Thin film crystal growth of Si on fused silica: Effects of growth front dynamics on crystallography

Reflective high speed video microphotography was used to study the advance of the resolidification front during CO2 laser melting of encapsulated polycrystalline silicon thin film structures on bulk fused silica substrates. Prepatterned silicon films were laser recrystallized, removed from the substrate, and then examined by transmission electron microscopy. The crystal structure which results from seeded and unseeded growth and from various liquid-solid growth front shapes was characterized. Supercooling of the melt and subsequent dendritic polycrystalline regrowth is observed in cases where nucleation occurs in isolated molten regions. Transmission electron micrographs demonstrate the necessity of providing controlled seeding conditions, such as regrowth through a narrow neck of silicon. A flat liquid-solid interface supports a [111] growth direction whereas concave thermal profiles cause twinning or low angle grain boundaries in the films.