Interferometer for measuring thickness variations of semiconductor wafers
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United States of America Patent
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Jun 1, 1999
Grant Date -
N/A
app pub date -
May 30, 1997
filing date -
May 31, 1996
priority date (Note) -
Expired
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Abstract
Thickness variations of semiconductor wafers are measured by interfering two beams of infrared light that are relatively modified by reflections from opposite side surfaces of the wafers. Non-null interferometric measurements are made by illuminating the wafers with diverging beams and subtracting errors caused by varying angles of incidence. Null interferometric measurements are made of both thickness variations and flatness. Infrared light, which can transmit through the wafers, is used for measuring thickness variations; and visible light, which cannot transmit through the wafers, is used for simultaneously measuring flatness.
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