Analysis of the formation of interweaved strips in cast quasi-single crystal silicon ingots

Abstract

Unlike the impurity behavior of conventional polycrystalline silicon ingots, we have found that impurities are generated at the solid–liquid interface during the growth of quasi-single crystal silicon ingots. Due to the absence of large-angle grain boundaries in quasi-single crystal silicon ingots, impurities become enriched at the solid–liquid interface of the silicon ingot and exhibit a specific directional tilt during crystal growth. The accumulated impurities areas often exhibit a dark interweaved strip morphology detected by an infrared detector of quasi-single crystal silicon ingots. In this study, the dark interweaved strip is identified as an “interweaved shadow”. Additionally, the use of chemical corrosion technology and microscope observations revealed that interweaved shadows were present within the silicon ingot and could be extracted as white filament impurities. Subsequently, the interweaved shadows and dislocations of various morphologies in the silicon brick were analyzed. The interweaved shadows contained a mixture of carbon, oxygen, and nitrogen impurities. The degree of dislocation depended on the size of the filament impurities in the interweaved shadow. Specifically, the concentrations of carbon and nitrogen exceeded the solid solubility and the filament impurities with a diameter greater than 2.1 μm resulted in more severe dislocation defects.