FACTORS INFLUENCING THE K-AL2O3-]ALPHA-AL2O3 PHASE-TRANSFORMATION DURING CVD GROWTH

Chemical vapour deposition (CVD) of Al2O3 layers on silica substrates by the AlCl3/CO2/H2 process was studied at temperatures from 950-degrees-C to 1080-degrees-C. Kappa-Al2O3 was grown initially in the whole temperature range. The growth direction of the kappa-Al2O3 layers changed during the CVD process and eventually a phase transformation to alpha-Al2O3 occurred. The phase transformation rate increased with increasing process temperature. Additionally, the influence of different background contamination sources on the phase transformation was studied. X-ray diffraction analysis and morphological examination of the Al2O3 layers showed that the AlC13/CO2/H2 process is extremely sensitive to impurities. The kappa/alpha phase content as well as the morphology and microstructure of the aluminium oxide layers were strongly influenced by the presence of impurities and the air leak rate of the CVD system.