Quality of electroplated copper films produced using different acid electrolytes

Copper films were electroplated on either W/TiN/Si(100) or Cu/TaN/Si(100) surfaces with copper electrolytes containing different types of acids, namely, H2SO4, HCl, HNO3, and HF. The properties of these copper films were then characterized in terms of their microstructure and electrical properties. Dense copper films were obtained from H2SO4 and HNO3-based electrolytes, which produced films consisting of small equiaxed grains with average grain sizes of 0.25 μm whereas larger grains of 0.5 μm were obtained from a HF-based electrolyte. However, a very rough Cu film with copper chloride residues was obtained from the HCl-based electrolyte. For W seeded substrates, strong 〈111〉 oriented copper films were produced while both 〈111〉 and 〈220〉 were observed as the preferred orientations of the film on Cu seeded substrates. Both H2SO4- and HNO3-based electrolytes were able to produce films with bulk resistivity as low as 1.82 μΩ cm on Cu seeded substrates. For W seed, the bulk resistivity varied between 1.92 and 2.31 μΩ cm. The HF-based electrolyte produced the highest bulk resistivity of 2.23 μΩ cm. In terms of the deposition rate, both HNO3 and HF achieved higher deposition rates than H2SO4.