Displacement Activation of Tantalum Diffusion Barrier Layer for Electroless Copper Deposition

Activation of Ta/SiO 2 /Si substrates using a PdCl 2 buffered oxide etch (BOE)/HNO 3 displacement solution and electroless Cu deposition have been investigated in this paper. Surface morphologies and distribution of Pd nuclei on the Ta layer were strongly dependent on the ratio of BOE/HNO 3 during activation as confirmed by scanning electron microscopy and atomic force microscopy surface observation. Using an activation solution with a ratio of BOE/HNO 3 of 3:2, electrolessly deposited Cu films with good surface coverage and low electrical resistivity were obtained. The surface coverage of electroless Cu grains on the Ta layer degraded with longer activation time and other activation solutions due to the Pd removal resulting from lateral under-substrate cut during activation, No preferred orientation of the electrolessly deposited Cu films was found from X-ray diffraction analysis. Good selectivity of electroless Cu deposition contributed to the preferred nucleation of Cu on Pd nuclei which deposited only on the Ta layer rather than on SiO 2 during activation.

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