The Dependence of the SiO2 Defect Density on Both the Applied Electric Field and the Oxide Thickness

Abstract

By using liquid crystals in contact with the oxide and simultaneously applying an electric field across such a sandwich structure, defective regions can be nondestructively identified. By examining the number of defects as a function of the applied electric field and oxide thickness, it is possible to obtain information on the variation of the defect density with the applied electric field and oxide thickness. Experiments of this type indicate that the defect density was found to exponentially increase with the square root of the positive applied electric field. Also the total leakage current density was found to exponentially increase with the square root of the positive applied electric field in the presence of the liquid crystals. The defect diameter was found to be in the range of 0.14–0.42 μm. For oxide thickness above 0.2 μm the defect density exponentially decreases with increasing oxide thickness. But for oxide thicknesses less than 0.2 μm it is very difficult to judge the variation since the defect density increases very rapidly with decreasing oxide thickness. Spikes of were observed to protrude into the silicon substrate for thin oxides (about 0.1 μm); however, these spikes could be eliminated by increasing the oxide thickness (greater than 0.3 μm). With increasing oxide thickness the interface becomes evener and the density of the interface irregularities decreases. The electron space‐charge effects were postulated as a second explanation for the variation of the oxide defect density with the oxide thickness. This theoretical treatment agrees well with the experimental results. The space‐charge (electron) density in the oxide was equal to which is in agreement with the trap density of the silicon dioxide.