[labnetwork] PR bubbles where exposed

Sun Nov 7 15:01:52 EST 2021

Hi Joe,
I have seen this problem particularly with thick resists like SPR-220 and
AZ4620. After spin coating and before the exposure, a wait time of 3-8 hrs
helped in getting rid of these problems. Also, this step helps in longer
resist survival in the plasma (DRIE etch in particular).

Thanks & br,
vamsi

On Fri, Nov 5, 2021 at 3:03 PM Katharine Beach <beach at umich.edu> wrote:

> 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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-- 

___________________________________________________

N.P.  Vamsi Krishna, PhD

*Staff Scientist*

Pritzker School of Molecular Engineering, *The University of Chicago *

*Resident **Associate*

Center for Nanoscale Materials, *Argonne National Laboratory *

Phone: 1 (331) 757-8565
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