I am trying to make very small gap (preferebly ~100 nm)electrodes. My recipe roughly is:
1. Cleaning SiO2 with acetone and ipa
2. Dehydration bake @180C for 1 min
3. Spin coat PMMA A4 @3k rpm for 1 min
4. Softbake for 5 min
5. Expose e-beam ~350 uC/cm2 (JEOL JSM)
6. Cold Develop MIBK:IPA= 1:3 (5C) for 1 min
7. Sputter Ti 1nm, then Pt 15 nm
8. Liftoff @60C acetone for 1 hour
For some reason, the metal is not coming off from the gap region. Any idea on why this is happening and what to change? Thanks.
Hello
First of all, I think Acetone and IPA are not suitable for SiO2 removal. After washing with acetone and IPA, you need to remove oxide with HF (Either diluted or HF vapor). Second, the narrow gap might be problematic due to the large mean free path of metal (I am not sure by the way). One alternative method can be depositing metal on the substrate, then after a lithography step, try to etch the metal and keep a 100 nm narrow gap.
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