C-V PROFILING OF STEEP DOPANT DISTRIBUTIONS

An exact expression for the incremental capacitance of a partially depleted n-channel with steep dopant gradient is given in terms of the position dependence of the peak electron concentration when the gate bias voltage is changed. The C-V concentration profile derived from this expression differs from the actual dopant profile in two respects: (i) The peak of the C-V profile for a heavily doped implant is about twice the peak dopant concentration, and lies somewhat closer to the depleting contact. This discrepancy arises from the gradual decay of the electron distribution into the depletion layer. (ii) The tail of the C-V profile extends far beyond the dopant profile. This discrepancy arises from the variation with applied voltage of the built-in potential between the position of peak electron concentration in the partially depleted channel and the bulk of the substrate. A procedure is given to reconstruct the actual dopant distribution from the tail of the C-V profile, a task for which the Kennedy method is found to be inadequate.