Backscattered electrons from gold surface films deposited on silicon substrates: a joint experimental and computational investigation to add new potentiality to electron microscopy

Abstract

This paper addresses the problem of the thickness determination of thin gold overlayers deposited on silicon bulk substrates by looking at the electron backscattering coefficient involved in scanning electron microscopy (SEM). A Monte Carlo code, used to calculate the backscattering coefficient, together with a simple experimental setup, which uses a conventional SEM, allow to determine thin film thickness (in the range 25-200 nm) with an estimated accuracy of 20%. This adds obviously new potentiality to SEM.

Nanoscale Estimation of Coating Thickness on Substrates via Standardless BSE Detector Calibration

“…The measured thicknesses match the nominal ones very well (note that the nominal thicknesses are not entirely accurate and may slightly vary) because we achieved an accuracy of around several tenths of a nm in most cases. Thanks to the precise BSE detector calibration, we achieved better results with low-thickness films than is described in [9], where the thickness of a 10 nm Pd layer was immeasurable and, in the case of a 25 nm Au layer, an error of 20% was attained [10]. We achieved an error lower than 10% for an Au layer down to a thickness of 6.7 nm and, even in the case of a 5.1 nm Au layer, the error was only 13%.…”

“…We have continued previous work where the back-scattering coefficient is estimated as a function of the over-layer thickness [9,10]. The authors there used Pd and Au layers on a Si substrate, the thicknesses of which were estimated using calibrated BSE imaging together with Monte Carlo simulation.…”

“…The same detector settings for all samples were achieved by simultaneous imaging of all four samples (Pd bulk, Pd 10 nm, Pd 110 nm, and Pd 270 nm), and the BSE intensities are compared to each other. The same calibration was applied also in the case of measurement of Au layers on a Si substrate [10], where the upper limit is a measured BSE coefficient from bulk Au.…”

Quantitative analysis of backscattered‐electron contrast in scanning electron microscopy

“…9 BSE analysis was also utilised to determine layer thicknesses by comparing the measured BSE intensities with MC simulations. 10,11,12 MC simulations are also often carried out to optimise the BSE image contrast and distinguish features of interest in BSE images. In this way, Kowoll et al 13 understood the BSE contrast of complex nanoscale samples such as SiO 2 NPs deposited on indium-tin-oxide-covered glassy carbon substrates.…”

“…Furthermore, BSE‐SEM was applied to quantitatively analyse an Al 0.22 Ga 0.78 N/GaN‐layer system 8 and to quantify the composition of In x Ga 1– x As layers embedded in a GaAs matrix 9 . BSE analysis was also utilised to determine layer thicknesses by comparing the measured BSE intensities with MC simulations 10,11,12 . MC simulations are also often carried out to optimise the BSE image contrast and distinguish features of interest in BSE images.…”