Hi Eveybody,

I'm a graduate student in Stanford Uni. I am trying to refine
deep holes in silicon wafer (450 microns deep, 120 microns diameter) by
wet etch HNA (7%HF: 30%HNO3: 10%CH3COOH). These holes are etched by
RIE until ~50um silicon left, I need to keep this amount of silicon to be
support in the subsequent process steps and after everything is finished,
I would like to etch remaining silicon by isotropic etch to keep circular
symmetry.

However, bubbles are formed during isotropic etch and they are masking the
holes. Therefore, I couldn't atch remaining silicon.

I would deeply appreciate it if someone knows how to get around this
problem.

Thanks in advance.

Regards,

Gokhan Percin