Quantitative Study of Metal Gettering in Silicon
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QUANTITATIVE STUDY OF METAL GETITERING IN SILICON ETIENNE G. COLAS,* E. R. WEBER, and S. HAHN * Department of Materials Science and Mineral Engineering University of California, Berkeley, Ca 94720 ** Siltec, Mountain View, Ca. 94043
ABSTRACT Intrinsic gettering of iron in silicon has been investigated with a novel quantitative approach. Concentrations of electrically active, interstitial iron were determined by Electron Pararnagnetic Resonnance before, and after, various annealing cycles, using Cz silicon with oxygen precipitates of different well defined morphologies. Significant differences in the gettering rate in as-grown Cz and Cz silicon with high temperature oxygen precipitates were found. High temperature treatments after metal gettering resulted in the re-emission of the transition metal atoms for both as-grown and high temperature precipitated Cz silicon. This allowed the conclusion that gettering took place via FeSi 2 formation in these cases and did not involve any thermally more stable phases.
Introduction Transition metal impurities in silicon create deep energy levels in the band gap and therefore alter device characteristics if present in active areas of devices. The main problems are increases in leakage currents of diodes and yield limitations. Intensive research has been performed on ways to "getter" these transition metals away from the areas of the wafer where devices are built. In the intrinsic gettering technique, oxygen precipitation treatments are used to create gettering sites in the bulk of the wafer. However, there is still some controversy concerning the exact mechanism of this method of gettering. Previous interpretations gave a major role to dislocations that have been shown to act as gettering sites. But punched-out dislocations are not always present after precipitation, especially if rapid cooling is avoided, which is the case in normal device processing. The latest attempt to explain intrinsic gettering is based on silicon interstitials emitted during precipitation and it ascribes gettering to silicide formation [ I] , next to the oxygen precipitates. In this paper, we report some results of an on-going study, in which the efficiency and the stability of the gettering process will be studied quantitatively. The Electron Paramagnetic Resonnance (EPR) technique was used to determine iron concentrations in samples containing precipitates of well defined morphologies. These concentration measurements were performed after various annealing cycles at low temperatures and after subsequent high temperature re-emission treatments. The samples with oxygen precipitates obtained after high temperature heat treatments show increased gettering rates. The efficiency of these gettering treatments is investigated by re-emission and further annealing cycles.
Mat. Res. Soc. Symp. Proc. Vol. 59. 1 1986 Materials Research Society
342
N-type (3 0 .cm) Cz silicon samples were heat treated to obtain well defined oxygen precipitates. The precipitation treatments always started with a nucleation trea
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