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

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 A (≊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.