Synchrotron radiation x-ray lithography beamline optics alignment using the Hartmann method

Abstract

This article studies the effect of mirror misalignment on run-out overlay errors in a synchrotron radiation based x-ray lithography system. Using the ES-5 beam-line installation at the CXrL as an example, we found that the current beamline mirror alignment method, which relies on the final beam shape and orientation at the mask-wafer plane, is insensitive to the mirror grazing incident angle alignment. Simulations using the ray-tracing program shadow indicate that a smaller than ±0.5-mrad mirror grazing angle misalignment consumes the required run-out overlay error budget of the beamline. A direct beamline run-out overlay measurement technique based on the Hartmann method was developed for the beamline mirror alignment. This measurement technique was applied to our ES-5 beamline mirror alignment procedure. The measurement results show that the beamline induced run-out error of the installed ES-5 beamline is less than 0.014 μm in both horizontal and vertical direction for a 25-mm exposure field with a mask-wafer gap of 40 μm. The across field run-out error distribution is also compared with shadow simulation results. The good agreement between measurement and simulation data indicates that our measurement technique provides a sensitive, practical, and accurate method for x-ray lithography beamline mirror alignment and evaluation.