Copper electroless deposition ͑ELD͒ was investigated for applications that create a seed layer for Cu electrodeposition. On Pd catalysts formed on the Ta substrates through Sn sensitization-Pd activation, continuous Cu seed layer of 40 nm was electrolessly deposited in a diluted electrolyte. Dilution of the electrolyte enabled the film to make a thin and conformal layer without oxygen incorporation, by which the ELD Cu seed had properties comparable to the physical vapor deposited seed layer regarding surface roughness and resistivity, even after subsequent Cu electrodeposition, and had superior step coverage. Defect-free bottom-up filling by electrodeposition was achieved on these ELD seed layers.

To enhance the compatibility of electrodeposition with the chemical mechanical polishing process, we attempted to prevent step formation on active areas. In the absence of benzotriazole ͑BTA͒, the step heights increased with the decrease in the pattern width and the increase in the pattern density due to the locally condensed accelerator. However, the addition of BTA significantly suppressed the deposition kinetic through the deactivation of the accelerator. The two-step electrodeposition with modulated accelerator and BTA concentrations was found to be effective in the retardation of bump formation and the prevention of bumps from growing without an impact on the superfilling.

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