Automated Digital Measurements of CV Curves and Derivatives, and of Capacitance Transients for Semiconductor Evaluation

A system of instruments is presented for automated digital measurements of voltage and/or time dependent capacitances. The system has been designed for the evaluation of semiconductor materials and devices. It is based on a fast capacitance-inverse-to-frequency converter (FCFC), where a direct conversion is obtained with high accuracy, and where the device to be tested can be subject to dc, modulated, and pulsed voltage bias. The output frequency (of the order of 1 MHz) accurately foliows capacitance variations, even if occurring in short times (less than 100 Ms). Biasing circuits, a multichannel scaler, and logic interface circuits complete the system. Stationary and nonstationary CV curves and time variations of capacitances can be accuratety measured. The precision can be improved by averagng over many repetitions of the measurement. Derivatives (first and higher orders) of CV curves can also be directly and accurately measured by using a technique based on voltage modulation and synchronous reversible counting. This feature also makes it possible to obtain accurate measurements of doping profiles in semiconductors. Representative experimental results obtained with the system are shown.