Selective Si<sub>3</sub>N<sub>4</sub> Etching for 3D NAND Integration by Using Low Concentration of H<sub>3</sub>PO<sub>4</sub>

This study investigated the etching kinetics of Si 3 N 4 in various concentration of H 3 PO 4 solution and the effect of Si 3 N 4 etching enhancers on the etching process, particularly for 3D NAND trench structures. 30 wt% H 3 PO 4 was used to etch Si 3 N 4 , which can produce higher Si 3 N 4 /SiO 2 etching selectivity and similar Si 3 N 4 etching rate compared to a conventional 85 wt% H 3 PO 4 . 30 wt% H 3 PO 4 showed significantly improved etching performance for the Si 3 N 4 /SiO 2 3D NAND structure as compared to 85 wt% H 3 PO 4 . In particular, the transportation ability of H 3 PO 4 into 3D NAND trench structures can be improved by reducing viscosity of etchant, which can be obtained by reducing the concentration of H 3 PO 4 . In addition, Si 3 N 4 etching enhancers were introduced to accelerate the Si 3 N 4 etching kinetics in 30 wt% H 3 PO 4 . Addition of such additives improved the Si 3 N 4 etching rate and Si 3 N 4 /SiO 2 etching selectivity while suppressing oxide regrowth. The results provide valuable insights for optimizing selective Si 3 N 4 etching process in 3D NAND structures.