Effect of Chemical Composition on Adhesion of Directly Electrodeposited Copper Film on TiN

Copper citrate (Cu-Cit) baths are effective mediums for seedless electrochemical deposition (ECD) of copper with strong adhesion property on TIN. The chemical equilibrium diagrams of chemical fraction vs pH were used to explain the cause of good adhesion of copper deposits on TiN. The kind and the amount of Cu-Cit complexes in a bath were determined according to pH and the concentration ratio of copper and citrate, [Cu(2+)]/[Cit(-3)]. It was found that CuCit(-)among various Cu-Cit complexes participated in adherent copper reduction on TiN. When more Cu2(Cit)OH than CuCit(-) was contained in a bath, the reduction of CuCit(-) was hindered and the adhesion property of copper on TiN became degraded. Resultant ECD copper films on TiN, which were deposited in baths of [Cu(2+)]/[Cit(3-)] = 1 in the existence of CuCit(-) passed the ASTM D 3359 adhesion test showing strong adhesion.