光ヘテロダイン干渉式位置検出法

概要

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A new optical-heterodyne interferometry alignment technique with diffraction gratings is developed for quarter micron X-ray lithography. To obtain detection accuracy as good as a few tens of nanometers, a phase signal is utilized instead of a conventional intensity signal. The relative lateral displacement between mask and wafer is detected by measuring the phase difference between heterodyne beat signals generated by projecting two laser beams from +1st-order and -1st-order diffraction directions on the mask and wafer grating marks. The displacement signal is not influenced by gap variation using symmetric optics. A lateral displacement detection resolution better than 10 nm is obtained by the experimental alignment setup. Using this optical-heterodyne interferometry alignment method, a stepper is developed for synchrotron X-ray lithography. Alignment servo control is established by combining a 4-channel alignment system with highly accurate stages. The total overlay accuracies of ±0.07 μm (3σ) are achieved.
公益社団法人精密工学会の論文
1991-02-05