Modeling And Control Algorithm Of Immersion Liquid For Immersion Lithography

Currently, immersion lithographer is considered to be high-end product on the market. It achieves high resolution through filling the gap between the last lens of its projection system and silicon wafer with high refractive media. In order to improve the resolution of the lithographer smoothly, a high precision temperature control system and advanced temperature algorithm must be introduced, without any secondary pollution. This paper includes the following parts:By studying the requirements of immersion liquid temperature control system comprehensively, a new temperature control schematic diagram has been designed, which introduces a bypass loop to improve temperature stability and an injection branch to stabilize performance of liquid injection unit.Because of delay, disturbance and non-linear characteristics of the control system, this paper presents a cascade control structure with feedforward and lag compensation to reduce those negative factors. Then, the guide zone model, inert zone model and environmental perturbation model have been achieved using ‘gray' identification method.Based on above models, an algorithm composed of step algorithm, integral separation PI algorithm, feedforward algorithm and lag compensation algorithm has been proposed. And simulation has been done using Simulink, which shows that the algorithm improves the robustness of the system significantly, compensates the time-delay problem, and reduces the overshoot.Finally, an experiment rig has been built. The performance of the system, which includes resolution, stability, robustness, et al, has been tested. And the experiment results shows that the temperature stability of the immersion liquid can be controlled within 22 ±0.007?/30 mins, which meets the needs of immersion lithographer and verifies the validity of the control algorithm.