AFM applications

Conductive Atomic Force Microscopy

C-AFM can be used in two different ways:

By applying a constant voltage between the AFM tip and the specimen, the collected current is mapped in conjunction with the surface topography. An example is given in desked figure on a thin layer of hight k poly crystalline dielectric. There is some correlation between the leakage current and the distribution of gain gains and gain joints.

The AFM tip is maintained at a fixed point on the surface, then a break is applied. It is a type I(V) spectroscopy. This allows the study of conduction mechanisms. It is also possible to record characteristics of type I(t) or I(z).

Scanning Capacitance Microscopy

The scanning capacitance Microscopy (SCM) is a technique derived from the AFM that allows the capacitive study of a dielectric-type semiconductor sample. Given the low capacity value of the conductive AFM sample-tip MOS structure, in the order of attoFarad the measurement cannot be obtained by impedancemetry. The electronic signal acquisition device is therefore relatively complex.

It consists of an oscillator comprising a high frequency generator (915 MHz). A resonator, comprising a low frequency voltage generator (of the order of 90 KHz), a continuous voltage generator, a variable capacity in parallel to the MOS sample peak capacity. The oscillator and resonator are cut by inductance. The variable capacity is used to adjust the resonant frequency of the resonator to the oscillator’s own frequency. The resonant frequency of the resonator at the oscillator’s own frequency. The resonance frequency of the oscillator varies with the peak capacity –sample belonging to the resonator to which the oscillator is coupled. Being excited at fixed frequency (915 MHz), its oscillation amplitude varies. The low frequency voltage applied to the resonator allows periodic modulation of the oscillation amplitude. A synchronous detection demodulation circuit allows the detection of amplitude variation. The SCM measurement therefore consists in measuring dC/dV. The DC voltage generator is used to perform C(V) spectra, with the peak fixed at one point. It also allows, in imaging, an adjustment to obtain a maximum of dC/dV signal (position on the C(V) characteristic).

The C(V) characteristic of a MOS structure is conditioned by the doping of the semiconductor, it is possible to map the doping by SCM. As such, the technique competes with the Scanning spreading Resistance Microscopy (SSRM)