Suspended microstructures of epoxy based photoresists fabricated with UV photolithography

Abstract

In this work we present an easy, fast, reliable and low cost microfabrication technique for fabricating suspended microstructures of epoxy based photoresists with UV photolithography. Two different fabrication processes with epoxy based resins (SU-8 and mr-DWL) using UV exposures at wavelengths of 313 nm and 405 nm were optimized and compared in terms of structural stability, control of suspended layer thickness and resolution limits. A novel fabrication process combining the two photoresists SU-8 and mr-DWL with two UV exposures at 365 nm and 405 nm respectively provided a wider processing window for definition of well-defined suspended microstructures with lateral dimensions down to 5 µm when compared to 313 nm or 365 nm UV photolithography processes.

Cross-functional photoresists and photopolymers enhancing micro- and nanofabrication

“…In addition, the adapted spectral sensitivity allows 3D patterning in a multi-layer process with e.g. i-line sensitive SU-8 resist as first layer and an @ 405 nm LDW mr-DWL layer on top to manufacture even more complex 3D devices [4].…”

One-Step Mask-Based Diffraction Lithography for the Fabrication of 3D Suspended Structures

“…Suspended carbon structures are the typical 3D C-MEMS structures free of any intermolecularity [2], presenting significant advantages in sensors [6, 7], microelectrodes [8, 9], and energy storage applications [9]. Various C-MEMS microstructures have been achieved through pyrolysis of polymer, in which SU-8 is the most widely used precursor for pyrolytic carbon structures [10, 11]. With respect to its low light absorption, it is easy to fabricate high aspect ratio microstructures with SU-8 [12].…”

“…Diverse approaches have been developed to fabricate suspended microstructures, such as E-beam writer [13–15], X-ray [10, 16], and two-photon lithography [17–19]. Two-photon lithography is a feasible way for achieving complex suspended structures, such as suspended hollow microtubes, with great accuracy but low efficiency [17].…”

“…Grayscale photolithography has also been applied in fabricating suspended structures with grayscale masks or maskless lithography systems [11, 23]. Since SU-8 is almost transparent when the light wavelength is above 350 nm [12], it is very difficult to control the accuracy of the thickness of the suspended layer by adjusting the exposure dose [8, 10]. Hemanth et al [10] optimized the UV wavelength in the exposure process according to the properties of SU-8.…”

“…Since SU-8 is almost transparent when the light wavelength is above 350 nm [12], it is very difficult to control the accuracy of the thickness of the suspended layer by adjusting the exposure dose [8, 10]. Hemanth et al [10] optimized the UV wavelength in the exposure process according to the properties of SU-8. They chose the UV wavelength of 405 nm for the high ratio microstructures and 313 nm for the suspended layer.…”