Application of aspheric technique in immersion lithography lighting system

NA1.35 immersion lithography lighting system is the core of the very large scale integrated circuit device. In order to satisfy the high resolution requirement of lithography exposure optical system, aspheric lens could be added to decrease the lenses number and increase the energy usage ratio. To solve disadvantages of processing difficulty and low control accuracy of aspheric lenses, the optimization control and testing method of aspheric surface were proposed. By optimizing the aspheric shape to guarantee steradian as well as aspheric inflection point, processing and texting control range could be also satisfied. The illumination system had the largest number of module coupling lenses. By optimization of aspheric lenses, number of lenses decreased from 12 to 9, and energy utilization increased about 25%. In addition, prosperities of NA consistency, image telecentic rate, dispersion spot diameter and distortion were improved, which satisfied the exposure energy requirements on the mask surface of the optical system. So, the aspheric control technology had good processability and detectability.