In-situ melting and crystallization of sealed cooper wires can be performed by means of laser annealing for a duration of nanoseconds. The intensity of the laser irradiation is selected such that molten copper wets interconnect interfaces, thereby forming an interfacial bonding arrangement that increases specular scattering of electrons. Nanosecond-scale temperature quenching preserves the formed interfacial bonding. At the same time, the fast crystallization process of sealed copper interconnects results in large copper grains, typically larger than 80 nm in lateral dimensions, on average. A typical duration of the annealing process is from about 10's to about 100's of nanoseconds. There is no degradation to interlayer low-k dielectric material despite the high anneal temperature due to ultra short duration that prevents collective motion of atoms within the dielectric material.