ToF-SIMS depth profiling of Hf and Al composition variations in ultrathin mixed HfO2/Al2O3 oxides

Ultrathin (a few nm) mixed HfO2/Al2O3 oxides deposited by ALCVD on Si substrates were analyzed with low energy (250 eV) Csþ and Xeþ ions by ToF-SIMS in the dual beam mode. The analysis beam was 15 keV Gaþ. Several layers were measured, with different metal ratios (Hf:Al) and different number of deposition cycles.We observed a significant enhancement of the Al (and AlOx clusters) signal at the surface along with a Hf (and HfOx clusters) depletion at the film surface. However, the thinnest films were found to contain much more Hf than the thickest ones. Several ion ratios were used (e.g. HfOþ/AlOþ or HfO2 =AlO2 ) in order to quantify the Hf:Al concentration ratio in the films.We found that these ratios correlate well with each other, with the metal deposition ratio, and with XPS ratios, enabling us to reconstruct the Al and Hf composition variation in the film. # 2004 Elsevier B.V. All rights reserved