[ 단 신] 한국재료학회지 DOI: 10.3740/MRSK.2009.19.3.174 Kor. J. Mater. Res. Vol. 19, No. 3 (2009) 174 Corresponding author E-Mail : ymsung@korea.ac.kr (Y.-M. Sung). Effect of Post-CMP Cleaning On Electrochemical Characteristics of Cu and Ti in Patterned Wafer Kyung-Min Noh, Eun-Kyung Kim*, Yong-Keun Lee* and Yun-Mo Sung † Department of Materials Science and Engineering, Korea University, Seoul 136-713, Korea *Department of Nano/IT Engineering, Seoul National University of Technology, Seoul 139-743, Korea (Received December 13, 2008 : Received in reviced form January 29, 2008 : Accepted March 4, 2009) Abstract The effects of post-CMP cleaning on the chemical and galvanic corrosion of copper (Cu) and titanium (Ti) were studied in patterned silicon (Si) wafers. First, variation of the corrosion rate was investigated as a function of the concentration of citric acid that was included in both the CMP slurry and the post-CMP solution. The open circuit potential (OCP) of Cu decreased as the citric acid concentration increased. In contrast with Cu, the OCP of titanium (Ti) increased as this concentration increased. The gap in the OCP between Cu and Ti increased as citric acid concentration increased, which increased the galvanic corrosion rate between Cu and Ti. The corrosion rates of Cu showed a linear relationship with the concentrations of citric acid. Second, the effect of Triton X-100 , a nonionic surfactant, in a post-CMP solution on the electrochemical characteristics of the specimens was also investigated. The OCP of Cu decreased as the surfactant concentration increased. In contrast with Cu, the OCP of Ti increased greatly as this concentration increased. Given that Triton X-100 changes its micelle structure according to its concentration in the solution, the corrosion rate of each concentration was tested. Key words post-CMP cleaning , organic acid surfactant chemical corrosion galvanic corrosion. 1. Introduction Chemical mechanical polishing (CMP) has received great interests since it can induce the local and global planarization of copper (Cu) patterns in the integrated circuits (IC). 1-3) Cu as an interconnecting metal can replace aluminum (Al) in IC fabrication since Cu has low electrical resistivity, showing high immunity to electromigration compared to Al. 1-3) However, pure Cu can not sustain its structure during the conventional etching process. CMP is the planarization method using abrasive particles instead of conventional acid solution. Therefore, the Cu side walls are safe from the chemical attack during CMP. On the other hand, CMP slurry contains some chemically active slurries and abrasive particles, and thus there exist leftover particles on the wafer after CMP. Therefore, the post-CMP cleaning has to be introduced in order to remove residues derived from the slurry. Extensive studies have been carried out to enhance post-CMP cleaning ability. 4-6) However, there have been few studies on corrosion occurring during post-CMP cleaning. Since the corrosion can deteriorate device yields, the protection of Cu against the corrosion is a critical issue in post-CMP cleaning. In general, chemical and galvanic corrosion is reported in post-CMP cleaning. Chemical corrosion occurs due to an organic acid included in cleaning solution, while galvanic corrosion occurs due to the electrochemical potential difference building between Cu used as an interconnecting metal and Tantalum (Ta) or Ti used as a barrier metal in IC. 7) The objective of this study is to understand the effect of two major constituents in post- CMP cleaning solution on the corrosion reactions of wafer. In order to investigate the effect of the organic acid contained in cleaning solution on the wafer, the respective corrosion rate of Cu, Ti and the patterned wafer in the citric acid solution with various concentrations was measured using an electrochemical analyzer. The effect of Triton X-100 ® well known as an excellent surfactant for the post-CMP cleaning solution 8) on the corrosion rates was also investigated. Based on the experimental results, the Cu corrosion mechanism of wafer during post-CMP cleaning process was discussed in detail.