Local stress measurement

An optical metrology device determines the local stress in a film on a substrate. The metrology device maps the thickness of the substrate prior to processing. After processing, the metrology device determines the surface curvature of the substrate caused by the processing and maps the thickness of a film on the top surface after of the substrate after processing. The surface curvature of the substrate may be determined as basis functions. The local stress in the film is then determined using the mapped thickness of the substrate, the determined surface curvature, and the mapped thickness of the film. The local stress may be determined using Stoney's equation that is corrected for non-uniform substrate curvature, non-uniform film thickness, and non-uniform substrate thickness.