50-nm x-ray lithography using synchrotron radiation

A technology of proximity x-ray lithography has been developed to replicate patterns of sub-100-nm feature size using synchrotron radiation. Process modeling has been done in advance in order to optimize the mask absorber thickness. It is shown that with tungsten absorber, a 0.3 μm thickness is the most desirable for 50 nm linewidth processing. Masks compatible with a Karl Suss stepper have been fabricated using 50 keV electron-beam lithography and reactive ion etching techniques. As a result, well-defined 50-nm-wide isolated W lines and small gratings of period down to 100 nm have been fabricated. Then they have been replicated under proximity condition using Super ACO synchrotron radiation. We present details of a replication procedure with gap settings down to 5 μm and show how sub-100 nm structures can be 1:1 printed into both poly (methylmethacrylate) (PMMA) and (8.5%) MAA/PMMA resists. Finally, the results are analyzed in terms of a scaling rule to evaluate the resolution limit as a function of proximity gap using a synchrotron source.