Synergistic Action Mechanism and Effect of Ammonium Dodecyl Sulfate and 1,2,4-triazole in Alkaline Slurry on Step Height Reduction for Cu CMP

Abstract

For the copper (Cu) chemical mechanical polishing (CMP) of integrated circuit Cu wiring, the removal rate (RR) in the concave is lower because of the protecting of inhibitor in the slurry, and the step height is reduced by the high RR different between convex and concave, thus realizing planarization. With the decrease of technology node and the shortcomings of traditional inhibitors, new environmental inhibitors have become the focus of research. The synergistic inhibiting effect of ammonium dodecyl sulfate (ADS) and 1,2,4-triazole (TAZ) in the H2O2 based weakly alkaline slurry during the Cu film CMP process was studied. Electrochemistry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements were used to analyze the reaction mechanism between Cu and mixed inhibitors. It was found that ADS was absorbed on the Cu surface via electrostatic interactions, by which a thin porous film with small openings was formed. Then chemisorbed TAZ molecules effectively filled up the small openings, and a compact passivating film was formed to protect the Cu surface. Based on the background slurry, incorporation of 0.1 wt% ADS + 0.003 wt% TAZ (bulk) and 0.1 wt% ADS + 0.005 wt% TAZ (soft landing) at pH = 8.5 in this slurry, lower step height was achieved dropping from the initial 3800 Å to 654 Å, and the slurry can be stable for at least three days. Such results indicate that mixed inhibitors may become a trend of industrial application, and such research has certain guiding significance for industrial production.