Large-range lithography misalignment sensing with sub-2-nm accuracy through automatic dual-frequency Moiré fringes...

Lithography alignment techniques based on Moiré fringes have been widely adopted due to their high precision and simple structure. However, the sensing range for misalignment is limited by the periodic aliasing of the fringes. Additionally, spectral leakage during phase extraction leads to accuracy deterioration. These two significant drawbacks prevent this technique from meeting the requirements of next-generation lithography manufacturing. To address these limitations, we propose a novel composite alignment mark comprising upper and lower sets of differential gratings, which interfere to generate dual-frequency Moiré fringes. Moreover, an automatic lookup difference table algorithm is developed to analyse the offset of the dual-frequency Moiré fringes, enabling large-range misalignment sensing between the wafer and the mask. Furthermore, the excellent two-dimensional Hanning self-convolution window is established to effectively suppress spectral leakage. Both simulations and experiments validate the rationale and feasibility of the proposed scheme. The results demonstrate a significant increase in the effective range, from 2.6 µm to 120 µm, while maintaining real-time (0.15 s) misalignment measurement with sub-2-nm accuracy. Moreover, this proposed strategy can be extended to similar fields where relative position measurements between objects are required.