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Non-Intrusive Optical Detection of Oxide Precipitates in Silicon

IP.com Disclosure Number: IPCOM000100500D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 127K

Publishing Venue

IBM

Related People

Batchelder, J: AUTHOR [+3]

Abstract

A sub-band interferometric light-scattering technique is described which permits detection of single precipitates and other inclusions in semiconductors. The Optical Precipitate Profiling (OPP) technique permits non-intrusive and non-contact determination of the Precipitate Free Zone (PFZ) depth, its uniformity across an entire wafer, and the density and size distribution of precipitates.

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Non-Intrusive Optical Detection of Oxide Precipitates in Silicon

       A sub-band interferometric light-scattering technique is
described which permits detection of single precipitates and other
inclusions in semiconductors.  The Optical Precipitate Profiling
(OPP) technique permits non-intrusive and non-contact determination
of the Precipitate Free Zone (PFZ) depth, its uniformity across an
entire wafer, and the density and size distribution of precipitates.

      An infrared laser at 1.3 mm is circularly polarized and passed
through Nomarski optics, which create two beams that are retarded in
phase by 90o with respect to one another and are focused into two
partially overlapping spots within the bulk of the sample.  The light
in each spot can be scattered by crystal imperfections and its phase
can be altered by strain localized around oxide precipitates.

      Mixing of the scattered light with a primary beam can change
the phase of one beam relative to the other, in the same manner as
traversing a region of inhomogeneous strain. As the beams are rapidly
raster scanned over the wafer and a defect traverses the volume of
the two partially separated, focused spots, a change in the optical
phase occurs in one beam rapidly followed by a change of phase in the
other beam.  A second Nomarski objective on the opposite side of the
wafer captures the transmitted laser light, recombines the two
polarization components, and collimates the transmitted light into a
nearly circularly polarized beam. The transmitted beam is circularly
polarized in the absence of crystal defects.  The phase shift of one
beam relative to the other causes the recombined beams to become more
elliptically polarized.  A signal that is proportional, for small
phase shifts, to the deviation from circular polarization is detected
by a Wollaston polarizing beam splitter.  The Wollaston analyzer
divides the reconstituted (transmitted) beam into two orthogonal
linearly polarized components tha...