[labnetwork] Direct write + plasma etch residue

[Fouad Karouta]

Hi Dave,

A couple of remarks:
1- A Cl2-based chemistry react with resist materials and form a kind of a
compound that is very hard to remove in classic ways, even an O2-ashing may
not be helpful. I usually avoid using resist mask to etch III-V materials
and instead I use a hard mask like SiNx or SiOx (PECVD deposited) as a
mask, pattern it with a resist mask in a F-based chemistry), strip the
resist before going to the Cl2-based ICP RIE etch. After the etch the
remaining hard mask can be removed in BHF or a diluted HF
2- what is the wafer temperature during etch? In does require T>150C to get
the etching product InCl3 volatile. Not doing so will result in
micro-masking (check a paper I published in 2014).

Happy to discuss further details (offline) if you wish.

Fouad Karouta

On Fri, 29 Apr 2022 at 9:39 pm, Hollingshead, Dave <hollingshead.19 at osu.edu>
wrote:

> 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
> <https://www.google.com/maps/search/1381+Kinnear+Road,+Columbus,+OH+43212?entry=gmail&source=g>
> 614.292.1355 Office
> hollingshead.19 at osu.edu osu.edu
>
>
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