Determination of overlayer thickness by QUASES analysis of photon-excited KLL Auger spectra of Ni and Cu films

Quantitative characterization of overlayer nanostructures is important for many practical applications and has become a feasible task for electron spectroscopy. The QUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy) software package, developed recently, provides a general tool for quantification in XPS by analysing the spectral shape of the background caused by inelastic scattering of the signal electrons and has been applied successfully for determining the thickness of surface films in the nanometre range. In this work the application of such analysis is extended to metallic films having several tens of nanometre thickness and the accuracy of the results is tested by using independent methods. Both Ni and Cu KLL Auger spectra were photoexcited from Ni and Cu overlayers (deposited onto Si substrates) of different thicknesses in the 10-60 nm range, and were measured with high energy resolution. The film thickness values from the QUASES spectral shape analysis are compared with the data obtained by using a quartz crystal microbalance, cross-sectional transmission electron microscopy and scanning probe microscopy (SPM). Good consistency has been found for the thickness values obtained from the spectral shape analysis and from microscopy, especially for Ni films. Assuming nominal film thickness, the values of the inelastic mean free path of 6-7 keV energy electrons in Ni and Cu were also determined, showing good (Ni) or reasonable (Cu) agreement with those proposed by Powell and Jablonski. The effect of island formation was shown by the QUASES spectral shape analysis and confirmed by SPM, Copyright (C) 2001 John Wiley & Sons, Ltd.