Nickel-Silicon Phases by Ion Implantation

Composition, phase and microstructural developments resulting from the implantation of silicon ions into nickel were investigated, using Auger electron spectroscopy, transmission electron microscopy and other methods. Implanted silicon content ranged from 10 to 90 atomic percent at temperatures from 25°C to 650° C. The results are discussed in terms of thermodynamic phase stability and radiation damage processes. Below 200° C, implanted silicon concentration was high at the surface, fell, rose with depth to a maximum value near 1400 X, then decreased to zero by 3000 X. The maximum concentration of silicon increased with increasing fluence. However, radiation induced segregation, combined with sputtering, tended to reduce the silicon concentration and penetration depth, as revealed by comparison with the implantation of aluminum ions into nickel. Above 350°C, increasing fluence had little effect on the peak silicon concentration, which remained below 28 atomic percent. However, increasing fluence at high temperature resulted in penetration of the silicon two or three times deeper than at room temperature. Phases resulting from implantation above 350°C resemble the equilibrium phase diagram in composition and temperature. However, the Ni3Si phase was observed only at temperatures exceeding 500°C. Below 500°C, the Ni5Si2 phase was seen instead, even at compositions where NisSi alone or in equilibrium with the FCC solution was expected at thermal equilibrium. The microstructural results of implanting fluences greater than 1 x 10^-8 Si + /cm2 depended upon temperature. Above 250°C the matrix recrystallized. Polycrystalline Ni3Si, Ni5Si2» or Ni2Si, possibly mixed with FCC nickel, formed, depending upon fluence and implantation temperature. Below 200°C, very strong diffuse rings were observed at d-spacings shared by several nickel silicides. Dark field images showed that at least some of the material contributing to the rings is microcrystalline. A major morphological development was the growth of holes in the implanted layer at elevated temperature and fluences over 1 x 1018 Si + /cm2. The diameter of these holes is of the same order of magnitude as the thickness of the implanted layer.