US Patent 7639861 Method and apparatus for backlighting a wafer during alignment

A method and apparatus is provided for illuminating a wafer during wafer alignment using machine vision. An illumination device is fabricated using electroluminescent material, that provides diffuse illumination uniformly over the surface of the lamp to provide backlighting of the wafer. Contrast between the image of the wafer and the diffuse illumination produce edge features in the image that can be analyzed to determine the position and orientation of the wafer.