Transition Metal Defect Behavior and Si Density of States in the Processing Temperature Regime

Keywords: Si, effective density of states, Fe, defect level, processing temperature In order to make predictive models of transition metal gettering during semiconductor processing, a complete understanding of the process variables in high temperature ranges is essential. These variables are the internal gettering site density and capture radius, the intrinsic metal solubility, silicon doping level, the band gap, the effective density of states of the conduction and valence bands, and the transition metal defect level position in the gap. The least understood of these parameters is the temperature dependence of the transition metal defect level position. The work of Gilles et al and McHugo et al demonstrates that the doping enhancement of the solubility of Fe in p-type silicon vanishes at temperatures above 1000ºC. They model this behavior by proposing movement at high temperature of the defect level for interstitial Fe from within the energy gap into the valence band. We explore the available models for Si effective density of states as a function of temperature and generate a third density of states model based on 0 K ab initio band structure calculations with the temperature appropriate carrier occupations given by Fermi-Dirac statistics. We also consider uncertainty in E G in the processing temperature regime. We show that uncertainties in the Si intrinsic properties database in the processing temperature regime can account for the available dopant enhanced solubility data by assuming that E T remain at a constant fraction of E G. To quantitatively model gettering processes at high temperatures, more reliable estimates are needed for the densities of states of the conduction and valence bands, E G and the behavior of defect levels as temperature rises.