Atomic scale characterization of HfO2 Al2O 3 thin films grown on nitrided and oxidized Si substrates

Abstract

One and three bilayers of Hf O2 (9 Å) Al2 O3 (3 Å) thin films were grown by atomic layer chemical-vapor deposition on Si(001) substrates whose surfaces were nitrided or oxidized. The films as-grown and postannealed in an ultrahigh vacuum were analyzed by atomic force microscopy, photoelectron spectroscopy, and medium energy ion scattering. For the one- and three-bilayer films grown on the nitrided Si substrates, the Hf O2 and Al2 O3 layers are mixed to form Hf aluminates at temperatures above 600 °C. The mixed Hf aluminate layer is partly decomposed into Hf O2 and Al2 O3 grains and Al2 O3 segregates to the surface by postannealing at 900 °C. Complete decomposition takes place at 1000 °C and the surface is covered with Al2 O3. The surfaces are uniform and almost flat up to 900 °C but are considerably roughened at 1000 °C due to the complete decomposition of the Hf aluminate layer. In contrast, for one- bilayer films stacked on the oxidized Si substrates, Hf silicate layers, including Hf aluminate, are formed by annealing at 600-800 °C. At temperatures above 900 °C, Hf Si2 grows and Al oxide escapes from the surface. © 2004 American Institute of Physics.