Determining the drain doping in DMOS transistors using the hump in the leakage current

The hump in the leakage current of double-diffused metal-oxide-semiconductor (DMOS) transistors observed for low drain voltages is explained. This hump is due to surface generation current of the gate-controlled diode formed by the base-drain p-n junction. The drain bias of the DMOS transistor is shown to have the same effect on the charge at the drain surface as the body bias in the conventional MOSFET. The body effect is used to develop a new method for determining the drain doping in DMOS transistors. This method is nondestructive, and does not require special test structures. Instead, electrical measurements are performed on conventional DMOS transistors. The method is ideally suited for determining the doping in the drain region of interest. Specifically, in DMOS transistors in which a surface implant is used to reduce the on-resistance, the method provides the doping concentration in the implanted region. In DMOS transistors which do not have the surface implant, the method yields the doping concentration in the drain epitaxial layer. In this study, the method is illustrated by determining the drain doping for six discrete power MOSFET device types from three different manufacturers.<
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