Metal ion contamination and removal on oxide surfaces and polyvinyl acetal brushes during the tungsten post-CMP cleaning process

Abstract

Metal contamination by titanium (Ti) and tungsten (W) ions on tetraethyl orthosilicate (TEOS) surfaces poses a critical challenge in post-chemical mechanical planarization (CMP) cleaning processes. This study investigates the effectiveness of chelating agents such as citric acid and EDTA in combination with mechanical scrubbing using a polyvinyl acetal (PVA) brush for removing Ti and W ions from TEOS surface. Dipping in chelating agents alone showed limited Ti removal, but when incorporated with PVA brush scrubbing at a -2 mm gap, Ti removal efficiency increased significantly from 30 % to 99 % at pH 4. Citric acid demonstrated superior performance over EDTA due to its ability to hydrolyze Si–O–Ti bonds and form stable Ti–citrate complexes. X-ray photoelectron spectroscopy (XPS) confirmed that Ti forms more stable and difficult-to-remove Si–O–Ti bonds on TEOS, the mechanical action of the brush effectively removed these complexes. Additionally, Ti ions were found to enhance silica particle loading onto the PVA brush through electrostatic interactions, as supported by zeta potential measurements and field emission scanning electron microscopy (FE-SEM). Chelating agents proved to be efficient in reducing particle loading in presence of Ti ions. These results highlight the synergistic role of chemical chelation and mechanical force in efficient Ti ion removal and emphasize the importance of chelating agent selection in optimizing post-CMP cleaning performance. © 2025