MAPPING OF SILICON CARBIDE AND SILICON NITRIDE PRECIPITATES ON CHEMICAL-MECHANICALLY POLISHED MC-SILICON WAFERS

摘要

Large SiN and SiC precipitates, ranging from a few microns to a few hundred microns in size, are frequently found in MC-silicon wafers. Such precipitates may generate shunts in processed solar cells. Their concentrations are largely dependent on the feedstock quality, atmospheric conditions inside the furnace during directional solidification and interactions with the silicon nitride coating. During chemical mechanical polishing (CMP) of MC-silicon wafers, silicon is removed from the surface, whereas the hard SiN and SiC particles are not as affected by the polishing process, resulting in a clean, polished surface with SiN and SiC protrusions. Pvscan 6000 is an instrument originally designed for mapping dislocation density and grain boundaries on polished and etched wafers by inerpreting their characteristic reflectance. The same instrument can be used for precipitate mapping due to high-angle light scattering from precipitate protrusions. We studied the effect of different polishing schemes on the detectability of precipitates. Comparison with Electron MicroProbe Analysis (EMPA) were made to verify the correspondence of protrusions with actual precipitates. Reflectance measurements on chemical-mechanically polished silicon wafers provides a fast and convenient method of mapping large-scale precipitates. The method has industrial relevance.