Reseach On Local Permittivity Method And Its Application Of Si/SiO₂ And Si/HfO₂ Interface Structure

With the decrease of one component’s dimension of the multi-component systems in a device structure to the atomic or nanometer size, structure and chemical nature of the interface is becoming increasingly important, and sometimes dominates the properties of the whole structure. It’s important to clarify the electronic and dielectric properties of the interface containing material in the nanometer region. However, many methods used to calculate the dielectric constant of the material as a whole is no longer applicable in particular for the calculation of the dielectric properties considering interfacial effect. Therefore, it is necessary to explore the calculation method which can reflect the local dielectric property, and research specific the impact of possible interface defects on the dielectric properties.This paper we introduce the basic content of first-principles calculation method and critical approximation method used in CASTEP firstly, then on basis of combing the local theory of dielectric, we give the concrete steps of detailed theoretical derivation of the local dielectric constant. Those are the basic tools and theoretical basis of this study.After the comparative analysis of the advantages and disadvantages of the current domestic and foreign local dielectric method, local dielectric method based on band structure is proposed. On the one hand on the basis of dielectric function of the whole system of direct band gap, combined with the layered density of states(La-DOS), by extracting the relevant local parameters and local direct dielectric belt gap expression is obtained; on the other hand under the premise of the experience discussion and theoretical analysis, local dielectric function obtained by numerical fitting relationship.The actual calculation process and the results indicate that the two methods based on the band structure to some extent have theoretical deficiencies and poor reliability.After taking into account the characteristics concerning about capacitor of dielectric coefficient, the local dielectric method based on layered capacitors is proposed. We divide MOS structure into several layers that are perpendicular to the interface. Each stacking interval could be considered as a plate capacitor. Then the dielectric constant is obtained by the ratio of capacitors. Furthermore we analysis the advantages of the method, and we study the local dielectric properties of MOS structure in this paper based on this method.In order to study the effect of interface defects on Si/SiO2 dielectric properties, we study the local dielectric properties of different four Si/Si O2 models: with transverse dangling bonds, with transverse dangling bonds passivated by H, with longitudinal dangling bonds, and with longitudinal dangling bonds passivated by H. Comparative analysis of the changes produced by different types of defects, and summarizes the factors to produce the changes: the local dielectric properties is determined by the oxidation states of Si and the bond length at the interface.To study the effect of different types of oxygen vacancies at Si/HfO2 interface on the band structure, we simulate the band structure of O3(1Hf)、O3(2Hf)、O3(3Hf)、O4(2Hf)、parallel O4(2Hf) and O4(4Hf) vacancy compared to the defect-free model. The results showed that: the V3 oxygen vacancies group of O3(1Hf)、O3(2Hf) and O3(3Hf)vacancy, and the V4 oxygen vacancies group of O4(2Hf)、parallel O4(2Hf) and O4(4Hf)vacancy compared to the no vacancy defect model, both introduce band gap near oxygen vacancies around Hf ion, and the band gap states of each group in turn increases.In order to study the effect of defects at Si/HfO2 interface on dielectric property, we calculate the local dielectric properties of Si/HfO2 models with defect-free 、 with O3(1Hf)、with O3(2Hf)、with O3(3Hf)、with O4(2Hf) 、with parallel O4(2Hf) and with O4(4Hf) vacancies by layered capacitors method. Through comparative analysis of different groups we get: exposed non-bonded electron in Si atoms determine dielectric properties around it, while which in Hf atoms doesn’t matter with it; in different atomic configurations of oxygen vacancies, only bond length of Si-O play a decisive role in dielectric constant, while Hf-O bond length is not obvious; when the atom don’t have the same configuration, the oxygen vacancies effects on the dielectric properties atomic configuration, when atomic configuration is the same, the impact of oxygen vacancies on the dielectric properties of the oxygen vacancies is mainly determined by bond length.In summary, referring to the study of local dielectric properties about Si/SiO2 and Si/HfO2 in this paper, different calculation methods are proposed. Layered capacitor method is selected after a comparative analysis among these methods. We study the effect of interface defects at Si/SiO2 and Si/HfO2 on dielectric properties. The research has a significant guidance for device structure design, process improvement, failure mechanism analysis, device performance and improvement of the reliability.