Process of Thin Liquid Film Formation in Spin Coating

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Theoretical and experimental analysis has been performed on the film formation phenomena. In this phenomena the solutions diluted by volatile solvents are deposited on a rotating disk, film flow is formed resulting from centrifugal forces, and then a thin dry film is obtained after the entire solvent evaporation.In the theoretical study performed here ; An axisymmetric 2-dimensional numerical analysis including heat and mass transfer is performed for the liquid film and the adjacent gas phase. In this analysis the solution forms and radial dependency are determined for all of the variables. A 1-dimensional modeling is performed using these solution forms and then the entire process from the spin-up to the thin dry film formation is analyzed. The behavior of the radial flow convection and the solvent evaporation, the solute concentration increase in the film, and the effect of the process parameters such as spinning speed and the initial solute concentration, are clearly shown in this analysis.In the experimental analysis a spin-coater is set up and the following experiments are performed ;1. Thin film is coated on the silicon wafer for integrated circuits and the final film thickness is measured by ellipse thickness analyzer. 2. Transient film thickness in the process is measured using laser displacement meter. For these experiments the thickness prediction by the numerical method mentioned above is performed and the results are compared. Excellent agreement is observed between them and the validity of the 1-dimensional calculation modeling is assured. 3. A shadowgraph visualization technique using argon-ion laser is applied on the film flow and showed that the surface wave observed in the initial stage vanishes in the process. 4. Mach-zehnder interferometer using argon-ion laser is applied and the distribution of the film thickness is measured. It can be concluded that almost uniform thickness is obtained.