Level Set Modeling of Nickel Silicide Growth
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Level Set Modeling of Nickel Silicide Growth Ashish Kumar1 and Mark E. Law2 1,2
Department Electrical and Computer Engineering, University of Florida, Gainesville, Florida 32611-6200 ABSTRACT
Level set methods have been used for Solid phase epitaxial regrowth, etching and deposition. This study is to model the growth of nickel silicide accurately using the level set method. NiSi growth has been observed to follow a linear-parabolic law which takes into account both diffusion and interfacial reaction. This linear-parabolic system is very similar to the Deal and Grove model of SiO2 growth. This model uses similar diffusion transport and reaction rate equations. This simulation models the growth of silicide coupling diffusion solutions to level-set techniques. Dual level sets have been used for top and bottom interface propagation of silicide; velocities were estimated based on nickel concentrations at both interfaces as well as diffusivity and reaction rate of nickel. This is important to predict precise shape of silicide that will allow current crowding and field focusing effects to be modeled in transport out of the intrinsic device into the contacting layers. These simulation models can be used for latest technology nodes at 45, 32, 22nm and special devices such as FinFET’s etc. The level set method is successfully implemented and verified in Florida Object Oriented Process Simulator and growth shapes matches well with the literature Transmission Electron Microscopy data. INTRODUCTION Nickel silicide (NiSi) is being used as an industry standard for ohmic contacts, Schottky barrier contact and local interconnect for current and advanced CMOS technology. Nickel silicide is a preferred material after CoSi2 due to many advantages such as low thermal budget, formation controlled by Ni diffusion, less silicon consumption and low resistivity phase formation possible on SiGe [1]. Low resistance contacts to source, drain and gate have been a great challenge for the semiconductor industry. So it has become necessary to model and simulate the two-dimensional (2D) and three-dimensional (3D) growth on silicon to accurately predict the silicide shape on source/drain, poly, and extension under spacer. Nickel silicide growth is a thermally activated process (for temperature range of 300-700 °C) with activation energy reported from 1.4 - 1.6 eV [4-6]. It is shown that silicide formation is a diffusion-controlled process with nickel as the main diffusing species. There are many phases of nickel silicide observed during the thermal processing at various temperatures. Several literatures show that nickel film completely reacts with silicon at 300 °C to form Ni2Si then subsequent annealing at higher temperature causes phase transformation to NiSi [4,5]. Nickel diffuses in silicon through interstitial diffusion mechanism. Nickel silicide formation kinetics follows a parabolic law implying it is a diffusion-controlled growth [5,7] where nickel
diffuses through Ni2Si to react with Si. The orientation of substrate is known to have an i
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