Transition metal defect behavior and Si density of states in the processing temperature regime

In order to make predictive models of transition metal gettering during sem iconductor processing, a complete understanding of the process variables in high temperature ranges is essential. These variables are the internal get tering site density and capture radius, the intrinsic metal solubility, sil icon doping level, the band gap, the effective density of states of the con duction and valence bands, and the transition metal defect level position i n the gap. The least understood of these parameters is the temperature depe ndence of the transition metal defect level position. The work of Gilles et al. and McHugo ct al. demonstrates that the doping enhancement of the solu bility of Fe in p-type silicon vanishes at temperatures above 1000 degrees C. They model this behavior by proposing movement at high temperature of th e defect level for interstitial Fe from within the energy gap into the vale nce band. We explore the available models for Si effective density of state s as a function of temperature and generate a third density of states model based on 0 It ab initio band structure calculations with the temperature-a ppropriate carrier occupations given by Fermi-Dirac statistics. We also con sider uncertainty in E-G in the processing temperature regime. We show that uncertainties in the Si intrinsic properties database in the processing te mperature regime can account for the available dopant-enhanced solubility d ata by assuming that E-tau remain at a constant fraction of E-G. To quantit atively model gettering processes at high temperatures, more reliable estim ates are needed for the densities of states of the conduction and valence b ands, E-G and the behavior of defect levels as temperature rises. (C) 1999 Elsevier Science B.V. All rights reserved.