I apologize for this late posting of the responses to my original inquiry
about carbon etchants. Thanks to all of you who provided me with
suggestions and helpful references. Below is a listing containing my
original inquiry, my results, and the responses to my inquiry.
Nigel Sharma.
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email: sharma@u.washington.edu
voice: 206-685-6878
web site: http://lettuce.me.washington.edu/micropump/
MicroFluidics Laboratory
University of Washington, Seattle, USA.
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ORIGINAL INQUIRY
====================================================
>From sharma@u.washington.edu Mon Nov 8 10:45:44 1999
Date: Thu, 7 Oct 1999 09:47:35 -0700 (PDT)
From: nigel r. sharma
To: MEMS@ISI.EDU
Subject: Carbon Etchant?
Does anyone know of methods and liquids for etching carbon (soot
particles)? I have soot particles deposited onto silicon or Pyrex
substrates and I need an etchant that will dissolve the soot without
attacking either substrate. I've tried a number of etchants listed for
carbon in the CRC Handbook of Metal Etchants without luck. The only
removal effect I get, in some cases, is liftoff from the substrate
surface.
I'll compile a list of answers and post it back to this discussion group.
Thanks for your help.
Nigel Sharma.
MY RESULTS:
====================================================
I did not have any luck with liquid etchants at room temperature, but I
did manage to remove carbon from glass slides using an oxygen plasma. I
could not, however, remove the carbon from the insides of a narrow chamber
(my primary problem), I suspect this was because of the low diffusion rate
of reactants and products to/from the chamber.
RESPONSES I RECEIVED
====================================================
From: "Vig, John"
Nigel, have you considered dry-etching? UV-ozone can remove carbon w/o
damaging Si or Pyrex, and, probably, so can oxygen plasma.
For UV-ozone cleaning, see
J. R. Vig and J. W. LeBus, "UV/Ozone Cleaning of Surfaces," IEEE Trans. on
Parts, Hybrids and Packaging, Vol. PHP-12, pp. 365-370, 1976.
J. R. Vig, "Ultraviolet-ozone cleaning of semiconductor surfaces," in
Handbook of Semiconductor Wafer Cleaning Technology, W. Kern, Editor,
Noyes
Publications, pp. 233-273, 1993.
..............John Vig
====================================================
From: "Vig, John"
Nigel, must you use Pyrex? Could you use quartz? High purity quartz is
tranparent to UV, so, UV-ozone would probably work. UV-ozone is an
inexpensive process. All it takes is a short-wave UV lamp and atmospheric
O2, plus a few safety precautions. You can build a UV-ozone cleaner for
~$1K, or buy one for several $K (e.g., from UVOCS). In the 2nd reference
below, I provide a simple recipe for building your own.
..............John.
====================================================
From: bob lyness
I suggest you try ashing the carbon off in a plasma etcher or asher in an
oxygen atmosphere. Another possibility is to use a part of the RCA
cleaning
procedure. 5-1-1-parts by volume H2O-NH4OH-H2O2 at 80dgrees C. Good luck
====================================================
From: "Mavoori, Jaideep"
Nigel,
Here are some hydrocarbon wet etchants that might work in your case:
piranha (H2SO4 + H2O2 + O3)
Ashland has a few other strippers. You can get more info from their web
site at http://www.ashland.com
Goodluck with your research.
Jaideep
====================================================
From: "Mavoori, Jaideep"
Nigel,
Piranha technically is just a mixture of sulphuric + peroxide. The O3 is
typically spiked into the tank. I take it that you are using a wet bench
for your experiments. I can't think of a good way to introduce ozone into
a wet bench. You could try heating the piranha, maybe to 90C.
You might also try ashing --- basically O2 with plasma (and other
chemistries as needed). And if necessary, follow it with a piranha etch.
I shall let you know if I think of anything else.
Regards,
Jaideep
====================================================
From: Jon Bernstein
Nigel: there are no room temperature etches for pyrolytic carbon, so if
it
is carbon you must
do one of the following:
- Plasma etch: Fluorine, oxygen, etc will attack carbon in an RIE, or
- Burn it off, in oxygen at > 500 C
- Undercut it.
Depending on the temperature at which the soot was deposited, you may
have
other elements than carbon still in there which may affect the etch rate.
We published a paper on etch kinetics in Journal of the Electrochem
Society:
J.J. Bernstein and T. Bruce Koger, "Carbon Film Oxidation-Undercut
Kinetics"
J. Electrochem. Soc., 135(8), pp. 2086-2090, (Aug. 1988).
More recently a student at BSAC Elliot Hui published some work continuing
the use
of carbon as a sacrificial layer under polysilicon.
Jon Bernstein
Jonathan Bernstein
MEMS Technology Center
Draper Labs, MS 37
555 Technology Square
Cambridge, MA 02139 USA
jbernstein@draper.com
Tel. (617) 258-2513
Fax (617) 258-4238
====================================================
From: Albert V. Tamashausky
Dear Mr. Sharma,
Unfortunately we do not have any materials available which would aid in
the removal of soot particles. However, I can make a few
recommendations.
1. Strong oxidizing acids such as sulfuric, fuming sulfuric, or
chromic/sulfuric digestion solutions may aid in the breakdown and
removal of soot particles
2. Detergents, if compatible with your system, can be effective
materials for removal of soot.
3. JT Bake, Co., Philipsburg, NJ, sells a line of special cleaning
solutions used in the electronics industry. They may be able to provide
assistance.
Please feel free to contact me if you have any other questions.
Albert V. Tamashausky
Director or Technical Services
====================================================
From: rlinard@ashland.com
I am in receipt of your E-mail to Paul Litzinger expressing an interest in
Carbon Etchants. Our carbon black expert has said that there are no
solvents or
etchants for carbon. He did say you may have a chance if you get a
surfactant
solution and pressure the carbon particles out. We will look to see if we
can
recommend some surfactant solutions for your use.
If you need additional information or have any questions please feel free
to
contact me at the following numbers:
Phone: 360-256-2526
Fax: 360-256-9009
====================================================
From: Martina Moran
Facts About Salt, a brochure on salt, states that NaCl can be thrown into
the fire place when you have a fire and it will help remove soot from the
chimney. It doesn't give measurements but tells the person that an added
benefit is a organge flame caused by the NaCl.
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END OF RESPONSES