Formation and Properties of Three Copper Pairs in Silicon
- PDF / 485,761 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 12 Downloads / 221 Views
Formation and Properties of Three Copper Pairs in Silicon S.K. Estreicher1, D. West1, J.M. Pruneda2, S. Knack3, and J. Weber3 1 Physics Department, Texas Tech University, Lubbock, TX 79409-1051, USA 2 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK 3 Institut für Tieftemperaturphysik, TU Dresden, 01062 Dresden, Germany ABSTRACT Copper in silicon is a feared contaminant in device processing. It diffuses quickly as an interstitial and forms electrically active precipitates that are difficult to dissolve. Several complexes assigned to copper pairs have been observed but have yet to be unambiguously identified and fully characterized. We present the results of joint theoretical-experimental studies of several pair structures. The theoretical work involves ab-initio molecular-dynamics simulations, and the results include configurations, binding energies, electronic structures, vibrational modes and formation dynamics. The experimental work combines electrical and optical techniques. One characteristic of the photoluminescence spectra is the presence of phonon replicas that imply the existence of very similar low-frequency and localized vibrational modes in two distinct copper pairs. These modes are theoretically identified. INTRODUCTION The microscopic properties of rapidly-diffusing transition metal impurities in Si are not well understood. Copper is often introduced by in-diffusion at high temperatures followed by rapid quenching. This results in the supersaturation of interstitial copper (Cui), forcing it to trap at vacancies, form complexes and precipitates, or out-diffuse to the surface.[1-5] These processes are facilitated by the very low activation energy for diffusion of Cui+, measured [6] to be 0.18eV, close to the predicted value.[7] A donor level at Ec-0.15eV has been assigned to Cui.[8] Copper efficiently passivates shallow acceptors,[9] traps at pre-existing vacancies (where it becomes substitutional Cus) and, upon hydrogenation, forms up to three {Cus,H} complexes.[10] Cus has three levels in the gap, at Ec-0.17, Ev+0.20 and Ev+0.41eV, respectively. These levels shift upon hydrogenation. Channeling data [11] in n-type Si show two Cu-related centers following 300 and 600oC anneals, respectively. The low-temperature one has been modeled as a single Cu atom displaced off the perfect substitutional site toward the bond-centered (BC) site by 0.5Å. However, only and displacements of an isolated Cu atom have been considered [12] in the modeling. It is not known if the data can also be explained by a pair of copper atoms at different sites. The high-temperature center, substitutional Cu at an undistorted site, is seen in n- and p-type, CZ and FZ Si. It anneals out with 2.9eV activation energy. Several copper pairs have been reported in the literature. The EPR NL58 center[13] has two equivalent copper atoms, probably in the –1 charge state. However, the best fit to the angulardependence of the spectrum suggests tetragonal symmetry which implies that the two Cu’s must be one lattice const
Data Loading...
