Hi guys,
I am trying to make a 4 um gap between my Au electrodes on glass. So after HMDS, I have spun on 1813 photoresist, followed by 60 s softback. After lithography, develop, and a post bake for 5 mins at 140 C, my gap feature is about 4 um. So I think my lithography step is ok. However, after Au etch, my gap size is greatly increased (about 10 um). My Au layer is only 200nm, and I have calculated the etching time based on etching rate. It seems that some of my Au areas that are suppose to be under my photoresist are etched away. So is it possible that there are cracks between my photoresist and Au layer ? If so, how could I improve the adhesion between my photoresist and Au layer?
What you use to etch the gold is rather important. Some gold etchants work rather quickly and can cause a great deal of under etching. Using Ferric Chloride typically leaves a lot of underetching, so I would suggest using a gold iodine etch. There is a formulation from Transcene that you can use.
If the etching medium is not the problem. there are several methods for increasing photoresist adhesion on gold. One of the more popular methods is using HMDS (hexamethyldisilazane). Apply the HMDS before spinning the photoresist on the gold surface.
Another alternative is to use a metallic adhesion layer between the gold and photoresist. Depositing a thin layer of titanium on the gold layer will work well. I suggest applying a layer of HMDS between the titanium and photoresist.
I think you have to verify your etching solution and its etching rate...So, you can also reduce etching time to test if you are in over etching situation which is classical in this field; you can add a buffer layer as like titanium.
I suggest you to test lift-off process which is very original solution to avoid etching of gold : you deposit first photoresist and then the thin layer of gold, then you strip the photoresist by diluent as like acetone etc..; I’ve test it before several years it work very well...Good Luck
https://snf.stanford.edu/SNF/processes/process-modules/photolithography/lift-off-lol-procedures/liftoff
Photoresists often have bad adhesion to gold. I would suggest a metal interlayer as mr. Harrower said: our experience is with a chromium layer which is easily removable via wet etch. We use AZ456 series resists.
regards
Avise
As other colleagues mentioned, it is better to use more adhesive layer on top of gold either HMDS or another thin (10 nm is enough) metal layer. Titanium works very well for this purpose.
Also If you overexpose your photoresist even if you use positive photoresist, you may have undercut profile in your photoresist. So the distance between features will be larger than you expected on the bottom of photoresist. You may check this with SEM for better understanding the sidewalls of your photoresist and later you can adjust exposure settings again.
Regards,
Murat
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Carbon Materials
- Graphite
- Graphene