Effect of complexing agent on ceria particle removal in post-STI CMP cleaning process

Abstract

Ceria (CeO2) abrasive is extensively used in the chemical mechanical polishing process (CMP) for shallow trench isolation (STI) owing to its capability to form Ce-O-Si bonds with the silicon dioxide (SiO2) dielectric layer. However, although this interaction substantially improves its CMP performance, it increases the difficulty of removing ceria particles and exacerbates the challenge of post-CMP cleaning. In this study, the cleaning effect of three complexing agents on ceria particles on the polished silicon dioxide surface at pH 11 was investigated: glycine (Gly), ethylenediamine tetraacetic acid (EDTA), and 1.2-bis-(3-aminopropylamino) ethylenediamine (TAD). The cleaning efficacy of the complexing agents on ceria particles was evaluated using zeta potential, contact angle, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Then the desorption mechanism of ceria particles was then explored by UV–visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS) and molecular dynamics simulation. The results of multiple measurement results indicate that the three complexing agents have obvious removal effects on ceria particles, and 0.15 wt% EDTA at pH 11 can remove 99% of ceria particles from the SiO2 substrate. The cleaning efficacy of carboxyl functional groups is superior and increases with the growth of the number of functional groups. The removal mechanism of ceria abrasives by complexing agent was proposed. Through the undercutting effect of carboxyl functional groups, EDTA can break the Ce-O-Si chemical connection formed during the CMP process and complex Ce3+ ions to prevent particle redeposition. Additionally, it accelerates particle desorption by enhancing the electrostatic repulsion force between the CeO2 and SiO2 substrate.