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.