Fabrication of polyimide films with imaging quality using a spin-coating method for potential optical applications

Abstract Optical polyimide (PI) films were prepared by spin-coating from nearly non-volatile dimethylacetamide (DMAc) solutions. The uniformity of film thickness met the requirements of diffraction imaging quality. The results show that the final rotating speed ω , dynamic viscosity η , and initial polymer solid concentration c are the main factors affecting the film thickness T , and an empirical relationship which describes the film thickness as a function of the measured parameters was established to be T ∝ c 3.473 , η 0.586 , ω − 0.811 . $T \propto {c^{3.473}},{\rm{ }}{\eta ^{0.586}},{\rm{ }}{\omega ^{ - 0.811}}.$ Moreover, the viscosity dependence on concentration is system specific. Unlike traditional photoresist, the thickness uniformity of the PI film is determined by both spinning and precure process, which is intensively discussed in the present work. Uniform, 22-μm thick, PI films with transmitted wavefronts peak to valley (PV) ≤ 1/5 λ and root mean square (RMS) ≤ 1/50 λ were prepared under the optimum process: spin speed 900 rpm, initial fluid viscosity 10,500 cp, final spin time 120 s, precure temperature 70°C, spin process repeated 3 times. The results will find use in the production of optical quality membrane for ultra-lightweight optics or other applications.