High precision and stability temperature control system for the immersion liquid in immersion lithography

The temperature stability of immersion liquid is one of the main factors that affect the performance of the immersion lithography tool. Since the temperature control system of immersion liquid has the characteristics of time delays, full of disturbance and non-linear, the system and control algorithm should be carefully designed to control the temperature of the immersion liquid within the specification. In this paper, a control system of cascade structure with feed forward and lag compensation is proposed to reduce the time delays and the disturbance caused by the temperature fluctuation of ambient environment. Then, the mathematical model of the temperature control system is built, and the parameters of the model are obtained by 'gray' identification method. Based on the model, an algorithm which combines hierarchical control algorithm, integral separation PI algorithm, feed forward algorithm and lag compensation algorithm is designed. Last, experiments are conducted to evaluate the algorithm. The results show that the algorithm improves the robustness, compensates the time delays and reduces the overshoot. The system achieves a temperature stability of the immersion liquid within 22±0.01 °C/30 mins, and it also has a good characteristic of anti-interference.