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<p>Hi Savitha --</p>
<p><br>
</p>
<p>I agree with Norman and Nathan, as controlling the temperature
and bombardment of your substrate should address the blistering
problem. I'd like to add that your question reminds me of some
really cool tricks with PMMA that I've learned from one of our
most esteemed researchers, Jim Kruger (who is retired for the
second time, but still comes around to share valuable nuggets.)<br>
</p>
<p><br>
</p>
<p>Optical resists generally harden and carbonize at higher
temperatures and with ion bombardment. However, PMMA undergoes
thermal decomposition starting around 300 C, attributed to
depolymerization from chain ends. And at around 400 C, thermal
decomposition happens regardless of chain length, due to random
scission. Interestingly, good quality PMMA leaves no residue on
when heated briefly to 400-450 C. This makes it a really handy
method for bonding chips, if your samples can tolerate the heat.<br>
</p>
<p><br>
</p>
<p>Also, it turns out that xrays from Ebeam evaporation will fully
expose PMMA. This means you can use ordinary PMMA developer for
lift off. This opens up LOADS of possibilities for processing
because you can pattern with optical resist and PMMA and
selectively develop or lift-off one versus the other, using the
appropriate developer.</p>
<p><br>
</p>
<p>If anyone else has done this or has cool tricks to add, I'd love
to hear about it.</p>
<p><br>
</p>
<p>Cheers -<br>
</p>
<p><br>
</p>
<p>Mary<br>
</p>
<pre class="moz-signature" cols="72">--
Mary X. Tang, Ph.D.
Managing Director
Stanford Nanofabrication Facility
Paul G. Allen Building, Rm 141
420 Via Palou Mall
Stanford, CA 94305
(650)723-9980
<a class="moz-txt-link-abbreviated" href="mailto:mtang@stanford.edu">mtang@stanford.edu</a>
<a class="moz-txt-link-freetext" href="https://snf.stanford.edu">https://snf.stanford.edu</a></pre>
<div class="moz-cite-prefix">On 2/1/2019 3:53 AM, Savitha P wrote:<br>
</div>
<blockquote type="cite"
cite="mid:MA1PR01MB0906F50904D2CD6C5BECA609EF920@MA1PR01MB0906.INDPRD01.PROD.OUTLOOK.COM">
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Hello!</p>
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We need inputs deposition of metal film stack on PMMA coated
substrates. We see blisters on the PMMA which creates problems
during lifting off process.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
EmojiFont, "Apple Color Emoji", "Segoe UI
Emoji", NotoColorEmoji, "Segoe UI Symbol",
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<br>
</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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We are using a Leybold UNIVEX400 E-Beam Evaporator.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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<br>
</p>
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For a stack deposition of metals, example Cr/Au (10/50 nm)</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
EmojiFont, "Apple Color Emoji", "Segoe UI
Emoji", NotoColorEmoji, "Segoe UI Symbol",
"Android Emoji", EmojiSymbols; font-size: 16px;">
the film on Si and SiO2 substrate is smooth with good
resistivity value.The film deposited on optical lithography
patterned samples also give good lift off and the appearance
of metal film on resist is smooth and usual.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
EmojiFont, "Apple Color Emoji", "Segoe UI
Emoji", NotoColorEmoji, "Segoe UI Symbol",
"Android Emoji", EmojiSymbols; font-size: 16px;">
Whereas, for a film stack deposition on e-beam lithography
patterned samples, the metal on the PMMA resist
becomes completely blistered. The lift off is not clean,
leaving behind random patches of metal over resist on the
substrate even after longer duration in solvents.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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<br>
</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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Few tool and process details:</p>
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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Source to substrate distance- Minimum 20 cm and Maximum 35
cms. Blisters observed for both the distances.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
EmojiFont, "Apple Color Emoji", "Segoe UI
Emoji", NotoColorEmoji, "Segoe UI Symbol",
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Deposition rates of Cr 0.3 nm/s and Au 0.3 nm/s</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
EmojiFont, "Apple Color Emoji", "Segoe UI
Emoji", NotoColorEmoji, "Segoe UI Symbol",
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Base Pressure around 2 E-06 Torr</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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Deposition at room temperature</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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OPL resists used (AZ 5214E, S 1813, AZ 4562)</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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EBL resists(PMMA 950 A4, PMMA 495 A4, EL-9) </p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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<br>
</p>
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We have already tried different baking times for PMMA,
different deposition rates, wait times between depositions
and also grounding the substrate.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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<br>
</p>
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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Please let us know if anyone has an idea on how to solve this.</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
EmojiFont, "Apple Color Emoji", "Segoe UI
Emoji", NotoColorEmoji, "Segoe UI Symbol",
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<br>
</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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With best wishes,</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Emoji", NotoColorEmoji, "Segoe UI Symbol",
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<br>
</p>
<p style="font-family: Calibri, Helvetica, sans-serif,
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Savitha</p>
<br>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<div id="Signature">
<div id="divtagdefaultwrapper" dir="ltr" style="font-size:
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<div>Dr. Savitha P<br>
Chief Operating Officer</div>
<div>National Nanofabrication Centre<br>
Centre for Nanoscience and Engineering<br>
Indian Institute of Science<br>
Bangalore - 560012<br>
India.<br>
Ph. +91 80 2293 3319<br>
<a class="moz-txt-link-abbreviated" href="http://www.cense.iisc.ac.in">www.cense.iisc.ac.in</a></div>
<i><span style="color:rgb(0,111,201)"><b>*Please note the
change in my e-mail id*</b></span></i><br>
</div>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
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</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
Paul G. Allen Building, Rm 141
420 Via Palou Mall
Stanford, CA 94305
(650)723-9980
<a class="moz-txt-link-abbreviated" href="mailto:mtang@stanford.edu">mtang@stanford.edu</a>
<a class="moz-txt-link-freetext" href="https://snf.stanford.edu">https://snf.stanford.edu</a></pre>
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