Depth resolution in sputter depth profiling-characterization of a third batch of tantalum pentoxide on tantalum certified reference material by AES and SIMS

Depth profiles have been made for a new batch of the certified reference ma terial, BCR 261, of similar to 30 nm and 100 nm of anodic tantalum pentoxid e layers on tantalum foil, Atomic force microscopy studies show that the pr eparation method traditionally used provides an excellent substrate root-me an-square (rms) smoothness of 1.5 Angstrom. This goes part of the way to ex plain the exceptionally good interface resolutions readily obtained with th is material using AES, Further AES measurements, in the pulse counting mode , show that the same excellent depth resolution is obtained as previously ( 1.6 nm at 100 mn depth), Interestingly, the background of inelastic primary electrons under the oxygen peak increased with a characteristic length of only 4.0 nm at the interface for a 5 keV electron beam. Measurement of the ion-induced emission at the oxygen Auger electron energy, or in a broad ran ge around this energy, shows that this signal can be used to monitor the io n beam stability and the presence of the oxide without the electron beam, a lthough the signal levels are smaller than for AES, This emission is attrib uted to O- ions being detected through the electron spectrometer. Measureme nts using time-of-flight SIMS with a 12 keV Ga+ beam for analysis and 2 keV Ar+ or SF5+ beams for depth profiling show that the material may be used t o characterize aspects of SIMS instrumental performance, in addition to AES and XPS, at a very high level of quality. The optimum interface resolution s obtained are better than 1.0 nm, with trailing edge decay lengths down to 0.33 nm, The use of molecular ions gives excellent depth resolution, compa rable to the 0.8 nm depth resolution of AES at its best. Copyright (C) 2000 John Wiley & Sons, Ltd.