Formation and diffusion behavior of intermixed and segregated amorphous layers in sputtered NiCr films on Si

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Abstract
Sputter‐deposited Ni80Cr20 films on sputter‐cleaned Si substrates contain an amorphous layer at the substrate/film interface whose composition is a mixture of all the elements present at the interface. Subsequent thermal processing at 300 °C for 30 min produces a new segregated Cr‐rich amorphous layer as Ni atoms preferentially diffuse through and react with the initial amorphous layer and the silicon substrate. Further annealing results in the growth of uniform nanoscale NiSi layers, as long as the segregated a layer is sustained. The amorphous layers eventually crystallize at ∼500 °C and Kirkendall voids are observed at 550 °C. Whereas the formation of intermixed amorphous layers from metal–metal or metal–silicon systems has been reported by several authors, the segregated amorphous layer arising out of the interdiffusion and reaction between a metal alloy and Si is of both fundamental and technological interest due to its thermal stability and ability to control the silicide growth. In this work, we describe the evolution of both kinds of amorphous layers, i.e., intermixed and segregated, so as to elucidate their origins. The evolution of the two a layers is also observed when monolayers of Pt are introduced prior to NiCr deposition. In this case, the growth of the segregated amorphous layer is retarded and it dissolves earlier during thermal annealing.