Charge transport and trapping in silicon nitride-silicon dioxide dielectric double layers

Abstract

Time, electric field, and temperature dependence of the flat-band voltage shift in polysilicon-silicon nitride-(thick) silicon dioxide-silicon capacitors subjected to high field stress has been studied in this paper. A ‘‘turn around’’ effect in the behavior of the flat-band voltage shift versus time is observed, both in the accumulation and in the strong inversion mode, in the full range of temperatures investigated (77 K≤T≤453 K). Early time charge trapping seems to be dominated by transport of carriers, holes or electrons injected at the gate electrode, in the nitride layer. A Poole–Frenkel-active trap for holes is determined to be located at 1.0 eV above the nitride valence-band edge and a Poole-Frenkel-active trap for electrons 1.3 eV below the nitride conduction-band edge. The dark contact current-contact field characteristics at the silicon-silicon dioxide interface are obtained at room temperature for both gate bias conditions. The contact current for positive gate voltage J+ox appears to be dominated by tunneling (Fowler–Nordheim) emission of electrons from the silicon substrate. The contact current for negative gate voltage J−ox is several orders of magnitude smaller than J+ox and is tentatively attributed to tunneling (Fowler–Nordheim) emission of holes from the silicon substrate. The estimated tunneling barrier height for holes is φh0 =4.4±0.1 eV.