A study of the impact on telecentricity to the illumination system based on CCD imaging

One of the important properties of the illumination system is of determining telecentricity for the realization of the place of wafer in the optical lithography. In this paper, we present numerical simulations of the optical imaging using four different illumination models and based on CCD imaging. We simulate the imaging of light source for different illumination pupil distributions and determine the energy centroid through the imaging of the conventional illumination which exist telecentricity of 11 mrad. Furthermore, we discuss the influencing factors of two aspects on telecentricity. One is the non-uniformity of light intensity distribution, and the other is pinhole defocus in the wafer. The range between the non-uniformity of light intensity distribution and pinhole defocus are quantified by computing the allowed telecentricity error in the illumination system. Finally, experiments have verified telecentricity measurement feasibility and validity. The presented scheme that with CCD imaging instead the actual wafer which saves cost and improves the accuracy in the optical lithography. In comparison with the measurement methods of convention the CCD imaging has a series of advantages such as fast response, high sensibility, high precision and the measurement is carried out on-line.