Identification of Microtopographic Surface Features and Form Error Assessment

This work is concerned with quality inspection of microtopographic surface features, such as those that may be commonly found in semiconductor products, microelectromechanical systems, and other microcomponents. Surface microtopography data are assumed to be available as a height map, acquired through raster scanning over the region of interest, by means of a 3D profilometer or a 3D scanning microscope. An algorithmic procedure is proposed for form error assessment, which comprises several steps: first the feature of interest is localized and identified within the height map; then it is extracted and aligned with a reference (i.e., nominal) geometry modeled by means of a CAD system; finally, form error is evaluated from the volume enclosed between the two aligned geometries. Feature identification is implemented through a modified version of the ring projection transform, adapted to operate on topography height maps; alignment comprises two steps (coarse alignment, consisting in an exhaustive search over discrete angular positions; and fine alignment, done with the iterative closest point technique). The final form error assessment procedure is applied to aligned geometries. The approach is illustrated and validated first through its application to an artificially generated case study, then to a real-life case of industrial relevance.