Electrodeposition of copper thin film on ruthenium - A potential diffusion barrier for Cu interconnects

The electrochemical deposition of copper (Cu) thin film on polycrystalline ruthenium (Ru) electrode surface was investigated in a sulfuric acid plating bath. Scanning electron microscopic characterization indicated that a continuous thin Cu film (150 Angstrom and above) could be conformally coated on Ru with good control of thickness. The nucleation and growth of Cu on Ru was studied using the potentiostatic current-transient method. The results support a predominantly progressive nucleation of Cu on the Ru surface. In addition, X-ray diffraction patterns indicated (i) a principally (111) texture of the electrochemically grown Cu on Ru and (ii) the absence of any new phase or compound formation between the two metals, even after annealing up to 800degreesC. Scotch tape peel tests showed that Cu films adhered strongly to Ru, both before and after the annealing treatments. The lack of metallurgical interaction and strong adhesion between Cu and Ru at elevated temperatures underscore the potential application of Ru as a new Cu diffusion barrier. (C) 2003 The Electrochemical Society.