Automated MOS Transistor Gamma Degradation Measurements Based on LabVIEW Environment

Abstract

In recent years, the study of the effects of ionizing radiation in thin gate oxides has received increasing attention. This is due not only to the appearance of new lithography tools for ultra low scale integration (ULSI) technologies, that use Xrays or e-beams, but also for the interest of space, medical, military or high-energy applications, where the complementary metal-oxide-semiconductor (CMOS) read-out circuitry will be subjected to a very hostile radiation environment. A major concern in the reliability of metal-oxide-semiconductor field effect transistor (MOSFET) devices is the formation of interface traps and near-interface oxide traps; called also border traps; under hot carrier injection, irradiation and processing. Traps at or near the semiconductor/gate dielectric interface can cause degraded transconductance (Doyle et al., 1990), the shifting of threshold voltage (Tsuchiya et al., 1987) and may lead to dielectric breakdown (Chen et al., 1985). In order to improve the resistance of MOSFET devices to these effects, it is necessary to have a reliable method of determining the densities of both interface traps and oxide traps (Djezzar et al., 2004). The reliable test procedure to predict radiation response of integrated circuits (IC’s) from standard test laboratory, for example in space, is very important and requires a development of simple and rapid electrical characterization techniques easily mountable in production line. Therefore, intensive works have been carried out on the electrical characterization techniques for MOS gate oxide and Si/SiO2 interface degradation caused by radiation (Schwank et al., 1993). The charge pumping (CP) technique (Groeseneken et al., 1984) is a valuable tool for all kind of traps characterization. In this article, we present an automatic measurement bench programmable by the IEEE-488 bus that permits to characterize MOSFET device degradation induced by gamma radiation at low doses. This characterization permits to extract threshold voltage and flatband voltage for virgin and irradiated samples. Moreover, the determination of the breakpoint frequency that represents the limit between interface and border trap contributions to the charge trap is automatically extracted. The measurement bench is managed by a program, written by a graphical language LabVIEW. LabVIEW is a powerful, platform-independent, graphical programming development system which is ideally suited for data acquisition, storage, analysis, and presentation.