MOSFET doping profiling

An automated technique was developed for rapid measurement of MOSFET channel doping profiles. The technique is based on the well-known relationship between the device threshold voltage and substrate bias. It uses only DC voltage measurements and is not subject to the limitations of conventional capacitance-voltage (C-V) methods. An operational amplifier feedback circuit is used to determine the threshold voltage automatically as the substrate bias voltage is varied. Doping profiles determined with this technique agree very well with those obtained from C-V and from spreading resistance measurements, as well as with those predicted by SUPREM-3. The devices were fabricated with processes representing two generations of CMOS technology. The doping concentrations, channel implants, and gate oxide thicknesses varied significantly between the two, allowing the assessment of the accuracy of doping profile extraction techniques for devices representing a wide performance range