Interface characterization of fully-depleted SOI MOSFET by a subthreshold I-V method

Interface state densities can dramatically affect the performances of MOSFETs by causing threshold voltage shift and mobility degradation. In SOI structures, due to the complex multi-interface nature and small gate area, the interface state characterization still remains a very challenging problem. Conventional C-V method is not suitable for investigating interfaces in SOI MOS devices, mainly because of the large area needed and the high series resistance in thin-film. Several other measurement techniques based on currents rather than capacitance have been proposed. In this work, an evolved technique for characterizing interface state density in fully-depleted SOI MOSFETs is presented. By measuring subthreshold swing of the SOI MOSFETs, the interface state density can be determined. The distribution of both front- and back-interface state densities in the bandgap can be evaluated by applying a rigorous one-dimensional analytical model for FD-SOI MOSFETs operating in the weak inversion regime. In addition, this technique has been applied successfully to the comparison of interface qualities of various SOI wafers and the study of electrical stress effect. The SOI devices used in this study were n-channel and p-channel MOSFETs fabricated with submicron CMOS technology on both SIMOX and Bonded-and-Etchback SOI (BESOI) wafers