What is the best way to solve edge bead in spin coating process? On solving the vibration and stability issues we found that the quality of coating improved, but the edge bead is a problem linked with the method itself. Apart from the high RPM spinnning what is a more optimal solution ?
It's a typical problem with viscous solution. I am not sure what exact materials (solute/ solvent) you are using, however, following can be used to minimize it.
- Choice of solvent: It's wise to make solution using solvents which don't severely evaporates at room temperature. (e.g. chloroform dissolves almost everything but not a good choice as it evaporates quick.
- I also have seen people dropping the solution on the substrate and then start the spin-coating machine. The lag between the time you drop the solution and the time you start the spin-coating machine might worsen the edge and the overall quality of the film. I would rather start the spin-coating machine first and drop the solution after it ramps up to highest RPM.
- Increase in RPM does help but may not work while depositing thicker films.
Article Study of optimization condition for spin coating of the phot...
I hope the attached link might help.
There are a variety of ways to address this problem. Check out the notes at: http://research.engineering.ucdavis.edu/cnm2/wp-content/uploads/sites/11/2014/07/spin_coating_photoresist.pdf
Perhaps the simplest solution is to increase the spin speed dramatically after the point is reach where the thinning of the film is dominated by solvent evaporation rather than convective thinning. This way one can still control the film thickness, while at the same time increasing the centrifugal forces acting on the edge bead. Check out out paper in AICHE journal of spin coating of colloidal particles to understand the interplay of the various thinning mechanisms during spin coating. Copy of paper can be found on ResearchGate.
Thanks for your answers. We are actually trying out different viscous solutions to solve the edge bead problem. Currently the solution we have implemented in our Spin Coaters is to run an automatic cycle at the end to remove edge bead with the help of AI according to the parameters of the solution.
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