LPCVD OF AL2O3 LAYERS USING A HOT-WALL REACTOR

We have studied the chemical vapour deposition of alumina (Al2O3) using aluminium chloride (AlCl3) as a source of aluminium and nitrous oxide (N2O) or carbon dioxide (CO2) as the oxygen vector. We also used hydrogen (H-2) and a carrier gas (N2). A preliminary thermodynamic study indicated the influence of temperature, total pressure of the reactants and the composition of the gas mixture. The synthesis of the alumina deposited was carried out in a hot-wall reactor at temperatures between 1000 and 1300-degrees-C and at pressures varying from 133 to 665 Pa. All deposits were crystallised and adherent to the substrates of silicon carbide (SiC) or aluminium nitride (AlN). The structure and crystallographic orientation of the Al2O3 films were investigated by X-ray diffraction. Particular attention was paid to the morphology of the deposits. Observations were made with the help of a Scanning Electron microscope (SEM). Two studies were carried out as a function of temperature, one for the deposits made from nitrous oxide and the other for those made using carbon dioxide. The crystal size of Al2O3 increases with temperature but, more importantly, the crystal habit changes too.