The InGaAs high mobility channels are vowed as serious candidates for alternative channel materials for sub-10 nm technology nodes urging studies for analogous contacts to the dominant silicide contacts in the Si technology mainstream. The Ni-InGaAs (nickelide) contact technology has been demonstrated as a suitable self-aligned contact technology for InGaAs channels with record small specific contact resistivity. However, the majority studies on nickelide contact formation were conducted on planar InGaAs films and little studies focused on the contact metallurgy specific in nanoscale InGaAs nanowire or Fin channels. Here, we utilized a novel wafer bonding technique to transfer thin (50 nm) In0.53Ga0.47As layers onto SiO2/Si substrates and Si transmission electron microscopy (TEM) frames. InGaAs Fins with variable widths, lengths, and orientations were fabricated through a combination of electron-beam lithography and top-down dry etching steps, followed by Ni contact deposition. Rapid thermal annealing and in-situ TEM thermal heating cycles were conducted to react Ni with the InGaAs channel and deduce the reaction kinetics, dynamics, and resultant nickelide and interface structures. The nickelide phase was found to gradually extend into the InGaAs fin channels, introducing a 32% ï¿½ 7% height increase to the channels with negligible lateral expansion. The morphology of formed nickelide phase strongly depended on the orientation of fin structures, as we observed sharp and abrupt nickelide-InGaAs interfaces for oriented fin channels, while rough interfaces with multiple facets in oriented ones. Systematical measurements of the length of nickelide segments according to different annealing times, temperatures, and fin widths, revealed a Ni diffusion limited kinetic growth process, which agrees well with the derived equations from a kinetic competition model. A transition from surface diffusion limited kinetic process to volume diffusion limited one was reported for the first time, related to the increase of InGaAs fin widths. We extracted a surface diffusion coefficient of 1.3x10-15 ~ 1.5x10-15m2/s at a reaction temperature of 250 ï¿½C, which is ~5 times larger than the extracted volume diffusion coefficient. The crystalline structure analysis with TEM revealed a hexagonal lattice of formed nickelide phase, adopting a NiAs (B8) structure. Cross-sectional TEM measurements were achieved by focus ion beam (FIB) cut along the fin channels, showing a slanted nickelide-InGaAs interfaces towards the base, which is possibly induced by the stress from underneath dielectric layers. These results contrasted with the conventional contact metallurgy studies in nanowires with free surface, and the detailed structure, interface and reaction dynamics will be discussed.