[labnetwork] PR bubbles where exposed

Fri Nov 5 12:05:31 EDT 2021

At the LNF we have recently started using AZ 12xt. It is a
chemically amplified photoresist and doesn't require the wait times of the
DNQ resists. So far it's working well and for our users the time savings
and repeatability have made it worth the increased cost. We have processes
for 10-25um.

Katharine

On Fri, Nov 5, 2021 at 11:59 AM Michael Yakimov <yakimom at sunypoly.edu>
wrote:

> Both water and N2 are part of photochemical reaction.
>
>
> https://www.microchemicals.com/technical_information/exposure_photoresist.pdf
>
>
>
> 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> *On Behalf Of *Morrison,
> Richard H., Jr
> *Sent:* 04 November 2021 15:45
> *To:* Maduzia, Joseph Walter <jmaduzi2 at illinois.edu>;
> 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> *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
>
> https://cleanroom.mechse.illinois.edu/
>
> <http://illinois.edu/>
>
> *Under the Illinois Freedom of Information Act any written communication
> to or from university employees regarding university business is a public
> record and may be subject to public disclosure.*
>
>
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