[labnetwork] Direct write + plasma etch residue

[Hollingshead, Dave]

Good afternoon everyone,

We have recently run into some very 'interesting' (completely perplexing) issues while trying to etch some III-V samples in our ICP. Essentially we are seeing some sort of residue on the protected regions of the devices after stripping the resist. Whatever it is, the material seems to also be affecting our etch profiles. The odd part is that the residue has a clear directionality to it and in the present case only appears on two edges. This has led us to believe that is must in some way be a result of some non-uniform / "angled" exposure from our MLA150. While I can completely understand differing etched sidewall slopes or skewed features if the resist sidewalls are not uniform on all sides, I am having difficulty understanding how this might cause the residue we are seeing (especially in a positive resist).

Any thoughts or possible explanations would be greatly appreciated.

Attached are some microscope and SEM images of what we are seeing. I have plenty more I'd be happy to share with those that may be interested!

A few relevant processing notes:

  *   All etches were done using a BCl3/Ar chemistry in our Plasmatherm 770 system
  *   ~18-20 minutes of etch time, total depth of ~2.5-3.0µm
  *   We have repeated these issues on InGaAs device samples as well as bulk GaAs test samples
  *   Issue repeated with both SPR220 and S1827 resist masks (both were un-hardbaked, but this is also something we are going to look into)
  *   Exposures seem to be properly dosed, but we are planning an etch test on a dose/defocus array to see if exposure has any effect
  *   All resist removal was done in 80C NMP
  *   We have attempted some follow-on O­2 plasma etches, that seem to remove the material, but it is very slow

Thanks,
-Dave

Dave Hollingshead
Manager of Research Operations - Nanotech West Lab
The Ohio State University
Suite 100, 1381 Kinnear Road, Columbus, OH 43212
614.292.1355 Office
hollingshead.19 at osu.edu<mailto:hollingshead.19 at osu.edu> osu.edu<http://osu.edu/>

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