Scanning Capacitance Microscopy

Scanning capacitance microscopy (SCM) is one of the extended operation modes of atom force microscopy (AFM). The main purpose of SCM is to detect the majority carrier type and relative concentration inside the material. This technique is widely used in semiconductor failure analysis.

Basic working principle

In SCM measurement, a conductive tip is brought to in contact with the sample surface to form a metal-insulator-semiconductor (MOS) interface. As an applied AC electric field is applied, capacitance variation is generated at the surface and can be detected by resonant capacitance sensor. The tip then scans across the sample and give both topography and 2D capacitance profiling at the same time. The benefit of SCM is that the topography and 2D capacitance information do not mix at the same detected signal. Under the applied driving AC field, carriers are alternately accumulated and depleted at the surface, thus changing the MOS capacitance. The feedback carrier motion can be considered as a simple harmonic oscillator. The magnitude and the phase of the capacitance give the information of the majority carrier type and its relative concentration.

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