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Real-time correction of periodic nonlinearity in homodyne detection for scanning beam interference lithography

Abstract. Scanning beam interference lithography (SBIL) is an advanced large-area grating manufacturing technology. To produce gratings with nanoscale phase accuracy, the phase detector is demanded for a high precision in SBIL. A well-designed homodyne detector with a four-orthogonal detection is proposed to meet the harsh measurement requirements. However, the phase detection could suffer from periodic nonlinearity error, which changes slowly over time. A real-time correction method based on an extended Kalman filter is applied to estimate and compensate the periodic nonlinearity. The simulation results show that this method has great advantages in eliminating the time-varying periodic nonlinearity, compared with the conventional least squares fitting method. An experimental setup is also established to validate the proposed correction method.