Small spot ellipsometer
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United States of America Patent
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Mar 22, 2005
Issued Date -
N/A
app pub date -
Mar 26, 2004
filing date -
Feb 8, 2001
priority date (Note) -
Expired
status (Latency Note)
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Abstract
An ellipsometer capable of generating a small beam spot is disclosed. The ellipsometer includes a light source for generating a narrow bandwidth probe beam. An analyzer is provided for determining the change in polarization state of the probe beam after interaction with the sample. A lens is provided having a numerical aperture and focal length sufficient to focus the beam to a diameter of less than 20 microns on the sample surface. The lens is formed from a graded index glass wherein the index of refraction varies along its optical axis. The lens is held in a relatively stress free mount to reduce stress birefringence created in the lens due to changes in ambient temperature. The ellipsometer is capable of measuring features on semiconductors having a dimensions as small as 50.times.50 microns.
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