Thin Photoresist Film Thickness Characterization Using 96-GHz Slotted Ring Resonator

Non-destructive thickness measurement offers a valuable feature for thin polymer-based applications in both industrial and medical utilization. Herein, the author developed a novel, non-destructive, millimeter-wave WR-10 waveguide sensor for measuring a dielectric film layer on a transparent substrate. Complementary split-ring resonator (CSRR) was integrated on top of a customized WR-10 waveguide and operated at 96 GHz. The thickness of the SU-8 layers, ranging from 3-13 μm, coated on a glass substrate was then examined using the resonant frequency shift. The thickness values obtained from this novel sensor strongly resemble the values obtained from standard surface profiler measurement method, with less than 5 % difference. Thus, our novel design offers a comparable accuracy with a better cost effectiveness when compare with an existing commercial instrument.