Study of direct Cu electrodeposition on ultra-thin Mo for copper interconnect.

Direct electrodeposition (ECD) process of copper film on ultra-thin molybdenum film is investigated in both copper sulfate - sulfuric acid (CuSO 4 - H 2 SO 4 ) acidic bath and copper sulfate - ethylenediamine (CuSO 4 - En) neutral bath (pH = 7.5). The neutral electrolyte containing 0.03 M CuSO 4 and 0.06 M En was chosen to avoid excessive corrosion of Mo and introduction of other ions. The complexing effect of En affects the electrodeposition process of Cu on Mo. Potentiodynamic polarization curves and scanning electron microscopic characterization show that Cu can be electroplated in CuSO 4 - En bath with lower corrosion rate, greater nucleation density and shorter fully-covering time than that in CuSO 4 - H 2 SO 4 bath. The fitting results of current-time transients using Scharifker and Hill's model support the instantaneous nucleation and growth of Cu on Mo in both CuSO 4 - H 2 SO 4 bath and CuSO 4 - En bath (with background electrolyte) at the initial stage of electrodeposition. By using an optimized two-step plating process (at the current density of 8 mA/cm 2 in the first step for a short time and 4 mA/cm 2 in the second step), the resistivity of direct ECD Cu on Mo was almost the same to that of ECD Cu on Cu/Mo in the same plating bath. [ABSTRACT FROM AUTHOR]