Low Resistance "Lindeck' Measurements; Resistivity Measurements; Diode Characterization - Keithley 263 Instruction Manual

APPLICATIONS
85.5.3 Low Resistance "Lindeck"
Measurements
The Model 263 AMPS source can be used in conjunction
with the Model 181 Digital Nanovoltmeter to measure low
resistance. The Model 263 is placed in parallel with the
low unknown resistance (see Figure 5-15). In a circuit with
a 0.01R resistance, a current source delivering 10x1~4
(Model 263) will provide a resolution of 0.01% with the
Model 181 on the 2mV range. With this method, the
resistance may be found by dividing the voltage on the
Model 181 by the current source value of the Model 263.
With a lOmA current source and O.OlQ resistance, a
voltage of lC@V will result across the measured resistance.
5.5.4 Resistivity Measurements
Refer to Figure 5-16 for an illustration of resistivity
measurement. The voltmeter in the circuit requires a high
input impedance to overcome lead resistance problems.
The Keithley Model 617 has the high input impedance
(greater than 2OOT0 in parallel with 20pF) required to make
the measurement accurately. For most wafers the resistivi-
ty is calculated as follows:
V
p=-
ktI
where
k = constant based on the geometry of the wafer and
probe
t = sample thickness
Certain semiconductor materials, such as silicon, have
V = measured voltage
hieh resistivities. The measurement of their resistivitv can
I = current in the sample
be-a difficult measurement. To aid in their measure&at,
special probes of a hard metal, such as tungsten, are used.
Because contact resistance is so high, a four point probe
is used. The outer contacts supply a constant current, and
the inner two contacts measure the voltage drop across
a portion of the sample. With the geometry of the probe
and wafer known, resistivity can then be calculated.
The current source must be stable and accurate. The Model
263 AMPS source is ideal for this application.
5.5.5 Diode Characterization
With the Model 263 it is possible to obtain the necessary
data to plot I-V (current-voltage) characteristics of a diode
over several decades. Figure 5-17 shows the configuration
to be used. The Model 617, with its high input resistance
in the volts function, allows the measurement to be made
accurately. Figure 5-18 shows several examples of diode
curves which have been plotted using the configuration
of Figure 5-17.
MODEL 263
MODEL 181
(AMPS SOURCE)
(NANAVOLTMETER)
Figure 5-15. Low Resistance Measurement Connections
5-21