Peculiarities of capacitive characteristics of dielectrics with high permittivity

The rapid pace of development of microelectronics towards nano miniaturization dictates the inevitable introduction of dielectrics with high permittivity (high-k dielectrics), as alternative materials for replacing conventionally used silicon as insulating oxide. Therefore, studying these materials in terms of their characteristics, especially in terms of reliability, is of great importance for proper design and manufacture of devices that incorporate dielectrics with high permittivity. In this paper, different properties and behavior of a group of samples that contain dielectrics with high permittivity are investigated, by analyzing the characteristics of capacitive curves, which are product of this powerful technique for characterization, reflecting a great number of elements for the overall behavior of the material, especially their behavior in working conditions. Samples investigated here belong to the group of tantalum based metal oxides, whereas here we examine layers of pure Ta2O5, but also layers of Hf and Ti doped tantalum pentoxide, i.e. Ta2O5: Hf and Ta2O5: Ti. All samples are considered as ultrathin oxide layers with thicknesses less than 15 nm, and they are obtained by thermal oxidation or by radio frequency sputtering on p-type silicon substrate. From capacitive characteristics we have obtained the specific parameters that determine the properties of materials (capacitance in accumulation, equivalent oxide thickness of dielectric layer, the thickness and time evolution of the interfacial SiO2 layer, characteristic values of flat band and threshold voltage, density of oxide charges present in the layer, as well as interface and border states), and properties that show the behavior of the materials in working conditions (such as the process of creation of additional charges when voltage is applied, or charge trapping dynamics). Particular attention has been paid to determining the impact of the type of top electrode (the gate), on the overall characteristics of the examined structures, for which purpose MOS (metal oxide semiconductor) capacitors with different metal gates (conventional Al and also W, Au, Pt, Mo, Ti N, Ta) were formed. The results obtained, converge toward series of conclusions about the properties of these materials, hence their reliability has been evaluated, as a final goal of this research, in order to determine the possibilities for more intensive use of studied materials in new technologies. (Author)