The effect of surface activation on electroless Ag(W) deposition

Electroless Ag(W) films were deposited from the ammonium-acetic silver complex solution in 450 nm deep damascene channels with aspect ratio ranging from 1 to 2.5 activated either by wet Pd solution or by dry sputtered Cu seed. A small addition of PEG-1500 (PEG with molecular weight of about 1500) to the electrolyte and lower deposition temperature were found to be necessary to achieve the trench filling without voids or seam creation. The critical effect of activation procedure on Ag(W) nucleation and layers resistivity is shown. Deposition on thin metal seed leads to decrease of incubation period, conformal trench filling and low resistivity of sub-100 nm layers. The film resistivity value after post-deposition vacuum annealing at 350 C for 2 h was in the range 2-3 μΩ cm.