| Slurry stability is an important factor in Chemical Mechanical Polishing (CMP) efficiency. However, few studies have been done in this respect. In settling tests at pH 4, adding various amounts of ceria to colloidal silica slurries was shown to change the stability of the resulted mixed abrasive slurries (5 wt% of silica). Within a range of ceria-to-silica weight ratios, known as the transition range, the mixed abrasive slurries were observed to be unstable. A mathematical estimation based on zero net surface charge was proposed. The modification of particle surface charges through the attachment of positively charged ceria particles to negatively charged silica particles made the mixed slurries unstable. TEM images confirmed such attachments at pH 4. Compared to the slurries containing a single kind of particle, such mixed abrasive slurries were more effective in the CMP of PECVD oxide under the same conditions. |
