FORMATION OF TISI2 FROM TITANIUM AND AMORPHOUS-SILICON LAYERS FOR LOCAL INTERCONNECT TECHNOLOGY

In this paper we describe the TiSi2 local interconnect (strap) formation for d.c. magnetron sputter deposited titanium and amorphous silicon (a-Si) layers. D.c. magnetron deposition is found to be advantageous compared with r.f. diode sputter deposition. The primary advantage is the formation of smooth silicide films even for silicon-rich deposited Ti/a-Si bilayers. The silicon-rich deposited Ti/a-Si bilayers are favoured as they give better device performance. Since TiSi2 straps are formed over diffusion areas as well as over oxide surfaces, the influence of the substrate on the Ti-a-Si reaction was investigated. For a titanium-rich deposited stack on a monocrystalline silicon substrate, the deficient amount of silicon is withdrawn from the substrate to form a stoichiometric TiSi2 layer after annealing. On oxide substrates, the excess titanium is nitrided, resulting in a Ti(N) layer on top of the TiSi2. If the deposited stack is silicon rich, the products are the same for both monocrystalline and oxide substrates: all the titanium is converted into TiSi2 with the excess silicon remaining on top.