Impact of wet ceria abrasive size on initial step height removal efficiency for Isolated SiO2 film chemical mechanical planarization

Abstract

In 3-dimensional memories such as NAND flash and cross-point memory, the integration fabrication processes face a notable initial-step-height of an isolated SiO2-film deposition, which is an extremely critical process removing such initial-step-height perfectly via chemical mechanical planarization (CMP). The SiO2-film polishing-rate difference was generated between upper and lower locations of initial-step-height and was evidently depended on the nano-ceria abrasive size in an isolated SiO2-film CMP slurry; that is, the polishing ratio of the upper location to lower location remarkably increased from 4.5:1 to 11.5:1, as the ceria abrasive size increased from 21.3 to 81.0 nm. The difference of polishing rate was associated with a local pressure difference between upper and lower locations of initial-step-height; that is, the local pressure at the upper location remarkably increased from 5.2 to 14.2 PSI, while it at the lower location very slightly decreased from 1.0 to 1.3 PSI, as the ceria abrasive size increase from 21.3 to 81.0 nm. Thus, a larger ceria abrasive size in an isolated SiO2-film CMP slurry led to better removal ability (i.e., a shorter polishing time of initial-step-height and a thicker remaining isolated SiO2-film thickness).