Microsecond UV laser annealing annihilating Ru grains smaller than electron mean free path

Enlarging metal grain size over electron mean free path is one of the ways to reduce resistivity in BEOL interconnect because it suppresses electron scattering at grain boundaries. In this work, by means of microsecond UV laser annealing (μs UV-LA), the mean grain size of an as-deposited 30-nm-thick Ru thin film has increased from 10.2 nm to 70.1 nm, reducing sheet resistance for 45% without damaging the Ru surface. The results highlight a potential benefit of μs UV-LA on future Ru-based BEOL interconnect.