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Figure: 1. Arrangement of contacts when measuring ρ by the spreading resistance
method.
1 probe, 2 semiconductor, 3 ohm contact.
The electric potential distribution for a semi-infinite homogeneous sample
with a contact in the form of a flat disk with radius r
0
can be obtained from the
solution of the Laplace equation, from which the spreading resistance R
p
can be
obtained.
(4)
For a hemispherical contact with a radius r
0
, the spreading resistance is:
(5)
By measuring the voltage drop across such a contact V when a current I is p assed
through it, it is possible to determine the specific
resistance of the sample
or
for the second case.
Usually, in practice, two-probe and three-probe measurement schemes are
used to measure the spreading resistance and then determine the resistivity of a
semiconductor [5].
Eddy current testing method is one of the methods of non-destructive testing
of products made of conductive materials. It is based on the analysis of the
interaction of an external electromagnetic field with the electromagnetic field of
eddy currents induced in the controlled object by this field [6]. The eddy curr ent
control method is based on the analysis of the
interaction of an external
electromagnetic field with the electromagnetic field of eddy currents induced by a
driving coil in an electrically conductive control object (OC) by this field. An
inductive coil (one or more), called an eddy-current converter (ECP), is most often
used as a source of the electromagnetic field.
The accuracy of this method is much lower than that of the four -probe
method, but it is indispensable for use in various types of automatic sorters - both
wafers and epitaxial layers, and structures of the silicon -on-insulator type, for
scrub rejection in the production of monocrystalline
silicon and other similar
1
2
3
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technical problems. But there are also several features and advantages of this
method:
- the ability to check a large number of product parameters;
- checking of layers of material of small thickness;
- contactless control;
- high sensitivity to microscopic defects;
- high speed of control;
- the ability to control objects with complex geometry, places of difficult access;
- eddy current method does not pose a health hazard to the operator.
The first two methods described above have a big drawback - in fact, they
are destructive, have a short lifetime of the probes, they are very sens itive to the
surface treatment before measurements, to the material and geometry of the probe,
and the force of pressing the probe to the surface. And eddy current control cannot
be: control of structural elements and parts with abrupt changes in magnetic or
electrical properties; discontinuities were found, the opening p lanes of which are
parallel to the controlled surface and make an angle with it less than 10 degrees. It
will be impossible to carry out control if electrically conductive protective coatings
are applied to the surface of the object (the option when the defect does not come
to the surface of the coating), defects are filled with electrically conductive
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