Alignment free characterization of 2D gratings

TL;DR

This paper presents a rapid, alignment-free method for characterizing 2D gratings using Fourier optics and optimization, enabling precise measurement of lattice parameters and alignment corrections from a single measurement.

Contribution

It introduces a novel Fourier lens and differential optimization approach for alignment-free, single-measurement characterization of 2D gratings, improving accuracy and efficiency.

Findings

Successfully measured lattice vectors and angles for hexagonal and checkerboard gratings.

Reduced measurement uncertainty through alignment correction.

Applicable for automatic and inline grating characterization.

Abstract

Fast characterization of 2-dimensional gratings is demonstrated using a Fourier lens optical system and a differential optimization algorithm. It is shown that both the grating specific parameters such as the basis vectors and the angle between them and the alignment of the sample, such as the rotation of the sample around the x-, y-, and z-axis, can be deduced from a single measurement. More specifically, the lattice vectors and the angle between them have been measured, while the corrections of the alignment parameters are used to improve the quality of the measurement, and hence reduce the measurement uncertainty. Alignment free characterization is demonstrated on both a 2D hexagonal grating with a period of 700 nm and a checkerboard grating with a pitch of 3000 nm. The method can also be used for both automatic alignment and in-line characterization of gratings.