Method for automatically establishing a wafer coordinate system

Abstract

An automated method for establishing a wafer coordinate system for a wafer characterization system. Specifically, under computer control, a high-magnification imaging system images a wafer at a low, initial magnification level. From this imaging process, the method first determines the location of the center of the semiconductor wafer mounted within the imaging system and then determines the wafer orientation therein. The method then repeats the imaging process at increased magnification levels until a desired degree of magnification is used to accurately define the location of the wafer center and the wafer orientation. Together the wafer center and orientation define a wafer coordinate system. This wafer coordinate system is then related to the coordinate system of the imaging system by a coordinate system transformation. As such, once the coordinate systems are related, the imaging system can quickly and accurately determine any point on a wafer. The method uses various wafer edge locations to determine the wafer center location and wafer orientation. These edge locations are determined by either: (1) using a scanning electron microscope in conjunction with an image processing technique, or (2) using an energy dispersive x-ray detector to detect changes in the SiK.sub..alpha. line intensity.