Homogeneity of carbon microdistribution in edge-defined film-fed grown polycrystalline silicon

Edge-defined film-fed grown polycrystalline silicon sheets are known to contain carbon impurities in a state of extremely high supersaturation. During very rapid growth, carbon is incorporated with an unusually high effective segregation coefficient close to unity; therefore it is of interest to study its microdistribution over the sheet. We performed a scanning IR absorption microanalysis over macroscopic distances in order to evaluate the homogeneity of carbon microdistribution in as-received samples grown in an inert or oxidizing atmosphere, as well as on samples annealed for 72 h in air at different temperatures, up to 1150-degrees-C. As-received samples revealed a very good homogeneity of carbon distribution, which is not even disturbed by the presence of oxygen. However, the homogeneity of carbon microdistribution was found to be significantly disturbed upon annealing. This must be taken into consideration when studying the electrical characteristics of solar cells produced from such material upon various thermal treatments