LPCVD OF AL2O3 LAYERS USING A HOT-WALL REACTOR

We have studied the chemical vapour deposition of alumina (Al2O3) usin g aluminium chloride (AlCl3) as a source of aluminium and nitrous oxid e (N2O) or carbon dioxide (CO2) as the oxygen vector. We also used hyd rogen (H-2) and a carrier gas (N2). A preliminary thermodynamic study indicated the influence of temperature, total pressure of the reactant s and the composition of the gas mixture. The synthesis of the alumina deposited was carried out in a hot-wall reactor at temperatures betwe en 1000 and 1300-degrees-C and at pressures varying from 133 to 665 Pa . All deposits were crystallised and adherent to the substrates of sil icon carbide (SiC) or aluminium nitride (AlN). The structure and cryst allographic orientation of the Al2O3 films were investigated by X-ray diffraction. Particular attention was paid to the morphology of the de posits. Observations were made with the help of a Scanning Electron mi croscope (SEM). Two studies were carried out as a function of temperat ure, one for the deposits made from nitrous oxide and the other for th ose made using carbon dioxide. The crystal size of Al2O3 increases wit h temperature but, more importantly, the crystal habit changes too.