Investigation on the Transformation of B-Defect in As-Grown Czochralski Silicon Crystal during Annealing Process

When a silicon ingot is grown by the Czochralski method, different defects, such as A-defect (a dislocation loop or dislocation loops cluster), B-defect (widely accepted as an interstitial atoms cluster), COP (crystal originated particle, a void), and grown-in oxygen precipitates will emerge. Nowadays most crystal defects can be characterized directly. However, due to the extremely small size and stress, B-defects can only be indirectly characterized by the formation of oxygen precipitates. What's more, it is unclear whether B-defects transform into oxygen precipitates directly or B-defects grow and transform into A-defects firstly and further facilitate oxygen precipitation via the dislocation pinning effect. In this work, after implementing an optimized anneal at 900 degrees C for 3 h and HCl vapor-phase etch at 900 degrees C for 2 min, nano-scale defects transformed from B-defects are efficiently detected by a surface particle counter. Scanning electron microscope and energy-dispersive X-ray spectroscopy results prove that these nano-scale defects are all oxygen precipitates. This explicit result indicates that B-defects can induce the formation of oxygen precipitates directly rather than relying on the formation of A-defects, which would help to better understand the characteristic of B-defect in relatively low temperature and the transformation process between different defects in silicon ingot.