Experimental Implementation and Investigation of Real-Time Metrology for Exposure Controlled Projection Lithography

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.