Optimal design of illumination field performance relating to scanning slit in step-and-scan lithographic system

Scanning slit is an important element to form illumination area and control exposure dose in step-and-scan lithographic system. If the penumbra of blade’s edge generated by scanning slit is too large, the exposure performance can be affected. Moreover, the distortion in the corner of illumination field also has great impact on the integral uniformity of illumination. Firstly, the generation principle of penumbra of blade’s edge at reticle plane was introduced according to the illumination principle of the step-and-scan lithographic system, and then the calculation expression of penumbra of blade’s edge at reticle plane was derived by analyzing the relationship between the intensity distribution of light and the location and the thickness of blades along the optical axis. Secondly, according to different types of blades, the distortion at the junction of adjacent blades of coplanar scanning slit was analyzed. At last, based on the optical model of step-and-scan lithographic system with the numerical aperture of NA0.75, the illumination fields at reticle plane generated by the four blades in scanning slit were simulated. The results indicate that the penumbra of blade’s edge generated by coplanar scanning slit could be significantly reduced and the distortion in the corner of illumination field could also be improved by optimizing the structure design of the blades of coplanar scanning slit properly.