Studies On The Influence Of Mps, PEG And Cl~ˉ Additives On Copper Electrodeposition

Copper is a preferred material for the fabrication of interconnect structures in integrated circuits because of its lower resistivity and superior electromigration properties than aluminium. Electrochemical deposition is a simple technique to realize copper superfilling in the micron- or submicron-size trench of chip due to the presence of organic and inorganic additives in the electrolyte. The most commonly additives employed are 3-mercapto-1-propanesulfonate sodium salt (MPS) or bis-(3-soldiumsulfopropyl disulfide) (SPS), polyethylene glycol (PEG) and chloride ions (Cl~-). In this work, the influence of MPS, PEG, Cl~- and their synergistic effect on the copper electrodeposition on a glass carbon electrode (GCE) from CuSO4-H2SO4 electrolytes were studied by using cyclic voltammetry (CV), linear sweep voltammetry(LSV), chronoamperometry(CA), AC impedance and scanning electron microscopy (SEM) techniques.The experiment results of CV, LSV and EIS indicated that MPS inhibited copper electrodeposition. And the inhibition effect became stronger with the increase of MPS concentration. In the presence of MPS-Cl~-, the cathodic potential peak of CV curves shifted to positive direction. The LSV curves positive shifted and the charge transfer resistance became smaller compared to with Cl~- ions alone. These results indicated that MPS-Cl~- had a significant acceleration on copper electrodeposition and the acceleration was greater than the Cl~- ions. Moreover, the accelerated effect of MPS-Cl~- became stronger with the increase of MPS concentration. MPS-PEG had a stronger inhibition than either MPS or PEG. The inhibition effect of MPS-PEG became stronger with the increase of MPS concentration. The copper electrodeposition was accelerated in the presence of MPS-PEG-Cl~-. And the acceleration effect of MPS-PEG-Cl~- became stronger with the increase of MPS concentration.The experiment results of CA and SEM indicated that MPS accelerated the electrocrystallization process of copper and the nuclear number density was increased with the increase of MPS concentration. MPS-Cl~- could increase both the nuclear number density and Cu2+ diffusion coefficient. However, the nuclear number density decreased with the increase of the concentration of MPS in electrolytes with MPS-PEG. The nuclear number density increased with the increase of MPS concentration in electrolytes with MPS-PEG-Cl~-. The diffusion coefficient of Cu2+ did not changed observably in solution with MPS and MPS-PEG.The experiment results of CA demonstrated that copper electrocrystallization from the 0.05 M CuSO4-0.5 M H2SO4 electrolytes either with or without MPS followed instantaneous nucleation with three-dimensional growth. The addition of MPS-PEG did not change the nucleation mechanism, and still followed the instantaneous nucleation with three-dimensional growth. In the presence of MPS-Cl~- or MPS-PEG-Cl~-, the nucleation mechanism was 3-dimentional instantaneous nucleation during the early short time of electrocrystallization, and then it changed to 3-D progressive nucleation gradually in the late stage of electrocrystallization. The experiment results of SEM demonstrated that copper electrocrystallization from the 0.05 M CuSO4-0.5 M H2SO4 electrolytes with MPS or MPS-Cl~- followed 3-D instantaneous nucleation.EIS results showed the inhibition effect of MPS or MPS-PEG on copper electrodeposition was reduced with the increase of polarization potential. Whereas the promoting function of MPS-Cl~- or MPS-PEG-Cl~- on copper electrodeposition was enhanced with the increase of polarization potential. The reaction resistance of copper in electrolytes with any additive packages decreased with the increase of polarization potential.