Bubbles in AZ P4620 after UV exposure on polyimide

19 July 2025 1 6K Report

Hello everyone,

My name is Woonghee Cho, currently a Ph.D. student in South Korea.

I'm reaching out because I've encountered an issue that I couldn't resolve on my own, and I would truly appreciate any insights or suggestions you might have.

After forming a polyimide film using an amic acid solution purchased from Sigma-Aldrich, I attempted to pattern AZ P4620 on top. However, as shown in the attached image, a large number of air bubbles appeared after exposure. I suspect that humidity may be a contributing factor, but I’m not certain about the exact cause.

If anyone has experience with this issue or knows of a possible solution, I would be very grateful to hear your advice.

To help clarify the process, I’ve included a detailed description of the fabrication steps below.

Performed piranha cleaning followed by standard degreasing of the glass substrate (acetone, IPA, DI water).

Carried out sufficient dehydration at 110 °C.

Spin-coated PMMA and fully cured it on a hot plate at 180 °C.

Spin-coated the amic acid solution, removed the solvent by baking at 150 °C for 30 minutes on a hot plate, and then conducted imidization in a vacuum oven at 220 °C for 4 hours.

Due to high humidity during the summer monsoon season, an additional moisture removal step was added by baking at 110 °C.

Spin-coated AZ P4620 and performed soft-baking at 115 °C for 3 minutes.

Upon exposure, air bubbles like those shown in the image appear.

Note: This issue did not occur before the summer monsoon, even without step 5.

Marco Asa

Not that I have a direct experience with that to help you, but this is not clear to me. By "exposure" you mean exposure to UV light or just air exposure?

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