Planetary mechanism-based centrifugal force control technology to reduce undulation film thickness in spin-coating

One of the most widely used film-forming technologies in industry and research is the spin-coating method. Spin coating is a technology in which a coating solution containing dispersed functional materials is dropped onto a rotating substrate and the film is formed by centrifugal force generated on the rotating substrate. One of the major challenges in spin coating is the control of undulation film thickness. The authors have proposed a method to control the centrifugal force on the substrate by employing a planetary rotation mechanism that adds orbital rotation to the substrate's spinning rotation. Undulation film thickness is often caused by the centrifugal force in one direction due to the spinning rotation of the substrate, and a planetary rotation makes it possible to achieve homogeneous film formation by varying the centrifugal force on the substrate over time. In this paper, based on the results of film formation experiments using alumina slurry by planetary spin-coating and the observation of coating liquid flow on the substrate using black-and-white ink, the suppression effect of uneven film thickness was investigated, and undulation film thickness was successfully suppressed by planetary spin-coating and the suppression mechanism was discussed through the observation of coating liquid flow.