Test and Measurement
connected to the C-V instrument
through a prober, a probe card adapter,
and a switch matrix. Even if no switch is
involved, there is still a prober and
significant cabling. At high frequencies,
special corrections and compensation
must be applied. Usually, this is
achieved with some combination of an
open, short, or calibration device.
Because of the complexity of the
hardware, cabling, and compensation
techniques, it is a good idea to confer
with C-V test application engineers.
They are skilled at working with various
probe systems to overcome many types
of interconnection problems.
In addition to the accuracy issues
mentioned earlier, practical
considerations in C-V data collection
include the instrumentation’s range of
Figure 4. Basic electrical variables available from C-V measurements test variables, versatility of parameter
extraction software, and ease of
hardware usage. Traditionally, C-V
which is below the capabilities of many testing has been limited to about 30V
20
Challenges to successful LCR meters. Even those claiming to and 10mA DC bias. However, many
C-V measurements measure these small capacitance values applications, such as characterising LD
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The block diagram of a C-V test setup may have confusing specifications that MOS structures, low-Î interlayer
.eur (Figure 3) is deceptively simple. make it difficult to determine the final dielectrics, MEMS devices, organic TFT
oasiasemiconductor
However, certain challenges are accuracy in the measurement. If displays, and photodiodes, require tests
associated with this testing. Typically, accuracy over the instrument’s full at higher voltage or current. For these
test personnel have problems in the measurement range is not explicitly applications, a separate high voltage
following areas: stated, the user needs to clarify this DC power supply and C meter are
ring6 Low capacitance measurements with the manufacturer. required; DC bias up to 400V
(picofarads and smaller values) High D (Leaky) Capacitors differential (0 to ±400V) and a current
.com
ring6 C-V instrument connections In addition to having a low C value, output up to 300mA are very useful.
(through a prober) to the wafer a semiconductor capacitor may also be Being able to apply differential DC bias
device leaky. That is the case when the on both the HI and LO terminals of the
square4
Issue I 2009
ring6 Leaky (high D) capacitance equivalent R in parallel with C is too C-V instrument offers more flexible
measurements low. This results in resistive impedance control over electric fields within the
ring6 Using hardware and software overwhelming the capacitive DUT, which is very helpful in the
to acquire the data impedance, and the C value gets lost in research and modelling of novel
ring6 Parameter extractions the noise. For devices with ultra thin devices, such as nanoscale components.
oxide layers, D values can be greater The instrumentation software
Overcoming these challenges requires than five. In general, as D increases, the should include ready to run test
careful attention to the techniques used accuracy of a C measurement is rapidly routines that do not require user
along with appropriate hardware and degraded, so high D is a limiting factor programming. These should be
software. in the practical use of a C meter. Again, available for the most widely used
Low Capacitance Measurements higher frequencies can help solve the device technologies and test regimens,
If C is small, the DUT’s AC response problem. At higher frequencies the which were mentioned in the first three
current is small and hard to measure. capacitive impedance is lower, resulting paragraphs of this article. Some
However, at higher frequencies, the in a C current that is higher and more researchers may also be interested in
DUT impedance is reduced, so the easily measured. less common tests, such as performing
current increases and is easier to C-V Measurement Connections both a C V and C f sweep on a Metal
measure. Often semiconductor In most test environments, the DUT Insulator Metal (MIM) capacitor,
capacitance is very low (less than 1pF), is a test structure on a wafer: It is measuring small interconnect
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