Signal weighted overlay optimizer for scatterometry metrology

A new algorithm called Single Wavelength Overlay Optimizer (SWOOP) enhances the performance of single-wavelength optical diffraction-based overlay metrology. SWOOP combines statistical learning with a physical model to advance the performance of single-wavelength measurements to that of multi-wavelength measurements. This is achieved by making a set of multi-wavelength measurements on the first wafer during a train phase and extracting the characteristic signature of the overlay inaccuracy at the pupil plane. This inaccuracy signature is then evaluated and removed in real time for single-wavelength measurements, resulting in improved accuracy and robustness to process variation without compromising throughput.