Structural Investigation of Alumina Thin Films Deposited by Chemical Vapor Deposition

Abstract

The present study concerns the deposition of α–Al2O3 for diffusion barrier applications on superalloy substrates. The growth of α–Al2O3 has been achieved by chemical vapor deposition (CVD) using an AlCl3/CO2/H2 gas mixture at 1080 °C. Among several growth-controlling parameters with potential importance for the whisker growth process, the reactor pressure during deposition seems to be highly influential on the resulting film structure. Deposited films at low pressure presented solely a fine whisker structure. This non-closed structure is not suitable as diffusion barrier; however, the observed high porosity makes the deposit a potential candidate as a catalysis support. An increase of the deposition pressure led to a competitive growth of whiskers and grains. A suitable microstructure was attained at relatively high pressure (100 mbar) where the surface was fully covered by 2 μm large alumina crystals that formed a closed structure. Further increase of the pressure led to an irregular and rough surface microstructure.