SU8

SU-8 is a negative photoresist widely used in microfabrication and micromachining. It is an epoxy-based polymer designed to yield thick, high-aspect-ratio structures with strong chemical and thermal resistance. SU-8 patterns remain insoluble after exposure and development, making them robust for molds, microfluidic channels, and MEMS components.

The resist comprises an epoxy resin, a crosslinker, and a photoinitiator. When exposed to near-UV light, the exposed regions crosslink and become resistant to the developer, while the unexposed areas are dissolved. This property enables precise pattern transfer with relatively tall features compared to many other resists.

Processing involves several steps. The resist is spin-coated to achieve the desired thickness, typically ranging from tens to hundreds of micrometers. A prebake drives off solvent, followed by UV exposure through a photomask. A post-exposure bake enhances crosslinking, after which the pattern is developed in a PGMEA (propylene glycol monomethyl ether acetate) solvent or a compatible developer, rinsed, and often hard-baked to improve adhesion and stability.

Key advantages include the ability to fabricate high-aspect-ratio, thick films with good chemical and thermal resistance and compatibility with common silicon, glass, and PDMS workflows. This makes SU-8 popular for microfluidics, optical components, and masters for soft lithography, among other applications. Limitations include the need for careful processing control (solvent content, bake profiles) and limited ability to rework cured features. SU-8 is available in multiple formulations designed for different thickness targets, so process guidance from suppliers is essential. Safety considerations include proper ventilation and handling of epoxy resins and solvents.