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First-principles Study of the Work Function of Metal Gate

Author: XuGuiGui
Tutor: HuangZhiGao
School: Fujian Normal University
Course: Condensed Matter Physics
Keywords: Gate electrode Work function Disorderly effect Surface effect Surface orientation First-principles calculations
CLC: TN304
Type: Master's thesis
Year: 2009
Downloads: 60
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Abstract


With the rapid development of the integrated circuit, SiO 2 as traditional gate dielectrics will not meet the requirements of MOSFET devices are highly integrated, needs a new High-k materials to replace the the traditional SiO 2 < / sub>. There will be many problems combined polycrystalline silicon and HfO 2 high-k gate dielectric material, such as polysilicon gate depletion effect, the Fermi level pinning too high gate resistance, severe boron penetration and so on. Therefore, the use of a metal gate instead of the polysilicon gate electrode will be the development of an inevitable trend. This paper, using first-principles methods based on density functional theory study disorder effects, surface effects and surface orientation of the metal alloy gate electrode work function. The results showed that the important influence of the surface effect and surface alignment on the metal work function; given the atom concentration and the surface orientation of the surface layer of the different atomic distribution is less impact on the metal work function; changes not only of the metal work function and charge transfer , was kind enough surface charge distribution have a great relationship. We also studied the adsorption characteristics of the different coverage O Ni (111) surface. The purpose of this study is to experimentally difficult to achieve the results theoretically by first-principles methods, to provide guidance and assistance in the research and design of metal alloy as the gate electrode material. This paper is divided into four parts: First, the traditional SiO faced with the problem of reduced thickness 2 gate dielectric, metal gate instead of the necessity of the polysilicon gate electrode and challenging. Also described in detail in this paper the basic theoretical foundation - First-principles calculation. Second, using first-principles methods to study the Ni 1-x Pt x alloy work function. The calculation results show that the surface layer of Pt atom concentration on the alloy work function have important implications; different distributions for a given atom concentration in the surface layer of Pt, Ni alloy / Pt atoms less impact on the work function. The results obtained for the experimenter indicates the surface atoms and modification may be a modulating effective method of the metal work function. Next, based on different surface orientations Ta 1-x Mo x alloy work function. The calculated results indicate that the important influence of the surface alignment on the metal work function; less influence on the alloy work function for the distribution of surface alignment and a surface layer of a given Mo atom concentration, the surface layer of Mo atom; changes not only of the metal work function and charge transfer relevant , was kind enough surface charge distribution has a great relationship. Finally, the different coverage O adsorption properties of the Ni (111) surface. The results show that the O Ni (111) surface adsorption with increasing coverage decreases, O induced Ni (111) surface work function of the change in the amount of coverage a nearly linear relationship, and with the coverage the increase; O in the Ni (111) is the adsorption of the surface so that the Ni surface electron transfer to the 0 atom, forming a surface dipole moment, resulting in increased work function; 3d orbital and O 2p orbit via a coupling surface of Ni atoms, heteroaryl key state and anti-bonding state of formation, while the anti-bonding state hardly occupy, thus O-Ni bonding interaction, adsorption energies larger.

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