The thicknesses of a series of ultra-thin HfO 2 films were precisely determined by mutual calibration by x-ray photoelectron spectroscopy (XPS) and x-ray reflectometry (XRR) in the recent Consultative Committee for Amount of Substance (CCQM) pilot study P-190. From these well-defined reference film thicknesses, the measurement capability of medium-energy ion scattering spectroscopy (MEIS) for the thickness of HfO 2 films was investigated. The film thicknesses determined by MEIS showed a small difference, within 2%, from the reference thicknesses and an offset value of 0.017 nm. The MEIS thicknesses can also be determined by mutual calibration between the transmission electron microscopy (TEM) thicknesses and the MEIS intensity ratios in the region of the substrate and HfO 2 film. From linear fitting with the reference thicknesses, the MEIS thicknesses determined by mutual calibration showed a slope value of 1.011 and an offset value of 0.015 nm. As a result, MEIS can be a traceable method to determine the absolute thickness of ultra-thin HfO 2 films, and a zero-offset method for application of the mutual calibration method.
The measurement traceability of Rutherford backscattering spectroscopy (RBS), medium energy ion scattering spectroscopy (MEIS) and isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS) was compared for the quantitative analysis of alloy thin films. A set of thin Ag x Cu 1−x alloy films were selected as a model alloy system for the quantitative analysis of MEIS and ID ICP-MS. Two sets of five Ag x Cu 1−x alloy films with different mole fractions were grown on Si (100) wafers by ion beam sputter deposition. The mole fractions of thick Ag x Cu 1−x alloy films (100 nm) measured by RBS and ID ICP-MS showed a great agreement within 0.4% difference. The mole fractions of thin Ag x Cu 1−x alloy films (10 nm) measured with MEIS and ID ICP-MS also showed a small difference of about 1.0%. As a result, ID ICP-MS, RBS and MEIS can be used to certify the mole fractions of thin alloy reference films. ID ICP-MS is an absolute method for the mole fraction analysis of thin Ag x Cu 1−x alloy films. Although the contribution of sample homogeneity was included, the uncertainties of ID ICP-MS results were much smaller than those of RBS and MEIS.
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