[labnetwork] Blisters on PMMA resists

[Edmond Chow]

We found that we don't have blistering problem with ZEP or PMMA if we have
PMGI underneath.
Below is the picture of 5 samples we put in for ebeam evaporation (Ti/Au
5nm/50nm) Ti deposition rate is at 0.5A/s and Au deposition rate is at
0.5A/s for first 5nm and then ramp to 1A/s for the rest.

Sample1: Si sample with 250nm SF6(PMGI) and 300nm ZEP and ebeam pattern -->
smooth surface after evaporation
Sample2: Si sample with no resist --> smooth surface after evaporation
Sample3: glass slide --> smooth surface after evaporation.
Sample4: Si sample with 300nm ZEP (no ebeam pattern) --> blistering problem
Sample5: Si sample with 300nm PMMA (no ebeam pattern) --> blistering problem

We are using SF6 as liftoff resist anyway, so it is just an added bonus
that it solve the problem with ebeam resist blistering problem, but we
don't understand why it helps, does anyone have some explanation for that?

Thanks.

Edmond

Micro and NanoTechnology Lab (MNTL)

Rm 2300 Micro and Nanotechnology Lab, MC-249

208 North Wright St.

Urbana, IL 61801


[image: image.png]

On Thu, Apr 6, 2017 at 3:52 PM Shivakumar Bhaskaran <bshiva at stanford.edu>
wrote:

> Yes, higher deposition rate helped in reducing the blisters or completely
> gone. However, some users want to do at a low deposition rate. Sometimes we
> start at low rate and change to a higher rate.
>
>
>
> -thanks
>
> -Shiva
>
>
>
> *From:* Mark Giulio Chiappa [mailto:mark.chiappa at ntnu.no]
> *Sent:* Thursday, April 6, 2017 10:37 AM
> *To:* Price, Aimee <price.798 at osu.edu>
> *Cc:* Shivakumar Bhaskaran <bshiva at stanford.edu>; LabNet (
> labnetwork at mtl.mit.edu) <labnetwork at mtl.mit.edu>
> *Subject:* Re: [labnetwork] Blisters on PMMA resists
>
>
>
> Hi Shiva,
>
>
>
> I agree it's probably a thermal issue. When we had the same issue we
> experimented with PMMA from different batches, baking times and temps as
> well as thermally conductive mounts (mung etc) to no avail. Interestingly
> we solved the issue by increasing the deposition rate.
>
>
>
> So it seems there is no definite answer I suppose it is dependant in the
> distance between source an substrate. I don't remember how much we
> experimented with wait times but that sounds like a good idea.
>
>
>
> Kind regards
>
> Mark.
>
>
> Sent from my iPhone
>
>
> On 6 Apr 2017, at 18:23, Price, Aimee <price.798 at osu.edu> wrote:
>
> Hi Shiva,
>
> I believe we’ve had a thread on this subject in the last year or so.  Can
> someone remind me how to find the old/archived threads (or do we just look
> in our email history)?
>
>
>
> Past that, we have had this several different times on a couple different
> evaporators, almost always with Ti/Au or Ni/Au …  Assuming we’ve baked the
> PMMA sufficiently it appears to be heating, though we’ve tried thermal dots
> alongside and not found very high temps.  Our solution has been to slow the
> deposition rate and put a “wait” step in during thick Au, Ni, sometimes Pt
> steps.  The rate we use is 1-2A/s in most cases and the wait times vary but
> are usually halfway through the Au step.
>
>
>
> Lastly, we have a lot of people working with piezoelectric materials and
> this happens sometimes with those.  That’s a separate topic.  I’m assuming
> you are working with more “standard” semiconductor substrates and the issue
> is caused by the metal/PMMA not the substrate itself?
>
>
>
> Feel free to reach out to me off-line at price.798 at osu.edu if you want
> more details.  We did a lot of work with this at two different times, about
> 3 years ago and 10 years ago.  We even had students travel back to UlUC to
> use their evaporator when we were diagnosing this issue the first time.
>
>
>
> Best of luck.
>
>
>
> Aimee
>
>
>
> *From:* labnetwork-bounces at mtl.mit.edu [
> mailto:labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu>] *On
> Behalf Of *Shivakumar Bhaskaran
> *Sent:* Wednesday, April 05, 2017 10:03 PM
> *To:* LabNet (labnetwork at mtl.mit.edu)
> *Subject:* [labnetwork] Blisters on PMMA resists
>
>
>
> Hi All,
>
>
>
> We are getting blisters or metal film peeling off when depositing metals
> (Ti/Au/Al) on PMMA resists using EBeam Evaporation.
>
>
>
> Did anyone had this issue in your EBeam Evaporation tool. If so how did
> you fix this?
>
>
>
> -thanks
>
> -Shiva
>
>
>
> SNSF
>
> http://snsf.stanford.edu/
>
>
>
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-- 
Edmond Chow
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