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Scanning capacitance microscopy& Piezo force microscopyDI*NESH.K.2009206027M.E.CIM (III SEM)

ScanningCapacitance Microscopy (SCM)Scanning capacitance microscopy(SCM) is a variety ofscanning probe microscopy.

Scanning Capacitance Microscopy (SCM) is preferably used to: image dopant variations in semiconductor devices.

HOW SCM WORKS?A Metal/Oxide/Semiconductor (MOS) capacitor is formed between the SCM tip and the sample surface when the SCM tip is brought into close proximity with the sample surface.where:M - metal probe, S - semiconductor materialO -thin dielectric formed on the semiconductor surface.

Scanning capacitance microscopy

Scanning capacitance microscopy

HOW SCM WORKS?Free carriers within the sample move under the influence of an AC electric field applied by the conductive probe (tip).

HOW SCM WORKS?

HOW SCM WORKS?The capacitance measured by GHz resonant capacitance sensor varies as the carriers move towards (accumulation) and away from (depletion) the probe.

HOW SCM WORKS?When the sample is fully depleted the measured capacitance is that of the oxide plus the depletion layer.When carriers are accumulated at the surface, the measured capacitance is that of the oxide layer.This capacitance variation in response to the tip-applied field forms the basis of the SCM measurement.

capacitanceThe capacitance between two parallel plates is given by;

C = A/tWhere: is the dielectric constant A is the area t is the spacing between the plates

Therefore capacitance is high when the plates are closest.

CV curves for a heavily and a lowly doped n-type semiconductor

CV curveFor heavily doped materials the carriers do not move far. Hence, the measured capacitance variation between accumulation and depletion is small.

The lightly doped semiconductors yield a large capacitance change.

CV curveFrom the CV curve we infer that an applied AC bias V between the tip and sample will produce a corresponding capacitance variation, C.The amplitude of this capacitance variation yields information about the level of dopant directly beneath the tip.

HOW SCM WORKS?A lock-in amplifier amplifies the capacitance variation, C, measured by the sensor.

Output from the lock-in amplifi er in the form of C/V amplitude and/or phase is then displayed as an image.

A contrast mechanism for the image is the change in the measured capacitance and hence contained within the image is information on both the dopant level as well as the dopant species.

SCM images of SRAMsupport circuitry

Scanning capacitance microscopy

ADVANTAGESCM functions even through an insulating layer, thus a finite conductivity is not required to measure the electrical properties.

Applicationsnanospectroscopy characterizationmapping thedopantprofile in semiconductordevice on a 10nm scale.image compressible strips in a two-dimensional electron gas (2DEG) buried 50nm below an insulating layer in a large magnetic field and at cryogenic temperatures.[7]

PIEZO FORCE MICROSCOPY

Piezo force microscopy (PFM)Piezo force microscopy (PFM), or piezo response atomic force microscopy (PR-AFM) is used to characterize the electromechanical response of a ferroelectric material.

Piezo Force Microscopy (PFM) For accessing ferroelectric properties on the nano scale.For imaging of ferroelectric domain structures on the 3-10 nm level.For providing direct information on localized electromechanical activity.

How PFM works?In PFM operation, a conductive AFM tip is brought into contact with the surface of the studied ferroelectric or piezoelectric materials, A pre-set voltage is applied between the sample surface and the AFM tip, establishing an external electric field within the sample.

Set up of PFM

Set up of PFM

How PFM works?Due to the electrostriction, or "inversed piezoelectric" effects of ferroelectric or piezoelectric materials, the sample locally expands or contracts according to the electric field. If the initial polarization of the electrical domain of the measured sample is perpendicular to the sample surface, and parallel to the applied electric field, the domains would experience a vertical expansion.

How PFM works?Since the AFM tip is in contact with the sample surface, the domain expansion bends the AFM cantilever upwards, and results in an increased deflection compared to the status before applying the electric field. Conversely, if the initial domain polarization is anti-parallel to the applied electric field, the domain would contract and in turn result in a decreased cantilever deflection.

How PFM works?The amount of cantilever deflection change is directly related to the amount of expansion or contraction of the sample electric domains, and hence proportional to the applied electric field.

How PFM works?Mapping of the amplitude and phase of the displacement allows imaging of ferroelectric domain structures with ~3-10 nm resolution. Therefore, PFM imaging provides direct insight into the nanoelectromechanics of ferro- and piezoelectric materials on the length scales defined by radius of the tip-surface contact and the radius of curvature of the tip.

PFM amplitude and phase images obtained on PZT-5H sample

ADVANTAGESPiezoresponse Force Microscopy (PFM) is popular due to ease of implementation, high resolution and insensitivity to topography.

ReferencesScanning Capacitance Microscopy by Andy Erickson, Peter Harris of MULTIPROBEScanning Capacitance Microscopy (SCM) C. C. Williams, J. Slinkman et al (1989)http://en.wikipedia.org/wiki/Scanning_capacitance_microscopy Dual frequency resonance-tracking piezo force microscopy Keef, Asylum Researchwww.parkAFM.com

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