[labnetwork] PR bubbles where exposed

[Price, Aimee]

Hi Joe,
In our experience at OSU, SPR220 is one of those resists that requires a "re-hydration" step for thicker films or you get bubbles.  In our case we suggest a wait of 2hours after exposure before PEB(which seems ridiculous I realize) for films thicker than 7um.  If we don't wait, this is the result.
[cid:image002.png at 01D7D172.EBCAC390]

If you have good control of your humidity in your lab, then you might look at various wait times.  If you don't, that might explain why sometimes you don't see these defects.  We had an issue with our humidifier (long story) that resulted in times of very low humidity.  We believe that's where the 2 hour time came from, which would likely be less now that our humidity is under control.  We don't use 220 much anymore, so haven't studied it further.  Our spin coater has a hygrometer so we ask users to note the humidity for all of their lithography processes, however they don't always.

By chance, we also have EV 620 aligners.  I don't think that makes a difference but we have not studied it with either our MLA or our old MJB-3.  Happy to discuss further if you'd like.

Best,
Aimee

Manager, Nanofabrication
The Ohio State University
Nanotech West Lab
Institute for Materials Research
1381 Kinnear Road
Suite 100
Columbus, OH 43212
614-292-2753


From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Maduzia, Joseph Walter
Sent: Thursday, November 4, 2021 9:59 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] PR bubbles where exposed

Hello All!

Thank you again for all your feedback on SiO2 etch around Al. It has been very helpful and we are moving down multiple paths suggested via the Lab Network to try to solve the issue. More to come once we solve it!

I have another issue I was hoping for feedback on. We have bubbling in our PR (SPR-220-4.5) (pos tone) that we haven't been able to track the source of. It only bubbles during exposure and only where it is exposed. Unexposed areas are unaffected. I've attached some images of the bubbling where you can see the exposed (lighter) and unexposed (darker) areas. The bubbles are visible to the naked eye. The wafer is silicon w a dry thermally grown SiO2 surface. We typically expose via EV620 mask aligner with Vac+HardContact. However, even in a flood exposure with the mask just set lightly down it still bubbles. Without a mask there are also bubbles randomly distributed across the wafer, but they don't get stuck to the mask so they don't pop. We tried various pre-bakes, HMDS coat vs not, piranha treat vs not. In the past these bubbles show up, we trial and error to get rid of them and suddenly they disappear. Our process, although seemingly repeatable, does not yield repeatable results.

Thank You,
JOE MADUZIA
MNMS Laboratory Specialist

The Grainger College of Engineering
Mechanical Science and Engineering

2239 Sidney Lu Mechanical Engineering Bldg
1206 W. Green
Urbana, IL 61801
217.244.6302 | jmaduzi2 at illinois.edu<mailto:jmaduzi2 at illinois.edu>
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