Ceria CMP Slurry for the Construction of Floating Gates in MLC NAND Flash Memory below 51 nm

Abstract

A ceria slurry, which is capable of high removal selectivity between silicon oxide and poly-Si, in the chemical mechanical planarization (CMP) process was investigated for the construction of poly-Si gates of a multilevel cell (MLC) NAND flash memory below 51 nm. Anionic phosphate fluorosurfactant was incorporated into the ceria slurry for use as a passivation agent to suppress poly-Si removal. The ceria slurry with fluorosurfactant showed high silicon oxide-to-poly-Si removal selectivity (295:1), resulting from the passivation layers on the poly-Si due to the selective adsorption of the fluorosurfactant. The selective adsorption behavior of the fluorosurfactant can be explained by the difference in surface characteristics between the oxide and the poly-Si, which was supported by the experimental results.