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http://dx.doi.org/10.9725/kts.2018.34.6.226

Effect of Citric Acid in Cu Chemical Mechanical Planarization Slurry on Frictional Characteristics and Step Height Reduction of Cu Pattern  

Lee, Hyunseop (School of Mechanical Engineering, Tongmyong University)
Publication Information
Tribology and Lubricants / v.34, no.6, 2018 , pp. 226-234 More about this Journal
Abstract
Copper chemical mechanical planarization (CMP) has become a key process in integrated circuit (IC) technology. The results of copper CMP depend not only on the mechanical abrasion, but also on the slurry chemistry. The slurry used for Cu CMP is known to have greater chemical reactivity than mechanical material removal. The Cu CMP slurry is composed of abrasive particles, an oxidizing agent, a complexing agent, and a corrosion inhibitor. Citric acid can be used as the complexing agent in Cu CMP slurries, and is widely used for post-CMP cleaning. Although many studies have investigated the effect of citric acid on Cu CMP, no studies have yet been conducted on the interfacial friction characteristics and step height reduction in CMP patterns. In this study, the effect of citric acid on the friction characteristics and step height reduction in a copper wafer with varying pattern densities during CMP are investigated. The prepared slurry consists of citric acid ($C_6H_8O_7$), hydrogen peroxide ($H_2O_2$), and colloidal silica. The friction force is found to depend on the concentration of citric acid in the copper CMP slurry. The step heights of the patterns decrease rapidly with decreasing citric acid concentration in the copper CMP slurry. The step height of the copper pattern decreases more slowly in high-density regions than in low-density regions.
Keywords
chemical mechanical planarization (CMP); copper; citric acid; step height reduction; friction force;
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