A simple model for light scattering by a Crystal Originated Particle (COP) was studied using surface scattering theory. By use of this model, we can explain the base of the separate detection technique for COPs and particles, which is one of the important features of the Wafer Surface Analyzer WM-3000 (Topcon, Japan). As the first approach, Angle Resolved Scattering (ARS) formula was applied and the cross-section of a COP was assumed to be a square in general, but it sometimes changed the shape from a triangle to a trapezoid due to a beam scanning path on a wafer. The intensity distribution of the scattered light was calculated for each shape of many kinds of cross-section, and was averaged over them. Then, the relative intensity distribution of the scattered light was calculated. The optical system of WM-3000 has two incident beams with different conditions. It is possible to detect COPs and particles separately using difference between their scattering characteristics. To compare the results of calculation with the measurement, the ratio between two scattered beams caused by two different incident beams was calculated. It was shown that calculated ratio is qualitatively agreed with the value measured with WM-3000.
"Simple model for light scattering by a COP", Proc. SPIE 3998, Metrology, Inspection, and Process Control for Microlithography XIV, (2 June 2000); doi: 10.1117/12.386518; https://doi.org/10.1117/12.386518