Dependence of Film Thickness on Speed in Spin Coating

Abstract

The observed variation of film thickness with spin speed (i~) in spin coating is summarized for resists, spin-on glasses (SOGs), and polyimides. While the thickness measurements of resists and SOGs show an ~ 1/2 dependence, the data for polyimides show a wide variation in speed dependence, from ~l-1 to gt-~/2. The possible non-newtonian nature of the fluid (modeled as a truncated power law) cannot explain this behavior since predictions indicate that non-newtonian effects are always accompanied by a variation in the thickness with radial position, a variation which has not been observed experimentally. However, the type of evaporation model used for the fluid can cause the thickness to vary with speed in the observed fashion. This suggests that the polyimide behavior is a result of differences in the evaporation rate of the solvent.

Spin coating of conjugated polymers for electronic and optoelectronic applications

“…It has been well documented that the film thickness plays a critical role in the morphology and properties of conjugated polymers and the performance of devices based on polymer semiconductors [1][2][3][4][5][6][7][8][9][10]. Although there have been many studies of the spin coating process for many other materials , including photoresists [12,16,22,23], polyimides [13,24,30], sol-gel materials [25] and polyimide-silica hybrid materials [31], neither experimental nor theoretical analysis of the spin coating of conjugated polymer solutions has been reported.…”

“…The dry (final) film thickness, h f , after spin coating of a polymer solution was found to be correlated to the initial polymer weight fraction, x 1,0 , and the spin speed, x, by Eq. (1) [12,22]: where k is a constant that depends on the concentration, solution viscosity, and other properties of the polymer and solvent. In the case of most photoresists or spin-on-glass (SOG) materials, the exponent b of spin speed is close to 0.5 [12,22].…”

“…(1) [12,22]: where k is a constant that depends on the concentration, solution viscosity, and other properties of the polymer and solvent. In the case of most photoresists or spin-on-glass (SOG) materials, the exponent b of spin speed is close to 0.5 [12,22]. However, for polyimides or hybrid materials, the exponent b shows a wide variation from 0.5 to 1.0 [22].…”

“…In the case of most photoresists or spin-on-glass (SOG) materials, the exponent b of spin speed is close to 0.5 [12,22]. However, for polyimides or hybrid materials, the exponent b shows a wide variation from 0.5 to 1.0 [22]. Such a variation of the exponent b has been explained as due to the relative evaporation rate of solvent or achievement of steady state during spin coating [21,22].…”

“…However, for polyimides or hybrid materials, the exponent b shows a wide variation from 0.5 to 1.0 [22]. Such a variation of the exponent b has been explained as due to the relative evaporation rate of solvent or achievement of steady state during spin coating [21,22]. Typically, the film thickness of spin coated photoresists or waveguide materials is in the range of several micrometers [12,30,31].…”