Co2 Snow Cleaning

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replied on Thu, Jan 7 2010 5:14 PM

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CO2 snow cleaning is an effective surface cleaning process aimed at both

particle and hydrocarbon removal. Under good working conditions, particle

removal has been measured from visible down to .03 microns (30 nanometers).

Hydrocarbon removal is as good as solvents which means it depends on the CO2

or solvent grade. Details on the cleaning mechanisms and also applications

for AFM, SPM, can be found at www.co2clean.com and also

www.co2clean.com/afm.htm. We have cleaned many AFM samples and also have

cleaned AFM standards as well. We have some unpublished data on the later.

Overall, as one user said "it removes the nanoscum" and yield better images.

You asked "Does it clean everything" - everything is an unclear term. CO2

snow cleaning removes what is physically bound to a surface. Coatings

properly deposited will remain. Items taped, glued, seized, etc, will not

be removed. As a guide, I say if its chemisorbed, it should stay on, if its

physabsorbed, it is likely to come off. Generally, cleaner and superior

images result.

Limitations - they exist. You must secure the sample, else it will fly

away. The sample must be able to take some thermal stress. Though many

worries exist, thermal failures have been rare and limited to a few optical

based materials. We never seen thermal effects on semiconductors, metals or

ceramics. Avoid KBr, LiF, MgF2, etc; however, we have cleaned ZnSe, diamond

turned optics, many different glasses, quartz, and metals oxide coatings on

glass (SnO, ITO, etc). Wirebonds can be broken. AFM tips have been

broken, some survived. Loose micromachined features such as gears will be

destroyed. Etched patterns will survive. Additionally, the cold CO2 snow

will cool your sample and cause moisture condensation. To counter this, use

a CO2 gas source (reduces the moisture condensation) for cleaning and also

provide some direct thermal input (about 30 - 40C).

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replied on Thu, Jan 7 2010 5:15 PM

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It has recently been discussed with respect to the cleaning of AFM calibration grids. For curiosity reasons, I asked several people, who worked with this technique, about its capabilities.

The below is what I found out. Apparently, this method has been used since mid 80's. It works well for removing organics (liquid CO2 is a great organic solvent) and microparticles

(via a not completely understood process, presumably involving big thermal gradients, tribo-electricity, etc.). Removing nanoparticles is tricky, and depends on the nature of

nanoparticle-surface interaction (how strong it is). There were several attempts to utilize CO2 show cleaning for post-CMP (chemical-mechanical planarization) process,

in which one needs to remove attached residues and nanoparticles. It was not entirely successful. The culprit was in condensation of organics from the air and the electrostatic

charges induced when cleaning an insulating surface. It means that an organic-free environment may be needed if the surface must be molecular clean.

There is another sibling technology, argon gas to make cryogenic aerosols (was tried by IBM). This method removes nanoparticles much more effectively. However,

this technique consumes large amount of argon, and has to be done at 0.5 atm pressure, which makes it not very convenient..

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replied on Thu, Jan 7 2010 5:16 PM

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We use CO2 snow for cleaning a variety of samples (not usually AFM ones though, those are mostly clean enough after sample prep). It's special gun hooked up to a tank of CO2 - a pretty simple setup.

The blast with our gun is quite powerful so holding small samples is a bit of a challenge. The sample should also be heated slightly to stop condensation. Typically we hold a sample down on a hot plate (~50C) with tweezers and give it a blast and it works really well to clean off debris on the surface.

Occasionally it works really well to blast the sample across the room if the tweezers slip :)

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olly replied on Fri, Feb 15 2013 10:49 AM

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Hello, I have a question, better later then never.... heh. Did you try to clean ITO on PET? How does the snow cleaning works for flexible substrates in general? Is it possible?

Thank you very much if you answer!

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Dmitry Sokolov replied on Sun, Feb 17 2013 2:04 AM

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Hi Olly,

I did not try myself but I don't see why it would not work with the sample fixed properly. Vacuum chuck (from a spin coater) should be helpful:

http://confocal-manawatu.pbworks.com/w/page/63714895/Vacuum%20Chuck%20for%20Spin%20Coaters

Please tell me how it worked.

Cheers,
Dmitry