High purity nano abrasives for chemical mechanical planarization application

With the scaling of device feature size, chemical mechanical planarization (CMP) becomes an essential process that uses an abrasive corrosive slurry to physically grind flat and chemically remove the microscopic topographic features. Nano size abrasive in slurry plays an important role in CMP especially its mechanical effect. In this paper, high purity colloidal silica with the particle diameter from 5 nm to 130 nm was synthesized from sodium silicate. The sodium concentration in the colloidal silica with 30% solid content was less than 8 ppm. The effect of abrasive on the polishing performance of oxide and pattern copper had been characterized through process experiments. Results showed that high remove rate and good surface quality were obtained by the slurry with colloidal silica as abrasive. In the slurry for shallow trench isolation (STI), ceria is the mainstream abrasive. However, new material is required to replace ceria because of the disadvantage of ceria such as high cost and many scratch defects. In this paper, particles with silica core and ceria shell were fabricated. From the TEM results, it can be seen that the silica was wrap up homogeneously by ceria. The abrasive with core-shell structure combines the advantage of silica and ceria.