Intercomparison of surface analysis of thin aluminium oxide films

Abstract

Abstract A round robin test organized by the European Federation of Corrosion (EFC) Working Party on Surface Science and the Mechanisms of Corrosion and Protection, supported by the European Community Bureau of References (BCR), and further extended under VAMAS (Versailles Project on Advanced Materials and Standards), has been performed. The aim of the test was to study the reproducibility of surface analyses in different laboratories on well‐documented samples by ESCA and Auger spectroscopy. The reference material is aluminium, oxidized at 250°C in oxygen. Test samples were distributed to 22 laboratories in Europe, North America and Japan. Data have been received from 20 laboratories. The test results collected are: peak positions, intensities, chemical shifts. The reference energies of the ESCA spectrometers are 84.0 eV for Au 4f 7/2 and 932.7 eV for Cu 2p 3/2 . The binding energies of the metallic states of Al 2p and Al 2s are 73.0 (±0.1) eV and 118.0 (±0.2) eV, respectively. The chemical shifts of Al 3+ in the oxide layer are 2.8 (±0.1) eV and 2.5 (±0.1) eV. The oxygen content of the oxide layer, measured by nuclear reaction analysis, is 16.3 × 10 15 atoms cm −2 . This corresponds to an oxide thickness, d , of 23 (±1) Å. The value of d /λ (λ is the attenuation length) calculated from the measured ESCA intensities is 1.13 (±0.03) for Al 2p with an Mg Kα x‐ray source, taking into account the take‐off angle. The values of the attenuation length obtained for Al 2 O 3 are λ(Al 3+ ) Mg Kα = 20.2 (±2.0) Å and λ(Al +3 ) Al Kα = 24.8 (±3.3) Å. The ratios of the photoelectron yields of oxygen and aluminium are Y (O 1s )/ Y (Al 2p ) = 6.2 (±0.8) and Y (O 1s )/ Y (Al 2s ) = 5.4 (±0.8) with an Mg Kα x‐ray source and Y (O 1s )/ Y (Al 2s ) = 6.6 (±0.6) and Y (O 1s )/ Y (Al 2s ) = 4.9 (±0.5) with an Al Kα x‐ray source. The LMM and KLL AES energies of Al in Al 2 O 3 are 53.4 (±2.8) eV and 1389.4 (±3.5) eV, respectively. The corresponding values for aluminium metal are 66.4 (±2.7) eV and 1394.4 (±4.0) eV. For thin films where the attenuation length is of the same order of magnitude as the film thickness, an exponential fit of the experimental depth profile is proposed. The ratio of the sputtering rates of Al 2 O 3 and Ta 2 O 5 is thus found to be 0.72 (±0.14). The consistency between measurements performed in the different laboratories is excellent in many instances but certain problems are identified, which would deserve further work.