Improvement of oxide removal rate in chemical mechanical polishing by forming oxygen vacancy in ceria abrasives via ultraviolet irradiation

Highlights: • An effect of UV-irradiation on nano-sized ceria slurry was investigated. • The UV-irradiation generates oxygen vacancy on the surface of the ceria particle. • The oxygen vacancy increases Ce³⁺ concentration at the surface of the ceria particle. • The removal rate was significantly correlated with the concentration of Ce³⁺. In highly integrated semiconductor chips, three dimensional (3D) stacked integrated circuits have increasingly required a high removal rate of the oxide film via chemical mechanical polishing (CMP). In this study, a new method is introduced to enhance the removal efficiency of ceria slurries, i.e., by irradiating ultraviolet (UV) light directly on the ceria slurries. When ceria abrasives were exposed to UV light, an oxygen vacancy leading to an increase in a concentration of Ce³⁺ occurred on the surface of ceria particles. At this time, the concentration of Ce³⁺ was related to the removal rate and it was possible to improve the removal efficiency of ceria slurry through UV irradiation. First of all, the ceria abrasives were characterized by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The formation of the oxygen vacancies on the ceria surface was estimated by using XRD, TEM, UV–visible spectroscopy, and X-ray photoelectron spectroscopy (XPS). By increasing the exposure time to UV light, the concentration of Ce³⁺ gradually increased and the growth of the removal rate with increasing Ce³⁺ concentration was confirmed. When UV light was irradiated to the ceria slurries for 50 h, the removal rate of the oxide film was increased by about 40 % compared to baseline slurry. Finally, a reliable correlation between the concentration of Ce³⁺ and the rate of oxide removal was identified.