Effect of nonionic surfactants on the stability of alumina slurry for Cu CMP

In this work, the effect of the physical characteristics of alumina slurry on the variation in the pH value and the effect of nonionic surfactants on the alumina slurry used for copper chemical mechanical planarization (CMP) slurry were investigated. After the pH value of the slurry containing alumina abrasive was changed by adding various amounts of HNO3 or KOH, the differences in the settling rate, particle size, and ζ-potential were estimated. Better settling rates were shown in the slurries containing alumina abrasive at near pH 1. The particle size was smaller within the pH range from 2 to 4; on the other hand, it increased at pH values above 10. A higher ζ-potential was shown at around pH 2 in the alumina slurry, and the point of zero charge (PZC) was found to be about pH 9–10. A nonionic surfactant was added to the slurry containing 5 wt.% alumina abrasive to evaluate its effect on the slurry practically. The abrasive size was increased to a lesser extent when the amount of surfactant was increased in the slurry containing P-4 as an abrasive; on the other hand, the abrasive size was decresed when the amount of surfactant was decreased in the slurry containing AES-12. The variation in the ζ-potential showed no change when the surfactant was added; however, the values of the ζ-potential were between 35 and 50 mV. The proper amount of surfactant was 0.1–1.0 wt.% in the slurry containing P-4 and 0.5–1.0 wt.% in the slurry containing AES-12. Excellent dispersion stabilization was obtained through the addition of a nonionic surfactant to the alumina slurry.