Effect of NF3, WF6, and MoF6 Additive Gases on High Aspect Ratio Contact SiO2 Etching in c-C4F8/C4F6/Ar/O2 Plasmas

Abstract

Etch profile control of high aspect ratio contact (HARC) is one of the key issues in developing next-generation memory device manufacturing because the HARC etch result can determine the device integration and device performance. In this study, the effect of F-based additive gases such as nitrogen trifluoride (NF₃), tungsten hexafluoride (WF₆), and molybdenum hexafluoride (MoF₆) on the HARC SiO₂ etching was investigated. A few sccm of NF₃, WF₆, and MoF₆ added to the base gas recipe did not change the SiO₂ etch rate and etch selectivity over the amorphous carbon layer (ACL) noticeably. However, the addition of NF₃ flow enlarged the etched HARC SiO₂ top hole size by decreasing the polymer layer thickness deposited on the sidewall. On the contrary, metal-containing additive gases such as WF₆ and MoF₆ resulted in decreased HARC SiO₂ top hole size enlargement. For the base recipe and with NF₃ addition, distorted and oval-shaped SiO₂ bottom holes were observed possibly due to the charging of the SiO₂ sidewall during the etching. But, for the addition of WF₆ and MoF₆, rather circular-shaped SiO₂ bottom holes could be observed possibly due to the decreased SiO₂ sidewall charging by the formation of a more conductive polymer through the inclusion of metals.