Residual Stress Mechanisms in Aluminium Oxide Films Grown by MOCVD

Residual stresses in amorphous aluminium oxide films were investigated with in situ wafer curvature measurements. The films were deposited from aluminium tri-isopropoxide, on sapphire substrates. Large tensile stresses of 1-2 GPa occurred during growth. These values are well above the fracture stress in bulk materials, but they are sustainable in thin film form. Subsequent heat treatment of these films produced additional tensile stress, even at low temperatures prior to crystallization. The mechanisms responsible for all of these stress contributions are discussed. The variety of operative mechanisms at low to moderate temperatures in these amorphous films suggests that different processing routes can be used to engineer significant differences in the final stress state of these materials.