Scanning capacitance microscopy (SCM) is a variety of scanning probe microscopy

Scanning probe microscopy

Scanning Probe Microscopy is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. An image of the surface is obtained by mechanically moving the probe in a raster scan of the specimen, line by line, and recording the probe-surface interaction as a...

 in which a narrow probe electrode is held just above the surface of a sample and scanned across the sample. SCM characterizes the surface of the sample using information obtained from the change in electrostatic capacitance between the surface and the probe.

SCM uses an ultra-sharp conducting probe (often Pt/Ir or Co/Cr metal covering an etched silicon probe) to form a metal-insulator-semiconductor (MIS/MOS) capacitor with a semiconductor sample if a native oxide is present. When no oxide is present, a Schottky capacitor is formed. When the probe and surface are in contact, an AC bias is applied, generating capacitance variations in the sample which can be detected using a GHz resonant capacitance sensor. The tip is then scanned across the semiconductor's surface in 2D while the tip's height is controlled by conventional contact force feedback.

By applying an alternating bias to the metal-coated probe, carriers are alternately accumulated and depleted within the semiconductor’s surface layers, changing the tip-sample capacitance. The magnitude of this change in capacitance with the applied voltage gives information about the concentration of carriers (SCM amplitude data), whereas the difference in phase between the capacitance change and the applied, alternating bias carries information about the sign of the charge carriers (SCM phase data). Because SCM functions even through an insulating layer, a finite conductivity is not required to measure the electrical properties.

SCM resolution

On the conducting surfaces, the resolution limit is estimated as 2 nm. For the high resolution, the quick analysis of capacitance of a capacitor with rough electrode is required. This SCM resolution is an order of magnitude better than that estimated for the atomic nanoscope

Atomic nanoscope

The atomic de Broglie microscope is an imaging system which is expected to provide resolution at the nanometer scale....

; however, as other kinds of the probe microscopy, SCM requires careful preparation of the analyzed surface, which is supposed to be almost flat.

Applications of SCM

Owing to the high spatial resolution of SCM, it is a useful nanospectroscopy characterization tool. Some applications of the SCM technique involve mapping the dopant

Dopant

A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...

 profile in a 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...

 device on a 10 nm scale, quantification of the local dielectric

Dielectric

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...

 properties in hafnium

Hafnium

Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869. Hafnium was the penultimate stable...

-based high-k dielectric films grown by an atomic layer deposition

Atomic layer deposition

Atomic layer deposition is a thin film deposition technique that is based on the sequential use of a gas phase chemical process. The majority of ALD reactions use two chemicals, typically called precursors. These precursors react with a surface one-at-a-time in a sequential manner...

 method and the study of the room temperature resonant electronic structure of individual germanium

Germanium

Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

 quantum dot

Quantum dot

A quantum dot is a portion of matter whose excitons are confined in all three spatial dimensions. Consequently, such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. They were discovered at the beginning of the 1980s by Alexei...

 with different shapes.
The high sensitivity of dynamical scanning capacitance microscopy, in which the capacitance signal is modulated periodically by the tip motion of the atomic force microscope

Atomic force microscope

Atomic force microscopy or scanning force microscopy is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit...

 (AFM), was used to image compressible strips in a two-dimensional electron gas (2DEG

2DEG

A two-dimensional electron gas is a gas of electrons free to move in two dimensions, but tightly confined in the third. This tight confinement leads to quantized energy levels for motion in that direction, which can then be ignored for most problems. Thus the electrons appear to be a 2D sheet...

) buried 50 nm below an insulating layer in a large magnetic field and at cryogenic temperatures.