Real-Time Process Measurement and Feedback Control for Exposure Controlled Projection Lithography

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.