[labnetwork] Blistering of metal film stack on PMMA

[Shivakumar Bhaskaran]

Hi Savitha,

I had the same issue with blistering on PMMA sample. You can try increasing the rate and see whether this reduce, (Ex in my case I had deposition of Ti 5A/s and Au 10 A/s).
You can also add spacer between the crucible and pocket, this might help in reducing the current to evaporate the metals (and hence less electrons)
As others have suggested we did install Ebeam optimizer to get rid of the blistering.

The beam optimizer - enhances the magnetic field (can degrade over time) so that all electrons will be captured during the 270 degree turn from the filament and then hit the pocket. If the magnetic field is off or weak higher velocity electrons can escape the confines of the magnetic field and be driven to the substrate.  The beam optimizer just added some B field to account for this.
Attaching the picture how the Beam optimizer looks.
Hope this helps.
Shiva

Shivakumar Bhaskaran, Ph.D.,
John D. O'Brien Nanofabrication Laboratory
Michelson Hall, 1002 Childs Way, MCB LL121,
Los Angeles, California 90089, 213 821 2374
[Sign]







From: labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu> On Behalf Of Savitha P
Sent: Friday, February 1, 2019 3:54 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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