On-wafer investigation of SiC and Si 3N 4 inclusions in multicrystalline Si grown by directional solidification

Abstract

Commercial multicrystalline Si (mc-Si) wafers containing SiC and Si 3N 4 inclusions and wire-sawing defects on their surfaces were collected from an mc-Si wafer manufacturer. The mc-Si, used for solar cells, was grown using industrial directional solidification systems. The technique of controlled etching was applied to these mc-Si wafers to dissolve a certain amount of silicon from the surface of each wafer and to partially expose SiC and Si 3N 4 inclusions inside these wafers to allow for direct observation. The physical presence and morphologies of the SiC and Si 3N 4 inclusions within the mc-Si wafers were investigated using scanning electron microscopy. SiC inclusions were composed of SiC particles of different sizes, and they were usually present as clusters embedded within the mc-Si wafers. Si 3N 4 inclusions were present as rods distributed within the mc-Si wafers. It has been shown that the presence of SiC particles is responsible for the formation of the wire-sawing defects, while Si 3N 4 particles are readily sawed across without introducing wire-sawing defects during the wire-sawing process. This work will provide an important base-line for further investigation on how these inclusions affect the photovoltaic performance of mc-Si solar cells.