Computational metrology method of collector mirror for EUV lithography

Abstract

The characterization and measurement of the grating structures fabricated on the collector mirror are critical for achieving high spectral purity of the extreme ultraviolet lithography (EUVL) light source. In this paper, we propose a two-step method to enhance metrology for measuring the deformed grating structures on the EUVL collector. A scalar diffraction model is established for the deformation analysis of the collector gratings with high efficiency and accuracy. Then, a two-step method is applied, of which a “Go, No-Go” model acts as the first step to directly identify whether the gratings are qualified, reducing unnecessary calculations. As the second step, only for those unqualified gratings, an improved multi-objective particle swarm optimization model is brought out to accurately make a quantitative reconstruction on the key dimensional parameters of the collector gratings. The proposed method offers a novel scheme for facilitating the inverse scattering problem of the measurement on collector gratings. It eliminates the need for complex numerical calculations and the reliance on a large dataset while still providing accurate results, which is promising for the inline dimensional metrology.