On the mechanism of annealing effect in electrical resistivity of sub-100 nm Ag (1% W) films

Abstract

Our 50 nm Ag(1% W) film deposited by electroless onto Pd activated SiO2 shows rather high resistivity ρ≈35 μΩcm, which is caused most likely by open porosity and weak contacts between the grains [E. Glickman, A. Inberg, V. Bogush, Y. Shacham-Diamand, N. Croitoru, Microelectron. Eng. 70 (2003) 45]. The resistivity does not decrease after long aging at 20 °C or vacuum annealing at 80 °C, but shows a 3-fold drop after 1 h of isothermal vacuum annealing at 100 °C. Assuming the diffusion nature of the process responsible for the resistivity decay, we derived from the annealing kinetics ρ(T,t) at 100–300 °C the diffusion activation enthalpy E=0.19 eV and pre-factor D0∼(10−8–10−12) cm2/s. It is shown that these extraordinary small values are not compatible with any mechanism of bulk- or grain boundary diffusion in Ag, but can be explained in terms of surface diffusion (SD) controlled, surface tension driven sintering. It is assumed that surface of the film is contaminated/oxidized that prevents production of thermal equilibrium adatoms. Formation of non-thermal Ag adatoms, which are considered to mediate SD mass transport, is explicable in terms of decomposition of non-stable silver oxides on the film surface. The AFM, HRSEM, DSC and SIMS observations are in general agreement with the proposed sintering mechanism.