CeNSE Center for Nanoscale Science and Engineering

 

The "CV", or more correctly "C-V", in C-V profiling, stands for capacitance-voltage, and refers to a technique used for characterization of semiconductor materials and devices. The technique uses a metal-semiconductor junction (Schottky barrier) or a p-n junction ^[1] 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.^{[2], [3]} Measurements may be done at DC, or using both DC and a small-signal AC signal (the conductance method ^{[3], [4]}), or using a large-signal transient voltage.^[5]

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).

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. This 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.

These measurements continue to be important after other process steps have been performed, such as lithography, etching, cleaning, dielectric and polysilicon depositions, and metallization. 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.