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Use of Reflectivity Measurement in Infrared to Assess Stress in N-58 Ceramic Wafers

IP.com Disclosure Number: IPCOM000117025D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Deshpande, AP: AUTHOR [+4]

Abstract

Ellipsometry and X-Ray defraction are generally used to measure stress, nondestructively, in ceramic wafers. These methods are not very reliable in a material like N-58 which is a composite of alumina and titanium carbide (about 25%). The described method is a nondestructive test having a fine resolution.

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Use of Reflectivity Measurement in Infrared to Assess Stress in N-58
Ceramic Wafers

      Ellipsometry and X-Ray defraction are generally used to measure
stress, nondestructively, in ceramic wafers.  These methods are not
very reliable in a material like N-58 which is a composite of alumina
and titanium carbide (about 25%).  The described method is a
nondestructive test having a fine resolution.

      There are two primary reasons for the stress in this kind of
composite material.  The first is due to nonuniform cooling
(annealing) and secondly nonuniform mixture of alumina and titanium
carbide.  In modern fabrication methods, use of automatic ovens
reduce the stresses to a minimum due to the first cause.  The major
stress then is due to the second cause; as these two components have
different coefficients of expansion.  The nonuniform strain in the
material causes the stress which is proportional to the nonuniformity
of the mixture in the body of the material.  The wafer is polished to
make the reflectivity measurement.  An infrared beam of light is
reflected on the surface.  Alumina is totally transparent to this
wave length.  The amount of reflected light is proportional to the
amount of titanium carbide in the composite.  Entire wafers can be
scanned and contour maps of the percentage composition can be
plotted.  Stresses will be proportional to the variation of the
carbide material.