Influence of tilt moire fringe on alignment accuracy in proximity lithography

A moire fringe alignment method based on dual gratings is proposed. This method uses the phase of moire fringe to measure the relative linear displacement between the mask and the wafer. In practical application, the tilt moire fringe can occur due to the incorrect positions of the mask alignment mark and the wafer alignment mark or one of them. In this work, the presence of tilt moire fringe and its influence on the alignment accuracy are thoroughly analyzed. The analysis and discussions on the relationship between the revised linear displacement and the theoretical linear displacement reveal that moire fringes with different tilt angles have different influences on the alignment accuracy. Experimental results are given to verify that the proposed method is accurate and feasible, which can be applied to lithography and other correlated fields. (C) 2012 Elsevier Ltd. All rights reserved.