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Module 3: Fabrication Techniques

20257m

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.

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