Metrology and characterization of SU-8 microstructures using autofluorescence emission

Sophisticated three-dimensional microstructures fabricated using the negative tone SU-8 photoresist are used in many biomedical and microfluidic applications. Scanning electron microscopy (SEM) and profilometry are commonly used metrological techniques for the dimensional characterization of fabricated SU-8 microstructures but are not viable for non-destructive measurements and characterization of subsurface features like hidden microchannels. In this study, we report a unique methodology for the non-destructive dimensional characterization of SU-8 microstructures using the emitted autofluorescence radiation from fabricated SU-8 microstructures to generate depth profiles. The relationship between autofluorescence emission intensities and the thicknesses of the microstructures measured using SEM was determined and used to characterize the dimensions of unknown SU-8 microstructures based on their autofluorescence intensities. Lateral dimensions were also measured. This relationship was used to create highly accurate depth profiles for different types of microstructures including hidden subsurface features. These results were validated by comparison with SEM. The results suggest a feasible and accurate non-destructive, low cost, metrological technique to characterize SU-8 surface and subsurface microstructures using autofluorescence emission intensities.