Ni/4H-SiC interaction and silicide formation under excimer laser annealing for ohmic contact

Nickel silicidation reactions were activated on 4H-SiC using laser annealing at wavelength of 308 nm to study interaction and reaction of the involved atomic species. With this intent, the deposited nickel layer thickness was scaled from 100 nm to 10 nm and the laser fluence was spanned from 2.2 to 4.2 J/cm2. A combination of structural characterization by X-ray diffraction, Energy-Dispersive X-ray spectroscopy, Raman Spectroscopy, Transmission Electron Microscopy and morphological investigations through Scanning Electron Microscopy with theoretical predictions as a function of the applied laser fluence, have unveiled that the starting nickel thickness plays a main role, especially above the threshold for nickel melting (2.8 J/cm2). As a general paradigm, sufficient silicon release from the substrate occurs above this threshold that is available for silicidation, with amount increasing with the laser fluence. This addresses stoichiometry and morphology of the silicided contact that indeed depend on the available Nickel atoms (i.e., the Ni layer thickness) and on the thermal profile, as tested at a fixed fluence of 3.8 J/cm2. In addition, a layer-by-layer variable stoichiometry is established in each sample through the contact, with the deepest silicide being relatively more Si-rich. All those findings have impact on the electrical parameters of testing diodes. Based on data cross-linking, NiSi2 contacting layers and C-free interfaces provide a convenience in reducing resistance contributions.