Hello,
I use PMMA as a resist for E-beam lithography (EBL) to pattern structures on top of graphene. I remove PMMA by using acetone. However, there is always some thin layers of PMMA left on top of my structures. I tried to use sonification or exposing it again but it doesn't help. There is always more PMMA residue if I have more lithographic steps. I wounder if somebody observe same results after EBL? How can I remove PMMA residue? Also, How PMMA residue affects contact resistance?
Thank you very much,
Salamat
Chloroform and benzene/toluene/Xylene make very good solvent for PMMA. When you are using E-beam lithography the PMMA undergoes crosslinking as the beam can generate radicals which can undergo crosslinking. If crosslinked it can not be removed with solvent or sonication. The adherent layer will enhance the resistivity for conducting surface.
A few solvents for poly(methyl methacrylate), i.e. PMMA, were mentioned elsewhere at this forum: https://www.researchgate.net/post/With_PMMA_which_solvent_to_use
I used NMP @ 70 degree for 8 min to remove PMMA after transferring CVD grown graphene on SiO2/Si.
It's true that PMMA is unlikely removable. NMP works better than other solvents I tried
Oh yes! It is typical for PMMA! Try oxygen plasm treatment of surface to remove PMMA residue. In soft oxygen process usualy necessary only 4-5 seconds.
It depends from which part you want to remove the residue; from contact area and before metal deposition, soft oxygen plasma is good but plasma is not recommended on the channel area. Usually, channel area is cleaned either by benzene based chemical or by thermal annealing with Ar and H2 gases. Multiple current sweep is also helpful in improving the contact resistance via joule heating.
There is also the possibility of cleaning it mechanically using an AFM tip. Source is attached.
Article Cleaning graphene using atomic force microscope
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