Dark-field Digital Holographic Microscopy (df-DHM) with a single lens exhibits high potentiality for future overlay metrology on semiconductor wafers. It is a powerful technique to assess the vertical alignment between structures in integrated circuits and chips, by detecting shifts between reference gratings located in different layers. However, increasing its sensitivity and accuracy is needed to meet the demand of new materials and processes. This requires minimizing artifacts introduced by the microscope setup. In this context, a computational apodization of the optical field in the exit of the microscope pupil is proposed here, with the initial aim of reducing coherent imaging artifacts. Moreover, a complete study is performed to determine the impact of the different sources of noise onto the efficiency of the method. These are: speckle noise originated from the roughness of the silicon wafer, shot noise provided by the photonic detection and scattering due to lens imperfection. The results are assessed both with simulation and experimental data on metrology targets. They show that the apodization procedure significantly reduces the impact of scattering from lens imperfections. This paper demonstrates that df-DHM has the potential to be a powerful tool in optical wafer metrology as the presented method can suppress lens scattering to very reduced levels.

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