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

Electroless Ag(W) films were deposited from the ammonia-acetic silver complex solution in 450 nm deep damascene channels with aspect ratio ranging from 1 to 2.5 activated either by Pd solution or by dry sputtered metal 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 homogeneous trench filling without voids or seam creation, which may contribute to increase resistivity of interconnect metallization. The effect of activation procedure on Ag(W) film: nucleation, electrical and mechanical properties, is shown. Thin metal seed instead of wet Pd activation, leads to: decrease of the film electroless deposition incubation period, conformal trench filling and low resistivity of sub-100 nm layers. Thin 60 nm Ag(W) films with resistivity value of about 2 μΩ·cm after vacuum annealing at 350 C for 2 h were obtained that makes them promising for future ULSI microelectronic application as conductive layers.