Metallurgical interaction among aluminum, polycrystalline silicon, and TaSi(2) or single-crystal silicon, in VLSI contacts.

We have found and investigated a metallurgical reaction that occurs between the aluminum and the contact polysilicon in fine-line NMOS devices made using the poly-plug contact process. The reaction takes place during the 450C H(2) annealing step, and it results in the aluminum attacking and penetrating through the polysilicon layer. It occurs mostly with polysilicon on top of tantalum silicide, and to a much lesser degree with polysilicon on top of silicon dioxide or single-crystal silicon. It is more pronounced on contacts with small areas. We have investigated aluminum/polysilicon/silicide thin-film structures to clarify the causes and effects of this reaction. The susceptibility to reaction correlates with the smaller polysilicon gain size that is found for polysilicon on top of tantalum silicide, and it correlates with the dopant type of the polysilicon, being more pronounced for phosphorus diffused polysilicon than for arsenic implanted polysilicon.