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SEMI MF1392 Document Information:
Title
TEST METHOD FOR DETERMINING NET CARRIER DENSITY PROFILES IN SILICON WAFERS BY CAPACITANCE-VOLTAGE MEASUREMENTS WITH A MERCURY PROBE
Semiconductor Equipment and Materials International
Publication Date:
Mar 1, 2007
Scope:
This test method1 covers the measurement of net
carrier density and net carrier density profiles in epitaxial and
polished bulk silicon wafers in the range from about 4 ×
1013 to about 8 × 1016
carriers/cm-3 (resistivity range from about 0.1 to about
100 O·cm in n-type wafers and from about 0.24 to about 330
O·cm in p-type wafers).
This test method requires the formation of a Schottky barrier
diode with a mercury probe contact to an epitaxial or polished
wafer surface. Chemical treatment of the silicon surface may be
required to produce a reliable Schottky barrier diode.2
The surface treatment chemistries are different for n- and
p-type wafers. This test method is sometimes considered
destructive due to the possibility of contamination from the
Schottky contact formed on the wafer surface; however, repetitive
measurements may be made on the same test specimen.
This test method may be applied to epitaxial layers on the same
or opposite conductivity type substrate. This test method includes
descriptions of fixtures for measuring substrates with or without
an insulating backseal layer.
The depth of the region that can be profiled depends on the
doping level in the test specimen. Based on data reported by
Severin2 and Grove,3 Figure
1 shows the relationships between depletion depth, dopant density,
and applied voltage together with the breakdown voltage of a
mercury silicon contact. The test specimen can be profiled from
approximately the depletion depth corresponding to an applied
voltage of 1 V to the depletion depth corresponding to the maximum
applied voltage (200 V or about 80% of the breakdown voltage,
whichever is lower). To be measured by this test method, a layer
must be thicker than the depletion depth corresponding to an
applied voltage of 2 V. 2.5 This test method is intended for rapid
carrier density determination when extended sample preparation time
or high temperature processing of the wafer is not practical.
This test method provides for determining the effective area of
the mercury probe contact using polished bulk reference wafers that
have been measured for resistivity at 23°C in accordance with SEMI
MF84 (see Note 1). This test method also includes procedures for
calibration of the apparatus for measuring both capacitance and
voltage.
Warnings and precautionary notes regarding potential safety
hazards are provided throughout the document.
NOTICE: This standard does not purport to
address safety issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety and health practices and determine the
applicability of regulatory or other limitations prior to use.
Net carrier density is a critical parameter in growth of
epitaxial layers of silicon. This test method provides a means for
determining net carrier density without formation of a special
diode structure on the layer. It may also be used in characterizing
net carrier density in polished silicon wafers.
This test method can be used for research and development,
process control, and materials specification, evaluation, and
acceptance purposes.
In the absence of inter-laboratory test data to establish its
reproducibility (see ¶ 14.2), this test method should be used for
materials specification and acceptance only after the parties to
the test have established reproducibility and correlation.
1 DIN 50439, Determination of the Dopant
Concentration Profile of a Single Crystal Semiconductor Material by
Means of the Capacitance-Voltage Method and Mercury Contact, is
technically equivalent to this test method. DIN 50439 is the
responsibility of DIN Committee NMP 221, with which SEMI maintains
close liaison. DIN 50439 is available in German and English from
Beuth Verlag GmbH, Burggrafenstraße 4-10, D-10772, Berlin,
Germany
2 Severin, P. J., and Poodt, G.
J.,"Capacitance-Voltage Measurements with a Mercury-Silicon Diode,"
J. Electrochem. Soc, 119, 1384–1388
(1972)
3 Grove, A. S., Physics and Technology of
Semiconductor Devices (John Wiley and Sons, New York, 1967) §§
6.2 and 6.7c
Keywords:
- capacitance-voltage method
- carrier density
- carrier density profile
- depth profile
- epitaxial wafers
- mercury probe
- net carrier density
- polished wafers
- profiles
- resistivity
- silicon
- single crystal silicon
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