Impact of sodium carboxymethyl cellulose on redispersibility and polishing performance of lanthanum-cerium-based slurry containing sodium hexametaphosphate

Abstract

The lanthanum-cerium-based slurry (LC-slurry) is extensively utilized in the chemical mechanical polishing (CMP) of TFT-LCD glass substrates, optical lenses, and other glass products. Sodium hexametaphosphate (SHMP), as a dispersant, is commonly employed to enhance the dispersion properties of LC-slurry for improved polishing performance. However, the tendency of sedimentation to form a compacted sediment layer, which is challenging to redisperse, increases storage difficulty and polishing equipment failure risk, thereby limiting its utilization in CMP. In the present study, sodium carboxymethylcellulose (CMC-Na), a long-chain organic polymer, was employed to enhance the redispersibility of LC-slurry containing SHMP. A comprehensive investigation was conducted on the influence of CMC-Na dosage and slurry pH on dispersibility, redispersibility and polishing performance. Additionally, an analysis was carried out to elucidate the underlying mechanism behind the effect of CMC-Na. The study demonstrates that the LC-slurry, containing 250 ppm SHMP and 500 ppm CMC-Na, exhibits excellent dispersibility and redispersibility. Further polishing tests demonstrate that compared to the LC-slurry containing only SHMP, utilizing the slurry containing both SHMP and CMC-Na at various pH for polishing thin film transistor liquid crystal display (TFT-LCD) glass substrates results in a reduction of both material removal rate (MRR) and surface roughness (Sa). Specifically, when adjusting the slurry to a pH range of 5–6, the MRR can reach up to 330 nm/min, which closely approximates the MRR achieved by LC-slurry containing only 250 ppm SHMP at corresponding pH values. Meanwhile, after polishing, the surface roughness of the glass substrate measures approximately 0.47 nm.