Wet oxidation of Ti34Si23N43 thin films with and without pre-annealing

Films of a ternary alloy of composition Ti34Si23N43 and of a structure consisting of homogeneously distributed similar to 2 nm sized TiN-like grains in an amorphous matrix wer deposited by reactive magnetron sputtering to thickness of 250-1000 nm and then oxidized with steam at 600, 800, or 1000 degrees C, with and without first annealing the film in vacuum at 800 degrees C for 1 h. The microstructure of the nitride and the oxide was analyzed by X-ray diffraction and plan-view transmission electron microscopy. The thickness of the grown oxide scale was monitored by backscattering spectrometry. At 600 and 800 degrees C, the oxide scale has the composition of Ti20Si13O67, corresponding to a full and lossless oxidation of Ti and Si to TiO2 and SiO2. During that process, the nano-grains in the alloy grow several-fold. The oxide is also a two-phase mixture of TiO2 nano-grains in an amorphous matrix. As a function of the oxidation duration, t, the oxide grows in a log(t)-like fashion. Pre-annealing in vacuum reproduces the growth of TiN grains in the alloy observed during oxidation. This structural change does not alter the log(t)-type dependence but drastically reduces that rate of oxidation. The observations are interpreted as resulting from the compositional changes of the matrix induced by the growth of the TiN grains in the alloy. (C) Published by Elsevier Science S.A. All rights reserved.