Amplitude and Phase Asymmetry Estimation in Imaging Technologies to Achieve High Accuracy in Overlay Metrology

摘要

A metrology method is provided for deriving metrology measurement parameter value (s) by identifying the value (s) where the corresponding metrology measurement signal (s) have minimal amplitude asymmetry. Selecting measurement parameter values as disclosed significantly reduces measurement inaccuracies. For example, wavelength values and / or focus values may be detected to indicate minimal amplitude asymmetry and / or minimal phase asymmetry. In some embodiments, the wavelength value providing the minimum amplitude asymmetry also provides the minimum signal sensitivity to the focus. The developed metrics may further be used to indicate process robustness across the wafer and the lot. In some embodiments, imaging accuracy may be improved by thru-focus landscape of amplitude asymmetry and parameter value detection with minimal amplitude asymmetry.