A Simple Test Structure for Evaluating the Variability in Key Characteristics of a Large Number of MOSFETs

The increase in the electrical characteristic variability of MOSFETs caused by the miniaturization of MOSFETs is one of the critical issues for realizing the low power consumption of large-scale-integrated circuits and the high accuracy of analog devices. It is necessary to easily evaluate the variability of a very large number of MOSFETs in a very short time for short-period-developing fabrication processes and device structures. We have proposed and developed a simple test structure for evaluating the electrical characteristics of over 1.2 million MOSFETs such as threshold voltage (V_th), subthreshold swing (S-factor) in around 30 min. The accuracy of the test circuit developed is 1.9 mV, as 3σ. We have also evaluated the V_th distribution, the S-factor distribution, and the dependence of V_th variability on the gate size and antenna ratio of MOSFETs. The measurement results are very useful in developing fabrication processes, process equipment, and device structures, that suppress the variability.