Sub-1 nm Misalignment Sensing with Cascaded Interference in Polar Coordinate for Lithography

In previous work, we introduced a structured illumination strategy using linear gratings to achieve sub-nanometer misalignment sensing, which significantly enhanced accuracy and sensitivity. However, the approach was limited to linear gratings, as maintaining consistent fringe patterns during interference and modulation is essential for precise alignment. To overcome this limitation, we propose qhat we believe to be a novel misalignment sensing method based on cascaded interference in polar coordinates, enabling the use of sub-wavelength circular gratings for sub-nanometer alignment. Experimental results demonstrate that this method achieves 2D misalignment measurement with an impressive accuracy of 0.62 nm across a 50 µm range, providing a robust solution for wide-range, high-precision 2D alignment.