Streaking during spin coating

[sandip179]

I am spin coating a polymer solution in toluene (bp=110C). However, after spin coating, I see streaks of the polymer on the substrate. Any idea as to how to solve the issue? I have played with polymer concentration and speed without any effect.

 

[aspearin1]

I've been there on this one. Describe the streaks. It could be particles in the polymer, which cause a defect known as comet tailing. It could also be a function of how you are wetting the surface, fluid viscosity, ramp rate, or even your surface preparation before coating.

Aaron A. Spearin
ASQ CSSBB
Engineering Six-S'$

http://www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee

 

[sandip179]

The streaks emanate from the center of the substrate to the periphery. I dont think it is due to particles in the solution, as I filter the solution with a 0.7 micron filter. I apply the solution by covering the entire substrate with a thin layer of solution and then spin-coating. Reducing the concentration and increasing the spin-rate reduces the streak formation to some extent, but not entirely. Also, the viscosity is that of water.

 

[aspearin1]

So it sounds like a "starburst" type defect where these streaks are sort of a "ripple" of coating, but not a bare area of coating. It could be that air in the coating chamber is not solvent rich enough, should be saturated vapor. This should delay the evaporation of the solvent from your surface, preventing localized zones of cured, dried, concentrated or viscous fluid. I've also had luck dispensing the fluid while the coater is running, in general my conditions were a dynamic dispense at about 300 rpm to spread the solution, then ramp up to 1000 for spin-off, then 3000 final spin-off/drying stage.

Aaron A. Spearin
ASQ CSSBB
Engineering Six-S'$

http://www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee