Theoretical analysis of kink effect in C-V characteristics of Indium-implanted NMOS capacitors

Experimental observation of an anomalous "kink" effect in C-V characteristics of Indium-doped NMOS capacitors is reported and explained, for the first time, via the impact of incomplete ionization of Indium. A new analytical formulation of the total semiconductor capacitance is developed, that takes incomplete ionization phenomenon into account. Thanks to this new C/sub SC/(/spl phi//sub s/) relation, we have demonstrated that the carrier freeze-out is responsible for this kink near V/sub FB/ in C-V curves, and also for an intrinsic lowering in the threshold voltage. This kink has been shown to be very sensitive to Indium dose and temperature. It is also demonstrated that the deformation of the C-V characteristics due to Indium incomplete ionization may be (and probably has often been) miss-interpreted as appearance of high fixed charge densities in parameter extraction from C-V fitting. Our analysis is in full agreement with experimental results.