How to make PMMA micropillars of size 50-100 microns in diameter with thickness of up to 100 microns? My question is what mol. wt. of PMMA has to be used to get 100 microns thickness and what process I have to carry out? I have UV lithography for patterning.
Dear Jaroslav, I don't have PMMA sheet for stamping. I have PMMA in liquid form i.e 950PMMA A Resists Solids: 2% in Anisole. I want a pillar of 100 micron length with dia of 50 micron. Do you have any idea about how to do it?
Dear Jaroslav Sir Thanks for the suggestion. I was planning to do the same method which you have mentioned but I have a query in that, do have any idea how release the PMMA from PDMS? Can I use toluene to release it or any other way I can do it.
I appreciate your reply.
There are two problems I can see:
1) PMMA is responsive to UV below 250 micron wavelengths. Most UV lithography tools have emission wavelengths of 365 micron or 430 micron. Please check the UV wavelength of your instrument.
2) I noticed you mentioned 950k PMMA A2. This formulation is often stocked by people performing electron beam lithography. The thickest film one can get with this formulation using spin-casting is approx. 200 nm i.e., 0.2 um. However, you need 100 um!
2-A) Please find PMMA in a thicker formulation, and/or
2-B) Please find a spray-coater. I have doubts spin-coating of such thick films can even be done.
Thanks for message Mr. Mohammad.
The lithography m/c that we have can do lithography on PMMA, there is no prolem with that.
It is true that from 950k PMMA A2 we can get max thickness of 0.2um and I have find some other thicker formulation of PMMA. With the spray coating method I am not sure whether I can get a uniform thickness, do you have any idea about it?
Yes, I am also worried about the uniformity. A few years ago I saw a conference presentation about EBL on spray coated PMMA on topography. I have managed to find that paper and another paper showing some interesting results. However, I think you will need to contact specialists in this subject (journal article authors) or ask this question from researchers on researchgate. Best wishes for your research.
Spray coating of PMMA for pattern transfer via electron beam lithography on surfaces with high topography
http://dx.doi.org/10.1016/j.mee.2010.12.106
Spray coating of photoresist for pattern transfer on high topography surfaces
http://dx.doi.org/10.1088/0960-1317/15/4/003
Mr.Mohammad, Thank you very for the papers I greatly appreciate your help.
You're welcome. Best wishes. Let us know when you publish your work. :))
E-Beam lithography is definitely the solution. Experiment with PMMA A2. Work with different spincoat RPM and baking temperature and time, and do some test run writing. For sure you can get the desired thickness you need. As for pattern transfer technology you need to use, as said, E-beam not UV. UV system, available in typical labs can't support anything below 2-5um resolution, besides UV optical mask has already a limitation of 2um when writing it using conventional laser writer, unless you are talking about industrial scaled stepper in Intel.
As for the period structures, you may want to watch out for charging effect when the structures are very close and scattering effect. Making holes is easier than pillars. But definitely can be done with proper tuning of the exposure dose and writing method.
Charging can be ground with conductive seeding layer on the substrate if this is not an issue for your device you are making. Good luck.
Hi Sivakumar,
I have doubt that using PMMA A2 we can get a thickness of 80um and doing EBL is difficult task on it. EBL used at micron and submicron range.
Ooops. Sorry about that. You are right. I didn't notice the (um) scale at your post, must have missed my coffee. You are very correct. My apologies. So for 80-100um, UV litho would be ok, but as far as I know there is no way to spincoat a PMMA to that thickness. So an alternate solution would be use SU8. This will solve your problem. You can fabricate any pillars or any geometry easily with UV (365nm). Unless you need PMMA-only pillars specifically, there is a solution but can be costly. X-ray lithography is an option. You need to get PMMA sheet with high molecular weight, and hot-press it to about the thickness you need. That is not an easy task. And you can do the pattern transfer using X-ray litho. Here is the catch, you will need to make an x-ray mask, not cheap. This involved 2 different pattern transfer process, graphite wafer and gold electroplating. And finally a synchrotron radiation facility equipped with X-ray lithography beamline.
So my recommendation is try replacing PMMA with SU8. It works like a charm. If you could explain what you are working on, it would be easier for discussion.
Regards,
Siva.
Thanks Siva for your comments. I am trying make PMMA micropillars, to do mechanical characterization at micron scale. I will trying doing the x-ray lithography before that I have figure out whether the facility is available in our institute.
There is an alternative technique to create nano and micropillars. For more details, please find attached file.
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