Initial stages of silicon-crucible interactions in crystallisation of solar grade silicon: Kinetics of coating infiltration

Photovoltaic silicon ingots are currently grown in SiO2 crucibles coated with a porous silicon nitride layer which acts as an interface-releasing agent between silicon and the crucible. The present investigation focuses on the initial stages of Si crucible interactions, involving infiltration of the porous coating by molten silicon. In this study, performed using the sessile drop technique in flowing argon, three types of infiltration are considered: infiltration under the drop, which is representative of infiltration occurring at the crucible/bulk silicon interface; infiltration at the coating surface in front of the nominal triple line, leading to the formation of a silicon-rich film; and infiltration under this film. The experimental results, obtained by varying the infiltration duration, the temperature of the coating heat treatment prior to the infiltration experiment and the argon flow, are interpreted with the help of an analytical model, taking into account diffusive transport in the infiltrated coating, in the bulk liquid and in the flowing gas. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.