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

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 (NF 3 ), tungsten hexafluoride (WF 6 ), and molybdenum hexafluoride (MoF 6 ) on the HARC SiO 2 etching was investigated. A few sccm of NF 3, WF 6, and MoF 6 added to the base gas recipe did not change the SiO 2 etch rate and etch selectivity over the amorphous carbon layer (ACL) noticeably. However, the addition of NF 3 flow enlarged the etched HARC SiO 2 top hole size by decreasing the polymer layer thickness deposited on the sidewall. On the contrary, metal-containing additive gases such as WF 6 and MoF 6 resulted in decreased HARC SiO 2 top hole size enlargement. For the base recipe and with NF 3 addition, distorted and oval-shaped SiO 2 bottom holes were observed possibly due to the charging of the SiO 2 sidewall during the etching. But, for the addition of WF 6 and MoF 6, rather circular-shaped SiO 2 bottom holes could be observed possibly due to the decreased SiO 2 sidewall charging by the formation of a more conductive polymer through the inclusion of metals.