Abrupt current increase due to space-charge-limited conduction in thin nitride–oxide stacked dielectric system

Abstract

In this article, the conduction mechanisms in nitride–oxide stacked structures on Si are investigated experimentally and theoretically. Amorphous silicon nitride films (3–5 nm thick) were deposited by low-pressure chemical vapor deposition. The ultrathin oxide layers (1–1.5 nm thick) were formed by reoxidization of the nitride layer at about 900 °C in wet ambient. The current–voltage characteristics for negative and positive gate polarities are asymmetric. An abrupt current increase under negative gate bias prior to dielectric breakdown is reported for this structure. This current–voltage phenomenon is attributed to trap-controlled single-carrier steady-state space-charge-limited conduction—the solid state analog of space-charge-limited current in a vacuum diode. Details of space-charge-limited conduction parameters depend on the thickness of the dielectric film and temperature. The study of those parameters can yield information about the traps inside nitride–oxide films. Such information can provide considerable insight into charge transport mechanisms and carrier trapping in these materials, which are important in understanding the physical processes involved in the basic film properties.