Abstract
The effects of photo-oxidative degradation of polyacids at various concentrations and with different durations of ultraviolet (UV) irradiation on the photo-reduction of ceria nanoparticles were investigated. The effect of UV-treated ceria on the performance of chemical mechanical polishing (CMP) for the dielectric layer was also evaluated. When the polyacids were exposed to UV light, they underwent photo-oxidation with consumption of the dissolved oxygen in slurry. UV-treated ceria particles formed oxygen vacancies by absorbing photon energy, resulting in increased Ce3+ ions concentration on the surface, and when the oxygen level of the solution was lowered by the photo-oxidation of polymers, the formation of Ce3+ ions was promoted from 14.2 to 36.5%. Furthermore, chain scissions of polymers occurred during the oxidation process, and polyacids with lower molecular weights were found to be effective in ceria particle dispersion in terms of the decrease in the mean diameter and size distribution maintaining under 0.1 of polydispersity index. With increasing polyacid concentration and UV irradiation time, the Ce3+ concentration and the dispersity of ceria both increased due to the photo-oxidative degradation of the polymer; this enhanced the CMP performance in terms of 87% improved material removal rate and 48% lowered wafer surface roughness.
Highlights
The effects of photo-oxidative degradation of polyacids at various concentrations and with different durations of ultraviolet (UV) irradiation on the photo-reduction of ceria nanoparticles were investigated
Polyacids used as dispersing agents in ceria slurries, such as poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA), are degraded under the exposure of UV light and a low-oxygen environment is achieved by the photo-oxidation process
Photoreactions of ceria and polyacids were performed in a basic solution to improve the Chemical mechanical polishing (CMP) performance of ceria slurry
Summary
The effects of photo-oxidative degradation of polyacids at various concentrations and with different durations of ultraviolet (UV) irradiation on the photo-reduction of ceria nanoparticles were investigated. With increasing polyacid concentration and UV irradiation time, the Ce3+ concentration and the dispersity of ceria both increased due to the photo-oxidative degradation of the polymer; this enhanced the CMP performance in terms of 87% improved material removal rate and 48% lowered wafer surface roughness. Wang et al found that the ratio of C e3+ to Ce4+ ions on the abrasive surface increases with decreasing concentration of ceria slurry, which results in improved removal rates in optical glass C MP22. Polyacids used as dispersing agents in ceria slurries, such as poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA), are degraded under the exposure of UV light and a low-oxygen environment is achieved by the photo-oxidation process. We propose a new strategy to improve the oxide CMP performance by photo-degradation of polyacids, which accelerates oxygen vacancy formation of ceria abrasives under UV-light irradiation. The photocatalytic degradation behavior of polymers in ceria slurry was studied, and its effect on the concentration of C e3+ ions and CMP performance was evaluated
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