My go-to recipe for ebeam-RIE nanopores
- spin-coat: a 100-nm thick layer of poly (methyl methacrylate) (PMMA) electron sensitive resist (molecular weight 950k, 3% dissolved in anisole, MicroChem Corp) on 20 nm free-standing silicon nitride membranes (usually a 4-by-4 chipset): 5000rpm, 1min
- ebeam with EBPG5200, Raith, 4000-5000 µC/cm2 dose, 16-nm beam size, 2-nm beam step size (can be different)
- Develop: methyl-isobutyl-ketone (MIBK) and isopropanol (IPA) with a ratio of 1:3 for 1 min, stop in IPA for 30 sec.
- O2 plasma descum (optional): PVA Tepla 300, with faraday cage!, 200 cm3/min O2, 100 W, 30 sec
- RIE with fluoroform and argon: 200-250 s, 50 W, 50 sccm of CHF3, 25 sccm of Ar, 10 μbar, Sentech Plasma System SI 200. Etch rate might vary between batches. Discuss with your supporting staff and do some tests (note down the bias voltage during etching. Usually it is a sign of the actual etch rate)
- O2 plasma to remove resist: PVA Tepla 300, without faraday cage, 200 cm3/min O2, 100 W, 1-2 min
- Clean with acetone for 5 min (if resist is not completely removed by plasma. Usually, I do it anyway, it can be shorter as long as PMMA is removed), then immerse into IPA before spin-dry
I've been using this recipe over the last 4 years and it works perfectly. Please let me know if you have any questions about this. I would be very happy to help!