Novel exposure methods based on reflection and refraction effects in the field of SU-8 lithography

Abstract

Thick-film photolithography based on SU-8 has gained great interest in the field of microreplication technologies. For replication applications the SU-8 structures themselves or electroplated copies of the resist structures are used as casting or embossing tools. In this paper, a simple estimation model is proposed to predict the sidewall profiles of SU-8. This model is based on the effects of Fresnel diffraction and absorption resulting in useful approximations for the pattern profile of SU-8. Its usefulness is successfully verified by experimental results; the estimated and experimental results show similar trends. In addition, by utilizing this model two exposure methods based on reflection and refraction could be developed which avoid negatively sloped sidewall profiles of SU-8. Using these exposure methods, SU-8 preforms without undercut for the replication of optical waveguides have been achieved.

Cell architecture–cell function dependencies on titanium arrays with regular geometry

“…Fig.1B shows a close-up of the SU-8 3 Â 3 pillars viewed from the side and from the top. The dimensions of the resulting structures agree well with the intended design, except for rounded corners and a slight tendency towards negatively sloped side walls as a result of the relatively short exposure time [38]. Longer exposure times would result in sharper edges and steeper side walls, but at the expense of enlarged structures.…”

Controlled electroporation of the plasma membrane in microfluidic devices for single cell analysis

“…As reported by Kang et al, 26 the use of glycerin results in improved edge feature resolution through reducing diffraction effects, as evident in micrographs of the developed SU-8 with minimum line widths of 5 lm, also maintained in PDMS. The side wall angle approached 86.…”

“…23,24 It was applied to the coated glass substrate and spun at 3000 rpm for 15 s resulting in a 20 lm thick layer. Pre-exposure soft bake times were 3 min at 65 C, followed by 20 min at 95 C. A glycerin layer acted as gap filler and refractive index compensating media between the SU-8 and the photomask, 25,26 and a black matt transparency was placed under the glass substrate to absorb transmitted UV light. Post-exposure bake times were 1.5 min at 65 C and 30 min at 95 C, with the chemical development accelerated to 1 min through rigorous agitation, followed by a spray rinse with 99% isopropanol for 10-15 s and high pressure air drying.…”

Optimized SU-8 Processing for Low-Cost Microstructures Fabrication without Cleanroom Facilities

“…On the other hand, excessive UV exposure can lead to the hardening of the SU-8 parts that are not exposed since photoacid diffusion can occur. Moreover, it can also cause light diffraction/dispersion effect resulting in severe sidewall distortions [18]. The optimal exposure times using the equipment and tools presented above are shown in Table 3.…”