Simulation and correction of lateral color and dispersion effects on image-based overlay

Overlay performance is critical to semiconductor device fabrication, and image-based overlay (IBO) remains a mainstream technique due to its simplicity and robustness. A key challenge in IBO is minimizing the tool induced shift (TIS), which stems from optical aberrations such as lateral color and dispersion. As device nodes continue to scale down and overlay tolerance shrinks to 1.4 nm, controlling TIS and reducing measurement uncertainty are of growing importance. This paper presents a comprehensive simulation-based study on how lateral color and dispersion affect TIS under various field decentering conditions and overlay target configurations. We find that when lateral color exceeds 252 nm and the target center deviates by more than 10 um from the object field of view center, TIS becomes unacceptable. Dispersion, on the other hand, introduces wavelength-dependent imaging position shift, disproportionately impacting inner and outer layers of overlay target. We propose a precise method to correct system dispersion using a dual prism wedge compensator. Experimental results show that the dispersion in both X and Y directions can be reduced to below 4 nm, effectively minimizing its impact on TIS. Furthermore, the repeatability of the multi-band dispersion test method provided in this paper is also very high. This work enhances the precision of IBO measurements and provides a foundation for future investigations into multi-aberration interactions in advanced optical metrology systems.