US Patent 9831110 Vision-based wafer notch position measurement

A wafer alignment system includes an image capture device that captures an image of a wafer positioned on a pedestal. An image analysis module analyzes the image to detect an edge of the wafer and a notch formed in the edge of the wafer and calculates, based on a position of the notch, first and second edge positions corresponding to the edge of the wafer. An offset calculation module calculates an angular offset of the wafer based on the first position and the second edge positions. A system control module controls transfer of the wafer from the pedestal to a process cell based on the angular offset.