In situ TEM crystallization of free-standing amorphous silicon nitride (a-SiNX)

• In-situ TEM visualizes crystallization in free-standing a-SiNₓ membranes. • Laser-heated Al agglomerates enable localized, controllable nucleation. • Agglomerate size drives crystallization kinetics: two-stage vs. rapid front growth. • Crystallographic orientation mapping visualizes highly directional growth. • Stresses drive crystallization fronts causing cracks and membrane failure. Amorphous silicon nitride (a‑SiN X ) is widely used in microelectronics and MEMS, however its long‑term structural stability under elevated temperatures and repeated thermal cycling remains an active field of study. This study employs in situ transmission electron microscopy (TEM) to investigate the crystallization mechanisms and kinetics of amorphous silicon nitride thin films. Real-time observation during localized laser-induced heating enables direct visualization of devitrification processes and phase evolution with nanometer-scale resolution. In situ TEM observations show that localized material defects can lower the stability of the amorphous phase and promote crystallization. Notably, the magnitude and distribution of thermal stresses appear to strongly influence crystallization dynamics: intense, localized heating leads to rapid nucleation and near-instantaneous growth, whereas broader, lower-intensity heating induces a slower, two-stage crystallization process. These results are consistent with a strong role of thermal stress in modulating crystallization behavior and offer insights into the thermal reliability of a-SiN X . Such insights contribute to a deeper understanding of the thermal stability and inform the design of robust thin-film components for high-performance microdevices.