Optical device for the alignment of two superimposed objects
Photoelectric detecting apparatus
Device for and method of aligning two bodies Patent #: 4553845
ApplicationNo. 06/868506 filed on 07/31/1986
US Classes:250/548, Controlling web, strand, strip, or sheet356/401With registration indicia (e.g., scale)
ExaminersPrimary: Westin, Edward P.
Assistant: Ruoff, Jessica L.
Attorney, Agent or Firm
International ClassG03F 9/00 (20060101)
AbstractAn alignment apparatus wherein a wafer having a wafer target thereon and a reticle having a reticle target therethrough are aligned to each other. An alignment image is formed on the wafer, and the wafer and reticle are scanned relative to the alignment image. The alignment image has a linear extent normal to the scanning direction which is longer than the wafer target so that a portion of the alignment image is reflected by the wafer. The portion of the alignment image reflected by the wafer is reimaged onto the reticle target. Collecting optics are provided to collect light from the alignment image that is backscattered by the wafer target as the wafer target is scanned past the alignment image. Two detectors are provided: one to detect the backscattered light, the other to detect light which passes through the reticle target. The output from each of the detectors is compared to determine any misalignment.