Synchrotron radiation beamline for x-ray lithography

Abstract

We designed a synchrotron radiation (SR) beamline for x-ray lithography and optimized the beamline based on ray-tracing calculations. For a beamline with a single toroidal mirror, the intensity uniformity in the horizontal direction can be improved by making the meridian radius different from that of the general focal condition. We used this method to determine beamline parameters. Converging the SR beam gave an intensity gain of about 4, and we reduced the nonuniformity of intensity distribution to less than 3%. We also estimated the overlay error due to incorrect mirror parameters to be a maximum of 14 nm with a gap of 20 μm. We calculated an exposure-gap diagram using simulation codes; the calculation accounted for absorbed energy distribution due to Fresnel diffraction, penumbral blur, electron ranges of the secondary electrons in the resist, and development properties. We found that there is a dose margin of at least ±5% to achieve ±10% linewidth control for 0.15 μm feature size for gaps below 20 μm. We made preliminary measurements of spectra and intensity distributions for the constructed beamline, and showed that the performance is as predicted by our calculations.