Gokhan Percin wrote:
>
> 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

>
>
The same thing occationally happed to me when opening thick oxide
windows with BOE, after reimmersing the wafer to complete the etch. Some
windows did and others did not open. I found theat a thorough DI water
rinse (hand gun across surface) took care of the problem.

Another thing to try might be to place your etch vessel in an ultrasonic
bath and to switch it on for a couple of seconds at the beginning of
your etch.

A drop of surfactant might also help ("Joy").

Or, why don't you finish the etch with RIE, which is a lot less of a
pain to work with?
--
Alexander Hoelke

graduate student

University of Cincinnati
ECE - CMSM

Phone:  (513)556-1997 / (513)556-4795
FAX:            (513)556-7326