Abstract: A method and apparatus to maintain image focus on parts such as wafers, circuit boards, or high-density substrates as the part is being inspected. Focus performance is independent of feature and trace orientation and density. This apparatus can be easily integrated into an inspection system and can maintain focus on parts with high aspect ratio structures and or low or non-reflective insulators. It enables the inspection of high-density fine line products requiring the use of high resolution, high numerical aperture (NA) imaging optics with small depths of focus (DOF) that must be kept in focus during the inspection.

Abstract: Methods and apparatus for inspection of electronic parts such as semiconductor wafers, high-density circuit boards, multi-layer substrates, chrome on glass masks, and other fine line products which compensates for reference misalignment. Conductor linewidth and space measurements are performed along the entire length of every conductor to sub-camera pixel, sub-micron accuracy in real time as the part is scanned. Billions of metrology measurements are also performed in real time to sub-micron accuracy. A self-learning automated method to extract measurement values from Computer Aided Design (CAD) files is described. This method automatically determines locations to perform these billons of operations within defined allowed manufacturing tolerances.