Time-delay-integration dark-field digital holography with extended depth of field for wafer defect inspection

Dark-field inspection systems are widely used for front-end defect inspection on unpatterned wafers due to their non-contact operation, high sensitivity, and high throughput. However, with the adoption of objectives with high numerical aperture and the extension of illumination wavelengths into the ultraviolet range, micrometer-scale wafer surface variations can induce severe defocus, leading to degraded imaging performance and potential false negatives. Here, we propose a time-delay integration dark-field digital holographic microscopy framework to improve inspection throughput while extending depth of field. A time-delay integration camera replaces conventional area-array detectors for hologram acquisition, enabling continuous wafer scanning without time-consuming step-and-stop operation. Digital refocusing is then performed to recover an axial image stack across different defocus planes, which is subsequently processed by a depth-of-field fusion algorithm to generate a single all-in-focus image. Experimental results demonstrate that the proposed method achieves a depth-of-field extension exceeding 20 µm while restoring high image sharpness and signal-to-noise ratio, and shows good agreement with mechanically focused reference images. The proposed approach provides a promising solution for high-throughput defect inspection in semiconductor manufacturing and quality control.