Enhanced Measurement Accuracy for Nanostructures Using Hybrid Metrology

Abstract

Light-matter interplay is widely used for analyzing the topology of surfaces on small scales for use in areas such as nanotechnology, nanoelectronics, photonics, and advanced materials. Conventional optical microscope imaging methods are limited in resolution to a value comparable to the wavelength, the so-called Abbe limit, and cannot be used to measure nano-sized structures. Scatterometry and Mueller ellipsometry are spectroscopic optical methods that can measure structures smaller than the wavelength. However, the relative uncertainties of the structure dimensions measured with scatterometry increase with decreasing structure size, and the industry is therefore replacing simple intensity based scatterometry with Mueller ellipsometry for the most demanding measurements. The accuracy of Mueller ellipsometry and scatterometry are closely related to the ability of the employed regression and regularization algorithms to extract the structural dimension. In this work, we demonstrate how the measurement accuracy on three-dimensional periodic structures may be increased by measuring the same periodic structure with multiple techniques and applying a χ2-regression method that finds the best solution based on the input from all the instruments. We furthermore report on a new and improved calibration method for Mueller ellipsometry and demonstrate how the Mueller matrix may be used to find the geometrical anisotropy of the structure.

Hybrid metrology for nanometric energy harvesting devices

“…AFM and SEM plays a big role in providing the height and diameter parameters. However, shape beyond height and diameter can be reconstructed by the optical scatterometry techniques [21].…”

“…If unavailable, one may obtain the nominal parameters from confocal microscopy, AFM or SEM measurements. If reliable nominal parameters with uncertainties exist, they may be used in a chi square merit function for hybrid metrology [21] to limit the parameters range that must be evaluated to create, a database library of back focal plane diffraction signatures. In the final step, all the solutions within the database library are tested for a minimum in the chi square merit function, the simulation matching the measurement result is selected and the geometric parameters are retrieved from the knowledge of the best matching simulation.…”

Non-normalized Mueller ellipsometry is better than normalized Mueller ellipsometry

“…Recently, a similar approach was demonstrated to enhance measurement accuracy of a two-dimensional grating, see Ref. 4. In this work, we focus on grating structures as shown in Fig.…”

Fine details of structural deviations in reference samples for scatterometry

“…In the experimental setup, which is described in detail in Ref. [9], we invoke photo-elastic modulators with 4 different angular settings to obtain all Mueller matrix elements except for the first one (m11). We record the spectrum of the Mueller matrix elements for wavelengths in the range 250 nm to 850 nm.…”