Abstract
The quality of high aspect ratio microstructures fabricated by deep X-ray lithography is highly dependent on the photoresist material used and the process parameters applied. Even with photoresists more suitable to this process, it is common to face defects in the final optical components, such as in case of X-ray gratings. The gratings need to be fabricated with critical dimensions on a sub-micrometer and micrometer scale, with periods of few micrometers and heights of hundreds of micrometers to be used in X-ray imaging techniques such as Talbot–Lau Interferometry. During the fabrication process, these features lead to challenges such as mechanical stability, homogeneity, and defect-free grating patterns. Usually, an epoxy-based negative photoresist is used in X-ray lithography, which needs to account for the shrinkage that takes place during polymer crosslinking in order to avoid defects in the final pattern. Nowadays, photoresist material still lacks certain suitable properties (chemical and mechanical) to fabricate gratings of high quality and with acceptable reproducibility. This work presents the results of TGA, FTIR, and MALDI-TOF analysis made on photoresists commercially available and suitable for X-ray lithography. The photoresists presented different profiles regarding the solvent content and oligomers composition, and in the case of some samples, there were high amounts of non-epoxidized oligomers.
Highlights
IntroductionDeep X-ray lithography (DXRL), which is the first step of the LIGA (a German acronym for “Lithographie, Galvanoformung, Abformung”) process, is used to manufacture high aspect ratio (HAR) micrometer and sub-micrometer structures out of polymer [1]
Negative photoresist solutions are usually based on epoxy resins, because this resin has mainly been used for microstructure fabrication (MEMS), optical sensors, micro-pieces of watches, radiation sensors, optical fiber components, conductive microstructures, photonic crystals, etc. [15,16,17]
Negative photoresists based on epoxy resins and applied in deep X-ray lithography were evaluated by Fourier-transform infrared (FTIR) and presented similar profiles concerning the organic groups in the mixture
Summary
Deep X-ray lithography (DXRL), which is the first step of the LIGA (a German acronym for “Lithographie, Galvanoformung, Abformung”) process, is used to manufacture high aspect ratio (HAR) micrometer and sub-micrometer structures out of polymer [1]. Depending on the structural requirements and other boundary conditions (e.g., tolerable exposure time), either a negative or a positive tone photoresist is used. Sci. 2018, 8, 528 prolonged exposure time especially for several hundred micrometer high structures [2,3]. Amplified negative tone photoresists are much more sensitive but show some structural deficiencies due to shrinkage during polymerization after exposure. It is evident that the quality of the products fabricated by the LIGA process is highly dependent on the raw materials used for patterning, as well as on their chemical behavior during processing. This resin is relatively cheap; the microstructures exhibit excellent properties, such as high mechanical resistance, thermal and chemical stability, and excellent transparency [14,17,18,19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
