Current Limitations of thin Film Conductors

Electromigration in thin film conductors is recognized as a potential wear-out failure mechanism for semiconductor devices. Design guidelines have been established limiting the maximum current densities for aluminum and aluminum alloy conductors. With the development of new lithography and etching techniques enabling the construction of very small conductors and spacings the validity of these guidelines has been questioned. Utilizing known experimental data of the lifetime of Al, Al 2% Si and Al 4% Cu 2% Si conductors new guidelines are presented which define the maximum design current density as a function of the conductor temperature and the conductor current. These maximum current densities established by electromigration considerations are further limited by the product of the thicknesses of the conductor and the underlying dielectric thickness which determine conductor temperature gradients caused by the conductor rise in temperature above that of the substrate. Data are presented for the above metal films on vitreous silica.