Hello!
I'm Hyunsu from hanyang university in Korea.
I have a problem with stripping off of az 4620 photoresist on Silicon when mask and photoresist is detached.
Photolithography process was done by down below order.
1. Spincoating to get 11 micro thick photoresist on silicon
2. Soft baking for 80 sec at 110 Celsius
3. Light exposure (1600 mJ/cm2)
4. Develop (5 min, AZ 400k (4:1))
What I have done to solve this problem was that
1. in order to enhance adhesion between Photoresist and Silicon, HMDS coating was used prior to the photoresist coating by spin coating, but this solution didn't work.
2. second, I thought that soft baking for 80sec is not long enough for hardening photoresist, so that it was stripped off when photoresist and mask were detached. Thus, I increased baking time longer (100, 120, 180, 240 sec), but they had the same problem.
I'm attaching optic microscope pictures that shows how the photoresist has been stripped off.
I hope you give me some advices on this problem.
Thanks
Sincerely,
Hyunsu Son
Hello,
Have you tried cleaning the Si surface first to remove organics and other contaminants
See https://www.inrf.uci.edu/wordpress/wp-content/uploads/sop-wet-silicon-solvent-clean.pdf
Hi,
often adhesion problems come from contaminants on the sample surface. So as suggested in the previous answer, try cleaning your samples. The standard clean is normally acetone followed by IPA, but stronger cleans, such as H2O2/HSO4 mixtures, or oxygen plasma etching can also be used.
Also, try a dehydration bake before spin coating.
And have you checked if the temperature control on your hotplates is accurate? 80 degrees is a relatively low baking temperature for most resists and if your hotplate is not accurate that might mean that the actual temperature is even lower and might not bake sufficiently.
Thank you all!
I followed your all suggestions.
As you all said, the problem was from contaminants on the surface.
Thus, I did the pretreatment for cleaning up the surface as you mentioned.
And it worked!
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