Focusing and leveling are two imperative processes to adjust the wafer onto the ideal focal plane of projection lithography tools. Based on moire fringes formed by particularly designed dual-grating marks, the four-channel focusing and leveling scheme is proposed and demonstrated. These relationships between the tilted amount of wafer, the vertical defocusing amount, and the phase distributions of moire fringes are deduced. A single-channel experimental setup is constructed to verify the performances of proposed method. Results indicate that the tilted amount and the vertical defocusing amount can be precisely detected with accuracy at 10(-4) rad and several nanometers level, respectively, and therefore meet the demand of the high-demanding focusing and leveling processes.
1.Chinese Acad Sci, Inst Opt & Elect, State Key Lab Opt Technol Microfabricat, Chengdu 610209, Peoples R China 2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China 3.Xuchang Vocat & Tech Coll, Xuchang 461000, Peoples R China
Di, Chengliang,Yan, Wei,Hu, Song,et al. A Moire-Based Four-Channel Focusing and Leveling Scheme for Projection Lithography[J]. IEEE PHOTONICS JOURNAL,2014,6(4).