Improved Selective Silicon Nitride ETCH for Advanced Logic and Memory Applications

Mechanisms of H 3 PO 4 -based selective etch of silicon nitride (Si 3 N 4 ) vs. silicon oxide (SiO 2 ) and oxide regrowth challenges in 3D NAND stack are reviewed. Effective additives have been developed to fortify phosphoric acid etchants and deliver up to 7.5 - fold selectivity enhancement over standard H 3 PO 4 . These additives are expected to give equal or better oxide regrowth control. They also provide built-in bath seasoning effects for more stable silicon nitride etch rate and process reproducibility.