Crystallization-induced stress in reactively sputter-deposited molybdenum nitride thin films

Thin films of molybdenum nitride have been produced by reactive dc magnetron sputtering of Mo in an Ar-N₂ gas mixture. The residual stress of a film having nearly the stoichiometric composition of Mo ₂N was measured as a function of annealing temperature by a wafer-curvature-based technique. When the initially amorphous film was heated to about 500°C, crystallization occurred and the stress of the film drastically changed from -0.75 to 1.65 GPa. Using a combination of X-ray diffraction, energy-filtered electron diffraction, electron-energy-loss spectrometry and atomic force microscopy, the stress development mechanism during crystallization was found to be a volumetric shrinkage of the film. The stress increase can also be explained in terms of an increase in the average grain size of the crystallized film and its densification.