Unambiguous determination of Fourier-transform infrared spectroscopy proportionality factors: The case of silicon nitride

Abstract

Fourier-transform infrared spectroscopy (FTIR) analysis is a widely used tool for the analysis of bonded hydrogen in hydrogenated silicon nitride $(\mathrm{Si}{\mathrm{N}}_{x}:\mathrm{H})$. However, the proportionality factors between the integrated absorbance and bond densities, necessary for accurate hydrogen quantification, are still under discussion. The evolution of the total hydrogen concentration in thermally stable $\mathrm{Si}{\mathrm{N}}_{x}:\mathrm{H}$ during an anneal, as determined by FTIR, using previously reported proportionality factors [E. Bustarret et al., Phys. Rev. B 77, 925 (1998); W. A. Lanford and M. J. Rand, J. Appl. Phys. 49, 2473 (1978)] appears to be inconsistent with the hydrogen concentration evolution as determined by elastic recoil detection (ERD) analysis. The differences indicate invalid proportionality factors for our samples. Since annealing experiments of thermally stable $\mathrm{Si}{\mathrm{N}}_{x}:\mathrm{H}$ offer a set of samples that differ only in N-H and Si-H bond densities, recalibration of these factors can be achieved by fitting the anneal time-dependent FTIR data to the evolution curves of the hydrogen concentration as detected with ERD. In this way a fully experimental calibration tool for the N-H and Si-H FTIR proportionality factors is obtained for individual, thermally stable, alloy films with multiple configurations of hydrogen bonds. Calibration was applied to $\mathrm{Si}{\mathrm{N}}_{x}:\mathrm{H}$ films in the range $1.09lxl1.35$, deposited at high deposition rate using the hot-wire (HW) chemical vapor deposition (CVD) technique. Each film was cut into 25 samples, which were annealed for different durations at $800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in ${\mathrm{N}}_{2}$ and investigated using FTIR and ERD analysis. ERD measurements show that for the HWCVD $\mathrm{Si}{\mathrm{N}}_{x}:\mathrm{H}$, no detectable change in $\mathrm{N}∕\mathrm{Si}$ ratio or mass density occurs during an anneal. The thermal stability of the samples is also confirmed by FTIR measurements, where the sensitive Si-H peak position shows negligible shift during the anneal treatment. Calibration of FTIR proportionality factors for these samples shows that both proportionality factors change with the composition of the deposited films, and that they differ from reported values.