durusmail: mems-talk: SU-8 2025 spinning & crater formation
SU-8 2025 spinning & crater formation
2012-11-10
Tom Yuzvinsky
2012-11-11
Andrew Sarangan
2012-11-12
Gareth Jenkins
2012-11-12
Eric Johnston
2012-11-14
Jocelyn Ng
SU-8 2025 spinning & crater formation
Jocelyn Ng
2012-11-14
Hi All,

I'm spinning SU-8 2005 onto an InP wafer with sputtered gold surface.
I use Omnicoat as the prime and encountered these problems :

1. After Omnicoat spinning, there are lines expanding from the center of
the wafer. I suspect this is due to contamination and i plasma clean the
wafer before priming with Omnicoat.
2. After post exposure bake, prior to developing process, the pattern looks
nice with no dark lines. However after developing, parts of the dies looks
dark. I have tried to reduce the exposure dose as well as increasing the
developing time, but nothing seemed to help.

Anyone encounters the above problems? Any ideas or thoughts is very much
appreciated.
Thank you!

Best Regards,
Jocelyn

On Tue, Nov 13, 2012 at 1:16 AM, Eric Johnston wrote:

> Hi Tom.
>
> We've had both of these problems.  The first you may be able to reduce, but
> probably not completely eliminate, by letting the SU8 rest before the soft
> bake.  We have left 3" wafers rest in 100mm petri dishes on a level
> surface, covered, for 24 hours.
>
> The second is probably due to small bubbles, as Andrew said.  I just had
> this experience.  Sometimes small bubbles can get trapped while pouring.
>
> Larger craters can be from contaminants in the air.  We partially cover our
> wafers during the soft bake.
>
> Good Luck.
>
> Eric
>
>
> Eric Johnston (ericdj@seas.upenn.edu)
> Hammer Lab, Department of Bioengineering
> University of Pennsylvania
> Phone: 215-573-6696
>
>
> On Fri, Nov 9, 2012 at 5:43 PM, Tom Yuzvinsky  wrote:
>
> > Hi all,
> >
> > I am spinning SU-8 2025 onto 4" silicon wafers and I have two possibly
> > related problems:
> >
> > 1. Unless I pour SU-8 to cover essentially the entire wafer, there is
> > a visible thickness transition between the region it was poured onto
> > and the region it was dispersed onto by spinning.
> > 2. Soft baking the wafers on a hotplate creates millimeter wide
> > craters in the SU-8 layer.  They don't extend all the way to the wafer
> > but there is an obvious, large thickness variation.  A few craters
> > sometimes form during the 65C bake but many form during the 95C bake.
> > Prior to the bake the SU-8 looks nice, no bubbles.
> >
> > I'm using Microchem's recommended process parameters.  I've tried
> > nanostripping the wafers beforehand, ashing them, letting the SU-8 sit
> > overnight before baking, nothing seems to help.  Any help or ideas
> > would be most appreciated!
> >
> > Thanks,
> > Tom
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