Explain the fabrication steps for high-aspect-ratio structures using SU-8 photoresist and Ultraviolet (UV) lithography.

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## SU-8 High-Aspect-Ratio Structures Using UV Lithography

SU-8 is a negative epoxy-based photoresist capable of forming thick, high-aspect-ratio structures.

### Fabrication steps
1. **Substrate preparation:** Clean and dehydrate the silicon/glass substrate.
2. **SU-8 coating:** Dispense SU-8 and spin coat it to the required thickness. For very thick layers, multiple coating steps may be used.
3. **Soft bake:** Heat the coated wafer to remove solvent.
4. **Mask alignment:** Place the patterned photomask over the wafer.
5. **UV exposure:** Expose the SU-8 through the mask. Exposed regions undergo cross-linking.
6. **Post-exposure bake:** Further cross-link the exposed regions.
7. **Development:** Developer removes the unexposed SU-8, leaving the patterned high-aspect-ratio structures.
8. **Rinse and dry:** Remove developer residue.
9. **Hard bake, if required:** Improves stability and mechanical robustness.

### Why SU-8 is suitable
It provides thick films, high aspect ratios, good chemical resistance, good mechanical strength and relatively high resolution, making it useful for microchannels, molds and microstructures.

SU-8 High-Aspect-Ratio Structures Using UV Lithography

Fabrication steps

Why SU-8 is suitable

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