Frictional behavior and particle adhesion of abrasive particles during Cu CMP
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Frictional behavior and particle adhesion of abrasive particles during Cu CMP Yi-Koan Hong, Ja-Hyung Han, Jae-Hoon Song, Jin-Goo Park Division of Materials and Chemical Engineering, Hanyang University, Ansan, 426-791, Korea Abstract The friction behavior and adhesion of abrasive particles were experimentally investigated during Cu CMP process. The highest particle adhesion force was measured in alumina slurry without citric acid. However, the alumina slurry with addition of citric acid had the lowest particle adhesion due to the adsorption of citrate ions on the alumina surfaces. While citrate ions could be easily adsorbed on alumina particles, silica particle showed the least effect on adsorption in citric acid solutions. The magnitude of adsorptions of citrate ions on the particle surfaces had significant effect on frictional behavior as well as adhesion force. Higher particle adhesion force resulted in higher friction, particle contamination and scratches in CMP process. It indicates that the magnitudes of particle adhesions on wafer surfaces in slurries can be directly related to the frictional behavior during CMP process. Introduction Cu has been widely accepted as an interconnection material in deep sub-micron multi-level device application because of its benefits such as lower resistance (1.7 µΩ⋅cm), superior resistance to electro-migration and reducing RC time delay compared with aluminum (2.66 µΩ⋅cm) [1]. The Cu interconnection formation is only possible by a novel damascene Chemical Mechanical Planarization (CMP) process. During Cu CMP, wafer surfaces are to be exposed to at least two different slurry solutions. Although, the CMP process is well recognized as a powerful method for global planarization, there are several issues such as local erosion, dishing, scratches and abrasive particle contamination after CMP process. After polishing, the residue of abrasive particles and remained scratches on the wafer surfaces becomes a great challenge [2]. The adhesion force acts as an additional normal load and increases the friction force. The friction force could also be increased contamination on the surface [3-5]. Although we have studied the effect of pH on removal and adhesion of silica particles in slurry solutions [6, 7], no study has yet reported on the frictional behavior, particle adhesion of abrasive particles and scratches on the wafer surfaces during Cu CMP process. The purpose of this study is to investigate the frictional behavior and particle adhesion of abrasive particles during Cu CMP. Since the least adhesion force and the lowest friction between abrasive particles and wafer surfaces is required for reducing the particle contamination and the scratches on the surfaces, the adhesion force and frictional curves of silica and alumina particles on Cu surfaces is studied in Cu CMP slurry solutions. The magnitude of abrasive particle contamination and scratches on the Cu surfaces is observed after the polishing to relate with the adhesion force and friction behavior. Experimental Procedure The
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