Application of Mueller polarimetry in conical diffraction for critical dimension measurements in microelectronics

Abstract

Fast and efficient metrology tools are required in microelectronics for control of ever-decreasing feature sizes. Optical techniques such as spectroscopic ellipsometry (SE) and normal incidence reflectometry are widely used for this task. In this work we investigate the potential of spectral Mueller polarimetry in conical diffraction for the characterization of 1D gratings, with particular emphasis on small critical dimensions (CDs). Mueller matrix spectra were taken in the visible (450-700 nm) wavelength range on a photoresist grating on a Si substrate with 70/240 nm CD/period nominal values, set at nine different azimuthal angles. These spectra were fitted with a rigorous coupled-wave analysis (RCWA) algorithm by using different models for the grating profile (rectangular and trapezoidal, with or without rounded corners). A detailed study of the stability and consistency of the optimal CD values, together with the variation of the merit function (the mean square deviation D2) around these values, clearly showed that for a given wavelength range, this technique can decouple some critical parameters (e.g., top and bottom CDs, left and right sidewall projections) much more efficiently than the usual SE.

Measurement configuration optimization for accurate grating reconstruction by Mueller matrix polarimetry

“…8 A recent study on spectroscopic MMP reported that the Mueller matrices obtained in some measurement configurations may help decorrelate the fitting structural parameters. 9 They further proposed to choose the measurement configuration with small parameter correlations and small estimated precision of the structural parameters. 10 It is also interesting to note from the previous works 4,5,10 that the accuracy of the extracted structural parameters varies greatly in different measurement configurations.…”

Modeling ellipsometric measurement of three-dimensional structures with rigorous coupled wave analysis and finite element method simulations

“…2 Optical critical dimension (OCD) analysis makes use of this data in conjunction with a structure that closely matches the experimental reality (using SEM, TEM, and so on, information) to model the system. 3 Typically, some regression-based fitting is involved, i.e., structural parameters are varied in order to minimize deviation from the experimental data. 4 When the figure-of-merit (usually mean square error) is minimized, the structural parameters are determined and compared again to other metrology tools for value confirmation, although some variation is expected depending on the method used for comparison.…”

Sensitivity analysis and line edge roughness determination of 28-nm pitch silicon fins using Mueller matrix spectroscopic ellipsometry-based optical critical dimension metrology

“…However, Mueller measurements have better sensitivities to small structural changes and provide more information about the sample than traditional spectroscopic ellipsometry (SE) and spectroscopic reflectometry (SR) measurement. 9,10 Profile reconstruction of patterned structures in scatterometry models that incorporate line roughness has been largely neglected likely because it increases the number of floating parameters and the correlation between these parameters and computation time. The multiparameter scatterometry models that include the surface roughness as demonstrated in this study can be used offline for predictive modeling and a librarybased search can be carried out as a quick and effective approach for LER measurements.…”