Multiple focal plane image comparison for defect detection and classification

摘要

An apparatus and method of analyzing particles on an integrated circuit wafer using a quasi three dimensional image analysis of the particles. The apparatus includes an optical system which has an optical axis and forms an image of that part of a focal plane which within a field distance of the optical axis. The apparatus holds a wafer perpendicular to the optical axis and allows the surface of the wafer to be moved in a plane perpendicular to the optical axes to view the entire surface of the wafer. The apparatus also allows the surface of the wafer to be moved a step distance below the focal plane. Images formed at a number of step distances are used to form a quasi three dimensional image of particles on the surface of the wafer. Automatic image analysis is used when appropriate.