Energy effect of the laser-induced vertical metallic link

In this paper, the energy effect of the laser vertical metallic link is investigated from a microscopic point of view through experimental observations and simulations. Sample structures that were irradiated under different laser energies were cross-sectioned and observed using a FIB/SEM dual-beam system. Failure criterion at the high energy level was defined by excessive material loss in the lower metal (metal 1) and passivation cracking. Micro-images also suggest that, for an optimal link structure, the upper metal (metal 2) opening should be larger than the lower metal linewidth considering the dielectric-step-induced lens effect. Taking into account both measured electrical resistance and observed voids in the lower metal, the normalized energy process window is defined to be the absolute energy range divided by the average energy. For the structures with 1-, 2-, 3-, and 4-/μm lower metal linewidths, the relative process windows are 0.83, 0.87, 0.9, and 0.96, respectively. Simulations also revealed consistent results with the experimental observations, which is a monotonically decreasing trend of relative energy process windows for more scaled links. A simple equation to evaluate the spot size of the laser beam for various link structures is presented. These results demonstrate the application of commercially viable vertical linking technology to VLSI applications.