Influence of tilt moiré fringe on alignment accuracy in proximity lithography

A moiré fringe alignment method based on dual gratings is proposed. This method uses the phase of moiré fringe to measure the relative linear displacement between the mask and the wafer. In practical application, the tilt moiré 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 moiré 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 moiré 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.

► Dual gratings-based moiré fringes alignment method proposed. ► Phase of moiré fringes is utilized to determine the relative linear displacement of the mask and the wafer. ► Presence of tilt moiré fringe and its influence on the alignment accuracy are thoroughly analyzed. ► Maximal alignment error less than 3 nm can be experimentally achieved.