Atomic scale characterization of HfO2/Al2O3 thin films grown on nitrided and oxidized Si substrates

One and three bilayers of HfO2(9 Angstrom)/Al2O3(3 Angstrom) 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 HfO2 and Al2O3 layers are mixed to form Hf aluminates at temperatures above 600 degreesC. The mixed Hf aluminate layer is partly decomposed into HfO2 and Al2O3 grains and Al2O3 segregates to the surface by postannealing at 900 degreesC. Complete decomposition takes place at 1000 degreesC and the surface is covered with Al2O3. The surfaces are uniform and almost flat up to 900 degreesC but are considerably roughened at 1000 degreesC 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 degreesC. At temperatures above 900 degreesC, HfSi2 grows and Al oxide escapes from the surface. (C) 2004 American Institute of Physics.