SHORT-TIME FAILURE OF METAL INTERCONNECT CAUSED BY CURRENT PULSES

Metal interconnect reliability studies are frequently concerned with lifetimes on the order of years at signal level current densities. Voltage programmable link (VPL) technologies impose a new criterion on the reliability of metal interconnect. Lines of metallization must support the full programming current, which can be many times larger than signal level current, for very short periods of time. For a sufficiently short high current pulse, the wire, encapsulated in oxide, will not reach thermal equilibrium and the current-induced heating can be modeled as being adiabatic. Energy conservation predicts a relationship between maximum current density that can be carried by a wire before it fuses, and the pulse duration time, j2t = 10(8) A2 . s/cm4. This relationship is based on a temperature rise in the metal line at failure of theta(f)* = 300-degrees-C. The time required for the metal to reach thermal equilibrium at a given current density is shown to be proportional to the square of the oxide thickness. These predictions are experimentally verified with layered AlSi/Ti metallization on thermal oxide on silicon substrates.