Chromatic aberration and dispersion in image-based overlay metrology: influence analysis and correction strategy

Overlay is a key determinant of lithography quality, and IBO is one of the mainstream techniques for overlay metrology. A crucial challenge in IBO is minimizing tool induced shift (TIS). We analyze, via simulation and experiment, how chromatic aberration and wedge induced dispersion (WID) affect TIS. Incorporating a realistic field of view decenter, we identify TIS-insensitive regions of lateral chromatic aberration to constrain optical design and show that WID couples to target layer thickness and focus accuracy. We derive compensation for a double-wedge prism corrector and demonstrate WID reduction from hundreds of nanometers to less than 3 nm. We also propose a fast WID testing method that mitigates temperature drift, achieving about 2 nm (3σ) repeatability, guiding advanced node IBO.