Experimental study of Talbot imaging moiré-based lithography alignment method

• A four-quadrant gratings alignment method is further studied for proximity lithography.
• The influence of the gap between the mask and the wafer on the contrast of moiré fringe is investigated.
• This paper concentrates on the optimization of parameters of alignment marks to achieve the resulting moiré fringes with an optimum contrast.

A four-quadrant gratings alignment method was presented for proximity lithography, which experimentally achieved the alignment accuracy of nanometer level. The alignment marks consist of gratings with slightly different periods, leading to different Talbot distances with the same monochromatic planar wave. The contrast of moiré fringe varies with the gap between mask (alignment mark) and wafer (alignment mark), which will affect the phase comparison, and induce more errors as well. This paper concentrates on the optimization of parameters of alignment marks to achieve the resulting moiré fringes with an optimum contrast. By simulation and experiment, we investigate effects of the gap on the contrast, based on which, the design principle of alignment marks is concluded, and it is helpful to the practicability with our proposed alignment method.