A Moiré-Based Four-Channel Focusing and Leveling Scheme for Projection Lithography
Photonics Journal, IEEE (2014)
Abstract
Focusing and leveling are two imperative processes to adjust the wafer onto the ideal focal plane of projection lithography tools. Based on moiré 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 moiré 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.
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Key words
diffraction gratings,focal planes,lithography,moire fringes,wafer level packaging,dual-grating marks,focal plane,four-channel focusing,imperative processes,leveling scheme,moiré fringes,projection lithography,moir?? fringes,focusing and leveling,fringe analysis
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