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Applications of Mueller polarimetry in the Fourier space for overlay characterization in microelectronics

We present a new optical technique using complete Mueller polarimetry in the back focal plane of a microscope objective to characterize the overlay defects in microelectronics industry. Exploiting the fundamental symmetries in the physics of periodic structures and polarized light and the redundancies in the angle-resolved images we prove that it is possible to measure overlay by this fast and non-destructive technique. The simulations of the one-dimensional structures have shown that the values of a chosen criterion exploiting the off-diagonal coefficients symmetries are proportional to the values of overlay defects and can reach 0.25 for a 25nm defect. The accuracy of the polarimeter used for this application becomes even more critical because it is directly linked to the overlay measurement. Beside the redundancies in the acquired data, the angular resolution allows us also to decouple the information along X and Y directions in the Fourier space. Due to this the overlay defect can be characterized and decomposed with respect to these two axes. We show that the proposed new technique is sensitive to both magnitude and sign of the shift. Thus, Mueller polarimetry in the Fourier space (MPFS) offers more parameters for the process quality control compared with conventional spectroscopic ellipsometry (SE). It means that MPFS should be more efficient than SE for the overlay characterization in microelectronic industry.