I'm making 10 micron SU-8 chips with the following protocol.
** Protocol **
- Clean the glass slide with ethanol and IPA before placing it in the plasma cleaner and cleaning it.
- I take the glass slide and put it on the spin coater, pouring in the necessary amount of SU-8 10 and using the following setting for the spin coater(0-500 rpm in 5 sec with a ramp up the speed at 100 rpm/sec and then 30 secs at 3000 rpm with the ramp up the speed at 300 rpm/sec)
- I heat the glass slide for 2 minutes on a 65 deg C heating plate followed by 5 mins at 95 deg C.
- I let the sample cool down in a covered petri dish for 3 minutes.
- Then I use UV KUB 2 and pass UV light for 8 sec in one continuous burst.
- Following this, I put it on the 65 deg C heating plate for a minute and then for 2 mins on the 95 deg C plate.
- Then I put it in the new developer for 3 mins and keep shaking it by hand and after the 3 minutes cleaning it with Ethanol.
What I am having an issue with is the definition of the edges. There seems to be a problem I don't know how to fix. I have tried various protocols but I am not getting sharp features. I have attached the images. It's worse for smaller features.
I'm not sure if I agree with the previous answer. It seems you have a lot of material in a sort of slope from the edges inwards. That could be due to insufficient exposure (but over-exposure could do inverted slopes), what type of mask are you using?
Also, it could be due to developer time being insufficient. It's harder to remove material closer to the edges, so it may need more time (again, too much time could also start to remove too much non-exposed SU-8).
Carlos Carreira, Hi I am using 32k DPI FIlm Photomask from FineLine Imaging, these need to be attached to the bottom plate of the top glass. I don't know if that answers your question. Also with regards to the developer time, I have tried to increase it by a few minutes going up to 7 and it hasn't shown a lot of difference.
Balaji Srinivasan Thank you so much for your suggestion. I will try them as I had thought about the fact that the thermal conductivity will be different and will change the time for pre-bake and post-bake. I didn't know about piranha solution treatment I will check it out. Thank you
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