Section 4: Multi-frequency capacitance-voltage unit
Model 4200A-SCS Parameter Analyzer Reference Manual
4-74
4200A-901-01 Rev. C / February 2017
Basic testing involves the following steps:
1.
At room temperature, generate a C-V sweep on the MOS capacitance.
From the C-V data,
extract the flatband capacitance (C
fb
), flatband voltage (V
fb
1), and the oxide capacitance (C
OX
).
The device should be measured on a hot chuck in a dark box. The dark box prevents static noise
problems that can affect the C-V measurements.
2.
Apply DC bias voltage and temperature stress.
A gate voltage of approximately 1 MV/cm of
dielectric thickness is applied across the device to drive the mobile ions to the interface. A
thermal chuck is used to temperature-stress at a temperature in the range of 150 °C to 300 °C,
depending on the type of ions. Typical temperature stress time is around five to 10 minutes. The
device is cooled to room temperature with the bias voltage applied. Mobile charges will be
trapped near the metal-oxide interface.
3.
Repeat the C-V sweep on a cooled sample and again extract the flatband voltage
(V
fb
2)
.
If
there are mobile charges in the oxide, the flatband voltage will be different from the first one.
4.
The sample is heated again, but the opposite polarity DC bias voltage is applied to the
sample.
This causes the mobile charges to be driven toward the oxide-silicon interface. Again,
the sample is cooled while the DC bias voltage is applied.
5.
Repeat the C-V sweep on the cooled sample and derive the flatband voltage
(V
fb
3)
.
Since
mobile charges are concentrated on the opposite interface, this flatband voltage will be different
from the first and second measurements. This shift in the flatband voltage is illustrated in the next
figure.
Figure 130: Flatband voltage shift caused by mobile charges in the oxide
