Direct observation of intra-grain defect formation during local solid-phase epitaxy

Despite relentless efforts to improve fabrication processes, the achievement of a defect-free polycrystalline film (poly-film) through solid-phase crystallization (SPC) remains challenging, as evidenced by structural analyses. Understanding the dynamics of intermediate processes, including the precursor phenomena, is crucial for developing strategies to suppress defect formation. In this study, we directly observed elementary processes during crystal growth at local interfaces between crystalline Si (c-Si) grains and uncrystallized amorphous Si (a-Si) regions within a Si thin film using in situ high-resolution transmission electron microscopy. By analyzing the sequential formation of Si atomic planes with a time resolution of 10 ms, we found that crystal growth at the local c-Si/a-Si interfaces proceeded via either continuous solid-phase epitaxy (SPE) or discontinuous SPE-a newly identified growth mode. Continuous SPE represents an ideal mode of layer-by-layer growth, resulting in defect-free Si grains. In contrast, discontinuous SPE leads to the formation of uncrystallized closed-shell regions inside the grains, which serve as the origin of intra-grain defects. These findings demonstrate that intra-grain defects, which degrade the electrical properties of poly-films, arise from the abnormal growth dynamics of the atomic planes.