A study of reverse selectivity slurry for SiO2 stop and Si3N4 CMP using cationic polymer

Abstract

Recently, DRAM and 3D NAND Flash memory devices are rapidly scaling down at the rates of 10 nm/year, so scratch-less, high polishing rate, and high selectivity CMP process is required. For this reason, the need for a CMP multi-selectivity control technique for various film qualities such as SiO2 and Si3N4 is increasing. Therefore, it is necessary to understand the polishing mechanism for freely realizing the selectivity in the SiO2, Si3N4-film quality and study on the implementation of the composition. In this study, a slurry for SiO2 stop and Si3N4 CMP was studied using wet-ceria as abrasive. The design concept of the Si3N4 polishing and SiO2-film polishing-stop CMP slurry requires the positive zeta potential of Si3N4-film surface but the negative zeta potential of SiO2-film surface, since the addition of the cationic chemical prefers to be adsorbed on the negative charged SiO2-film surface rather than the positive charged Si3N4-film surface. Thus, the difference of the absolute zeta potential between the negative charged SiO2 and positive charge Si3N4-film surface should be higher. At pH 6.0, positively charged PEI was adsorbed to form a hindrance layer on the negatively charged SiO2-film. As a result, a polishing rate of 36 A/min was achieved on the SiO2-film. On the other hand, since PEI was not adsorbed on the Si3N4-film, a polishing rate of 775 A/min was confirmed, and the SiO2:Si3N4 selectivity ratio was about 1:28. The SiO2, Si3N4-film slurry implemented based on the research results in this paper is expected to be a new solution in the next generation process.