SU-8 has become the favourite photoresist for high-aspect-ratio (HAR) and three-dimensional (3D) lithographic patterning due to its excellent coating, planarization and processing properties as well as its mechanical and chemical stability. However, as feature sizes get smaller and pattern complexity increases, particular difficulties and a number of material-related issues arise and need to be carefully considered. This review presents a detailed description of these effects and describes reported strategies and achieved SU-8 HAR and 3D structures up to August 2006.

https://iopscience.iop.org/article/10.1088/0960-1317/17/6/R01/pdf

SU-8: a photoresist for high-aspect-ratio and 3D submicron lithography

3.2. Two-Photon Lithography (TPL) 919 4. Serial Writing with Charged Particles 920 4.1. Electron Beam Lithography 920 4.2. Ion Beam Lithography 920 4.3. Scanning Probe Resist Lithography 921 5. Microand Nanomachining 921 5.1. Focused Ion Beam 921 5.2. Scanning Probe Nanomachining 921 6. Direct Writing and Material Deposition 921 7. Moulding 922 7.1. Mould Fabrication 922 7.2. Demoulding: Mould Treatment 924 7.3. Embossing Thermoplastic Materials: Nanoimprint Lithography (NIL) 924

Fabrication approaches for generating complex micro- and nanopatterns on polymeric surfaces.

A novel fabrication process was developed to create high aspect ratio (>10:1) carbon posts, all-carbon suspended bridges and wires, self-organized bunches of carbon posts, and carbon plates supported by carbon beams. The structures are all made from a two-step pyrolysis process with SU-8 photoresist as the starting material. In this paper we describe the fabrication of these various new C-MEMS structures and detail an important application of the high aspect ratio carbon posts arrays. The carbon post arrays can be reversible charged/discharged with Li ions, an application that may greatly impact the application of C-MEMS in three-dimensional microbatteries. Complex suspended C-MEMS structures, such as wires, plates, ribbons, and self-organized bunches of posts, were built. Methods to accurately and repeatedly fabricate all the above 3-D C-MEMS structures are given.

A novel method for the fabrication of high-aspect ratio C-MEMS structures

Removal of SU-8 photoresist for thick film applications

Free-standing SU-8 chips with enclosed microchannels and high density of fluidic inlets have been made in a three-layer process which involves SU-8 to SU-8 adhesive bonding and sacrificial etching. With this process we can fabricate microchannels with depths ranging from 10 to 500 μm, channel widths from 10 to 2000 μm and lengths up to 6 cm. The process is optimized with respect to SU-8 glass transition temperature. Thermal stresses and thickness non-uniformities of SU-8 are compensated by novel mask design features, the auxiliary moats. With these process innovations filling of microchannels can be prevented, non-bonded area is minimized and bonding yields are 90% for large-area microfluidic chips. We have released up to 100 mm in diameter sized microfluidic chips completely from carrier wafers. These free-standing SU-8 chips are mechanically strong and show consistent wetting and capillary filling with aqueous fluids. Fluidic inlets were made in SU-8 chips by adding one lithography step, eliminating through-wafer etching or drilling. In our process the inlet size and density is limited by lithography only.

/pdf/free-standing-su-8-microfluidic-chips-by-adhesive-bonding-1pilwlp6p4.pdf

Richard P. Janek

Papers

High aspect ratio patterning with a proximity ultraviolet source