Influence of annealing temperature on composition and stresses of alumina thin films elaborated by the sol-gel method

Alumina thin films were elaborated by the sol-gel method, using aluminium butoxide as precursor and acetylacetone as chelating agent to stabilise the sol. The dip-coating parameters (sol concentration and withdrawal speed) were optimised in order to get waveguiding films. For a 15 successive layers deposition and a 700degreesC annealing treatment, waveguiding films of about 900nm thickness were obtained, which have a 1.582 refractive index at 543.5nm. The influence of the annealing temperature was studied in the 100degreesC to 1100degreesC range, in order to follow the elimination of the organic compounds and the existence of stresses. IR spectroscopy shows that an annealing temperature of 800degreesC is necessary for the complete elimination of the OH and C=O groups of the residual organic compounds, which are derived from the chelating agent. In a parallel way, the Al to 0 atomic ratio tends to the theoretical Al2O3 composition, according to Rutherford Backscattering Spectroscopy results. The stresses in the film were measured by an optical method. Their evolution with annealing temperature is characterised by two regimes, depending on the organic compounds elimination and the crystallisation process.