Study On Doping Modification Of Hafnium-based Oxide Based On First Principles

As device size decreases,high-k gate dielectrics are widely used as replacements for gate dielectric Si O₂ in metal-oxide-semiconductor field-effect transistors(MOSFETs),and Hafnium-based high-k materials have been consistently due to their superior electrical properties.It has been valued by researchers,but there is no systematic theoretical study on the doping of high-k materials.In recent years,Hafnium-based dielectric materials have been widely used in negative-capacitance MOS transistors due to their ferroelectric properties.In particular,the negative capacitance effect of recently discovered MOS devices has placed new demands on the research of high-k materials.However,due to the complexity and uncontrollability of the experimental preparation of MOS devices,most researchers have only conducted a certain doping study on Hafnium-based high-k materials,and have not systematically compared the advantages and disadvantages of various dopants.At present,there is no convincing theoretical explanation for the microscopic mechanism of negative capacitance phenomenon of Hf-based high-k materials.At present,the more unified view is that the occurrence of negative capacitance phenomenon is related to the ferroelectricity of the material itself,and these problems are going deeper.Both are analyses at the atomic level.In view of the fact that the first-principle method has a more accurate calculation in terms of material properties and doping calculation,it can effectively analyze the material properties before and after doping.Therefore,this paper uses the first-principles method to give certain theoretical analysis and theoretical support to the above problems.In this paper,the first-principles method is used to systematically study the doped material properties of high-k gate dielectric Hf O₂ used in MOS devices.There are three main aspects to the research:(1)By simulating the doping of Zr,Al,Ta,Ti,Gd and Si in monoclinic phase Hf O₂,the k value,defect formation energy and band structure of high-k gate dielectric doped with different elements conduct a comparative analysis.It is concluded that the Zr-doped Hf O₂system can effectively increase the k value of the system;and compared with the doping of other elements,Zr doping can effectively inhibit the formation of defects in the system.(2)The structure of Hf_1-xZr_xO₂ after doping was analyzed by simulating the incorporation of different concentrations of Zr into Hf O₂.Comparing the total cell energy of different structures,it was found that Zr does not form impurity agglomerates in the doping system.The vacancy formation sites were analyzed,and it was found that the O vacancies were gathered around the dopant atoms,so that the formation position of the oxygen vacancies can be controlled by doping.Among them,the Zr-doped Hf O₂ sample with a content of 25%has the advantages of the largest k value,large energy band and high defect formation energy,and the overall performance is the best.(3)By using density functional phonon theory(DFPT)to solve the Helmholtz free energy of different concentrations of Zr doped into monoclinic phase,tetragonal phase and ferroelectric phase Hf O₂,the system is analyzed to generate ferroelectric phase.Degree of difficulty.The results show that 37.5%?50%Zr is doped to Hf O₂ to obtain the most ferroelectric phase;when the annealing temperature is controlled at 650°C,the ferroelectric phase is easier to form.Further,analysis of the polarizability shows that the higher the Zr concentration,the stronger the ferroelectricity.However,the study of the effect of oxygen deficiency on the ferroelectricity of the system shows that as the Zr concentration increases,the oxygen defect formation energy decreases,but the magnitude of the decrease is small,and the effect on ferroelectricity is weak.This research provides a strong theoretical basis for the experimental preparation of ferroelectric HZO thin films.