Recently, we have diluted the SU8 using cyclopentanone for various thicknesses ranging from 500 nm to 5 microns. After diluting we have coated the diluted SU8 on Silicon substrate using a spin coater. After spin-coating we notice they are some bubbles formed on the substrate. After checking under the microscope, seems like there is no uniform coating that results in bubbles. Did anyone come across with the same scenario, if yes could you please advice what are the steps taken to avoid bubbles to form after spin-coating the diluted SU8 on the substrate
Aliquot your mixture into two (or more) bottles and centrifuge to remove bubbles. Dispense directly from these containers onto substrate.
1) Cleaning is very important, so clean the substrate using RCA process.
2) keep the mixture for 10 to 15 min inside the vacuum chamber or use desiccator to remove the air/gas inside the mixture.
3) Spin program should be in the steps (ramp-up & ramp-down)_very important for uniform thickness. refer: Article Nanomechanical characterization of SU8/ZnO nanocomposite fil...
4) pre-bake/soft-bake in two step temperature etc..
Is it really from bubble? I guess it's from aggregation. Please use other solvent with lower vapor pressure(PGMEA, HBM, etc..). If your issue is from bubble, really. You need to use anti-foaming agent. Good luck.
Dear Ron Reiserer,
I did not try before the centrifuge approach. Are there any specific parameters for centrifuge which need to be followed during the process?
Thank you
Dear Braj Krishna,
Yes, the substrate was clean thoroughly prior to coating and the bubbles were still there. Also, I have tried earlier all the approaches you have mentioned but the bubbles are still there.
Thank you.
Dear Dongkyu Ju,
After coating, I have checked under the microscope. There are some holes/bubbles formed upon coating and this makes the coating uneven where you can see certain spots there are some round holes on the surface of the substrate.
Anti-foaming agent? Could you pls elaborate on this?
Thank you.
No special procedures are required to centrifuge your material other than using a container that properly fits the centrifuge and that you balance the rotor using two or more equally filled identical containers. You should be able to get good results with just about any speed that your containers can handle and it shouldn't take more than about 5 minutes if you're getting above 50g. The reason that I specify that you should dispense directly from those containers is that you are likely to capture bubbles when you transfer the viscous liquid from one container to another.
Alternatively, there are companies that make centrifugal mixers that are capable of debubbling the mixture at the end. These are quite convenient if you want to mix small quantities (50mL or less) on the fly. We use a Thinky AR-100 in our lab for mixing thick materials.
Best of luck.
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