The Effect of Additives in Post-Cu CMP Cleaning on Particle Adhesion and Removal

Abstract

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...

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Surface energy of the silanol-covered surfaces was found to be 7.5 mJ/m 2 . Effect of different cleaning solutions used in chemical mechanical polishing of wafers in the semiconductor industry on the adhesion force was evaluated with silica colloid probes [604]. Lowest adhesion was found in a solution with citric acid, benzotriazole and NH 4 OH which also exhibited the best cleaning performance.…”

The Effect of Frictional and Adhesion Forces Attributed to Slurry Particles on the Surface Quality of Polished Copper

“…2a. Little adsorption of citrates on silica was observed by FTIR 10 which led no change in zeta potentials as indicated in Fig. 2b.…”

“…9,10 Both spherical silica ͑Duke Scientific Co.͒ and alumina ͑␣ phase, Micron Co., Japan͒ particles with a diameter of 40 m were attached to a Si 3 N 4 tipless cantilever as shown in Fig. 1.…”

“…[6][7][8] We have studied the effect of the pH on the removal and adhesion of silica particles in slurry solutions. 9,10 No study has yet reported, however, on the effect of the adhesion force of slurry particles on the frictional behavior and the defects such as scratches and particles in the copper CMP process.The objective of this research was to see the relationship among friction force, removal rates, adhesion forces, and defects such as scratches and particle contaminations in copper polishing. Because low adhesion forces and the minimal friction between abrasive particles and wafer surfaces are required for reducing particle contamination and scratches on the surfaces, the adhesion forces and frictional curves of silica and alumina particles on copper surfaces were studied in copper CMP slurry solutions.…”

“…[6][7][8] We have studied the effect of the pH on the removal and adhesion of silica particles in slurry solutions. 9,10 No study has yet reported, however, on the effect of the adhesion force of slurry particles on the frictional behavior and the defects such as scratches and particles in the copper CMP process.…”