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1079-N08-01

Pd Segregation at (001) B2-NiSi/Si Epitaxial Interface Studied by Density Functional Theory Dae-Hee Kim1, Hwa-Il Seo2, and Yeong-Cheol Kim1 1 Dept. Materials Engineering, Korea University of Technology and Education, 307 Gajeonri Byungchunnmyun, Cheonan, 330-708, Korea, Republic of 2 School of Information Technology, Korea University of Technology and Education, 307 Gajeonri Byungchunnmyun, Cheonan, 330-708, Korea, Republic of ABSTRACT Pd segregation at (001) B2-NiSi/Si epitaxial interface was studied by using density functional theory (DFT). An epitaxial interface between 2x2x4 (001) B2-NiSi supercell and 1x1x2 (001) Si supercell was first constructed by adjusting the lattice parameters of B2-NiSi structure to be matched with those of Si structure. We chose Ni atoms as terminating layer of the B2-NiSi, and an equilibrium gap between the B2-NiSi and Si was calculated to be 1.1 Å. The Ni atoms in the structure moved away from the original positions along z-direction in a systematic way during the energy minimization. Two different Ni sites were identified at the interface and the bulk, respectively. The Ni sites at the interface farther away from the interface were more favorable for Pd substitution. INTRODUCTION Nickel monosilicide (NiSi) is an important material for contact applications in the semiconductor industry as it transitions from the 65 technology node to 45 nm node.1 NiSi has many advantages over conventionally-used titanium silicide (TiSi2) and cobalt silicide (CoSi2) which include a lower temperature of formation, lower resistivity in narrow dimensions, reduced Si consumption, and formation kinetics that are controlled by diffusion of Ni, which leads to significantly smoother heterophase interface. Additionally, a one step annealing can be used for the self-aligned silicide process.2 NiSi, however, is less stable at high temperature than TiSi2 and CoSi2. It agglomerates or transforms into more resistive NiSi2 phase at high temperature, causing overall resistivity increase. Recent studies demonstrate that adding elements such as Pd, Pt, or Rh reduces the agglomeration of NiSi and increases the formation temperature of NiSi2. Laser-assisted localelectrode atom-probe (LEAP) tomography was employed to map the atomic-scale distribution of Pd in annealed Ni1-xPdx/Si(001) structure.3 The Pd was distributed nearly uniformly in the NiSi film and was segregated at the NiSi/Si (001) interface. We employed a first principles calculation to construct a NiSi/Si (001) interface and to study the effect of Pd substitution into Ni sites that are located near interface and away from the interface. B2-NiSi structure was chosen for NiSi/Si structure, as the stable orthorhombic structure of NiSi as a bulk phase has higher interface energy with Si (001) surface. CALCULATION Density functional theory (DFT) calculations were performed using the Vienna ab-initio Simulation Package (VASP) code with the projector augmented wave (PAW) potentials and the

local density approximation (LDA).4-8 The residual minimization