芯片制造工艺问答021：去除Si3N4时, 为何要在热磷酸之前加50:1 HF蚀刻? 此蚀刻时间太短有何影响?
Ans 50:1 HF is designed to remove any oxide above
SIN before H3PO4 strip. If HF etch time is too short, the oxide above SIN will
not completely removed, and SIN can not be stripped by H3PO4 and result
