Method for segmentation and modeling of lower surface of a cylindrical hole or overlap with an underlying feature

A method for determining the geometry of a feature bound by a lower surface of a hole in a semiconductor wafer, the method comprising:

• (a) obtaining a top level image containing a top surface of the hole and a bottom level image containing a bottom surface of the hole;
• (b) classifying occlusion of the bottom surface of the hole based on crude measurement of an offset between geometric centers of both surfaces;
• (c) if the bottom surface is classified as occluded, approximating the bottom surface by assigning weights to respective edge pixels of the bottom surface and finding a contour corresponding to an ideal reference geometry that best fits the pixels based on their respective weights.

A computer program product comprising a tangible memory storing computer program code which, when executed on a computer processor, accesses data stored in memory that is representative of a top level image containing a top surface of a hole and a bottom level image containing a bottom surface of the hole, and computes a geometry of a feature bound by a lower surface of a hole in a semiconductor wafer by:

• (a) classifying occlusion of the bottom surface of the hole based on crude measurement of an offset between geometric centers of both surfaces;
• and
• (b) if the bottom surface is classified as occluded, approximating the bottom surface by assigning weights to respective edge pixels of the bottom surface and finding a contour corresponding to an ideal reference geometry that best fits the pixels based on their respective weights.