Multiselectivity Chemical Mechanical Polishing for NAND Flash Memories beyond 32 nm

Abstract

Using chemical mechanical polishing (CMP) slurry for multiselectivity among SiO(2), Si(3)N(4), and poly-Si films is essential for NAND flash memory cells beyond 32 nm to reduce the dependency of the polishing rate on the pattern density in a chip. The polishing rate selectivity is controlled with an anionic surfactant [poly(acrylic acid) (PAA)] at the beginning of the CMP process and is controlled by a nonionic surfactant [poly(vinylpyrrolidone)(PVP)] for continuous CMP. The selective absorption of PAA on a Si(3)N(4) film surface suppresses the polishing rate of the Si(3)N(4) film, whereas the selective absorption of PVP on a poly-Si film surface suppresses the polishing rate of the poly-Si film. We achieved multiselectivity among SiO(2), Si(3)N(4), and poly-Si films of similar to 65: similar to 15:1 in a nanoceria-based slurry with a PAA concentration of 0.05 wt % and a PVP concentration of 0.2 wt %.