Effect of carbon on oxygen precipitation in Czochralski silicon



Isochronal anneals were performed in Cz-Si samples of high and low carbon concentrations, from room temperature up to 1200 °C. We report infrared studies on the thermal evolution of various bands of oxygen precipitates formed in the course of the annealing process. The effect of carbon on their spectral behavior is examined. It was observed that in the carbon-rich material the oxygen impurity appears to anneal out at a lower temperature than in the carbon-lean material, in agreement with earlier reports that carbon enhances the oxygen precipitation process in Si. In relation with that, two bands at 1060 and 1080 cm–1 attributed to spheroidal precipitates and another band at 1099 cm–1 related to the dissolution of platelet precipitates and the formation of microprecipitates make appearance in the spectra of carbon-rich Si at slightly lower temperatures and display higher intensities. This indicates that the enhancement of oxygen precipitation process is due to the effective formation of spheroidal precipitates having the lowest interfacial energy. The role of carbon in the enhanced precipitation process is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)