Microfluidics 1 - Mold Fabrication: Spin Coating of Photoresist
Serhat S, C. Yunus Sahan
Abstract
Microfluidic Lab-on-a-chip technology has several different materials and fabrication methods. PDMS (PolyDiMethylSiloxane) is a well-known material and due to its several advantages, it is one of the most prefered material. PDMS chip fabrication technique requires an initial master mold on which replicates can be done. Su8 is a photoresist resin used in MEMS technology for relatively thick structures. PDMS microfluidic chips fabrication is suitable for SU8+Si wafer molds. This protocol describes the coating of SU8 photoresist on silicon wafers by spin coating method in our laboratories.
Before start
This protocol is derived from
[Reference: Processing guidelines for permanent epoxy negative photoresist SU8 2025, SU8 2035, SU8 2050 and SU8 2075, MicroChem company ]
Steps
SpinCoater Instrument Adjustment
Dispense 1ml of photoresist (SU8) resin for each inch (25mm) of Si wafer substrate diameter.
Spin at 500 rpm for 10 seconds with an acceleration of 100 rpm/second.
Spin at "N" rpm for 30 seconds with an acceleration of 300 rpm/second.
Expected results of photoresist thickness:
40um film thickness with N=4000 rpm spin of SU8 2050
25um film thickness with N=4000 rpm spin of SU8 2025
75um film thickness with N=2000 rpm spin of SU8 2050
40um film thickness with N=2000 rpm spin of SU8 2025
Spin Coater Run
Place the wafer in the spin coater and run the device.
Microscope slides, Si/SiO2 wafers, and glass/PMMA wafers are alternatives substrates.
Equipment
| Value | Label |
|---|---|
| Spin Coater | NAME |
| Laurell | BRAND |
| WS-650MZ-23NPPB | SKU |
| www.nehirbt.com.tr | LINK |
Soft Baking of SU8 Coated Wafer
Soft baking is done depending on the thickness of the coated photoresist film.
It is a few minutes of baking at 65oC and 5-15 minutes of baking at 95oC are applied.
Equipment
| Value | Label |
|---|---|
| Hot Plate | NAME |
| Electromag | BRAND |
| LB.EM.M4060 | SKU |
| www.nehirbt.com.tr | LINK |
Stocking the Coated Wafer
In a petri plate, covered tightly with aluminum foil, photoresist-coated wafers can be stored in the cleanroom at room temperature for approximately one month.
