Rapid determination of semiconductor doping and flatband voltage in large MOSFET’s

A simple method is presented for accurate determination of the semiconductor doping concentration, flatband voltage, and gate-oxide thickness from capacitance measurements on large MOSFET’s. Conventionally, MOS capacitors are used to determine the doping profile from deep-depletion capacitance measurements, which unfortunately require a rapidly varying voltage across the capacitor. It is demonstrated that gate-substrate capacitance of MOSFET’s can be measured conveniently in deep depletion with a slowly varying gate-substrate bias. This is accomplished by reverse biasing the source and drain diodes to prevent the buildup of minority carriers at the semiconductor surface under the gate area. Measurements on MOSFET’s fabricated on n-type 〈111〉 Si gave ND=4.1×1014/cm3, VFB=−1.5 V, and tox=1064 Å, in agreement with resistivity, voltage threshold, and ellipsometry measurements, respectively.