Nucleation properties of undercooled silicon at various substrates.

When solidifying molten silicon in contact with a foreign substrate, the interfacial interaction between silicon and the substrate material can affect the nucleation behavior and therefore the final grain structure. This work illuminates the nucleation properties of different materials using differential scanning calorimetry to measure the undercooling below the melting temperature of molten silicon in contact with silicon oxides and nitrides. Both dry and wet thermal oxides show greater than 120 °C of undercooling before nucleation occurs, while silicon nitride consistently shows less than 17 °C. Variability in measured undercooling was minimized by improving coating uniformity but is not necessarily affected by overall sample deformation. A double-layer coating of silicon nitride over dry oxide reduced the dry oxide undercooling to <56 °C due to inter-layer thermal stresses, which can be minimized by reducing the outer layer of silicon nitride to <40 nm. The double-layer SiNx-SiO2 coating produced larger grains than the SiNx coating alone, when applied to a wafer recrystallization process. [ABSTRACT FROM AUTHOR]