Intermetallic reactions in vacuum-deposited nickel and gold films on (111) silicon single crystals

Pure nickel and gold thin films were vacuum-deposited on (111) silicon single crystals. When Ni/Au/Si or Au/Ni/Si samples were heated to about 550° insitu, hexagonal or deformed hexagonal shaped crystallites were formed on the silicon substrates. The composition of these crystallites was determined by using x-ray diffraction, scanning elec-tron microscopy and scanning Auger microprobe methods. The crystallites were identified as NiSi2. The crystal-lites on the (111) silicon plane parallel to the surface appeared as regular hexagons while the inclined crystal-lites resembled trapezia. The results of Auger spectra and in-depth composition profiles for Ni, Au, and Si showed that the NiSi2 crystallites are islands in a matrix of Au-Si eutectic.