Two-dimensional spin coating technology and the effect of artificial gravity on film's air-bubbling

This article mathematically and experimentally investigates the effects of increased artificial gravity acceleration on a film's air-bubbling defect. The controllable artificial gravity is generated using a two-dimensional (2D) spin coating method. In order to conduct these studies a 2D spin coater was designed and manufactured. The mathematics of particle motion in fluids (Stokes' Law) is investigated in order to analyze the motion of air-bubbles along the thickness of the film. The mathematic of particle motion in fluids is simulated using MATLAB in a wide range of variation of related parameters. These simulations illustrate that increasing the artificial gravity acceleration increases the velocity of air-bubbles motion and decreases the decay time of the air-bubble release. Simulations also show that the fluid viscosity and size of air-bubbles are effective factors which can affect the decay time of air-bubble release and their velocity along the thickness of the film. To investigate the simulation results, a high viscous photoresist (SU8-3050) is used as the coating material. The mentioned photoresist is coated with the both conventional and 2D spin coating methods and their results are compared. The surface and cross section of coated substrates are imaged with an SEM device. The natural results of mathematic simulations are in agreement with our experimental comparisons.