A vertical stepper for synchrotron x‐ray lithography Available to Purchase

A newly developed synchrotron x‐ray stepper installed at a port of an electron storage ring of the NTT Synchrotron Facility^1–3 is described. The stepper exposes wafers in a normal atmosphere to vertically scanned synchrotron x rays with continuous alignment control throughout the exposure. The key devices of the stepper are a vertical x–y stage and an optical‐heterodyne alignment system. The x–y stage fully utilizes air lubricated ceramic components including air bearing lead screws and achieves 5 nm motion precision over a 200 mm stroke. The optical‐heterodyne alignment system detects both lateral and gap displacements between the mask and wafer gratings with accuracies of 10 and 100 nm, respectively. After wafer step positioning using a laser interferometer, alignment between the mask and wafer is executed using the optical‐heterodyne signal. In several exposure experiments, alignment capability is estimated to be better than ±0.14 μm as a 3σ value of machine repeatability. Also, several applications to device fabrication confirmed that the vertical stepper is feasible in quarter‐ to half‐micron x‐ray lithography.