Wetting Phenomena in Silicon Processing Systems

Wetting phenomena govern the interaction between molten silicon and the surfaces it contacts during high-temperature processing, influencing both material integrity and device performance. At the heart of these interactions lies the balance of surface energies, which determines whether silicon spreads readily (wetting) or remains as discrete droplets (non-wetting). In silicon crystal growth, photovoltaic ingot production and thermal energy storage, uncontrolled wetting can lead to melt infiltration, crucible degradation and contamination of the silicon melt. Conversely, non-wetting conditions promote clean detachment of solidified silicon, reduce particulate generation and extend crucible lifetime. Control strategies span the selection of refractory substrates—such as silicon nitride, graphite or hexagonal boron nitride—and the application of engineered coatings that tailor surface chemistry. Process parameters including gas composition and temperature profiles further modulate wetting behaviour by affecting oxide formation and interfacial reactions. Advances in in situ characterisation techniques, especially sessile drop experiments, have elucidated dynamic contact angles and reaction kinetics, enabling predictive models that link thermodynamics to practical outcomes. As silicon continues to underpin microelectronics, solar energy and emerging phase-change applications, a rigorous understanding of wetting phenomena remains essential for enhancing yield, reducing cost and ensuring the global scalability of silicon technologies.

Research from Nature Portfolio

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Research from all publishers

A comprehensive review published in 2024 examined the roles of crucible materials and surface coatings in silicon melting and crystallisation. It highlighted how different crucible compositions—ranging from silica-based to carbon-reinforced ceramics—interact with silicon melt at temperatures above 1400 °C. The analysis of coating stability and wetting behaviour underscored the importance of thermal conductivity, chemical compatibility and oxide layer formation in achieving sustained non-wetting conditions.

In 2022, a study of graphite substrates for photovoltaic silicon crystallisation introduced novel multilayer coatings combining silicon nitride, silicon carbide and colloidal silica. Sessile drop experiments revealed that a two-layer approach with controlled oxygen content in the top layer effectively suppressed liquid infiltration, minimised coating degradation and reduced carbon monoxide evolution under isothermal holds. This work demonstrated a clear pathway to reusable graphite crucibles by fine-tuning coating composition and thickness.

Also in 2022, research into gas atmosphere effects on silicon wetting illustrated how nitrogen, carbon monoxide and argon influence interfacial reactions with coated graphite. Carbon monoxide was shown to promote formation of a silicon carbide barrier at the free surface, impeding droplet spreading, while nitrogen accelerated wetting through in situ silicon nitride growth at the triple line. These findings highlighted the intertwined roles of furnace atmosphere and coating chemistry in dictating melt behaviour and substrate integrity.

Wetting Phenomena in Silicon Processing Systems publication trend

The graph below shows the total number of articles in wetting phenomena in silicon processing systems across all publications each year (not limited to Nature Index journals).

Technical terms

Wetting: The extent to which a liquid spreads over a solid surface, determined by interfacial energies.

Contact angle: The angle formed at the junction of liquid, solid and gas phases; lower angles indicate better wetting.

Sessile drop technique: An experimental method in which a liquid droplet is placed on a substrate and its shape is monitored to assess wetting.

Crucible coating: A thin layer of material applied to a refractory container to modify surface chemistry and control melt interactions.

Liquid infiltration: The penetration of molten material into porous substrates or coatings, often leading to structural damage or contamination.

References

1. Crucibles and coatings for silicon melting and crystallization: An in-depth review of key considerations. Progress in Materials Science (2024).
2. Novel coatings for graphite materials in PV silicon applications: A study of the surface wettability and interface interactions. Solar Energy Materials and Solar Cells (2022).
3. Effect of gas atmospheres on the interactions between liquid silicon and coated graphite substrates. Solar Energy Materials and Solar Cells (2022).