Wetting, infiltration and sticking phenomena in Si3N4 releasing coatings in the growth of photovoltaic silicon

The growth of photovoltaic silicon ingots from the melt is currently performed in silica crucibles covered by a silicon nitride powder coating which prevents from sticking. The purpose of this study is to propose a comprehensive description of interactions in the Si/porous Si3N4-coating/SiO2 system responsible for the non-sticking behaviour. The interpretations are based on wetting experiments performed by the sessile drop technique and on microstructure characterizations carried out by optical and scanning electron microscopies.We show that the Si3N4 porous coating constitutes a barrier to wetting and infiltration due to the presence of a non-wettable SiO2 layer on nitride particles, and acts as a mechanical fuse due to its weak resistance resulting from its porous microstructure. The consequences of the study findings on the crucible used in solidification of photovoltaic silicon are discussed.