Influence of rectangular substrate chamfer on edge bead effect of a spin-coated thin film

Abstract

Spin coating is a common method for fabricating thin films. The edge bead effect is a major contributor to thin film non-uniformities. This study investigates the influence of chamfer angles and widths of a rectangular substrate on the edge bead formation mechanism in spin-coated films. Through the use of volume-of-fluid simulations and experiments, it was determined that the chamfer angle had a significant impact on the edge bead effect, while the chamfer width was not found to be a major factor. The use of a synchronous chamber in spin coating was found to negatively affect film planarization by restricting solvent evaporation and elevating its concentration, leading to a decreased film thickness. Additionally, the study concluded that the edge effect is not impacted by the Bernoulli effect or liquid accumulation along the edge if the average film thickness is below 1500 nm. The main reason for reducing the height of the edge bead was determined to be liquid fusion at the edge of the substrate, which only occurred when the chamfer width was close to the film thickness.