The adhesion force of silica particles to Cu films and the role of additives on adhesion and removal of particles have been theoretically and experimentally investigated in citric-acid-based post-Cu chemical mechanical planarization ͑CMP͒ cleaning solutions. The zeta potential of silica and Cu slightly increases when citric acid is added due to the adsorption of citrates. Citric acid is adsorbed on silica and Cu surfaces, resulting in more negative charges on these surfaces. The adhesion force of silica particles on Cu decreases as the citric acid concentration increases due to more repulsive electrostatic interaction between surfaces. The addition of benzotriazole in the cleaning solution initially decreases adhesion then increases it at high concentrations due to the change in zeta potentials. The addition of tetramethylammonium hydroxide to citric acid increases the particle adhesion force. However, the addition of NH 4 OH results in the lowest adhesion forces. The highest particle removal efficiency is observed when using cleaning solutions that yield the lowest adhesion force.Cu has been widely accepted as an interconnection material in deep submicrometer multilevel device applications because of its lower resistance, superior resistance to electromigration, and the reduction of resistance-capacitance ͑RC͒ time delay compared with aluminum. 1 The Cu interconnection is made possible by novel damascene chemical mechanical planarization ͑CMP͒. During Cu CMP, wafer surfaces are exposed to at least two different slurry solutions. After polishing, the removal of abrasive particles and trace metals left on the wafer surfaces becomes as important as the polishing process itself in order to maintain device yield. 2 Since the CMP process leaves these contaminants on the wafer surface, post-Cu CMP cleaning is a necessary step to eliminate or reduce them before the next process step. Earlier studies reported on the effect of pH on removal and adhesion of silica particles in slurry solutions, 3 however, very little has been reported on the effects of additives in cleaning solutions on removal and adhesion of particles of interest to post-Cu CMP cleaning.The objective of this study is to investigate the effects of additives in citric acid-based Cu cleaning solutions on the adhesion and removal of silica particles on Cu surfaces. Since the smallest possible adhesion force between abrasive particles and wafer surfaces is highly desirable for reducing particulate contamination, the adhesion force of silica particles on Cu was studied in post-Cu CMP cleaning solutions with different additives. The interaction forces between particles and wafer surfaces during post-Cu CMP cleaning were calculated based on the Derjaguin-Landau-Verwey-Overbeek ͑DLVO͒ theory. 4 The adhesion forces between the particles and surfaces were also experimentally measured using an atomic force microscopy ͑AFM͒. The level of particulate contamination on Cu surfaces was measured by field emission scanning electron microscopy ͑FESEM͒ before and after clean...

The removal and etching behaviors of Cu were evaluated in citric acid based slurries as functions of slurry pH and H 2 O 2 concentration during Cu chemical mechanical planarization ͑CMP͒. In an acidic slurry ͑pH 4͒, the dissolution reaction of Cu was more dominant than the passivation reaction. The static and dynamic etching rates reached their highest values at 10 vol % H 2 O 2 . The polishing rate, however, was linearly increased as a function of peroxide concentration. As the slurry pH increased to 6, the static and dynamic etching rates drastically decreased with increasing H 2 O 2 concentrations due to the formation of thick Cu oxide as a passivation layer. The removal rate reached a maxima in slurry at 7 vol % of H 2 O 2 then started to decrease. The removal rate of Cu was determined by both the chemical dissolution and mechanical abrasion of the passivation layer which were strongly related to slurry pH and H 2 O 2 concentration. In the slurry of low concentration of H 2 O 2 and low pH, the passivation layer was too thin to prevent the chemical dissolution from occurring. However, the increase of pH and H 2 O 2 concentrations grew a thicker oxide on Cu which made the removal rates dependent on the mechanical reaction.

The recycle of Chemical Mechanical Planarization (CMP) slurries has been actively considered in the industry to reduce the cost-of-consumables (COC) because of the sharp increase of the consumption of slurry in CMP. The main purpose of this study was to characterize the used oxide slurry physically and chemically to establish a means of reprocessing it. The characteristics of slurry were determined according to pH, solid content, specific gravity and particle size. These characteristics were affected and varied by deionized water inflow during the CMP process. The tetraethylorthosilicate removal rate was strongly dependent on the solid content and pH of slurry solutions. The solid content played a major role in determining the removal rates. Regardless of the number of polishings, the removal rate was almost the same at a solid content when it was modified by adding new slurry. The mean particle size of slurries did not change at all even in the five times recycled slurry. Even though there was a slight increase in the fraction of large particles in the range of 20 to 120 µm in the recycled slurries, no changes in thickness uniformity or defect density were observed when polishing was performed in either new or recycled slurry.

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