Transmittance of baked spin-coated poly(methyl methacrylate) films

Abstract

Thin films of poly (methyl methacrylate), or PMMA, were fabricated by a spin-coating method and the effects of two fabrication recipes – the 2nd-step spin-coating speed and the baking temperature after spin-coating – on the optical transmittance of the film over the visible-to-infrared region were examined. For the 2nd-step spin-coating speed, it was observed that the transmittance of the film increased with the speed, but with a decreasing rate. This could be attributed to the film thickness; the film with a faster coating speed would be thinner, leading to higher transmittance. For the baking temperature, all the baked films provided roughly the same level of transmittance regardless of their baking temperatures after spin-coating, except the one baked at 130 °C. The sample baked at such temperature provided approximately 5% lower transmittance than those of the others. This effect was supposedly contributed to the glass transition temperature of the PMMA. The baking temperature of 130 °C was closed to the glass transition temperature of the material which is at 105 °C. Thus the film baked at such temperature was supposedly in a mixture of glassy state and solid state, leading to a disordered morphology and hence lower transmittance. The results from this study could be used to help adjust the fabricating conditions of a spin-coated film of PMMA to provide a required optical transmittance.