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CV Doping Profile

CV stands for Capacitance Voltage.  The capacitor in CV Profiling is formed either via a metal contact to the silicon, creating a back-biased Schottky diode or by a conductive electrode on an oxide on the silicon.  The bulk silicon is the other side of the capacitor.

As the voltage on the capacitor changes, and the semiconductor surface goes into depletion.  If the voltage changes slowly (or if the semiconductor is exposed to light) carriers are generated somewhat quickly, and this depletion process reaches a maximum.  In CV doping profiling, the voltage changes quickly enough that equilibrium is avoided, and the semiconductor goes into deep depletion.

The capacitance at any voltage is inversely proportional to the depletion depth, so an array of capacitance measurements creates an array of depths.  The difference in capacitance between any two voltage levels is dependent on the doping concentration between the two depths, with low doping concentration producing a large change in capacitance.  Thus, an arrange of delta C can be converted to an array of Nsc.  Finally plotting Nsc as a function of depth produces a profile of doping concentration.  Of course Nsc can be converted to resistivity, using an appropriate conversion.

Epimet uses the same basic idea to create doping profiles of epi layer resistivity.  The theory is a bit more complicated with Epimet, due to the non-contact electrode and due to the existence of surface states on the silicon.