Characteristics of Si channel layer formed through recrystallization using nanosecond laser annealing for monolithic 3D integration

Monolithic 3-dimensional integration (M3D) is a promising solution to overcome the limitations of 2-dimensional device scaling. A key challenge in fabricating M3D is the formation of the upper silicon (Si) channel layer under a low thermal budget process. The most viable approach is recrystallizing the amorphous Si layer formed on the dielectric layer using the UV-pulsed laser annealing, due to its short annealing time and high absorption coefficient of amorphous Si. In this research, we aimed to form a continuous single-crystalline Si layer by developing recrystallization process using laser anneal. Notably, we introduced single- and multi-pulse annealing with varying energy densities. Microstructural analysis confirmed that at 700 mJ/cm² and 800 mJ/cm², the epitaxial seed fully melted and recrystallized without collapse of SiO₂ walls. In single-pulse annealing, lateral regrowth resulted in boundary traps and the formation of large grains. In comparison, multi-pulse annealing significantly reduced grain boundary defects and (111) stacking faults by promoting repeated recrystallization along the (100) direction. GI-XRD results further revealed that the Si (400) peak became significantly more dominant than in single-pulse annealing. The recrystallized Si layer through multi-pulse annealing exhibited a single-crystalline structure, aligned in the same (100) orientation as the bottom Si layer, with reduced residual defects.