exposure Controlled Projection Lithography (ECPL) is an additive manufacturing process that can cure microscale photopolymer parts on a stationary substrate with patterned ultraviolet beams underneath. An in-situ interferometric curing monitoring and measuring (ICM&M) system is developed to measure the ECPL process output of cured height profile. This study develops a real-time feedback control system that utilizes the online ICM&M feedback for automatically and accurately cure a part of targeted height. The experimental results directly validate the ICM&M system’s real-time capability in capturing the process dynamics and in sensing the process output, and evidently demonstrate the feedback control system’s satisfactory performance in achieving the desired height despite the presence of ECPL process uncertainties, ICM&M noises, and computing interruptions. A comprehensive error analysis is reported, implying a promising submicron control with enhanced hardware. Generally, the study establishes a paradigm of improving additive manufacturing with a real-time closed-loop measurement and control system.