[labnetwork] Blistering of metal film stack on PMMA

[Norman Gottron]

Hi Savitha,

Have you checked the temperature of the substrate?  That's one thing to check, but I suspect the issue is with exposure to electrons, particularly if regular lithographic resists are performing ok.

We saw a nearly identical issue with PMMA in our evaporator and it was solved by the installation of a permanent magnet to capture more of the electrons that are (perhaps) straying from the gun.  The difference was night and day (see images below).

Before magnet installation (100nm Ti dep on PMMA-coated wafer):
[cid:image001.png at 01D4BA13.640D86A0]


After magnet installation (100nm Ti on PMMA coated wafer):
[cid:image002.png at 01D4BA13.640D86A0]

Hope this helps, and if you've already investigated a host of issues, this might be the only remaining one.

Regards,

Norman Gottron
Process Engineer, Carnegie Mellon University Nanofabrication Facility
Electrical and Computer Engineering | Carnegie Mellon University
5000 Forbes Ave
Pittsburgh, PA 15213
Phone: 412-268-4205
www.ece.cmu.edu<http://www.ece.cmu.edu/>
www.nanofab.ece.cmu.edu<http://www.nanofab.ece.cmu.edu/>




From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Savitha P
Sent: Friday, February 01, 2019 6:54 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Blistering of metal film stack on PMMA


Hello!



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.



We are using a Leybold UNIVEX400 E-Beam Evaporator.



For a stack deposition of metals, example Cr/Au (10/50 nm)

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.

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.



Few tool and process details:

Source to substrate distance- Minimum 20 cm and Maximum 35 cms. Blisters observed for both the distances.

Deposition rates of Cr 0.3 nm/s and Au 0.3 nm/s

Base Pressure around 2 E-06 Torr

Deposition at room temperature

OPL resists used (AZ 5214E, S 1813, AZ 4562)

EBL resists(PMMA 950 A4, PMMA 495 A4, EL-9)



We have already tried different baking times for PMMA, different deposition rates,  wait times between depositions and also grounding the substrate.



Please let us know if anyone has an idea on how to solve this.



With best wishes,



Savitha



Dr. Savitha P
Chief Operating Officer
National Nanofabrication Centre
Centre for Nanoscience and Engineering
Indian Institute of Science
Bangalore - 560012
India.
Ph. +91 80 2293 3319
www.cense.iisc.ac.in<http://www.cense.iisc.ac.in>
*Please note the change in my e-mail id*
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