Atomistic Modeling of Amorphization in Silicon
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Atomistic Modeling of Amorphization in Silicon Lourdes Pelaz, Luis A. Marqués, George H. Gilmer1, Juan Barbolla Dept. Electricidad y Electrónica, Universidad de Valladolid, 47011 Valladolid, Spain. 1 Agere Systems (Formerly Bell Laboratories, Lucent Technologies) 600 Mountain Avenue, Murray Hill, NJ 07974, U.S.A. ABSTRACT We discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, a continuous amorphous layer may be formed. In that case, most of the excess interstitials generated by the implantation may be swept to the surface as the amorphous layer regrows, instead of diffusing through the crystalline region. This process reduces the amount of transient enhanced diffusion during annealing. This model also reproduces the dynamic annealing during high temperature implants. INTRODUCTION When energetic ions strike a silicon substrate, they create zones of disorder, populated by Si self-interstitials and vacancies. The lattice in these disordered regions exhibits different damage configurations going from isolated point defects or point defect clusters in crystalline silicon, to continuous amorphous layers, as the dose of the implanted ions increases and the damage from the ions accumulates. The heating of the wafer during ion implantation can impact the implantation damage and damage healing may occur as the implantation proceeds. This can prevent amorphization even at high doses. The diffusion of impurities in implanted Si is complicated as a result of the presence of implantation damage. As an example, the diffusivity of B in implanted single crystal Si is anomalously high compared to equilibrium values. This transient enhanced diffusion (TED) of B and other interstitial diffusers results as a consequence of the supersaturation of Si self-interstitials generated during ion implantation [1]. This phenomenon has important consequences for Si processing, since it causes the dopant profiles spread significantly compared to the as-implanted profile during the subsequent annealing steps required for dopant activation. Although the damage generated during ion implantation is quite complex and several Frenkel pairs are generated by each implanted ion, the “+1” model [2] has been very successful in explaining TED for most technologically relevant process parameters. The “+1” model implies that the Frenkel pairs generated during ion implantation rapidly recombine, and TED is caused by the Si self-interstitial generated as the implanted ion becomes substitutional. This excess interstitial has no vacancy partner to recombine with, and is likely to diffuse through the Si lattice interacting with dopants such as B until finally it is annihilated at the surface. In a previous paper we have discussed atomistic Monte Carlo simulations of implantation and annealing, that include th
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