Citric Acid as a Complexing Agent in Chemical Mechanical Polishing Slurries for Cobalt Films for Interconnect Applications. (10th August 2017)

• Record Type: Journal Article
• Authors: Popuri, R.; Sagi, K. V.; Alety, S. R.; Peethala, B. C.; Amanapu, H.; Patlolla, R.; Babu, S. V.
• Is Part Of: ECS journal of solid state science and technology. Volume 6:Number 9(2017)
• Page Start: P594
• Page End: P602
• Publication Date: 2017-08-10
• Subjects: citric acid -- CMP -- Co interconnects -- corrosion -- galvanic corrosion; Solid state chemistry -- Periodicals; Electronics -- Materials -- Periodicals; Electrochemistry -- Periodicals; 541.0421
• DOI: 10.1149/2.0111709jss
• Languages: English
• ISSNs: 2162-8777

Abstract

Abstract : A colloidal silica-based slurry (3–10 wt%) containing H2 O2 (1 wt%) and citric acid (50 mM) was found to polish chemical vapor-deposited (CVD) cobalt (Co) films with removal rates (RRs) of ∼180–500 nm/min and a dissolution rate (DR) of ∼0 nm/min at pH 8 along with an RMS roughness of ∼0.5 nm and a corrosion current of ∼50 μA/cm 2 . Our results suggest that, in the presence of H2 O2, the Co film surface was covered with a passive film of CoO in acidic conditions and Co3 O4 in alkaline conditions. However, in the presence of H2 O2 and citric acid in acidic conditions, formation of the soluble complex [Co(C6 H5 O7 )2 ] 3− from abraded Co enhanced the RRs significantly. The roles of H2 O2, citric acid, and silica abrasives as well as the pH on the Co material removal process are discussed and a removal mechanism is proposed. Two inhibitors namely, 1, 2, 4- Triazole (TAZ) and Benzotriazole (BTA), were tested in the presence of 50 mM citric acid at pH 8 but were found to be ineffective even at concentrations of 100 mM in reducing the ΔEcorr of Co-Ti couple to minimize galvanic corrosion that is essential when the Co/Ti structure is polished after the removal of bulk of Co and requires further study.