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 stabilize the sol. The dip-coating parameters (sol concentration and withdrawal speed) were optimized in order to get waveguiding films. For a 15 successive layers deposition and a 700°C 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 100°C to 1100°C range, in order to follow the elimination of the organic compounds and the existence of stresses. IR spectroscopy shows that an annealing temperature of 800°C 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 O 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 characterized by two regimes, depending on the organic compounds elimination and the crystallization process.