Distortion Control when Etching DRAM Metal Contact

Contact etch is a typical high-aspect-ratio etch, which highly requires less distortion at the bottom. We suspect that the non-uniform polymer deposition on the mask necking and the random charging on the side-wall will both result in distortion. The former mainly contributes to circularity. The later will cause the random direction at the bottom of hole. Based on the mechanism, we investigate some gases to improve the distortion by carbon mask modification and dielectric side-wall discharging.