Title:	Limitations of the Growth Rate of Silicon Mono Ingots Grown by the Czochralski Technique
Author(s):	F. Mosel, A.V. Denisov, B. Klipp, N. Sennova, C. Kranert, T. Jung, M. Trempa, C. Reimann, J. Friedrich
Keywords:	c-Si, Growth Rate, Active Crystal Cooling, Spiral Growth, Twisting
Topic:	Silicon Materials and Cells
Subtopic:	Feedstock, Crystallisation, Wafering, Defect Engineering
Event:	37th European Photovoltaic Solar Energy Conference and Exhibition
Session:	2DV.2.18
Pages:	468 - 473
ISBN:	3-936338-73-6
Paper DOI:	10.4229/EUPVSEC20202020-2DV.2.18
Price:	0,00 EUR
Document(s):	paper, poster

Abstract/Summary:

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In the PV industry, cost pressure subsists in the entire production chain of PV modules, affecting the further development of high-performance cell concepts and the manufacture of suitable high quality substrate crystals. The improvement of the quality of monocrystalline silicon ingots, grown by the Czochralski technique, while increasing productivity and reducing crystallization costs, is a major challenge. The reductions in production costs can be achieved by increasing growth rate and melt volumes. Both options were shown at EUPVSEC 2016 [1]. In this contribution we have investigated the basic limitations of the pull rate in the Czochralski process. As part of our investigations we have grown several crystals beyond the pulling speed limit resulting in a loss of the cylindrical shape of the ingot, often described as twisting or spiral growth. We performed these crystal growth experiments in various crystal growing configurations using different process parameters. We have analyzed the boundary conditions by means of numerical simulation calculations and compared the results with the crystal growth experiments. From this, we have derived diagrams that allow an estimation of the pull rate limit for the different growth conditions. We have found a simple relationship between the growth rate and the deflection of the phase boundary allowing the growth conditions to be assessed in terms of the stability criteria mentioned above. We show that by the application of an active crystal cooler during the growth process in combination with a suitable inner heat shield the deflection of the growth interface can be influenced. This fact can be used to realize a higher pull speed and to influence the material quality of the growing crystal.