I have ~150nm PMMA coating Al2O3 (50nm) which I would like to etch ebeam fabricated patterns out of the Al2O3.
For UV litho patterns I use AZ 4533 and etch the Al2O3 with 80% H3PO4 at 110C. However, this etches through my PMMA as well.
I tried 5% H3PO4 (at 50C) for a gentler etch (needs 10+ minutes), but I can't tell if my PMMA will hold up to it.
Any thoughts?
What is your PMMA thickness? you could spin on your PMMA twice to double the thickness. First layer, bake, spin on the second and baking again. This is going To change your exposure etch time, I guess…
Dear Megan O. Hill
Thank you for your interesting question. As I not full expert in this field, I will borrow for you the following paragraph from [1]:
"Taking into account Al2O3/PMMA etch selectivity, the 750–2500 nm thick resist mask is required to provide high-quality 100 nm features etching. In this case, the aspect ratio for the e-beam lithography process varies from 1:7.5 to 1:25, which is an extremely difficult task for standard PMMA-like resists and 50/100 kV e-beam tool."
Hope this be helpful. Best regards
[1]https://www.proquest.com/docview/2533675485
Dear Megan O. Hill
Hu & al. (Appl. Phys. Res. 2009, https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.651.6657&rep=rep1&type=pdf) have etched anodic aluminum oxide in 3% H3PO4 at room temperature, so it's possible that you could use milder conditions than what you have tried. You can also raise the pH of your 5% H3PO4 by adding a small amount of base (e.g. 0.1-0.3% NH3).
You can also try chelating agents, like HEDP (1-hydroxyethylidene-1,1-diphosphonic acid a.k.a. etidronic acid), citric acid, nitrilotriacetic acid...
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