Nonlinear PI-control temperature control algorithm for projection lens

Abstract

Image quality is the most important performance of optical lithography tool and it is influenced by many factors. Temperature stability of projection lens is one of the main factors. It is difficult to control temperature stability of the projection lens because of its features of big inertia, multi-time-delay and multi-perturbation. Temperature control unit (TCU), which is used to control the projection lens temperature, is required to operate far away from projection lens, otherwise it will increase COO of lithography tool and its vibration will affect the performance of projection lens. So a remote temperature control method is proposed. A two-input and two-output intelligent algorithm is presented to improve convergent rate and steady-state accuracy of the temperature control system for projection lens. Control process is divided into five phases according to the ideal dynamic response curve. A nonlinear PI algorithm is recommended to precisely adjust temperature and an intelligent decision decides the switch of five multi-phases. The experiment results show that ±0.006°C temperature stability can be realized and the algorithm has advantage of quick convergent rate, strong robustness and self-adaptability. This algorithm has been used in optical lithography tool with 100nm CD and has achieved good temperature stability.