Engineering Ni-Silicide Nanocontacts for 3D Silicon Devices via Geometrical Confinement Control

Nanoscale Ni-silicide alloys are critical components for future generations of 3D electronic devices based on active Si nanostructures, with applications in nanoelectronics, energy conversion, and sensing. This study investigates how geometrical confinement in such nanostructures influences diffusion-driven silicidation, ultimately determining the alloy formation sequence, phase composition, and volumetric expansion. The silicidation of controlled Ni volumes is investigated on vertical silicon nanowires (NW) and nanosheets (NS) under various annealing conditions. The silicide phases and interface morphologies are characterized using high-resolution (scanning) transmission electron microscopy (HR-TEM, HR-STEM), energy-dispersive X-ray spectroscopy (EDX), and four-dimensional scanning transmission electron microscopy (4D-STEM) for nanoscale Ni-Si phase mapping. Under conditions of strong geometric confinement, NiSi₂ is observed to form with faceted, prism-like morphologies aligned with Si (111) planes, features not typically present in planar or bulk samples. This anisotropic growth is associated with preferential Ni diffusion along nanostructure surfaces and limited Si counter-diffusion through the silicide. The resulting NiSi₂ interfaces are structurally distinct and may contribute to reduced contact resistance in both p-type and n-type silicon nanostructures, supporting their integration in 3D device architectures.