Chemical characterization of SiC and Si3N4 precipitates in multicrystalline silicon by NIR microscopy and ToF-SIMS

During the crystallization process of multicrystalline silicon precipitates may be formed, which can cause electrical and mechanical problems in the later manufacturing process of solar cells. Typical precipitates in multicrystalline silicon (mc-Si) ingots are SiC and Si3N4, the exact chemical composition is not known until now, especially regarding dopants. After localization with near infrared (NIR) microscopy, we used Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for chemical investigations. Reproducible fingerprints of the elemental composition for several SiC and Si3N4 precipitates were determined and it is shown that characteristic polyatomic fragments can be assigned to each type of precipitate. Doping elements in the different precipitates explain the origin of the electrical conductivity