Complete Elemental Analysis of Low-k a-SiC:H Thin Films by Transmission FTIR Spectroscopy

Abstract

Fourier transform infrared (FTIR) spectroscopy is a popular technique for qualitatively investigating the chemical bonding of low dielectric constant (low-k) materials utilized in nanoelectronic Cu interconnects. However, quantitative FTIR analysis of low-k materials with widely varying stoichiometry has proven challenging due to numerous optical interference effects, variations in IR absorption strength with optical constants, and a negligible IR activity for homopolar bonds. In this paper, these challenges are overcome to demonstrate full elemental composition analysis by applying multivariate partial least squares (PLS) modeling to the true IR absorbance spectra obtained using previously described methods for eliminating optical interference effects from thin film FTIR spectra. To demonstrate the validity of this approach, transmission FTIR spectra were collected from a series of low-k a-SiC:H thin films with hydrogen content ranging from 25–60%. The elemental concentrations determined from PLS analysis of the corrected low-k a-SiC:H FTIR spectra were found to be in agreement to within ±5% of results obtained from independent nuclear reaction analysis and Rutherford backscattering measurements. These results demonstrate a clear path for establishing transmission FTIR as a quantitative metrology for full compositional analysis (elemental and chemical bond) for a wide range of thin film materials.