Environmentally friendly buff cleaning of ceria nanoparticles using bubbles in gas-dissolved water

Abstract

Buff cleaning serves as a crucial preparatory step following chemical mechanical polishing, aimed at removing bulk particles from wafer surfaces present in slurries. Most cleaning solutions comprise a variety of complex chemical compounds. Conventional cleaning solutions typically consist of complex chemical compounds, including toxic or carcinogenic substances, which hinder wastewater recycling and exacerbate environmental impacts. Here, an eco-friendly buff-cleaning solution, oversaturated gas-dissolved water, is proposed for effective elimination of colloidal ceria nanoparticles. The growth of inherent bubbles that accompanies heating and shear in buff cleaning is associated with the particle-cleaning process and contributes to particle-removal efficiency (PRE). Various optical methods were employed to examine the size and quantity of bubbles, revealing nitrogen (N2) bubbles to be approximately 1 µm in diameter, while carbon dioxide (CO2) bubbles varied from 1 to 10 µm. Gas-dissolved water demonstrated improved PRE, with CO2 exhibiting superior performance in comparison to N2. Negatively charged bubbles were found to effectively capture positively charged ceria particles from oxide film surfaces, cleaning solutions, and pad asperity surfaces. Additionally, bubbles enhanced particle dispersion, as evidenced by a colloidal ceria slurry displaying an average size of 162.5 nm in water, 158.1 nm in N2 water, and 149.8 nm in CO2 water. Well-dispersed particles can easily be flushed from the pad-wafer gap to minimize the risk of recontamination.