Optical Transmittances of Spin-Coated Polymer Films with Different Spin Step Protocols

Abstract

In this report, we studied the effects of different spin-coating step protocol on the optical transmittance of thin film polymer. Thin films of poly(methylmethacrylate), or PMMA, were spin-coated with two different spin step protocols – the speed-up and speed-down protocols. In each protocol, the spin-coating had two steps, the first and the second steps. In the speed-up protocol, the first step was slow, while the second faster step was faster. In the speed-down protocol, the first step was fast, while the second step was slower. All the films were subsequently characterised for their optical transmittance over the visible region. There were at least three points worth explained from the experimental results. Firstly, for the speedup protocol, when the second-step speed was slower than 4000 rpm, the transmittance of the film were varied and did not show any relation with the first-step speed. However, when the second-step speed was faster, all the films, regardless of the first-step speed, provided roughly equal transmittance. Secondly, for the speed-down protocol, when the second-step speed was slower than 3000 rpm, transmittances from all films were varied. But when the second-step speed was faster, all the films from all first-step speed gave roughly equal transmittance. As the transmittance is related to the film thickness, these results indicated that, regardless of what the protocol was, if the second-step speed was fast, the film thickness from any first-step speeds would be roughly equal to each other. Finally, for the same pair of speeds but with different protocols, a film with a speed-down protocol provided a relatively higher transmittance than one from a speed-up protocol, implying a thinner film. The results from this study could be further developed to understand how the spin-speed protocol could be chosen to provide a thin film with required thickness.