Microstresses in molybdenum nitride thin films deposited by reactive DC magnetron sputtering

Thin films of molybdenum nitride (MoN_x with 0≤×≤0. 35) were deposited on Si(100) at room temperature using reactive DC magnetron sputtering. The residual stress of films was measured as a function of sputtering pressure, nitrogen incorporation, and annealing temperature by wafer curvature-based technique. It was found that the stress of the films was strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. The film stresses without nitrogen addition strongly depended on the argon pressure and changed from highly compressive to highly tensile in a relatively narrow pressure range of 0.8-1.6 Pa. For pressures exceeding ∼5.3 Pa, the stress in the film was nearly zero. Cross-sectional transmission electron microscopy indicated that the compressively stressed films contained a dense microstructure without any columns, while the films having tensile stress had a very columnar microstructure. High sputtering-gas pressure conditions yielded dendritic-like film growth, resulting in complete relaxation of the residual tensile stresses. It was also found that the as-deposited film was poorly ordered in structure. When the film was heated at ∼775 K, crystallization occurred and the stress of the film drastically changed from -0.75 to 1.65 GPa. The stress development mechanism may be due to volumetric shrinkage of the film during crystallization.