Simulation of light scattering from complex 3D structures for confocal microscope using accelerated boundary element method

Abstract

Optical metrology faces significant challenges as functional devices continue to shrink in size due to new patterning processes for semiconductor chips. Consequently, there is a growing interest in modeling optical systems to achieve more accurate measurements and to compare measurements from different optical instruments, such as confocal microscopes, white light interference microscopes, and focus-varied microscopes. Previous models have employed either a thin layer approximation or 2D periodic structures to simulate light scattering. However, to accurately simulate more complex structures and compare them with experimental data, there is a need for a physically accurate modeling and simulation tool that can handle large-scale aperiodic 3D surfaces. To address this need, we have developed a simulation tool called SpeckleSim, which utilizes the boundary element method. By incorporating a multi-level fast multiple method, we are able to calculate light scattering from 3D nanostructures within a reasonable timeframe. In this report, we adapt the method to a confocal microscopy model and investigate the extent to which it can reproduce surface profiles for different types of structures. The obtained results will be compared with experimental measurements and the results from other rigorous simulation tools such as rigorous coupled wave analysis (RCWA) method.