Effect of the additives on controlling ceria-brush chemical bonding during post-CMP cleaning

Abstract

PVA_b (polyvinyl acetal brush) scrubbing is a low cost with enhanced performance process in post-CMP cleaning. Nonetheless, the PVA_b can be a source of defects due to the residual CMP contaminants entrapment. Therefore, the chemical interaction between brush and residual ceria particles was investigated to fully uncover the mechanism behind ceria loading to brush during scrubbing. The study revealed that a high percentage of Ce³⁺ on ceria surface amplifies the chemical interaction between brush and ceria, leading to higher ceria accumulation on PVA_b as compared to silica abrasives. Different additives were evaluated to overcome this interaction. The presence of proline failed to inhibit the activity of Ce³⁺ which resulted in a significantly high particle loading due to the combined effect of chemical and electrostatic interaction between ceria and brush. In contrast to proline, the addition of lysine reduced the possibility of chemical interaction between ceria surface and PVA_b, significantly reducing the particle loading due to the presence of electrostatic attractions alone. Remarkably, additives such as PVA_s (polyvinyl alcohol solution) and citric acid proved highly effective in controlling Ce³⁺ and the surface charges, thereby limiting both chemical and electrostatic interaction. This led to a significant reduction in ceria loading to PVA_b. These findings highlight the importance of understanding ceria-brush interactions to control brush contamination and the subsequent cross-contamination issues in post CMP cleaning. This deeper understanding into additive efficacy opens new possibilities for optimizing CMP cleaning efficiency and reliability.