Hi. Thank you for looking into my question.
I have designed specific structures that need two layer of photoresist. The first layer is planned to be dual-tone negative and the second layer to be +ve.
The problem is, when I tried to spin-coat the second layer onto the first layer, the photoresist did not spread well. I could see it spread like a shape of star. My first layered structure also disappeared where the second layer of PR has covered.
I am using AZ5214E and I haven't hard-baked my PR because it will make it hard for my subsequent step (lift-off)..
Would you please share some experiences in fabricating two layer of photoresist? How can I solve this problem?
Thanks so much!
I found this article related to your question.
Conference Paper A high resolution double layer photoresist structure for lif...
If you don't want to hard bake the first layer, you can heat it at lower temperature or leave it under the room temperature for half an hour, so that the solvent evaporates partially making it more stable. Yet, I don't think it resolves your problem.
What are the two resists you are using?
I think when it comes to bi-layer resists you have to watch out for:
1. Chemical compatibility, does the solvent used for the 2nd layer resist dissolves the first layer. This can be improved by baking the first layer resist for longer duration. You should also start spinning the resist as soon as it is applied onto the first layer.
2. Modifying the surface energy on the resist surface so it will wet the second resist properly. This could be enhanced with a short, low power O2 plasma treatment.
You mentioned the "star" pattern when the second layer is applied. This could be from the insufficient material, or poor surface wetting. Did the second layer resist bead up like a water droplet when it was applied?
Hope this helps!
Hi,
This paper might be of interest Article Offset masks for lift‐off photoprocessing
. Former colleagues successfully used this method to make their micron dimension devices.I hope this helps.
Best regards,
Martin
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