Uniformity of photoresist film coated on concave sphere

The flow mechanism of the photoresist on the concave sphere under centrifugal state is elaborated by the analysis of the photoresist coating process with centrifugation force. The critical factors that affect the evenness of photosensitive resist and the film forming quality, such as viscosity of photoresist solution, velocity of spin coating and time of spin coating, are investigated with experiments. The various phenomena occurred due to these factors are listed and analyzed theoretically. A mathematic model which describes the relationship between layer thickness and velocity is established by quoting the formula for the spin coating of photoresist film on the concave sphere. The effect of the fluid speed on the uniformity of the layer in the limited circular space is explained according to the principle of fluid mechanics. Accordingly，the key technology for preparing microstructure patterns on the concave spherical surface is achieved.