Forward simulation of coherent beams on grating structures for coherent scatterometry

TL;DR

This paper introduces a new model for simulating how focused coherent light beams scatter off nano-scale periodic structures, improving the accuracy of optical scatterometry by accounting for wavefront aberrations and complex diffraction effects.

Contribution

The paper presents a coherent illumination model for focused beams interacting with periodic structures, incorporating optical aberrations and enabling more precise scatterometry simulations.

Findings

The model accurately predicts scattering patterns for Gaussian and Bessel beams.

It accounts for optical wavefront aberrations in illumination and detection.

Comparisons show improved results over large-scale super-cell methods.

Abstract

Modelling the scattering of focused, coherent light by nano-scale structures is oftentimes used to reconstruct or infer geometrical or material properties of structures under investigation in optical scatterometry. This comprises both periodic and aperiodic nano-structures. Coherent Fourier scatterometry with focused light exploits the diffraction pattern formed by the nano-structures in Fourier plane. While the scattering of a focused beam by a spatially isolated scatterer is a standard modelling task for state-of-the art electromagnetic solvers based, e.g., on the finite element method, the case of periodically structured samples is more involved. In particular when the focused light covers several grating periods of as it is commonly the case. We will present a coherent illumination model for scattering of focused beams such as Gaussian -- and Bessel -- beams by periodic structures such as line gratings. The model allows to take into account optical wavefront aberrations in optical systems used for both, the illumination and detection of the scattered fields. We compare the model with strategies implemented on large-scale super-cells and inverse Floquet-transform strategies to superimpose both near- and far- fields coherently.