The investigation of submicron copper electrochemical deposition bath chemistries and ageing process

Because of the lower electrical resistance of copper interconnects and void-free deposition capability in submicron features, copper electroplating has been widely accepted and implemented in chip manufacturing. Void-free deposition of copper can be achieved by proper control of the dilute organic additives added to the copper bath. Two organics additives, PEG and MPS, were studied in acidic copper sulfate solutions containing chloride, and with linear sweeping voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The experimental results from the electrochemical measurements were used to provide a better understanding of the interacting mechanism between the various species in the solution during the copper deposition process.; The interaction between Cu2+, Cl- and MPS was investigated, and a peak near 1.0 Hz in the impedance curve was observed when chloride ions were added into the electrolyte due to the reduction of Cu2+ by Cl- to form CuCl complex. In addition, complexation of MPS with Cu2+ and MPS with CuCl led to a peak at 0.1 Hz. Poly(ethylene) glycol (PEG) was also studied and a large inductive response was observed in the impedance Nyquist plot, indicating the adsorption of PEG-Cu and PEGCu-Cl at the copper surface. Reaction mechanisms related to the electrodeposition, complexation and adsorption reactions were proposed and implemented with an EIS model. The mechanisms involving the interactions between Cu2+, Cl-, MPS and PEG were discussed in this study as well.; A degradation study using a proprietary copper electrodeposition bath was performed and analyzed by the EIS technique. It was observed that the signal at 10 mHz of the real part and 100 mHz of the imaginary part of the impedance can effectively follow the condition of the bath compared to an EIS complete frequency measurement. Impedance data during bath ageing with a 10% bleed & feed of the copper bath demonstrated that control of the by-product level can increase the bath quality and prolong the bath life. If sufficient data on copper superfilling morphology can correlated with EIS measurements during ageing, it is possible to develop the EIS technique as an on-line indicator and improve the performance of copper superfilling in submicron vias and trenches.