Optimal Control for Stabilizing Fringe Phase in Interference Lithography

In interference lithography, the environmental disturbances will lead to a phase drift of the interference fringes during the exposure process, resulting in a decrease of exposure contrast. Feedback control is usually used to stabilize the phase, and the choice of control algorithm will affect the exposure effect. In this paper, a linear-quadratic-Gaussian (LQG) controller combined with a Kalman filter is applied to provide an optimal feedback control by solving the problem of minimizing the variance of the residual phase errors. The phase control method is described using a state-space approach. The simulation results show that the proposed control method can effectively suppress the low-frequency phase drift, as well as the phase perturbation caused by mechanical vibrations.