Spin Coating on Spherical Surface with Large Central Angles

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.

Uniform and bright light emission from a 3D organic light-emitting device fabricated on a bi-convex lens by a vortex-flow-assisted solution-coating method

“…2d, for a given volume of the solution V 0 of 0.2 ml, the film thickness h directly corresponds to the rotational speed; i.e., the thickness h of the vortex-spin-coated SY layer decreases continuously as the angular speed (ω) increases in both the centre and edge regions of the lens substrate. This result is similar to the theoretical description of the conventional spin-coating model, which can be explained using the empirical equation ( h ∝ a(1 + b(ω 2 + c)) −d ) 37–39 . The theoretical curves from the equation are shown in the figure as solid curves.…”

“…This excellent film-forming ability is mainly due to the reduced line tension levels among the solution, air, and substrate at the contact line during the coating process, in contrast to the typical coating methods mentioned above. Moreover, the film thickness of the vortex-spin-coated layer can be explained in terms of a typical spin-coating description 37–39 . As a proof of concept, we present vortex-spin-coated 3D OLEDs fabricated on bi-convex lens substrates which exhibit excellent device performance with a solution-processable hole-injecting polymer (poly (styrene sulfonic acid) doped poly (3, 4-ethylenedioxythiophene), PEDOT:PSS) as a hole-injecting layer (HIL) and a yellow-emitting copolymer (Super yellow, known as SY) as a light-emitting layer (EML).…”

Mathematical model for thickness of off‐center spin‐coated polymer films

“…Due to its versatility, spin coating has been modified to be applicable to fabricate a thin film not only on a flat, horizontal surface rotating around its center. Adaptations of the method include coating films on flat surfaces with small semiconductor nanoparticles and coating films on both concave and convex surfaces …”

“…Thickness of the film is a crucial parameter affecting properties of organic electronic devices including organic light‐emitting diodes, organic field‐effect transistors, and organic photovoltaic cells . Due to its significance, several attempts have been proposed to model the thickness of a spin‐coated film . Attentions have been paid on effects of various conditions on the thickness including mainly viscosity, spin speed, or shape of the substrate .…”

“…Due to its significance, several attempts have been proposed to model the thickness of a spin‐coated film . Attentions have been paid on effects of various conditions on the thickness including mainly viscosity, spin speed, or shape of the substrate . However, these reported models are not applicable to calculate the thickness of an off‐center spin‐coated film.…”