In this paper, we report a device model that has successfully described the characteristics of an anomalous CMOS NFET and led to the identification of a non-visual defect. The model was based on detailed electrical characterization of a transistor exhibiting a threshold voltage (Vt) of about 120mv lower than normal and also exhibiting source to drain leakage. Using a simple graphical simulation, we predicted that the anomalous device was a transistor in parallel with a resistor. It was proposed that the resistor was due to a counter doping defect. This was confirmed using Scanning Capacitance Microscopy (SCM). The dopant defect was shown by TEM imaging to be caused by a crystalline silicon dislocation.

In this paper, we report a transistor model that has successfully led to the identification of a non visual defect. This model was based on detailed electrical characterization of a MOS NFET exhibiting a threshold voltage (Vt) of just about 40mv lower than normal. This small Vt delta was based on standard graphical extrapolation method in the usual linear Id-Vg plots. We observed, using a semilog plot, two slopes in the Id-Vg curves with Vt delta magnified significantly in the subthreshold region. The two slopes were attributed to two transistors in parallel with different Vts. We further found that one of the parallel transistors had short channel effect due to a punch-through mechanism. It was proposed and ultimately confirmed the cause was due to a dopant defect using scanning capacitance microscopy (SCM) technique.