Chemical vapour deposition of κ-Al 2O 3

Abstract

The influence of experimental variables in combination with catalysis on the growth and microstructure of chemically vapour deposited κ-Al 2O 3 was investigated. The Al 2O 3 coatings were deposited in the temperature range of 800–1000°C and at pressures of 50–400 mbar. Hydrogen sulfide (H 2S) was used as a doping/catalysing agent. General deposition characteristics of κ-Al 2O 3 as a function of temperature, pressure and H 2S concentration are reported. In addition to scanning electron microscopy and X-ray diffraction, the microstructure and chemistry of the κ-Al 2O 3 layers were analysed using transmission electron microscopy. The growth rate of κ-Al 2O 3 could be strongly enhanced by applying H 2S doping and reasonable deposition rates for κ-Al 2O 3 could be obtained at 800°C. Relatively very high growth rates could be obtained by increasing the total pressure simultaneously with H 2S doping. Higher deposition pressure, however, increased the contribution of the homogenous gas phase reaction resulting in unacceptable thickness variations. In general, κ-Al 2O 3 deposited at different process conditions did not exhibit any pronounced microstructural or morphological differences, except at the deposition temperature of 800°C together with at higher doping levels (H 2S>0.8%). Under these experimental conditions γ-Al 2O 3 was obtained. Enrichment of sulfur could be confirmed to occur in γ-Al 2O 3 while no sulfur was found in κ-Al 2O 3. Production-scale aspects concerning deposition of κ-Al 2O 3 and α-Al 2O 3 will be dealt with.