FORMATION AND DIFFUSION BEHAVIOR OF INTERMIXED AND SEGREGATED AMORPHOUS LAYERS IN SPUTTERED NICR FILMS ON SI

Sputter-deposited Ni80Cr20 films on sputter-cleaned Si substrates cont ain an amorphous layer at the substrate/film interface whose compositi on is a mixture of all the elements present at the interface. Subseque nt thermal processing at 300-degrees-C for 30 min produces a new segre gated Cr-rich amorphous layer as Ni atoms preferentially diffuse throu gh and react with the initial amorphous layer and the silicon substrat e. Further annealing results in the growth of uniform nanoscale NiSi l ayers, as long as the segregated a layer is sustained. The amorphous l ayers eventually crystallize at approximately 500-degrees-C and Kirken dall voids are observed at 550-degrees-C. Whereas the formation of int ermixed amorphous layers from metal-metal or metal-silicon systems has been reported by several authors, the segregated amorphous layer aris ing out of the interdiffusion and reaction between a metal alloy and S i is of both fundamental and technological interest due to its thermal stability and ability to control the silicide growth. In this work, w e describe the evolution of both kinds of amorphous layers, i.e., inte rmixed and segregated, so as to elucidate their origins. The evolution of the two a layers is also observed when monolayers of Pt are introd uced prior to NiCr deposition. In this case, the growth of the segrega ted amorphous layer is retarded and it dissolves earlier during therma l annealing.