Thermal cycle impact on polycrystalline silicon: Direct observation of mechanical properties and interfacial nanocrystalline grain defects

In the field of integrated circuits, polycrystalline silicon (poly-Si) is widely used in the preparation and packaging of semiconductor devices, featuring excellent electron mobility and stability. With the development of three-dimensional (3D) and heterogeneous integration in the semiconductor field, the role of poly-Si has changed, and its mechanical properties have become crucial. Tracing nanocrystalline grain defects (NCGD) formation strained and deformation in thermal remains a challenging issue for poly-Si stable and reliable application in engineering. Here, by tracking the NCGD behavior of multilayer poly-Si with silicon dioxide (SiO₂) passivating during the manufacturing process of the technology, we explored the changes in the microstructure of the material when the strain deformation occurred, and concluded that the accumulation of thermal stress intensified the evolution of coherent twins (CTs) to incoherent twins (ICTs), and promoting the intensification of the strain behavior of the film layer. It is a pioneering work to explore poly-Si NCGD performance in the thermal fabrication. We obtain the thermal expansion deformation of poly-Si film and demonstrate it with the thermal cycle finite element model (TC-FEM). Then, we revealed the key factor to release compressive stress, in which the grain refinement (GR), grain size (GS), and grain boundary (GB) increasing induced CTs to ICTs. ICTs pose different obstacles to diffusion and dislocation movement and alter the rate and path of stress relaxation at high thermal conditions. Ultimately, this research enrich our understanding of NCGD in poly-Si materials. Our work highlights the complex interplay of polycrystalline structure, intra-and inter layer thermal exchange, as well as strained and deformation of poly-Si film. The findings of this work can have significant implications for the stability and reliability of 3D NAND flash memory and advanced semiconductor processing technology.