The evolution and analysis of electrical percolation threshold in nanometer scale thin films deposited by electroless plating

Extension of Ultra Large Scale Integration (ULSI) to a nanometer scale elevates the importance of interconnect resistivity in addition to conventional problems of coverage and electromigration. In this work we study electrical properties of ultra thin silver (Ag) and copper (Cu) films prepared by electroless deposition (ELD) in order to provide low resistivity, stable interconnect metallization technology and electrical contacts. The thin film is modeled by assuming metal conducting clusters separated by empty dielectric gaps. The continuity of the film or gap size is controlled by film thickness with respect to the growth mode of each metal. Analysis of the electrical properties of thin films at percolation threshold demonstrates that insulator-conductor transition occurs at the thickness about 35 nm and 30 nm for Ag and Cu films, respectively. At these thicknesses film roughness is constant, therefore, scattering on film walls remains unaffected and resistivity change can be associated with a percolation mechanism. The resistivity as a function of thickness varies according to power law and reaches saturation value of 2.5 mu Omega cm and 4.3 mu Omega cm at the thicknesses of 60 nm and 50 nm with critical exponents (tau) of 0.95 and 1.04 for Ag and Cu thin films, respectively. The X-ray Photoelectron Spectroscopy analysis has not detected contaminations or oxidation states. The strong dependence of the film surface roughness on metal ion concentration in solution was observed while the deposition rate and the resistivity remain unaffected. (C) 2011 Elsevier B.V. All rights reserved.