Investigation of thickness dependent composition of boron carbide thin films by resonant soft x-ray reflectivity

TL;DR

This study investigates how the composition of boron carbide thin films varies with thickness using multiple advanced characterization techniques, revealing a significant dependence of B/C ratio on film thickness.

Contribution

It provides a detailed analysis of thickness-dependent composition in boron carbide films using resonant soft x-ray reflectivity and other methods, which was not previously comprehensively studied.

Findings

Boron to Carbon ratio increases with film thickness.

RSXR and RRBS measurements agree on composition estimates.

Boron content decreases in thinner films, especially at the surface.

Abstract

Boron carbide thin films of different thicknesses deposited by ion beam sputtering were studied. The deposited films were characterized by grazing incidence hard x-ray reflectivity (GIXR), resonant soft x-ray reflectivity (RSXR), x-ray photo electron spectroscopy (XPS), resonant Rutherford backscattering spectrometry (RRBS), and time of flight secondary ion mass spectrometry (TOF-SIMS). An in-depth profile of the chemical elements constitute the films is reconstructed based on analysis of reflectivity curves measured in the vicinity of B K-edge. The composition of films is closely dependent on film thickness. Boron to Carbon (B/C) ratio reaches to ~4 as the thickness of deposited films increases. The B/C ratio estimated from RSXR measurements are in agreement with the RRBS measurements. TOF-SIMS data also suggested that decrease in boron content with decrease in film thickness. XPS measurements confirm the presence of little amount of B atoms on the surface of low thickness film.