Beta-Si₃N₄ particles as nucleation sites in multicrystalline silicon

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• 作者：K.E. Ekstrø ; m^a ; ^{kai.e.ekstrom@ntnu.no" class="auth_mail" title="E-mail the corresponding author} ; E. Undheim^a ; G. Stokkan^b ; L. Arnberg^a ; M. di Sabatino^a
• 关键词：Silicon ; Nucleation ; Solidification ; Grain refinement ; Microstructure
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：1 May 2016
• 年：2016
• 卷：109
• 期：Complete
• 页码：267-274
• 全文大小：2201 K

文摘

This work presents β-Si₃N₄ as being the main nucleation site for multicrystalline silicon grown by directional solidification in crucibles coated with Si₃N₄-based coatings. We argue for initial nucleation occurring on the largest β-Si₃N₄ particles at very small undercoolings, in accordance with the free-growth model, with an increasing nucleation potency for smaller particles as the nucleation undercooling increases. A nearly continuous layer of large β-Si₃N₄ particles forms between the α-Si₃N₄ coating and the solidified silicon, confirming a transformation from α-to β-Si₃N₄ in the presence of liquid silicon. The layer appears to be in contact with the solidified ingot only at localized positions, and the apparent accumulation of parallel twins and other grain boundaries suggest that nucleation has occurred at these positions. We suggest that rapidly growing dendrites have a pronounced effect on the grain structure of conventionally grown multicrystalline silicon, and that their unpredictable occurrence limits the grain refinement potential for the most common growth conditions. However, it is also suggested that a certain degree of refinement can be achieved by utilizing a uniform distribution of large Si₃N₄ particles together with a slow cooling procedure. By engineering the size of the Si₃N₄ particles one should therefore be able to control the initial grain structure and to a certain degree tailor the final grain structure of the ingot.