J. Phys. IV France 09 (1999) Pr8-395-Pr8-402
Low-pressure chemical vapour deposition of mullite coatings in a cold-wall reactorB. Armas1, M. de Icaza Herrera2, C. Combescure1, F. Sibieude1 and D. Thenegal1
1 Institut de Science et de Génie des Matériaux et Procédés, CNRS, BP. 5, Odeillo, 66125 Font-Romeu cedex, France
2 Departamento de Fisica Aplicada y Tecnologia Avanzada, Instituto de Fisica, UNAM, Apdo. Postal 20-364, 01000 Mexico D.F.
Nitrous oxide, together with aluminium and silicon chlorides, as precursor gases, while hydrogen and nitrogen as carriers, have been fed into a cold-wall reactor, in order to produce crystalline deposited layers of mullite (3Al2O3.2SiO2) on silicon carbide and aluminium nitride substrates. The corresponding deposition kinetics has been studied, for fixed flow rates of nitrous oxide, hydrogen and nitrogen, as a function : of the substrate temperature, from 1100 to 1300 °C ; of the gas pressure, from 10 to 90 hPa and of the AlCl3 to SiCl4 input ratio. The coating's chemical composition, crystal structure and morphology was precisely determined by means of WDS, XRD and SEM. The aluminium content of the deposits increases first as a function of pressure. It reaches a maximum for P = 20 hPa, whence it decreases steadily, to finally vanish completely for P = 100 hPa. The best experimental conditions to produce mullite coatings were then interpolated, experimentally tested, and the side compounds, under such conditions, identified.
© EDP Sciences 1999