Development of an autofocusing system using an electrically tunable lens in large area holographic lithography

Due to the limited processing accuracy of the platform and unevenness of the glass substrate itself, a holographic lithography system is prone to out-of-focus imaging problems; therefore, the real-time focusing components are critical for holographic lithography systems. In this paper, a real-time focus monitoring and adjusting system using an electrically tunable lens (ETL) for large-area lithography is introduced. Combined with the ETL, the limited depth of field of the microscopic objective has been effectively expanded, and the automatic focusing evaluation and adjustment are achieved. The development, including simulation using Zemax, optics system design and implementation, experiments, and evaluation are demonstrated in this paper. The results show that the out-of-focus problem in our large-area holographic lithography system has been significantly alleviated.