Electrolyte composition and galvanic corrosion for ruthenium/copper electrochemical mechanical polishing
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Rare Met. DOI 10.1007/s12598-014-0286-3
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Electrolyte composition and galvanic corrosion for ruthenium/ copper electrochemical mechanical polishing Yan-Fei Bian*, Wen-Jie Zhai, Yuan-Yuan Cheng, Bao-Quan Zhu
Received: 19 June 2013 / Revised: 6 September 2013 / Accepted: 16 April 2014 Ó The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2014
Abstract Electrochemical mechanical polishing (ECMP) is a new and highly promising technology. A specific challenge for integrating Ru as barrier in Cu interconnect structures is the galvanic corrosion of Cu that occurs during ECMP. To mitigate the problem, the benzotriazole (BTA) and ascorbic acid (AA) were chosen as selective anodic and cathodic inhibitors for Cu and Ru, respectively. The optimization of electrolytes at different pHs including BTA, hydroxyethylidenediphosphoric acid (HEDP), and AA were investigated using electrochemical methods. The Ru/Cu removal rate and the planarization efficiency during Ru/Cu ECMP can be approximated using electrochemical measurements of the removal rate, with and without surface abrasion. Chemical systems that exhibit a 1:1 selectivity between the barrier layer and copper would be ideal for the barrier removal step of ECMP. Optimized slurry consists of 20.0 wt% HEDP, 0.5 wt% BTA, and 0.3 wt% AA at pH 2.2. Using the optimized slurry, the selectivity of Ru to Cu is near 1. Electrochemical measurements of open circuit potentials, potentiodynamic polarization, and impedance spectroscopy were performed to investigate the galvanic corrosion between ruthenium and copper.
Y.-F. Bian*, W.-J. Zhai, B.-Q. Zhu School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China e-mail: [email protected] Y.-Y. Cheng School of Civil Engineering, Harbin Institute of Technology, Harbin 150001, China
Keywords Electrochemical mechanical polishing; Electrolyte composition; Galvanic corrosion; Benzotriazole; Ascorbic acid
1 Introduction Integrating copper with low dielectric constant (low-k) materials is critical to the development of next-generation ultra-large scale integrated circuit (ULSI) technologies. Chemical mechanical polishing (CMP) technology becomes a widely used technique for planarization removal. To reduce device resistance and capacitance (RC), copper will be coupled with low-k interlayer dielectric (ILD) materials [1–3] in dual-damascene architectures, thereby reducing RC time constant delays in interconnect devices. However, polishing structures comprising low-k dielectrics poses a great challenge [4–8]. Since low-k dielectrics are both soft and compliant compared with the traditional SiO2 dielectric, undesired surface damaged can be caused by excessive pressure during CMP. To overcome the inherent defects of CMP, electrochemical mechanical polishing (ECMP) technology was introduced and got more and more attentions. Electrochemical mechanical polishing (ECMP) is a compound technique that combines the mechanical action of a grinding process with an electroc
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