Ultraviolet transmittance of SU-8 photoresist and its importance in multi-wavelength photolithography

Abstract

The transmission properties of SU-8 photoresist in the ultraviolet (UV) range are reported for resist thicknesses between 1 and 150 μm in the soft-baked state prior to lithographic exposure. Multiple transmission wavelengths in the UV region between 200 and 400 nm are found to be suitable candidates for self-limiting exposure and thus polymerization depth. This enables a novel method to realize microarchitectures via standard photolithographic techniques. Examples of three dimensional hollow polymer microarchitectures are presented to demonstrate the advantages of this method. The coefficient of attenuation is calculated using Beer–Lambert’s principle for different resist thicknesses.

Towards Green 3D-Microfabrication of Bio-MEMS Devices Using ADEX Dry Film Photoresists

“…Above a wavelength of about 450 nm, the unexposed resist is almost transparent with a transmission of larger than 96%. Compared to SU-8, ADEX shows a slightly lower optical transmission, but an overall similar spectral behavior [45].…”

“…As a certain light absorption is required to activate the photoinitiators and to expose the photoresist, the transmission spectra of an unexposed resist can give valuable insights into the lithographically usable optical wavelength range to expand the overall DFP usability and to enable multi-wavelength and grayscale exposure [45,46]. Hence, we measured the transmission spectra of two non-exposed ADEX foils of 20 µm and 50 µm thickness, laminated on amorphous silicon oxide (SiO 2 ) chips, using a dispersive spectrophotometer.…”

A Power Compensation Strategy for Achieving Homogeneous Microstructures for 4D Printing Shape-Adaptive PNIPAM Hydrogels: Out-of-Plane Variations

“…The suspension heights of the standard prints are set to be as low as possible to minimize the power decay between the layer and the cover slip so that the power reduction can be ignored. The SU-8 adhesion layer is known to be transparent to NIR lights [ 46 , 47 ] so we assume the power reduction in the 500 nm adhesion layer is negligible since the wavelength of the laser for the TPP process is 780 nm in our system. Figure 2 b shows the standard calibration prints with different laser powers for a consistent scanning speed of 8 mm/s in DI water.…”

Silicon‐Based Integrated Label‐Free Optofluidic Biosensors: Latest Advances and Roadmap

“…Owing to the standard lithography process, it offers a precision alignment between the on‐chip devices and microfluidic channels. [ 71 ] SU‐8 channels can be directly patterned onto the sensor surface with high precision at different heights in a single step by using multi‐wavelength lithography, [ 72 ] in particular when a fine interconnection is required between the fluidic inlet/outlet and the sensor device. As a drawback, SU‐8 has to be processed in a cleanroom and several processing steps must be conducted for achieving a multilayer platform that consumes more time in comparison with replicated PDMS platforms.…”

“…Owing to the standard lithography process, it offers a precision alignment between the on-chip devices and microfluidic channels. [71] SU-8 channels can be directly patterned onto the sensor surface with high precision at different heights in a single step by using multi-wavelength lithography, [72] in particular when a fine interconnection is required between the fluidic inlet/outlet and Adv. Mater.…”