Prism-assisted inclined UV lithography for 3D microstructure fabrication

Abstract

A prism-assisted inclined ultraviolet (UV) lithography technique is introduced for the fabrication of three-dimensional (3D) microstructures. Slanted structures with exposure angles ranging from 0 • to 60 • in SU-8 photoresist have been easily achieved without immersion in the index matching liquid. The fabrication process of multidirectional slanted structures can be simplified by one-step UV exposure using a prism with multidirectional side surfaces. A corner prism and a cone prism have been used in our experiment to demonstrate this concept. Upside-down tripod structures and horn structures have been fabricated in one-step exposures. The effective exposure area as one key parameter of the one-step exposure is analyzed for practical applications. Examples of various 3D microstructures fabricated by this method are presented.

Sculpting Asymmetric, Hollow‐Core, Three‐Dimensional Nanostructures Using Colloidal Particles

“…The second shell angles are lower than the first shell angles on the same side, meaning increased obliqueness of the outermost surface of the nanostructure. This behavior is unique because of the existence of higher order side lobes in the scattering intensity pattern, compared to the oblique microlithography which adopts the non‐diffractive shadowing effect . The center hole angle closely follows Snell's law when ignoring the nanosphere for both FDTD simulation and experiments, indicating the particle has negligible effect on the center hole angle.…”

“…One interesting subgroup of 3D nanostructures are hollow‐core structures, where hollow nanoparticles and microneedles have been studied for drug delivery applications, spherical nanoshells can be used for broadband light trapping in solar cells, and hollow metal structures have extensive applications in plasmonics and photonics . Another interesting subgroup are tilted structures lacking mirror symmetry along one axis, which can induce anisotropic material properties . The well‐known directional adhesion of gecko's foot is enabled by the tilted arrangements of setae and spatula .…”

“…Gecko foot‐like structures have been realized using directional reactive‐ion etching (RIE) and soft lithography, directed growth of carbon nanotubes, and electron/ion beam bombardments . Engineered slanted surface structures with anisotropic wetting properties have been achieved using oblique‐angle microlithography, mechanical deformation, and holographic lithography, and structures with more complex symmetry can be achieved by using multiple exposures and elastocapillary self‐assembly . While these existing techniques can enable slanted microstructures, controlling geometry other than tilt angle can be difficult.…”

Multidirectional UV-LED lithography using an array of high-intensity UV-LEDs and tilt-rotational sample holder for 3-D microfabrication

“…A focused UV light stayed at a fixed position with on-and-off function is synchronized with an x-y-z movable sample holder to draw a pattern by layers to form 3-D structure. A prismassisted lithography introduced to change the light exposure angle to photopattern a slanted sidewall of the 3-D microstructure [4]. A backside UV exposure and multiple layer stacking method by the aid of a fine alignment system was also introduced to form several hundred micron 3-D structures for cell culture scaffold application [12].…”

Dimensionally controlled complex 3D sub-micron pattern fabrication by single step dual diffuser lithography (DDL)

“…Various kinds of microfabrication processes were developed and studied by the researchers over the decades including surface micromachining [2], bulk micromachining [3], and LIGA process [4] until recently, when three-dimensional (3D) microstructures like microlenses, micro/nanotips, microtrapezoids have been focused in various microsystems such as microfluidics, micro optics, electronic and mechanical devices [5][6][7][8] for which these processes have been considered inadequate. New processes were introduced in order to fabricate such complex 3D microstructures including deep reactive ion etching [9], inclined UV lithography [10], thermal reflow [11,12], focused ion beam [13,14], UV proximity printing [15,16], UV microstamping [17] and so on [18,19]. However, these 3D microfabrication processes revealed various kinds of limitations and disadvantages such as most of them require special equipments, process is costly, have low throughput and above all most of the processes are limited to specific pattern fabrication.…”