Chemistry at oxide surfaces: Reaction of water and HCl on alpha aluminum oxide(0001) and atomic layer deposition of tungsten

The adsorption and desorption of H2O and HCl on alpha-Al 2O3 (0001) were examined using laser induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The initial sticking coefficient for H2O on alpha-Al2O3 (0001) was ∼0.1 at 298 K. The HCl sticking coefficient on alpha-Al 2O3 (0001) was 10-3 at 298 K. For both H2O and HCl, the sticking coefficient decreases almost exponentially with coverage. The H2O and HCl desorption occurs over a broad temperature range of ∼300 K to 600 K. This broad range suggests a distribution of surface sites with different binding energies. The H2O and HCl desorption results versus coverage prepared by progressively annealing a fully exposed alpha-Al2O3 (0001) surface confirmed a wide range of binding energies. Additional TPD results showed that the H2 O and HCl randomly fill these sites independent of their adsorption energy. These results also suggest that surface diffusion between the adsorption sites must be negligible. Modeling of the H2O TPD data give a desorption energy range from 23--41 kcal/mol. The HCl model TPD data give a desorption energy range from 19--36 kcal/mol.;In addition to studying the H2O and HCl reactions on Al 2O3, the atomic layer deposition of tungsten was examined on Al2O3 and SiO2. The atomic layer deposition of tungsten can be achieved by separating the CVD reaction WF6 + Si2H6 → W + 2SiHF3 + 2H2 into two half-reactions. Successive application of the WF6 and Si2H6 half-reactions in an ABAB...sequence produces W atomic layer controlled growth. The nucleation and growth of W on SiO2 and Al2O 3 was examined using Auger electron spectroscopy. Auger electron spectroscopy studies at 473 K and 573 K reveal an initial nucleation phase that is followed by a layer-by-layer W growth regime. The Auger data is fit well assuming a Frank van der Merwe layer-by-layer growth. These studies reveal that the sequential surface reactions can facilitate metal wetting of oxide surfaces and conformal layer-by-layer metal growth.