Skjerven, Morrill, MacPherson, Franklin & Friel LLP
Method for characterizing defects on semiconductor wafers
 10A method is described for detecting and characterizing defects on a test surface of a semiconductor wafer. A three-dimensional image of the test surface is aligned and compared with a three-dimensional image of a defect-free reference surface. Intensity differences between corresponding pixels in the two images that exceed a predefined threshold value are deemed defect pixels. According to the method, the pixels of the reference image are grouped according to their respective z values (elevation) to identify different physical layers of the reference surface. Because different surface layers can have different image properties, such as reflectance and image texture, the groups of pixels are analyzed separately to determine an optimal threshold value for each of the groups, and therefore for each layer of the reference surface. 
Ultrapointe Corporation
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inventional inventional inventional inventional
Ke Bruce W. Ken K. Lakshman
Han Worster Lee Srinivasan