Interaction study of copper ions and polyvinyl acetal (PVA) brush during copper post-CMP cleaning: Experimental and density functional theory study

Abstract

Polyvinyl acetal (PVA) brush cleaning, used for over three decades, has undergone continuous improvements to achieve the desired defect-free surfaces. Despite its widespread use, challenges related to contaminant adsorption and desorption can significantly impact cleaning performance. This study explored the interaction between PVA brush and copper (Cu) ions, a prevalent contaminant during Cu post-chemical mechanical polishing (post-CMP) cleaning. PVA brush contamination with various Cu species at various pH conditions was analyzed by contaminating brush nodules by dipping and scrubbing methods. Brush microscopy images revealed severe brush contamination at neutral pH. The active sites and the possible chemical interactions were identified via various spectroscopic techniques. The interaction between each functional group and Cu ions species at various pH values was investigated via pH and conductometric titrations. Zeta potential analysis revealed electrostatic attraction at neutral pH between positively charged Cu species and negatively charged PVA brush. Severe contamination at neutral pH was also attributed to potential chemical interactions between Cu species and the hydroxyl groups in the PVA brush. Density functional theory (DFT) calculations provided further evidence of a coordination bond between copper ions and the PVA brush, confirming possible chemical interaction. The low Cu removal percentage (53.7%) suggests the need for the development of cleaning solutions for the prevention of Cu loading under neutral conditions.