Non-alkaline developer/resist for photolithography ?

Sebastian J. Osterfeld sjo at
Wed Dec 13 16:33:51 PST 2006

Dear Labmembers,

I am looking for a purely solvent-based photoresist/developer 
combination, so that the fragile spin valves (magnetoresistive sensors) 
on my wafer are not exposed to the alkaline developer LDD26W, which can 
severely corrode their very fine and essential copper layer. LDD26W 
etches Aluminum at a rate of roughly 30 nm per minute, and copper even 
faster - once when I tried to make a copper hard mask, the LDD26W 
literally tore through the copper film even before the resist 
development was complete.

I need to fabricate metallic leads for these copper-film containing spin 
valves by means of a lift-off process, and where these leads overlap 
with the sensors, the opening in the resist exposes the sensors to the 
developer, quite possibly damaging them in the process. This may be a 
concern especially for submicron sensors - the smaller the sensors, the 
shorter the time they can withstand immersion in a corrosive environment.

On the other hand, the required feature size is quite lenient - 2 micron 
should suffice for the lead mask. This means a "coarse" process or 
resist would be o.k.

In summary:

- Solvent-based resist & developer for optical photolithography
- Avoids alkaline or corrosive aqueous solutions
- Suitable for lift-off of up to 300 nm metal (bilayer if possible)
- Coarse resolution (cd = 2 microns) is o.k.

Please let me know if you have a working recipe.


Sebastian J. Osterfeld
PhD. Student / Shan X. Wang Group
Dept. of Materials Science & Engineering

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