Closed-loop Iterative Learning Strategy And Its Application In Precision Motion Platform Of Lithography

Lithography precision motion control system is the core part of the control system of the stages control system. It includes two parts, including the step-scan exposure control and the rotation control of the two stages. The two parts of the motion control greatly affect lithography’s control precision and cutting efficiency. Therefore, this paper focuses on the research of the wafer exposure control system, and analyzes the process of the step-scan exposure and the rotation of the stages.Firstly, I have a simp le analysis of the overall structure of the lithography machines, the structure of the stage control system, as well as the distribution of macro motor. Then I make detailed analysis of the movement of the step-scan control and the rotation control of the two stages and make clear the main points of motion and the motion process of the two processes.Secondly, an iterative learning control method is proposed for the two control processes of the step-scan control and the rotation control of the two stages. Then, the learning law and control structure of the closed- loop PID iterative learning control are introduced. The simulation results show that the tracking performance of the iterative learning control system is very good. In order to improve the convergence rate of the iterative learning control, higher-order closed- loop iterative learning control method is proposed. The simulation results show that this method has a faster convergence rate. Next, I make futher simulations about the inhibit ions of the system and find out that the higher-order closed- loop iterative learning control has strong inhibit ions on the periodic interference but the inhibit ions on the aperiodic interference is weak.Thirdly, based on the analysis of previous iterative learning control methods, we get that the inhibitions on the aperiodic interference is weak. Then the higher-order closed- loop iterative learning control with forgetting factor is proposed. According to the adjustment of the alpha coefficient, the control method of the initial correction term U 0 is designed. Based on the simulation of the system, it is concluded that this scheme still has a good tracking performance and learning convergence speed. The aperiodic disturbance of force and the measured signal are simulated, and it is concluded that the higher-order closed- loop iterative learning control with forgetting factor has good inhibitions to the aperiodic disturbance. Then I analysed the recovery rate of the system after the disturbance.In order to speed up the recovery rate, when disturbance comes, we used closed- loop PID iterative learning to reduced the amplitude of the effects of the disturbance and then system changes to the higher-order closed- loop iterative learning control with forgetting again. From the simulation, I find that this method has a higher recovery rate after the aperiodic disturbance.Finally, the iterative learning control is applied to the step-scan control system, including step- motion of X motor and synchronization control of Y motors. Then the control program flow chart of the system is designed, and the control program is written. Similarly, the iterative learning control is applied to the revolut ion motor control to finish the rotation of the two stages. Then the control program flow chart of the system is designed, and the control program is written. Fina lly, I make the iterative learning control experiment and collect the experimental data. After the analisis about experimental data, it is verified that the iterative learning control help lithography control system have better performance.