Determination of residual stress in low-temperature PECVD silicon nitride thin films

Two experimental techniques have been investigated to examine residual stress in low temperature plasma enhanced chemical vapour deposited (PECVD) SiNx thin films: one that measures the stress induced substrate curvature, and the other that takes advantage of the stress induced deformation of freestanding diagnostic microstructures. A general linear dependence of residual stress on deposition temperature is observed, with the magnitude of stress changing linearly from circa 300MPa tensile stress to circa 600MPa compressive stress as the deposition temperature is decreased from 300°C to 100°C. However, the results deviate from the linear dependence by a different degree for both measurement techniques at successively lower deposition temperatures. The stress values obtained via the substrate curvature method deviate from the linear dependence for deposition temperatures below 200°C, whereas the values obtained via the diagnostic microstructures method deviate from the linear dependence for deposition temperatures below 100°C. Stress uniformity over the deposition area is also investigated.