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  for Metal Finishing since 1989
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Cl plasma etch of Al using photoresist as a mask

I use a plasma etch based on Cl chemistry to etch anisotropically in Al. My plasma consists of Cl2, SiCl4 and He and I use S1813 as a mask for my Al. S1813 is a organic photoresist.

Using spin coating I deposit a few hundred nm thick layer of the organic photoresist. Using optical lithography I pattern my photoresist, develop it and use it as a mask for etching the Al layer (which is 200nm thick and on top of a Si substrate).

After the etch I clean the substrate with HNO3 to get rid of the organic photoresist. Using a SEM to inspect my samples I can see that most of the photoresist is gone. But at the sidewalls where the photoresist has been in contact with the plasma gas the resist can not be removed.

I therefore expect the Cl ions to react with my organic resist. Can anyone tell me what kind of reaction product I have on my samples and how can I remove this residue without destroying my samples. I've tried hot acetone, resist strippers like PRS3000 and REZI-28 (baker) but nothing works. I also tried HF but this is etching my Al away from my Si faster then it's etching the residue so that's not a solution.

It's very important that I get this mess off my samples. I use the described technique to make very small Josephson junctions so the Al area should be well defined. But part of the Al is now covered with this non conducting mess so it's impossible for me to determine accurately what the size is of my tunneling area. For the smallest junction area's the mess clogs up everything so these junctions don't work at all.

Thanx everyone.

Arjan van Zuuk
- Delft, The Netherlands
2000

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Tack an oxygen or argon/oxygen plasma/RIE step after chloride based aluminum etch (and assumed fluoride plasma passivation).

The material you are attempting to remove is heavily cross-linked photoresist. These residues are common in processes where organics are exposed to high energy particles, e.g., plasmas, ion implantation. The residue may be removed (slowly) by ashing in some cases. A more efficient approach would be an RIE using an argon/oxygen blend which should quickly strip the residue by a combination sputter etching and ashing.

Gene Garrett
- Dallas, Texas
2000

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Dear Finishing:

I would like to know where I can look at to get thermodynamics parameters such as free energies of CVD and etch reactions. Thank you very much for your information in advance.

Sincerely yours,

Park Sang Hyun
- Export, Pennsylvania
2001