Abstract
Spin coating is one of the dominant processes for producing photoresistant thin films in integrated circuit manufacturing. The application of this process mainly focuses on flat surfaces. With the development of science and technology, the spin coating process is no longer restricted to flattened geometry. The demand for uniform thin films on curved surfaces urgently needs to be met, such as for the fabrication of anti-electromagnetic metal shielding grids on the window of fairings and grating on spherical lens. This is a challenging problem, and a fundamental mechanism is indispensable to provide guidance. However, few models have been reported about spinning a coating on curved geometry with a large central angle. To provide support for solving the problem of spin coating on a spherical surface with a large central angle, this paper presents a formulation for modeling the spin coating process on a spherical surface with a central angle close to 90 degrees and experiments that were completed to validate it. The film thickness evolution and uniformity of film thickness on a spherical surface are studied using this model and are compared with the existing literature to determine the potential advantages of the new model. Simulation results show that the uniformity of final film thickness is not ideal for uniform initial film thickness distribution. One dimensionless parameter is defined as the dominating factor to control film thickness and uniformity, which is related to the processing parameters. As demonstrated by the experimental results, this model can be adopted to predict film the thickness profile on spherical surfaces with large central angles.
Highlights
The process of spin coating is one of the dominating techniques for producing uniform thin films on flat surfaces in the order of micrometers or nanometers
To provide support for solving the problem of spin coating on a spherical surface with a large central angle, this paper focuses on film thickness evolution on a spherical surface with a central angle close to 90 degrees in the spin-off stage
The boundary condition for Equation (10) is Equation (12), at θ ≈ 0,. This boundary condition for Equation (12) is obtained from the symmetric geometry of the final film coat, which is verified by experiments [19,20]
Summary
The process of spin coating is one of the dominating techniques for producing uniform thin films on flat surfaces in the order of micrometers or nanometers. It is widely applied in depositing photoresist layers on silicon substrates. The precursive research of spin coating was performed by Emslie et al in the late 1950s [1] In that model, they studied the flow of a Newtonian liquid on an infinite flat substrate spinning at a constant angular speed. They studied the flow of a Newtonian liquid on an infinite flat substrate spinning at a constant angular speed They analyzed the mechanism of the spin coating process from the point of fluid mechanics.
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