Design and research of zoom optic system applied in micro-processing using 248nm KrF excimer laser

The content of this paper is a design of zoom optic system applied in 248nm KrF excimer laser micro-processing. Due to the characteristic of KrF laser and the applied requests of micro-processing, it was determined that the maximal field of view is 1.2°, the optical material is fused quartz (JGS1) and the value of working distance is greater than 30mm. On the premise that the system has stable image surfaces and good imaging qualities under each different focal length, the goals of design include the continuous zoom ratio Γ=1~3.5 and the minimal magnification M≈0.1. In addition, the mechanically compensated method was employed to compensate image surface, so as not to change the position of the image plane in the whole range of focal lengths or magnification. The zoom optical system was composed of three parts: the front fixed group, the zoom group and the compensated group. After perfect optical calculation, the correlation of zoom ratio and focal length was obtained. The maximum of focal length is 129.2308mm and minimum is 39.92926mm when M=0.1. For continuous improvement of imaging quality, the initial configuration has been optimized by making use of ZEMAX. The result of design can achieve the goal of zoom ratio. During the zoom process, the total length of system is about 290.7065mm with the deviation Δ=±0.0403mm and the minimum of working distance is 59.3094mm. The whole system has good imaging quality and effective etching capability.