Patent ID: 6678055
Filing Date: 2004-01-13
Classification: G01B,G01R

Abstract:
Apparatus for measuring properties of a wafer, the apparatus comprising:at least one monochromatic light source, for producing monochromatic light for directing at said wafer, at least a first and a second beam director, each optically associated with said monochromatic light source for directing said monochromatic light from said source to provide respective substantially parallel light beams towards said wafer, said beam directors being configured to cause said respective beams to strike at respective places on a planar surface of said wafer, said first beam director being arranged to direct a first of said respective beams substantially centrally onto said planar surface and said second beam director being alignable to direct a second of said respective beams substantially outwardly of said center to a point at a selected distance from said first beam, an optical processor arranged to receive reflections of each beam and further comprising an interferometer unit to process said reflections together, thereby to detect any optical difference between said reflections, said optical difference being indicative of bow in said wafer, said bow being usable with said selected distance to calculate a stress within said wafer.