Optimization of a Pretreatment for Copper Electroless Deposition on Ta Substrates

Abstract

We investigated pretreatment methods for Cu electroless deposition on a Ta substrate. The native oxide on the substrate was effectively etched by the addition of HNO3 to a HF diluted solution and this was confirmed though X-ray photoelectron spectroscopy and chronopotentiometry. To form the Pd catalyst for Cu electroless deposition, a two-step Sn sensitization and Pd activation was carried out. The oxide removal enhanced the adsorption of the Sn ions on the Ta substrate and led to well distributed Pd clusters through Pd activation. By measuring the resistivity of the film, the Sn sensitization time and the Pd activation time were optimized through changes in the incubation time, at which the sheet resistance abruptly decreased by the film formation via the coalescence of Cu grains. The resistivity of the Cu electroless film deposited using the optimized pretreatment conditions was 3.59 cm, which was further reduced to 2.7 cm through an annealing process.