Synergic effect of benzotriazole and chloride ion on Cu passivation in a phosphate electrochemical mechanical planarization electrolyte

In this study, the effect of chloride ion (Cl−) in phosphate electrolytes of pH 2 containing benzotriazole (BTAH) developed for use in electrochemical mechanical planarization (ECMP) was investigated at various anodic potentials. According to D.C. and A.C. electrochemical analyses, the inhibition effect of the BTAH passive film formed in phosphate electrolyte containing both BTAH and Cl− was superior to that formed in phosphate electrolytes containing BTAH alone, even at high anodic potential. The effective window for BTAH passivation reached ∼1.3 V vs. Ag/AgCl nearly three times that of the ∼0.5 V vs. Ag/AgCl recorded for electrolyte containing BTAH alone. According to analyses conducted by atomic force microscopy (AFM) and secondary ion mass spectrometer (SIMS), the thickness of the passive film grown from the BTAH-only electrolyte at 0.3 V vs. Ag/AgCl was ∼52 ± 7 nm and ∼55 nm, respectively. As for the passive film grown from the BTAH and Cl− electrolyte, the thickness increased to ∼104 ± 18 nm and ∼106 nm, respectively. The mechanism for the enhanced inhibition capability was that the passive film grown from the BTAH and Cl− electrolyte was thicker compared to that formed from the BTAH-only electrolyte due to the incorporation of Cl− into the BTAH passive film. The ECMP polishing results also demonstrated an obvious step height reduction of ∼1000 nm in a patterned structure for only 60 s polishing at a high potential of 1.0 V vs. Ag/AgCl under a low downward pressure (∼0.5 psi). Subsequently, this study proposes that the control of Cl− in a phosphate ECMP electrolyte of pH 2 may be useful in enhancing the passivation capability of BTAH passive film, thus expanding the operating potential window.

Research highlights▶ The addition of Cl− in phosphate electrolytes containing BTAH only can increase the thickness of BTAH passive film. ▶ The enhanced inhibition capability of the Cl−-containing BTAH passive film was found, especially at high anodic potential. ▶ The control of Cl− concentration in the phosphate electrolyte can expand the operating potential window during ECMP process.