Capacitance–voltage profiling

Capacitance-voltage profiling (or C-V profiling, sometimes CV profiling) is a technique for characterizing semiconductor materials and devices. The applied voltage is varied, and the capacitance is measured and plotted as a function of voltage. The technique uses a metal-semiconductor junction (Schottky barrier) or a p-n junction or a MOSFET to create a depletion region, a region which is empty of conducting electrons and holes, but may contain ionized donors and electrically active defects or traps. The depletion region with its ionized charges inside behaves like a capacitor. By varying the voltage applied to the junction it is possible to vary the depletion width. The dependence of the depletion width upon the applied voltage provides information on the semiconductor's internal characteristics, such as its doping profile and electrically active defect densities.^, Measurements may be done at DC, or using both DC and a small-signal AC signal (the conductance method ^, ), or using a large-signal transient voltage.

Many researchers use capacitance voltage (C-V) testing to determine semiconductor parameters, particularly in MOSCAP and MOSFET structures. However, C-V measurements are also widely used to characterize other types of semiconductor devices and technologies, including bipolar junction transistors, JFETs, III-V compound devices, photovoltaic cells, MEMS devices, organic thin film transistor (TFT) displays, photodiodes, and carbon nanotubes (CNTs).

CV profile for a bulk MOSFET with different oxide thickness.

These measurements’ fundamental nature makes them applicable to a wide range of research tasks and disciplines. For example, researchers use them in university and semiconductor manufacturers’ labs to evaluate new processes, materials, devices, and circuits. These measurements are extremely valuable to product and yield enhancement engineers who are responsible for improving processes and device performance. Reliability engineers also use these measurements to qualify the suppliers of the materials they use, to monitor process parameters, and to analyze failure mechanisms.

A multitude of semiconductor device and material parameters can be derived from C-V measurements with appropriate methodologies, instrumentation, and software. This information is used throughout the semiconductor production chain, and begins with evaluating epitaxially grown crystals, including parameters such as average doping concentration, doping profiles, and carrier lifetimes.

C-V measurements can reveal oxide thickness, oxide charges, contamination from mobile ions, and interface trap density in wafer processes. A CV profile as generated on Nanohub for bulk MOSFET with different oxide thicknesses. Notice that the red curve indicates low frequency while the blue curve illustrates the high frequency CV profile. Pay particular attention to the shift in threshold voltage with different oxide thicknesses.

These measurements continue to be important after other process steps have been performed, including lithography, etching, cleaning, dielectric and polysilicon depositions, and metallization, among others. Once devices have been fully fabricated, C-V profiling is often used to characterize threshold voltages and other parameters during reliability and basic device testing and to model device performance.

See also

• Current–voltage characteristic
• Depletion region
• Depletion width
• Drive Level Capacitance Profiling
• Deep-level transient spectroscopy
• Metal–oxide–semiconductor structure

External links

• MOScap simulator on nanoHUB.org enables users to compute C-V characteristics for different doping profiles, materials, and temperatures.
• Online lecture on MOS Capacitors by Dr. Lundstrom