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Profilometry With a Coherence Scanning Interferometer

IP.com Disclosure Number: IPCOM000100542D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Lee, B: AUTHOR [+2]

Abstract

A new profilometry technique based on coherence scanning microscopy (*) has been developed which provides interferometric accuracy in profile measurements with very large ranges which are limited only by mechanical scanning constraints. The coherence scanning approach also provides twice the lateral resolution of conventional microscopy.

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Profilometry With a Coherence Scanning Interferometer

       A new profilometry technique based on coherence scanning
microscopy (*) has been developed which provides interferometric
accuracy in profile measurements with very large ranges which are
limited only by mechanical scanning constraints.  The coherence
scanning approach also provides twice the lateral resolution of
conventional microscopy.

      The basis for coherence scanning is the white light
interferometer, as shown in Fig. 1.  The target is scanned in the z
axis by either moving it or moving the reference mirror.  If light is
monitored at one point in the image as the object is scanned, white
light fringes appear as the object comes into focus (see Fig. 2).
The coherence function acts as an envelope on these white light
fringes. With the proper signal processing, the fringes can be
demodulated to find the peak amplitude Ao of the envelope and the z
location of the peak, Zo.  Extending this to finding the peak
amplitude and location for all points in the image, a high lateral
resolution image is created from all the Ao's.  Spatial incoherence
reduces the crosstalk between laterally adjacent points, which leads
to the increased lateral resolution.  This is analogous to the
improvement found in confocal microscopy.  Comparing all the Zo's
produces a profile of the surface.  Here temporal coherence limits
the crosstalk between vertically adjacent points.  This leads to a
depth slicing analogous...