Hi Bhargav,

Your description makes me feel that there are pin holes in the photoresist
(may even have formed during the DRIE) which have translated into the bottom
silicon wafer. If the resist is old, it tends to form small hard
microparticles which got knocked off during DRIE and leave pit holes on the
resist surface. I would suggest to use new resist and perform the same
experiment. Hard baking should also help though stripping the resist should
take you some time. If you still face the same problem, try double layer
resist patterning and hopefully it should solve the problem.

Regards,
Pavan

On Tue, Apr 7, 2009 at 4:27 PM, Bhargav Nabar  wrote:

> I am trying to etch silicon using a TRION DRIE etcher. I am using a SF6/O2
> /Ar/He chemistry for the etch. I am using 5.6um of SPR 220-7 positive
> photoresist for as the etch mask. After the etching is completed, I see
> minute pinholes (pits) on the silicon surface which was masked by the
> photoresist. I have checked my photomask and it does not have any
> pinholes.Did anyone have a similar experiance with this photoresist for
> DRIE
> ? What could be a possible reason for these pits on the silicon surface
> masked by the resist ? I am etching for 7 and a half minutes at 50W rie and
> 3000w icp power to etch 20um of silicon.
>
> Also, I am not doing any post exposure bake or hardbake of the resist.
>
> Thank you,
> Bhargav. - UTA

--
Pavan Samudrala