Profilometry and stress analysis of suspended nanostructured thin films

TL;DR

This study combines profilometry, simulations, and stress analysis to understand the structural and optical properties of suspended nanostructured silicon nitride films with subwavelength gratings.

Contribution

It introduces a method to predict optical transmission spectra from profilometry data and analyzes stress-induced deflections in patterned nanostructures.

Findings

Profilometry data can accurately predict transmission spectra via RCWA simulations.

Sharp vertical deflections occur at pattern boundaries due to stress modifications.

Finite element simulations confirm stress-related deflections in nanostructured films.

Abstract

The profile of suspended silicon nitride thin films patterned with one-dimensional subwavelength grating structures is investigated using Atomic Force Microscopy. We first show that the results of the profilometry can be used as input to Rigorous Coupled Wave Analysis simulations to predict the transmission spectrum of the gratings under illumination by monochromatic light at normal incidence and compare the results of the simulations with experiments. Secondly, we observe sharp vertical deflections of the films at the boundaries of the patterned area due to local modifications of the tensile stress during the patterning process. These deflections are experimentally observed for various grating structures and investigated on the basis of a simple analytical model as well as finite element method simulations.