Reduced metal contamination from crucible and coating using a silicon nitride based diffusion barrier for the growth of cast quasi-single crystalline silicon ingots

• Published in: Journal of crystal growth Vol. 514; pp. 49 - 53
• Main Authors: Wolny, Franziska, Krause, Andreas, Müller, Matthias, Fischer, Gerd, Neuhaus, Holger
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.05.2019; Elsevier BV
• Subjects: A2. Cast quasi-single crystalline silicon; A2. Crucible coating; A2. Diffusion barrier; A2. Directionally solidified silicon; A2. Quasi-mono; A2. Redzone; Chemical vapor deposition; Contamination; Crucibles; Crystal structure; Crystallinity; Crystallization; Diffusion barriers; Diffusion coating; Diffusion layers; Directional solidification; Ingot casting; Ingots; Organic chemistry; Photovoltaic cells; Silicon nitride; Silicon oxides; Silicon wafers; Solar cells; Wafers; A2. Cast quasi-single crystalline silicon; A2. Directionally solidified silicon; A2. Diffusion barrier; A2. Crucible coating; A2. Quasi-mono; A2. Redzone
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2019.02.055

•SiOx/SiNy coated wafers on crucible bottom reduce red zone in quasi-mono silicon.•Iron and copper concentration in ingot bottom reduced by one order of magnitude.•Height of cropped portion in a G5 quasi-mono ingot can be reduced by 2 cm.•PERC cells from reduced redzone bottoms have much larger efficiency than reference. During the crystallization of directionally solidified silicon such as multicrystalline or cast quasi-single crystalline silicon, the diffusion of metal impurities from crucible and coating into the solid silicon ingot at high temperatures creates a severe contamination issue in the edge region of the ingot, the so called red zone. We present an effective diffusion barrier which greatly reduces this detrimental metal diffusion. Silicon wafers are coated with a layer system of silicon oxide and silicon nitride by chemical vapor deposition and are placed on the bottom of the crucible. Using this technique, the metal contamination in the red zone can be reduced by about one order of magnitude. This leads to better solar cell performance of wafers fabricated from this ingot area. Also, less ingot material has to be discarded leading to higher wafer yield per ingot.