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Auger electron spectroscopy investigations of the oxide-metal interface between anodic Ta2O5 layers and polycrystalline tantalum
Thin Solid Films, 90 (1982) 337
337
PREPARATION AND CHARACTERIZATION
AUGER ELECTRON SPECTROSCOPY INVESTIGATIONS OF THE O X I D E - M E T A L I N T E R F A C E B E T W E E N A N O D I C Ta205 LAYERS AND P O L Y C R Y S T A L L I N E T A N T A L U M * H. OECHSNER A N D H. SCHOOF
Physikalisches Institut der TU Clausthal and Sonderforschungsbereich, 126 G6ttingen-Clausthal, D-3392 Clausthal-ZellerfeM ( F. R. G. )
Anodically grown T a 2 0 5 layers with thicknesses d between 15 and 300 nm on polycrystalline tantalum substrates were investigated by sputter depth profiling in combination with Auger electron spectroscopy (AES). Normally incident Ne ÷, Ar ÷ and Xe ÷ ions of energy 200 eV-3 keV were used for the sputter removal. A high depth resolution of less than one atomic distance was obtained by appropriate rastering of the ion beam and by carefully positioning the electron beam in the centre of the rastered area. The main results are as follows. (a) The width Ax of the T a 2 O s - T a interface was found to be independent of the layer thickness d in the thickness range investigated. Hence, Ax oc d t/2, as derived from the sequential layer sputtering model holds, if at all, only for d below 15 nm. (b) The measured interface profiles become more asymmetric with a prolonged tail into the metal substrate for increasing energy and decreasing mass of the bombarding ions. This behaviour is ascribed to atomic mixing in the ion-induced collision cascades. (c) Consequently the lowest and presumably true interface widths Ax are obtained for profiling with low energy Xe ÷. Taking the depth interval for the 90% to 10% decrease in the AES peak-to-peak amplitude for the 510 eV oxygen signal as Ax, we find the interface width to be 1.75 + 5 nm when the variations in the sputtering rate and in the mean atomic volumes across the interface are taken into account. Such low Ax values obtained for unpolished polycrys talline tantalum substrates are most probably due to smoothing field effects in the initial stage of the anodic oxidation process. (d) For establishing stoichiometric sputter removal of the oxide, considerable changes in the surface stoichiometry are induced by the bombarding ions. The tantalum surface concentration is always found to be greater than the bulk value, and varies from 50 to about 70 at.% when the ion energy is reduced from 3 keV to 200 eV. This behaviour is almost independent of the ion mass. A stationary surface stoichiometry is obtained after sputter removal of an oxide thickness Ad of several tens of atomic layers, increasing with bombarding ion energy. * Abstract of a paper presented at the Fifth International Thin Films Congress, Herzlia-on-sea,Israel, September21-25, 1981.
0040-6090/82/0000-0000/$02.75
© ElsevierSequoia/Printedin The Netherlands
337
PREPARATION AND CHARACTERIZATION
AUGER ELECTRON SPECTROSCOPY INVESTIGATIONS OF THE O X I D E - M E T A L I N T E R F A C E B E T W E E N A N O D I C Ta205 LAYERS AND P O L Y C R Y S T A L L I N E T A N T A L U M * H. OECHSNER A N D H. SCHOOF
Physikalisches Institut der TU Clausthal and Sonderforschungsbereich, 126 G6ttingen-Clausthal, D-3392 Clausthal-ZellerfeM ( F. R. G. )
Anodically grown T a 2 0 5 layers with thicknesses d between 15 and 300 nm on polycrystalline tantalum substrates were investigated by sputter depth profiling in combination with Auger electron spectroscopy (AES). Normally incident Ne ÷, Ar ÷ and Xe ÷ ions of energy 200 eV-3 keV were used for the sputter removal. A high depth resolution of less than one atomic distance was obtained by appropriate rastering of the ion beam and by carefully positioning the electron beam in the centre of the rastered area. The main results are as follows. (a) The width Ax of the T a 2 O s - T a interface was found to be independent of the layer thickness d in the thickness range investigated. Hence, Ax oc d t/2, as derived from the sequential layer sputtering model holds, if at all, only for d below 15 nm. (b) The measured interface profiles become more asymmetric with a prolonged tail into the metal substrate for increasing energy and decreasing mass of the bombarding ions. This behaviour is ascribed to atomic mixing in the ion-induced collision cascades. (c) Consequently the lowest and presumably true interface widths Ax are obtained for profiling with low energy Xe ÷. Taking the depth interval for the 90% to 10% decrease in the AES peak-to-peak amplitude for the 510 eV oxygen signal as Ax, we find the interface width to be 1.75 + 5 nm when the variations in the sputtering rate and in the mean atomic volumes across the interface are taken into account. Such low Ax values obtained for unpolished polycrys talline tantalum substrates are most probably due to smoothing field effects in the initial stage of the anodic oxidation process. (d) For establishing stoichiometric sputter removal of the oxide, considerable changes in the surface stoichiometry are induced by the bombarding ions. The tantalum surface concentration is always found to be greater than the bulk value, and varies from 50 to about 70 at.% when the ion energy is reduced from 3 keV to 200 eV. This behaviour is almost independent of the ion mass. A stationary surface stoichiometry is obtained after sputter removal of an oxide thickness Ad of several tens of atomic layers, increasing with bombarding ion energy. * Abstract of a paper presented at the Fifth International Thin Films Congress, Herzlia-on-sea,Israel, September21-25, 1981.
0040-6090/82/0000-0000/$02.75
© ElsevierSequoia/Printedin The Netherlands