Spin coating is an important method used to form a thin film in the microelectronics industry where the thin-film coating is needed. It is a process in which the solution is spread evenly over a surface using centrifugal force when the substrate is rotating. The spin coating process includes typically four steps: a deposition stage, substrate spin up or acceleration stage, a stage of substrate rotating at a constant rate where the fluid viscosity control fluid thinning and a stage at which substrate rotating at a continuous rate and the evaporation of the solvent continue to dominate the thinning behaviour of the spin coating fluid. There are many industrial applications based on curved surfaces such as protective coating against corrosion, metal shielding grid on the window of a fairing, UV light protection optical elements including curved grating, diffractive optical elements and the thin-film amorphous silicon solar cells.

The main objective of this research was to examine the spin coating on curved surfaces. An experiment was conducted on a hemispherical substrate on single-axis spin coater. The thickness of the film was compared using an Atomic Force Microscope (AFM) and Profilm3D optical profilometer. The thickness of the flat substrate (silicon wafer), and curved hemisphere (glass) were compared.

A 2D axi-symmetric COMSOL model has been designed around the z-axis of rotation. It was created by the Boolean operation of difference from two concentric spheres of constant thickness. The difference between these two layers of spheres represents the fluid thickness. The fluid material used in this model was engine oil since it has similar fluid properties to the polymer solution used for coating in the actual test. The laminar two-phase flow, coupled with moving meshes (ALE) was used for analysis. The boundary conditions included in this model acting on the inner surface wall of the fluid layer is a no-slip condition, whereas, for the outer surface, we applied zero radial displacement and free deformation.