Non-Invasive Millimeter-Wave Profiler for Surface Height Measurement of Photoresist Films

This work presents a low-cost non-invasive millimeter-wave surface-height measurement sensor of dielectric and polymer films on glass and quartz substrates. The surface-height profiler utilizes near-field resonance measurement technique operating at 96 GHz implemented by using a single complementary split-ring resonator (CSRR) integrated with a tailor-made WR10 rectangular waveguide. By placing a glass or quartz substrate uniformly coated with SU-8 photoresist on top of the CSRR, the thickness of the SU-8 polymer can be extracted based on the reflected and transmitted electromagnetic-wave energy interacting at the electrical boundary between the substrate and polymer film. Uniform single layers of SU-8 polymer with thicknesses from 3 to 13 μm, coated on top of glass substrate are measured and characterized. The extracted polymer-film thicknesses from the sensor in this work show an agreement of higher than 95% as compared to the commercial surface profiler instrument, while offering various advantages e.g. non-invasion, ease of measurement setup, low-cost and miniaturization.