Refractive index and adhesion of Al2O3 thin films obtained from different processes - A comparative study

Al2O3 thin films ranging from 50 to 200 nm in thickness are deposited by four different methods viz, electron beam evaporation of Al2O3 with and without chopping, and the oxidation of aluminium films by hot water and by steam. The prepared films are also subjected to heat at 120 degrees C for 3 h and moisture for 3 h. The pre ambient and post ambient refractive index and adhesion are compared for the four types of films. The chopped electron beam evaporated Al2O3 films give the highest refractive index and adhesion. The adhesion of steam oxidised aluminium films compare well with electron beam deposited Al2O3 films. The post ambient refractive index changes are thickness dependent especially for both the types of oxidised aluminium films. The post ambient changes do not seem to be only porosity dependent but some composite oxide formation seems to be taking place.