Organometallic vapour deposition of crystalline aluminium oxide films on stainless steel substrates

The organometallic vapour deposition of aluminium oxide films in a cold wall reactor was studied at temperatures between 773 and 1273 K and the pressure range of 55-1000 hPa. Aluminium acetylacetonate and oxygen were used as precursors. All films were characterized by scanning electron microscopy, electron dispersive X-ray spectroscopy and X-ray diffraction. Film growth at low pressure (55 hPa) was analyzed as a function of the deposition temperature: It is mainly surface kinetically controlled, and films grown at low temperatures (< 1073 K) are amorphous and transparent, while those grown at 1273 K are dark and crystalline. Thereby the latter ones consist of different phases: γ-Al2O3, θ-Al2O3, and α-Al2O3. These crystalline films are spalling. In addition, the influence of the total pressure on the deposition was studied for high deposition temperatures (1273 K): Film growth was significantly faster at pressures below 300 hPa. Additionally, a phase change is observed with increasing pressure: Films deposited at 55 hPa consist of three phases, γ-Al2O3, θ-Al2O3, and α-Al2O3, whereas above 200 hPa mainly the latter two phases are observed. Films grown at high pressures above 200 hPa are better adhering.