Interaction of interstitially dissolved cobalt and oxygen-related centres in silicon

We have studied external gettering of radioactive Co-57 in silicon containing different amounts of oxygen impurities. As a gettering layer we used a thin Au-layer. The amount of gettered cobalt was measured in-situ. We find that for oxygen concentrations below of 1.6(.)10(17)cm(-3) (ASTM F-121) cobalt diffuses into the Au:Si-layer according to the temperature dependent segregation coefficient which leads to an increase of the gettering effect with decreasing temperature. At an oxygen concentration of 7.8(.)10(17)cm(-3) however, the cobalt diffuses back into the sample when the temperature is lowered below about 930degreesC. Our observations show, for the first time, the binding of cobalt to oxygen related centers at gettering temperature.