[labnetwork] PR bubbles where exposed

Fri Nov 5 10:30:42 EDT 2021

Both water and N2 are part of photochemical reaction.
https://www.microchemicals.com/technical_information/exposure_photoresist.pdf
[cid:image002.png at 01D7D230.2DCF4320]

Bubbles formed in the resist under exposure are nitrogen. Hydration is only tangentially related, as lack of moisture calls for longer exposure times and overexposure of top layers which get hydrated first. I believe N2 can still be split off without water, but soluble molecule doesn’t form without H2O. My understanding is that normal resist exposure doesn’t involve 100% reaction.
Hydration process time goes as resist thickness squared;  If I remember correctly, 1 micron calls for 5-10 second of exposure to air at normal humidity; 7 micron would be on the order of 5 minutes. The only case when I really had to care was dealing with chemically amplified 25 micron resist.

From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Daniel Lloyd
Sent: Friday, November 5, 2021 06:18
To: Morrison, Richard H., Jr <rmorrison at draper.com>; Maduzia, Joseph Walter <jmaduzi2 at illinois.edu>; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] PR bubbles where exposed

Hi,

I’ve seen similar bubbles in the past, but not consistently. While I’m aware that the clean room I have access to is only loosely humidity controlled, what should be an acceptable range. The resist I use doesn’t mention anything. My relaxation time between pre-bake and exposure is typically 1 hour to let the substrates cool, does anyone have a guide to working that out?

Thanks,

Daniel Lloyd
Development Engineer,

From: labnetwork <labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu>> On Behalf Of Morrison, Richard H., Jr
Sent: 04 November 2021 15:45
To: Maduzia, Joseph Walter <jmaduzi2 at illinois.edu<mailto:jmaduzi2 at illinois.edu>>; labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] PR bubbles where exposed

HI,

These look like Nitrogen bubbles, how thick is the resist? Is the thickness in the recommended range?

We have this issue when the humidity is out of control, we solved the issue by reducing the thickness, to be in the recommended range and changing the prebake per advice form the resist supplier.

Rick

Richard Morrison
PMTS
Draper Laboratory
555 Technology Square
Cambridge Ma  02139
Office: 617-258-3420
Cell: 508-930-3461

From: labnetwork <labnetwork-bounces at mtl.mit.edu<mailto: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<mailto: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>
https://cleanroom.mechse.illinois.edu/

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