Synergistic effect of 1,2,4-triazole and phytic acid as inhibitors on copper film CMP for ruthenium - based copper interconnected and the surface action mechanism analysis

Abstract

Ruthenium (Ru) has been selected as the next-generation barrier material for copper (Cu) interconnects due to its excellent electrical properties, high breakdown voltage, low leakage current, low resistivity and while improving the electromigration resistance of Cu interconnects. However, during the one-step chemical mechanical polishing (CMP) of Cu film, high removal rate of Cu and close to zero removal rate of Ru are required, which brings great difficulty to realize Cu film planarization. Inhibitors play a crucial role in controlling Cu and Ru removal rate and inhibiting the surface corrosion during the Cu films CMP. In this study, phytic acid as a green corrosion inhibitor was introduced in the Cu slurry and compared with 1,2,4-triazole (TAZ) as traditional inhibitor. From removal rate, static etch rate, surface quality and inhibition efficiency, it revealed that the corrosion inhibition of Cu and Ru by phytic acid was stronger than that of TAZ, while the obtained surface quality was weaker than that of TAZ. Through the analysis of UV–Visble spectroscopy and adsorption isotherm calculation, it revealed that the physical-chemical adsorption of both, which favored physical adsorption, existed on the Cu surface caused by weak van der Waals's forces. Therefore, in order to obtain dual physical-chemical adsorption and improve the passivation performance and inhibition efficiency, the mixture of both was adopted. The inhibition efficiency of Cu and Ru was increased to 53.7% and 66.4% compared with phytic acid alone, respectively. The static etch rate of Cu was dropped by 200 Å/min. The surface quality was significantly improved, and the roughness dropped to 1.64 nm. Through X-ray photoelectron spectroscopy analysis, it was showed that Cu-TAZ and Cu-phytic acid generated by the mixed inhibitor and Cu formed a double-layer physical-chemical adsorption film on the surface, which increased the coverage of adsorption sites and improved the inhibition efficiency. Finally, the stability test shows that the slurry can be stable for at least 7 days, which has theoretical guiding significance for the research and development of low-node Cu film slurry.