Pd Seeding with the Sonochemical Method for Application of Cu Electroless Deposition to Cu Metallization

A sonochemical Pd seeding method for Cu electroless deposition (Cu ELD) is introduced in this study. Pd seeds, used as catalysts for Cu ELD, were deposited on a Ta/TaN diffusion barrier by ultrasound irradiation. The existence of Pd seeds on the substrate by irradiation was confirmed with X-ray photoelectron spectroscopy and atomic force microscopy. Cu ELD on the Pd-seeded substrate was successfully achieved. The formation of an electroless Cu film was strongly affected by the process parameters for sonochemical Pd seeding, such as the distance between the tip of the ultrasonic probe and a substrate, chemical composition of the seeding solution and ultrasound irradiation time. Those parameters were decisive factors in changing the deposition uniformity and number density of the Pd seeds. From the parametric study, we obtained a continuous electroless Cu film with good adhesion strength and low resistivity at the optimum condition. (C) 2014 The Electrochemical Society. All rights reserved.