Method and apparatus for determining the center and orientation

Details Method and apparatus for determining the center and orientation Method and apparatus for determining the center and orientation

1996-03-29

1997-07-01

Pham, Hoa Q.

Optics: measuring and testing

By alignment in lateral direction

With light detector

356150, 414754, H01L 2168

Patent

active

056444001

ABSTRACT:
A device and method for determining the center and orientation of a circular workpiece such as a semiconductor wafer. A beam of light from a light emitting diode is nearly collimated by a collimation lens before being reflected by a conical mirror. After reflecting from the conical mirror, the beam is reflected by a frustoconical mirror down to a flat annular mirror positioned below a semiconductor workpiece. That portion of the beam not intercepted by the workpiece is reflected back to the frustoconical mirror by the flat mirror. The return beam is then reflected by the conical mirror and passes through the collimating lens and forms a ring of light on a quadrature photodiode array. Light striking the quadrature photodiode array is converted into an electrical voltage or signal proportional to the amount of light striking each photodiode. By comparing the signals from each photodiode, the amount of light striking each diode can be compared to determine the position of the center and the orientation of a workpiece.

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