Fabrication of circular sawtooth gratings using focused UV lithography. (20th January 2016)

• Record Type: Journal Article
• Authors: Mi, Wujun; Karlsson, Staffan; Holmberg, Anders; Danielsson, Mats; Nillius, Peter
• Is Part Of: Journal of micromechanics and microengineering. Volume 26:Number 3(2016:Mar.)
• Publication Date: 2016-01-20
• Subjects: focused UV lithography -- three-dimensional sawtooth structures -- SU-8 -- UV lens -- Fourier optics; Microelectromechanical systems -- Periodicals; Micromechanics -- Periodicals; 621.38105
• DOI: 10.1088/0960-1317/26/3/035001
• Languages: English
• ISSNs: 0960-1317

Abstract

Abstract: This paper presents a novel micro-fabrication method using focused ultraviolet (UV) light to manufacture three-dimensional sawtooth structures in ultra-thick negative photoresist to fabricate a novel multi-prism x-ray lens. The method uses a lens to shape the UV beam instead of the photomask conventionally used in UV lithography. Benefits of this method include the ability to manufacture sawtooth structures in free form, for example in circular shapes as well as arrays of these shapes, and in resist that is up to 76 μ m thick. To verify the method, initially a simple simulation based on Fourier optics was done to predict the exposure energy distribution in the photoresist. Furthermore, circular sawtooth gratings were manufactured in a 76 μ m SU-8 resist. The UV lens was fabricated using electron beam lithography and then used to expose the SU-8 with UV light. This paper details the complete developed process, including pre-exposure with an e-beam and cold development, which creates stable sawtooth structures. The measured profile was compared to the ideal sawtooth and the simulation. The main discrepancy was in the smallest feature size, the sawtooth tips, which were wider than the desired structures, as would be expected by simulation.