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Epoxy SU-8: fabrication Tips recommandations

Epoxy SU-8: fabrication tips

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Epoxy SU-8: fabrication Tips recommandations

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    1. Epoxy SU-8: fabrication Tips & recommandations Prior spin casting Epoxy ?A thin Ti layer is recommanded in most cases. ?adhesion on SiO2? It is possible to treat the surface with an adhesion promoter (find the information). Dicing the mold ?This will prevent “long range” internal stress to develop through out the entire wafer. ?Round the corner of your molds to prevent stress concentration.

    2. Epoxy SU-8: fabrication tips & recommandations Spin-casting of SU-8: control of final thickness Weight the SU-8 before and after spin-casting. Run a couple of test wafers prior using any “unknown” bottle of epoxy and/or when changing from one wafer size to another. Procedure: pour, weight, spincast, weight, process as described in litterature. Control thickness under step-profiler . This method leads very accurate results for thick layers (>50 microns). Think about using hot plates carefully leveled

    3. Epoxy SU-8: fabrication Tips & recommandations Re-planarization on top of wafer with topology Excellent, even for ultra thick structures (>250 microns) Procedure: the amount of epoxy is defined in function with the geometrie, thickness and number of pre-existing structures. A good start is to use the equivalent mass of epoxy in order to spin a layer that would otherwise be as thick as the thickest structure present on the wafer. Tip: Fabricate a “test” wafer with “fake” epoxy pre-existing structures

    4. Epoxy SU-8: fabrication Tips & recommandations Photolithography Hardly successful on top of thick Al layer: epoxy that should not be exposed to UV light tends yet to cross-link. Solution: if possible, deposit a Ti layer. Ti is not as reflective as Al. Su-8 does not seem to be dramatically affected by direct exposure to regular light. Development of SU-8 Rinsing after PGMEA: quick TCE (more aggressive than PGMEA), quick Iso-propanol. If any white residues appear, immerse the wafer back into PGMEA. TCE is dangerous sometimes deleterious to thin tall structures! If possible: use a quick RIE (6-7 min, 300W, 50 sccm O2, 5 sccmCHF3, 300mT) once the SU-8 is completely developed.

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