[labnetwork] Seeking advice regarding developer/unexposed resist interaction

[Lewis,William]

Hi Gustavo,

You cannot expose these photoresists with developer more than once.  It will create a skin that takes longer to develop through on the 2nd pass and will cause you develop issues every time.  Use a pipetter and only develop and rinse the area that was exposed on the wafer.  I expose around the edge of the wafer but no closer than 1cm from the edge so pAF and resist edge bead isn’t an issue.  I use this method to shoot several tests on a single wafer.  Same applied to photomasks.


Bill Lewis
Research Service Center
University of Florida
walewis at ufl.edu
https://rsc.aux.eng.ufl.edu/


From: labnetwork <labnetwork-bounces at mtl.mit.edu> On Behalf Of Gustavo de Oliveira Luiz
Sent: Tuesday, June 15, 2021 11:03 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Seeking advice regarding developer/unexposed resist interaction

[External Email]

Hello everyone,

I am having some trouble developing recipes or testing performance on our Heidelberg MLA150. Especially when testing performance, it is required for us to expose the test pattern once, develop, inspect and repeat. We usually coat a larger sample (e.g. a 4" wafer) with resist and expose a small test design, allowing us to use the same sample many times. The problem that I encounter is that the development time increases after each iteration, and it is not due to the developer getting weaker (I tried using a new developer to make sure). This behavior is observed on AZ 1500 and AZ 4000 series resists, with the latter presenting a more drastic change.

It seems to me that the developer changes something on the unexposed resist, making it harder to develop. This is made obvious by the fact that we don't see this problem when processing multiple samples and developing them with the same developer bath. In that case the only problem we encounter is the developer getting weaker depending on the exposed area and number of samples, as expected.

I thought that it could be over-hydration, since the developer is a water solution and we rinse with water as well. But high water content tends to make development faster, not slower. Does anyone have more information on the interaction between developer and unexposed resist? I'd appreciate any input you may have.

Best regards,
--
Gustavo de Oliveira Luiz, PhD
Applications/Research Specialist
nanoFAB, University of Alberta
+1 (780) 619-1463
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