Hi,
I have deposited 100nm Au on 5nm Au using e-beam evaporation and conventional photo-lithography techniques. I used ~5nm Ni as an adhesion layer for 100nm Au, so basically the structure is Au 5nm/Ni 5nm/Au 100nm.
The lift-off of the 100nm Au is extremely hard. I usually rest the sample in acetone for couple of hours so the lift-off is complete. However, in this case even after days, the lift-off is not complete and there are lots of unwanted pieces of Au on the surface. I try to use ultrasound (40kHz) as little as possible because it damages to the structures and removes the main metal layer as well. However, for these samples I apply ~10sec ultrasound, but after ultrasound the quality of the 100nm Au is bad and so much of metal is gone.
Worth mentioning that I dip the samples in HCL (37%) for ~3sec and H2O for 5sec before the 100nm Au deposition to remove any unwanted organic particles on the surface.
Is there any solution to improve the deposition/lift-off process, so the final 100nm Au has a good quality and shape?
Thanks for your time!
Amir
From my experience, for easy lifting it is essential that before you deposit your material, the photoresist layer defining the pattern into which material is to be deposited has a negative side wall meaning this way \ instead of this /. So when you expose the deposited substrate to lifting off solvent, the solvent has access to underneath photoresist to dissolve it thereby lifting off. With sputtering deposition I am able to lift off layers of thickness up to 250 nm with no problem. Not sure how the coating process with ebeam evaporation, the direction with which material comes to substrate surface....
For features with lateral dimensions of 30 microns and bigger you should be able to lift off just by gentle shaking in acetone for 30 min or so. No need for sonication. It is not working probably the photoresist wall profile isnt right
Thanks for your answer. Did you deposit metal on metal or metal on semiconductor or insulator? If you have deposited metal on metal, have you encountered any issues during lift off? Unfortunately i only have access to positive photoresist and corresponding shadow mask to it at the moment.
My devices have lateral dimension of exactly 30 microns (or some times 20). Hoever the main issue if that i have another layer right next to this layer which is placed about 5 to 10 microns next to it. My main problem is the bad lift off in this narrow area which is extremely hard.
Worth noting i don't have issues depositing metal on semiconductor and my liftoff there is pretty good.
P.S. my developer is expired. Can this be effective?
I have 2 lift off processes in my fabrication. First is In2O3 on Si wafer. And then on that substrate I have Al as adhesion layer and then Au (Al/Au up to 250 nm thickness still lift off ok). If material thickness is too thick ( my case bigger than 250 nm) lifting off wont work for same old reason solvent doesnt have good access to underneath photo resist. So I was thinking you have trouble lifting off ~ 100 nm layer, probably the photoresist layer is too thin and doesnt have good nagative profile...
one of my feature size is 3.5 microns. For this I needed 20 min sonication in acetone. Then ok. But the expired photoresist could be an issue. For lifting off of those small features we use a process called image reversal with AZ5214E. It is image resersal so positive resist but it behaves like a nagative one giving you nagative profile for easy lifting off
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