KLA Corporation
Apparatus and method for gray field imaging

Abstract:

A beam of light is directed from a light source at a wafer on a chuck. The beam of light is reflected off the wafer toward a 2D imaging camera. Movable focus lenses in the path of the beam of light can independently change the illumination conjugate and the collection conjugate. A structured mask in an illumination path can be used and the beam of light can be directed through apertures in the structured mask. A gray field image of a wafer in a zone without direct illumination is generated using the 2D imaging camera and locations of defects on the wafer can be determined using the gray field image.