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I've worked with SU8 for quite a while and have run into this issue in the past. As mentioned below, if your SU8 is sticking to the mask, it is likely that it hasn't been baked long enough.</div>
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<div role="presentation" class="elementToProof">I have found that the bake times listed in the vendor sheet are "guidelines". </div>
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<div role="presentation">Always bake longer than prescribed in the sheet.</div>
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<div role="presentation" class="elementToProof">When fully baked, SU8 should have the consistency of hard candy. Your tweezers should not dent the film.</div>
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<div role="presentation" class="elementToProof">I have never run into a scenario where a film has been "over baked".</div>
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<div role="presentation" class="elementToProof">Ramp from room temp, up to 65 C, dwell, then ramp up to 95 C. Turn off the hotplate and allow to cool to room temp. This will keep film stress to a minimum.</div>
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<div role="presentation" class="elementToProof">Thicker SU8 films (100 um+) can be challenging to bake. The surface of the SU8 will tend to skin over from heat and air flow over the wafer, preventing the underlying solvent from leaving the film. Cover the wafer
with a beaker or petri dish to maintain a solvent environment during the bake. Prop one side of the dish up with glass slides to prevent any condensation from dripping on the film. This allows the film to bake from the wafer surface upward through the film.</div>
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<div role="presentation" class="elementToProof">For film thicknesses of 500 um+ I typically ramp to temperature and allow the film to bake overnight, switching off the hotplate in the morning for slow cooling.</div>
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<div role="presentation" class="elementToProof">With thicker SU8 films, I have seen the wafer begin to bow at around 60C. In these cases, I will reduce the bake temp to 55C and extend the bake time.</div>
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Cleaning your photomask.</div>
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<div role="presentation" class="elementToProof">In many cases, SU8 that has not been fully cured will stick to the mask in the exposure areas. This will lead to repeated sticking issues.</div>
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<div role="presentation" class="elementToProof">Exposed SU8 can be removed from the mask by soaking in either Acetone or Remover PG. It can take several hours to swell the material.</div>
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<div role="presentation" class="elementToProof">Gently clean stuck on SU8 with a cleanroom swab, taking care not to damage the Cr layer on the mask plate.</div>
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<div role="presentation" class="elementToProof">Once cleaned, quickly move to a bath of IPA, then rinse with DI water.</div>
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Tom Pennell</div>
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Cornell NanoScale Facility</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> labnetwork <labnetwork-bounces@mtl.mit.edu> on behalf of Demis D. John <demis@ucsb.edu><br>
<b>Sent:</b> Friday, February 13, 2026 9:38 PM<br>
<b>To:</b> Robert Nidetz <nidetz@umich.edu><br>
<b>Cc:</b> labnetwork@mtl.mit.edu <labnetwork@mtl.mit.edu>; Phillip Bauer <Phillip.Bauer@formfactor.com><br>
<b>Subject:</b> Re: [labnetwork] Photomask sticks to SU8</font>
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<div dir="auto">To add to this - once SU8 has been fully cured, it is very difficult to remove and doesn’t appear to dissolve in most solvents. Hence why you need to use piranha in this case. SU8 on your mask plate will have been exposed many times and possibly
is very old (perhaps similar to curing). <br clear="all">
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<div dir="ltr"><font face="georgia, serif" size="4" style="font-family:georgia,serif; color:rgb(0,0,0)">-- Demis
</font><font face="georgia, serif" size="1" style="font-family:georgia,serif; color:rgb(0,0,0)">(<a href="https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John" target="_blank" style="font-family:georgia,serif">contact info</a>)</font>
<div><i style="font-family:"times new roman",serif">Reminder</i><span style="font-family:"times new roman",serif">: The NanoFab has a </span><a href="https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab" target="_blank" style="font-family:"times new roman",serif">publications
policy</a><font face="georgia, serif" size="4" style="font-family:georgia,serif; color:rgb(0,0,0)"><br>
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<div dir="ltr" class="x_gmail_attr">On Fri, Feb 13, 2026 at 16:46 Robert Nidetz <<a href="mailto:nidetz@umich.edu">nidetz@umich.edu</a>> wrote:<br>
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<div dir="auto">Definitely try the developer first. If it has not been cross linked by the exposure then it will clean up easy. But if it’s been exposed, you’ll need piranha solution. </div>
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<div dir="auto">To prevent sticking in the future, make sure your tweezers cannot leave an impression after the soft bake once the wafer has cooled to room temperature. If they leave an impression, you’ll need to soft bake more. </div>
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<div dir="auto">Good luck!<br clear="all">
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<div dir="ltr">Robert Nidetz, PhD (he/him/his)</div>
<div>University of Michigan</div>
<div dir="ltr">LNF User Liaison and Domain Expert</div>
<div dir="ltr">1241 EECS Building</div>
<div dir="ltr"><a href="https://www.google.com/maps/search/1301+Beal+Ave+Ann+Arbor,+MI+48109?entry=gmail&source=g">1301 Beal Ave</a></div>
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<div><a href="mailto:nidetz@umich.edu" target="_blank">nidetz@umich.edu</a><br>
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<div>Book an appointment: <a href="https://calendly.com/nidetz" target="_blank">https://calendly.com/nidetz</a></div>
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<div dir="ltr" class="x_gmail_attr">On Thu, Feb 12, 2026 at 7:36 PM Phillip Bauer <<a href="mailto:Phillip.Bauer@formfactor.com" target="_blank">Phillip.Bauer@formfactor.com</a>> wrote:<br>
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Hello</div>
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I am somewhat new to SU-8 working with Positive resists throughout my career. I agree with data sheets are just guideline, for processing. I saw a note from another University to run a 65 deg post bake after the 95 deg soft bake. My question is about mask
cleaning. Is Sulfuric/Peroxide (Piranha ~ 60-90C) really needed. I would think the PGMEA or PGMEA/Acetone followed by IPA would be an effective clean. Just wanted to poll the audience. </div>
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<b style="font-family:Aptos,sans-serif">Phillip Bauer </b></div>
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