A study on the recrystallization and defect healing of silicon under rapid thermal annealing

Monocrystalline silicon is extensively employed in semiconductor industry and optical technologies, where the attainment of an ultrasmooth surface and a defect-free subsurface is imperative. Nevertheless, subsurface imperfections such as amorphous phases and dislocations are unavoidably introduced during ultra-precision machining, compromising material performance and reducing service lifespan. Thermal annealing is widely utilized to alleviate subsurface defects in silicon; however, the fundamental mechanisms underlying amorphous silicon recrystallization and dislocation annihilation remain insufficiently understood, resulting in persistent uncertainties regarding the processes that govern defect recovery. This study investigates the influence of thermal annealing on the recrystallization of amorphous regions and the healing of defects in silicon, employing experimental procedures and molecular dynamics simulations across varying temperatures and heating protocols. The findings elucidate three primary mechanisms governing amorphous silicon recrystallization: bottom-up epitaxial regrowth, omnidirectional solid-phase epitaxy, and dislocation-assisted atomic migration. Thermal annealing was found to restore machining-induced surface grooves and significantly decrease surface roughness. During annealing, perfect dislocations initially dissociate into partial dislocations, which then migrate toward the amorphous-crystalline interface, culminating in dislocation annihilation. This study offers critical insights into atomic-scale structural reorganization and amorphous phase evolution, thereby providing a fundamental basis for advancing damage-free processing techniques in the fabrication of monocrystalline silicon devices.