Studies Of The Copper Electrocrystallization In The Presence Of PEG, Cl~- And SPS Additives

The copper interconnection instead of aluminium interconnection represents an important transition in semiconductor industry. Electrodeposition has more advantages over other methods in copper superfilling in the trench of chip with high depth-width ratio. One of the key factors of electrodeposition method is additives. The main additives employed in this method are polyethylene glycol (PEG), chloride ions, and bis-(3-soldiumsulfopropyl disulfide) (SPS) or 3-mercapto-1-propanesulfonate (MPSA). Electrocrystallization is the initial stage of electrodeposition, and it has crucial affections on the subsequent deposition process. Electrochemistry methods such as linear sweep voltage (LSV), cyclic voltammetry (CV), chronoamperometry (CA), Tafel plot and A.C. impedance (EIS) were employed to study the influence of PEG, Cl-, SPS on copper electrocrystallization on glassy carbon electrode (GCE) from acidic cupric sulphate electrolyte in this work.It was shown from LSV and CV experiment results that PEG and SPS could inhibit copper electrodeposition when they were added alone in electrolytes, however Cl- ion was an accelerator when it added alone. In the presence of SPS-Cl-, the potential peak value copper of cyclic voltammetry plots became more negative than that without any additive. This result indicated that Cl- ion could enhance the inhibition effect of PEG. However, the CV potential peak value of copper became more positive in the presence of SPS-Cl- compared to with Cl- ions alone, which indicated that SPS-Cl- had a stronger promoting function than Cl- ions. Moreover, the current value of copper peak increased sharply with SPS-Cl-, which indicted that SPS-Cl- could accelerate the electrodeposition rate greatly. When PEG-SPS-Cl- was added in electrolyte, the CV potential peak value became more positive, which indicated that PEG-SPS-Cl- could promote. Furthermore, the current peak value increased, which indicated that it could accelerate copper electrodeposition. Tafel plots and A.C. impedance experiment also showed that PEG, SPS, and PEG-Cl- had a promoting effect, while Cl-, SPS-Cl-, and PEG-SPS-Cl- had an inhibition function.By the result from CA experiment, it was concluded that the nuclei number density was increased with high PEG concentration, and Cu2+ diffusion coefficient did not changed observably at any PEG. Concentration; SPS did not have obvious effect on both nuclei number density and Cu2+ diffusion coefficient; the additive PEG-Cl- reduced Cu2+ diffusion coefficient sharply, and could increase nuclei number when their ratio was right; Cl-, SPS-Cl-, and PEG-SPS-Cl- could increase both the nuclei number density and Cu2+ diffusion coefficient.It was demonstrated that the electrocrystallization of copper on GCE conformed to 3-dimentional instantaneous nucleation mechanism when electrolyte was additive free. The addition of PEG, SPS, and PEG-Cl- did not change the nucleation mechanism. The nucleation mechanism had common characters under in the conditions of the addition of Cl- ions, SPS-Cl-, and PEG-SPS-Cl-. The nucleation mechanism was 3-D instantaneous during the early short time of electrocrystallization, and then it changed to 3-D progressive nucleation gradually in the late of electrocrystallization.