I use thermal evaporation to deposit a 10 nm Cr and a 50 nm Al layer on a SU8 layer. I then transfer a nanotube film on top of the metal layer and dip it in Acetone. however, i see that there is a lot of cracking of the metal layer and it also peels away. How can I prevent this?
As the Cr/Al layer itself is unaffected by acetone it suggests the Su8 substrate is partially dissolving in the Acetone releasing the evaporated layer.
You could ensure the Su8 is well cross linked (and more impervious to acetone) by hard baking it at 200C. If this doesn't solve your problem it suggests the SU8 surface isn't forming a well crosslinked structure. You could try removing this weaker surface prior to evaporation by soaking it in acetone.
Once you hard bake it SU8 becomes very difficult to remove with solvents, keep this in mind as it may affect other processing steps.
As the Cr/Al layer itself is unaffected by acetone it suggests the Su8 substrate is partially dissolving in the Acetone releasing the evaporated layer.
You could ensure the Su8 is well cross linked (and more impervious to acetone) by hard baking it at 200C. If this doesn't solve your problem it suggests the SU8 surface isn't forming a well crosslinked structure. You could try removing this weaker surface prior to evaporation by soaking it in acetone.
Once you hard bake it SU8 becomes very difficult to remove with solvents, keep this in mind as it may affect other processing steps.
Maybe you can find useful to check: http://iopscience.iop.org/article/10.1088/0960-1317/15/1/N01/meta;jsessionid=153196B5666211271C1DED70F339BDCC.c1.iopscience.cld.iop.org
Nikolai - Thank you for your suggestions.
I am partially crosslinking the SU8 layer by UV exposure. I am using the metal layer as a barrier layer against the dissolution of SU8 in Acetone in future processing steps. So I don't want to hard bake the SU8 layer since I need to remove the uncrosslinked layer at a later stage.
Hi Shivaram,
It's like a reverse lift-off procedure, wanting the solvent to not penetrate you metal layers. The simplest explanation is that the Cr/Al layer is not complete allowing solvent ingress to your SU8 layer. The most likely location for this is around sharp features in the SU8 or the sample edges. I think the first step would be to examine your metal layers with a scanning electron microscope, holes in the metal film should be obvious.
As for ensuring complete metal coverage on all SU8 surface you could try a non-directional metalization technique such as sputtering. Also if possible evaporating thicker layers will also help ensure any holes in the metal are filled.
Good luck,
Nik
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