Oxygen detection in thin silicon dioxide layers by low-energy x-ray fluorescence spectrometry

Abstract

Light element detection using low-energy (<2 keV) x-ray fluorescence (XRF) is described. By tuning the energy of the incident x rays to slightly above the absorption edge, the minimum detection limits for low-Z elements can be greatly improved over conventional XRF and signal-to-background is significantly better than that obtainable for electron-excited x-ray spectra using an energy-dispersive detector. In particular, the minimum detectable thickness of SiO2 is experimentally determined to be 0.36 Å (≊0.1 monolayer) film thickness for 1.85 kV anode voltage using a Mg anode with an Al window. Good signal linearity with film thickness is established by comparison with measurements obtained on the same samples using ellipsometry and x-ray photoelectron spectroscopy.