CV profiling
Encyclopedia
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 electron
s 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).
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.
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
is varied, and the capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
is measured and plotted as a function of voltage. The technique uses a metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
-semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
junction (Schottky barrier
Schottky barrier
A Schottky barrier, named after Walter H. Schottky, is a potential barrier formed at a metal–semiconductor junction which has rectifying characteristics, suitable for use as a diode...
) or a p-n junction
P-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
or a MOSFET
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
to create a depletion region
Depletion region
In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have diffused away, or have been forced away by an...
, a region which is empty of conducting electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s and holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
, 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).
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
Nanohub
nanoHUB.org is science cyberinfrastructure comprising community-contributed resources and geared toward educational applications, professional networking, and interactive simulation tools for nanotechnology...
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 regionDepletion regionIn semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have diffused away, or have been forced away by an...
- Depletion width
- Drive Level Capacitance ProfilingDrive Level Capacitance ProfilingDrive Level Capacitance Profiling is a type of capacitance voltage profiling characterization technique developed specifically for amorphous and polycrystalline materials which have more anomalies such as deep levels, interface states, or nonuniformities...
- 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