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<p class="MsoNormal"><span style="font-size:11.0pt">Hi Gustavo,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">We’ve seen ghosting before, although as you mention it has usually been caused by mild etching of the substrate in the developer. Based on your comments I wouldn’t count out something else in this case.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">This reminds me of some strange behavior we have seen in some of our nLOF processes done on our MLA. We are still trying to investigate what is happening, but we get odd residue or material adhesion issues
on reworked samples. One working theory is that the high power density of the MLA laser exposure is either locally heating the resist to the point of excessive cross-linking or somehow modifying the surface during exposure. Microchem has a white paper that
seems to lend some credence to this theory (<a href="https://www.microchemicals.com/technical_information/exposure_photoresist.pdf">https://www.microchemicals.com/technical_information/exposure_photoresist.pdf</a>, see page 10).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Any chance you have tried (or could try) repeating the process using a contact aligner on the same substrate and see if you still get the same exposure? If it is an MLA-exclusive issue that would be very interested
to know and investigate further.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-Dave<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:11.25pt;background:white">
<b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#BA0C2F;background:white">Dave Hollingshead</span></b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#3F4443"><br>
Manager, Research Operations<br>
<br>
</span><b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#BA0C2F">The Ohio State University</span></b><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:#3F4443"><br>
Nanotech West Labs<br>
Suite 100, 1381 Kinnear Rd, Columbus, OH 43212<br>
614.292.1355 Office<br>
<span style="background:white"><a href="mailto:hollingshead.19@osu.edu"><span style="color:#0563C1">hollingshead.19@osu.edu</span></a></span> /
<a href="http://nanotech.osu.edu"><span style="color:#BA0C2F;background:white">nanotech.osu.edu</span></a><br>
<br>
Pronouns: he/him/his<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt">From:</span></b><span style="font-size:11.0pt"> labnetwork <labnetwork-bounces@mtl.mit.edu>
<b>On Behalf Of </b>Howard Northfield<br>
<b>Sent:</b> Friday, March 24, 2023 14:10<br>
<b>To:</b> Gustavo de Oliveira Luiz <deolivei@ualberta.ca>; labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] Strange "sample memory" with LOR 5B<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-line-height-alt:.75pt"><span style="font-size:1.0pt;color:white">Yes, previous litho leaves "ghosts", I have seen it often. Howard Northfield Research Associate Advanced Research Complex (ARC) University of Ottawa From: labnetwork
<labnetwork-bounces@ mtl. mit. edu> on behalf of Gustavo de Oliveira <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-line-height-alt:.75pt"><span style="font-size:1.0pt;color:white"><o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Yes, previous litho leaves "ghosts", I have seen it often. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Howard Northfield
<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Research Associate<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Advanced Research Complex (ARC)<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">University of Ottawa<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;color:black">From:</span></b><span style="font-size:11.0pt;color:black"> labnetwork <<a href="mailto:labnetwork-bounces@mtl.mit.edu">labnetwork-bounces@mtl.mit.edu</a>> on behalf of Gustavo de Oliveira Luiz
<<a href="mailto:deolivei@ualberta.ca">deolivei@ualberta.ca</a>><br>
<b>Sent:</b> Friday, March 24, 2023 1:37 PM<br>
<b>To:</b> <a href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a> <<a href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>><br>
<b>Subject:</b> [labnetwork] Strange "sample memory" with LOR 5B</span><span style="font-size:11.0pt">
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> <o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:9.0pt;color:#FF4233">Attention : courriel externe | external email</span></b><span style="font-size:9.0pt;color:#FF4233"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">Hello everyone,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">While working on a recipe for LOR 5B/AZ 1512 in our automatic development system, I encountered some intriguing effects when reusing wafers for my tests. This could be a problem
for our users when developing their own process, so we'd appreciate it if anyone could help us to understand what is going on.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">Below is a picture of a sample right before exposure, taken using our MLA150. The dark/bright features you see are NOT etched on the wafer (these wafers were never etched). The
marks are from a previous lithography test. They become apparent after coating the sample with LOR 5B and even more after adding AZ 1512. And I don't see them when coating only with AZ 1512 (I reused wafers for that process development without any issues).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><img border="0" width="542" height="387" style="width:5.6458in;height:4.0312in" id="Picture_x0020_2" src="cid:image001.png@01D95E73.1F416650"></span><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">And what is more intriguing is that these features affect exposure/development of my test mask. For instance, on a virgin sample I can expose and auto-develop with the same recipe
(dose and development time) I use for the manual process. On a reused sample, the reisst stack behaves as if it were underexposed (a dose test made this very obvious).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">Here are the steps during my tests:<o:p></o:p></span></p>
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<ol start="1" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Piranha clean<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">HMDS prime on a YES oven<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Spin-coat with LOR 5B/AZ 1512 (marks show up on a reused sample)<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Expose using either a mask aligner or DWL<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Auto-develop in our Laurell EDC-650 (resist seems underexposed over the marks)
<o:p></o:p></span></li></ol>
<ol start="5" type="1">
<ol start="1" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">AZ Developer 1:1 – 90 s<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Rinse (DI water) and dry (N2+spin) – 60-120 s<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">MF-319 – 5 s<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Rinse (DI water) and dry (N2+spin) – 60-120 s<o:p></o:p></span></li></ol>
</ol>
<ol start="6" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Strip resist with Remover PG<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
<span style="font-size:11.0pt;font-family:"Arial",sans-serif">Repeat all steps for every iteration<o:p></o:p></span></li></ol>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">At first I thought that this could actually be some etching of my Si wafers by MF-319, even though unlikely given the low TMAH concentration (and I'm not sure why that would
affect exposure/development). But the sample in the image above has 2 μm thermal oxide, so practically impervious to TMAH. Not to mention that the brightest crossing marks come from testing a recipe where TMAH was not used at all. This must be some strange
interaction between LOR 5B and the sample surface, which I'd expect to be practically reset after piranha and HMDS priming.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">My search for more information regarding LOR 5B and it's sensitivity to surface conditions has proven fruitless so far. And requiring a brand new sample for every iteration can
get expensive quite quickly. We'd appreciate it if you could point us to some references where this was discussed in any form, or if you know of a method to avoid this from happening.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">I'm sorry for the long email, and thank you in advance for any comments.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">Best regards,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Arial",sans-serif">--<br>
Gustavo de Oliveira Luiz, PhD<br>
Applications/Research Specialist<br>
nanoFAB, University of Alberta<br>
+1 (780) 619-1463<o:p></o:p></span></p>
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