4: Multi-frequency capacitance-voltage unit Model 4200A-SCS Parameter Analyzer
4-44 4200A-901-01 Rev. C / February 2017
MOS Capacitor C-V Project (cvu-moscap)
Maintaining the quality and reliability of gate oxides of MOS structures is a critical task in
semiconductor fabrication. A commonly used tool for studying gate-oxide quality in detail is the
capacitance-voltage technique. C-V measurements are typically made on a capacitor-like device
called a MOS capacitor.
An example of the construction of a MOS capacitor is shown in the next figure. As shown, the MOS
capacitor is an oxide placed between a semiconductor and a metal gate. The semiconductor and the
metal gate are the two plates of the capacitor. The oxide functions as the dielectric. The area of the
metal gate defines the area of the capacitor.
Figure 123: MOS capacitor
The most important property of the MOS capacitor is that its capacitance changes with changes to
applied voltage. As a result, the modes of operation of the MOS capacitor change as a function of the
applied voltage. As a DC sweep voltage is applied to the gate, it causes the device to pass through
accumulation, depletion, and inversion.
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