The optical cantilever beam technique utilizes a laser beam which is scanned across the sample substrate. The slope of the substrate surface is measured by monitoring the beam reflection angle along the scan direction. This algorithm corrects errors in the measured angles that are due to both sample tilt and curvature.
The algorithm also takes account of the fact that the apparent reflection angle is a function of the substrate surface height over the horizontal plane. Using this algorithm, the curvatures can be recalculated, and the corrected curvatures (triangles) can be plotted for comparison below.
Apparent and corrected curvatures of a flat sample as a function of sample tilt The square points are the measured curvatures without correction, the triangles represent the corrected curvatures with the improved algorithm.
When measuring samples that are irregular, the Toho FLX Series can help measure thin film stress. The improved algorithm takes account of the fact that the apparent reflection angle is a function of the substrate surface height over the horizontal plane.
For further information, find the full application note here.