Hi Kyle,
I think PMMA is underdeveloped in these images. You may want to try out few
things.

   1. Make sure that you are exposing PMMA with required dose. If you are
   using 100kV, apply 800uC or more.
   2. PMMA A6 would be really thick. It requires more time to develop in
   1:3 solution
   3. Pre-bake for more time. say, 5 min on hot plate.

If these things are not working, then you can suspect PMMA/developer. I
don't think PMMA can redeposit after development.

Regards,

Sangeeth

On Fri, Nov 7, 2014 at 3:49 AM, Kyle Godin  wrote:

> Hello. This fall I have been having trouble with my PMMA EBL processing.
> After development, the patterns are filled in randomly and also there are
> waves of PMMA deposited with macroscale features in-plane. I believe the
> issue is developed PMMA redepositing everywhere. I found some hints online
> about PMMA redepositing or scumming, but nothing to suggest a solution for
> me. I cannot figure out why this is happening as my process has been the
> same for two years and never had this issue until recently. Please see two
> photos:
>
>
> https://www.dropbox.com/s/rpmuv6heh9zfauj/ebl%20scum%20image%20width%201mm.jpg
?dl=0
>
> https://www.dropbox.com/s/wl3jgpo3tc66d5b/ebl%20scum%20image%20width%202mm.jpg
?dl=0
>
> I tried getting new resist from the main bottle, used different resists,
> inspected the resist optically before exposure and there is no thickness
> variation, have tried “developing” unexposed resist and optically
> everything looked fine.
>
> Process:
> SiO2 on Si, thickness 90nm or 300nm or 1um.
> PMMA 950 A4 or 950 A6.
> Spin 3k 30s, bake 180C hot plate for 60s.
> Sometimes I expose right away, sometimes the chips rest overnight - same
> results.
> Exposure is with a Jeol6300 at 2nA.
> Development is MIBK:IPA 1:3 for 55s.
> Then dunk in a large bath of DI water to quench development.
>
> Thanks,
> Kyle Godin
> kgodin@stevens.edu
>
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--




*Sangeeth KCenter for Nano Science and Engineering (CeNSE)Department of
Electrical Communication EngineeringIndian Institute of ScienceBangalore-12*
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