Wafer alignment sensor

Details Wafer alignment sensor Wafer alignment sensor

1994-06-20

1996-11-19

Evans, F. L.

Optics: measuring and testing

By polarized light examination

With light attenuation

356381, 356237, 25055927, 25055931, G01B 1100

Patent

active

055768318

ABSTRACT:
A surface height detection and positioning device for use in a surface inspection system. An incident beam of light impinges obliquely upon the surface, and a position detector is disposed to receive light reflected from the surface. The position detector has a sensitivity characteristic graded along a direction transverse to the surface, so that the output of the position detector is used to determine a height of the surface. The device can be incorporated into a particle detection system that scans patterned wafers with obliquely incident light to search for particles with a particle detector positioned to receive scattered light. In one embodiment, the position detector can have a width that is graded along the direction transverse to the surface, so that a scan line on the surface that is focused upon the position detector crosses the width of that detector in a time that varies as a function of the height of the surface. This time can be measured as an electrical pulse from the position detector that can be used for various purposes, including adjusting the height of the surface during scanning. In another embodiment, the position detector can have a periodic variance in light sensitivity that is graded, so that varying a height of the surface varies a phase of the output from the position detector.

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