Reaction of amorphous Ni-W and Ni-N-W films with substrate silicon

Amorphous films of Ni-W and Ni-N-W were deposited on single-crystal silicon with discharge gases of Ar or Ar+N2 by rf cosputtering of Ni and W. The reaction of these Ni-W and Ni-N-W films with the Si substrate were studied in the temperature range of 450--750 0C by a combination of backscattering spectrometry, x-ray diffraction, cross-sectional transmission electron microscopy, and resistivity measurements. Films with composition Ni36W64 are stable below 500 0C. NiSi and NiSi2 form at 500 0C, and WSi2 forms rapidly in the temperature range of 625--650 0C. The nickel silicide forms adjacent to and within the silicon, while the outer layer becomes a mixture of WSi2 and NiSi2. The morphologies of the reacted layers are revealed by cross-sectional transmission electron microscopy. The crystallization temperature of amorphous Ni36W64 films on SiO2 is near 650 0C also. Adding nitrogen to form amorphous Ni30N21W49 films lowers the crystallization temperature, but raises the reaction temperature with Si to 750 0C