Capture and tunnel emission of electrons by deep levels in ultrathin nitrided oxides on silicon

Abstract

Electron injection into ultrathin nitrided oxides on silicon reveals both high densities of electronic defects, which readily capture electrons, and efficient tunnel emission of trapped charge. High-temperature nitridation of thermally grown oxides was verified with Auger depth profiling. In 11–17-nm-thick nitrided oxides, the electron trap density is ≥1×1019 cm−3 as determined from saturated charge accumulation, the majority of the traps are energetically situated more than 2 eV below the conduction band as determined by post-injection anneals up to 300 °C, and the capture cross section is of the order of 10−14 cm2 as estimated from the trapping kinetics. Complete extraction of trapped charge is achieved in the thinnest films (e.g., ≤11 nm thick), and the tunnel emission mechanism is evidenced by the independence of the discharge time on temperature. Implications of the above findings for applications of ultrathin nitrided oxides in very large scale integration and for their low sensitivity to ionizing radiation are discussed.