Reflectometry technique for study of complex multilayer micro- and nanostructures with lateral periodicity

This study introduces a reflectometry-based technique for characterizing complex thin-film structures with lateral periodicity, using only a single, large-beam measurement to capture essential structural information. The PillarHall test chip structure, selected as a case study, features an air gap of 500 nm nominal thickness inside a layer structure with periodically repeated lateral structure elements. Using a non-destructive reflectometry technique, the sample's layer structure was analyzed through spectral reflectance measurements, conducted with a Cary 7000 spectrometer, and processed with a dedicated MATLAB code that incorporates the transfer matrix method to model and fit the reflectance spectrum. Two models, a basic and an advanced four-layer model, were developed and tested by fitting the simulated reflectance spectrum to a measured one. While the basic model provides sufficient information about the thin-film structure, the advanced model considers detailed variations in the thickness across the sample caused by specific structural features. Reflectometry results on structural sizes agree with direct profilometry measurements, supporting the method’s reliability. These findings demonstrate that a single, large-beam measurement can yield comprehensive insights, positioning reflectometry as a robust tool for the advanced thin-film characterization of complex periodic structures.