From: gadallah@wu2.wl.aecl.ca (Larry Gadallah; B300-1-115; x2603)
Subject: Re: Cleaning CCDs
Followup-To: poster
Summary: summary (long) 
Keywords: CCDs cleaning
Organization: AECL Research, Whiteshell
Date: Tue, 8 Sep 1992 15:53:34 GMT

Thanks to all who responded to my previous posting asking how to clean a
CCD device. I received about a dozen detailed responses which answered
my question quite well. The replies follow here:

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From: rreiss@te11.hq.eso.org (Roland Reiss)
Subject: Re: Help! How can I clean a CCD chip?

First, you have to find out which kind of CCD you have, front- or
back-illuminated.

For front-illuminated CCDs Tektronix gives the following notes on
cleaning CCDs (should apply to front-illum CCDs from other vendors
too).

" The easiest to clean are the front side devices. These devices are
protected with a silicon nitride passivation coating over the imager
area. This layer is hard and will allow most cleaning solvents or water
to be used. Cleaning with a soft material which oes not generate static
is also a possibility. However, after using a liquid one needs to
vacuum bake to assure that nothing has been trapped on the package. The
best cleaning solvents to remove organic residues are isopropyl
alcohol, toluylene and freon. To remove some particles, the device can
be blown off with a filtered, ionized, low pressure, low flow nitrogen
blow gun. To remove large particles a single hair brush is the best
way." (taken from a Tektronix note, Nov.1991).

If you have a thinned back-illuminated device things are more
complicated. In this case contact me via e-mail.

Good luck.


*  Roland Reiss				rreiss@eso.org		
*  Optical Detectors			+49-89-32006-390
*  European Southern Observatory	Karl-Schwarzschild-Str. 2
*					D-8046 Garching, Germany
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From: tmca@wairau.as.utexas.edu (Tim Abbott)
Subject: cleaning a CCD



Larry,

	Depending on how much your CCD means to you (cleaning is
*risky* no matter what):

1) light dust etc. can be removed using a very fine paintbrush with all
but one bristle removed. Be *very* careful.

2) Someone once blew the vacuum on one of our cryogenically coolled
TI 800x800 thinned CCDs and water condensed on it. After the water dried
the flat-field looked awful. We decided to attempt to clean it by
suspending it over boiling methanol. We placed the CCD face down
on a piece of metal with a hole cut in it that was big enough to
leave the CCD itself completely exposed but not so big that the package
fell through. We then placed this metal strip over the top of a
glass beaker with a little methanol in it. We then put the hole
thing on a (not very hot) heating plate. Remember that methanol
vapor is very flamable, so use a *warm* (not hot) electric
heater if you do this. The methanol then boiled and some of
the vapour condensed on the CCD, dripped off and took some of the
muck with it. Unfortunately, it didn't take it all off and redistributed
the rest. The result was slightly better than before, but was still
not as good as a clean chip.

I guess if we'd left it to cook a bit longer it might have got
a bit better, and we could have done it again. However, the
whole exercise gave me the shakes anyhow (TI CCDs back then were
the largest available, they were given to deserving institutions
by the NSF after HST took the cream, they are the nearest thing
to priceless that I have ever directly handled (ie, if I'd bust
it my ass => grass).

3) Tektroniks offer a CCD cleaning service, but it costs and I don't
know if they'll do devices they didn't make. If you like, I can put
you in touch with someone who can tell you more, or get a phone
number for Tektroniks...

	Tim Abbott

P.S. I'm just about to defend my Ph. D. after working 6 years with the
McDonald Observatory CCD group, just in case you were curious of
my sources, credentials, whatever...
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From: btree!charlies@UCSD.EDU (Charlie Schorner)
Subject: Cleaning your CCD

Larry,

I've been in the semiconductor industry for 13 years, and everywhere I've been
folks have used Freon, Isopropyl Alcohol and Acetone for cleaning semiconduc-
tors.  If the chip is in some piece of equipment, I would NOT recommend Acetone
as it will probably dissolve plastic pieces in the chassis.

Put the solvent in a Nalgene squirt bottle and squirt directly at the grease.
Don't be afraid to squirt hard.  Use compressed air (filtered) or Nitrogen
to gently blow off the dissolved residue.  If the chip is not in some
box, put it in a beaker of solvent and use an ultrasonic jewelry cleaner!

Most of all, do not touch the surface with anything like a brush!

Good luck....
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From: Chris Clark <chris@cfht.hawaii.edu>
Subject: cleanning ccds

cleaning the surface of a CCD requires a high degree of care and safety. You 
must be careful not to damage the wire bonds. They wont take much bending
and pop-off quite easily. You must take extreme care with electro-static
discharge and be well grounded. A tiny spark or static discharge will end
the show. Next you must try to determine what sort of chip-to-carrier
packaging "glue" was used. Will it desolve or incourage the chip to 
become delamenated from the carrier? This will likely be hard to determine
from inspection. If however, the chip can be operated very cold and fairly
warm (disregarding dark current aspects), then probably the bonding
"glue"
is forgiving. 

If you can insure the above then you might start by dipping the device
, very slowly so as not to flex the bond wires, in acetone. It is often
used to remove thin-film coatings (laser dyes etc) from CCD surfaces
and is sometimes used warmed. some types of alcohols will work too, but
a more active solution, such as acetone, may be needed. May want to 
rinse the device in distilled water.

In all steps be sure to have everything well grounded and never let anything
become charged up with refernce to the chip. 

You might try applying the solvent directly to the spot but might risk
contacting the surface with the dropper and just spreading the spot as
it mixes with the solvent. 

In any case, be gentle and use good ESD precautions.

good luck,
christopher clark

.
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From: Vincent Kujala <kujala@geog.ubc.ca>
Subject: cleaning CCD, solvents


As a physics graduate student I observed GaAs CCD
production at TRIUMF.  They used hot CMOS grade
Acetone for 5min, hot CMOS grade isopropanol for
5min.  Sometimes ultra sound in hot acetone for
about 5min was needed.  To do the job right we
would use a lot of solvent (no recycling!) about
500ml per beaker per 3in wafer.  And, to dry the
wafer off, a dry nitrogen blower was used.  How
hot is "hot"?  Hot enough to just barely boil
Acetone.  The reason for following acetone with
isopropanol was to remove any stuff that acetone
lifted off.  Apparantly, the acetone residues
can stick (adhere) to the clean surface and are
impossible to get off once the acetone evaporates.

a bit verbose... well, good luck.

PS. I'm interested in making/buying a CCD system.
    Any references or personal experiences you'ld
    like to share?

- vincent.
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From: "Patrick C. Mock" <mock@space.mit.edu>
Subject: cleaning CCD's

Larry

We've occasionally had to clean devices here.  Most CCD's are actually
fairly robust.  Your main concern is breaking a bond wire.  Secondary
problems are dissolving the glue that holds the chip in the package and ESD.

Find out what you can about the glue and avoid the appropriate solvents.
In general alcohols are probably ok.  Acetone is more risky.  Xylene works
well with pump oil and finger prints.  If you have access to a microfab
facility, broken bond wires can be fixed.  Use only reagent grade solvents.

The basic procedure is:

1)  Work in an antistatic environment and mount chip so that the surface
    is roughly 30 degrees from vertical.

2)  Direct a gentle stream of your chosen solvent onto the chip.
    (Do not soak the chip!)

3)  Before the solvent dries, rinse with pure alcohol.

4)  Before the alcohol dries, rinse with pure freon (TF or PCA grades).

The two rinses should be done from top to bottom in a sweeping pattern.
If done correctly this will leave no residue.  This technique also works
well for cleaning delicate optics.  You may want to practice on some
old filters or lenses.

Good luck
Pat


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From: kscott@chtm.eece.unm.edu (Kristin Scott)
Subject: CCD cleaning


	This is NOT an expert's opinion...but...

Acetone might work for you if there are no plastic parts nearby.
Moisten a Q-tip and test a corner of the CCD to see if there is
any harm done. If you can wash liberally the face of the chip, 
that is better than rubbing. Acetone works wonders on grease.

If not, then maybe isopropyl alcohol (IPA) which will not harm 
plastic.  In either case, rinse afterwards with optics-grade 
or microprocessing-grade methanol to take off the thin residue
that acetone or IPA leave behind.

In any event take your time cleaning the chip, it may take several
washings.

		-Kristin  kscott@chtm.eece.unm.edu
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From: dinsdale@chtm.eece.unm.edu (Don McDaniel)
Subject: Re: Help! How can I clean a CCD chip?


It seems that how the chip is mounted determines how you may best clean
it.  Both acetone and IPA (iso-propyl alchahol) are used in manufacture.

I'd start with the mildest, IPA.  If there are no wire bonds at peril,
you could use the laser-mirror technique of folding up a piece of lens
tissue, clamping it in hemostats, saturating it with solvent and wiping
the surface.  If that is not successful, you might try acetone, but only
if there is no plastic around that could get clouded by the solvent.

Good luck



-- 
_________________________________________________________________
Don McDaniel                           dinsdale@chtm.eece.unm.edu
Center for High Technology Materials
University of New Mexico
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From: colin@cypress.com (Colin Murphy/VDSP)
Subject: Re: Help! How can I clean a CCD chip?

I assume that CCD chips have a glass passivation as the "scratch protect".  I would
use freon as a first choice, I know that even de-passivated die can work after being
cleaned with freon.

Colin Murphy     -     colin@cypress.com    -    (408) 943-2887
Cypress Semiconductor, Inc., 3901 N. 1st St., San Jose, CA 95134
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From: Tony Arnerich <tonya@hpldsla.sid.hp.com>
Subject: Re: Help! How can I clean a CCD chip?

Don't touch it with anything. Even a soft cotton or tissue will
destroy the circuitry. A solvent of some type is the way to go.

If you could cobble together a vapor degreaser, great. This would
entail boiling a solvent (totally dangerous in the case of flammables!)
and letting the heavy vapor contact the cold circuit. Practically
pure solvent condenses on the chip & drips off. This is the ultimate
cleaning process.

Otherwise, do a simple flooding. Get the purest solvent that you can
("research" or "analytical" or "electronic" grades would be good).
Then be scrupulously clean - even a squeeze bottle has it's contaminants.
An old squeeze bottle has already had it's extractables extracted.

Isopropyl alcohol, freon, and water/detergent are all used in the
production of naked chips.

But your problem is entirley different, because you want to clean a
packaged & mounted chip. You have to be careful about ruining the
other components. Stay away from the stronger solvents like acetone.
Definitely stay away from using anything ionic (conductive) in water,
unless you VERY copiously wash with deionized water afterwards.

ALSO: avoid ultrasonics unless they are very weak. The fine connection
wires will get beaten up & will short or be torn off.

One thing we did when we had a flood of city water on some test instruments
worked out very well. We flooded the hell out of them with D.I. water,
then baked them in a big oven to dry them out. So don't let water scare you,
just be careful with it.

Good luck, and lay off the pizza in the observatory from now on!  :-)

Tony
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From: pmoore@eso.org (Peter Moore)
Subject: cleaning CCD'S

Hi Larry,

With reference to your sci.astro posting : cleaning methods for ccd's.

The type of solvent that can be used to remove that 'Baked On Grime' really 
depends on the type and manufacture of the ccd. As a general rule the cleaning 
methods fall into three catagories.

1). For front illuminated devices
 These are the tough guys because they generally have a hard passivation 
 coating on the surface. A Freon bath (optional 'LIGHT' brushing ) followed by 
 an isopropyl alcohol wash to remove residue is generally OK. If the device is 
 to be used under vacuum the device should be baked (I use 80 degrees C for 8 
 hours) to remove vapor.

2). Back illuminated bare chips i.e no anti reflection coating.
 These are probably the most delicate and risky to clean. Pure water, ideally 
 de-ionized, can be used but without brushing. I think a nitrogen or air jet 
 can be used with the bath in place of brushing and for drying. The problem 
 with this method is water marks left on the surface during drying. CCD's that 
 have been 'Well' thinned ie. with thick edges and a thinned center are the 
 most susceptible to water marks. The good news is that some of the earlier 
 thinned devices (eg RCA's) were mounted bottom down to a glass substrate 
 which protects the CCD surface (Backside). With these devices alcohol and 
 freon can also be used with care.

3). Back illuminated with anti reflection coating.
 Do not use water, it will probably dissolve the AR coating. I think using 
 freon in spray carries the least risk but the keyword here is patience as the 
 residues have to be carefully removed with nitrogen or air spray while 
 applying the solvent. 

In all cases of cleaning great care should be taken not to touch or cause undue 
stress to the bonds of the connecting wires. The brush I use for CCD surfaces 
is simply one hair plucked from a good quality camel hair paint brush and held 
in tweezers. I use the edge of the hair as a kind of scoop and never the 
point and always with long motions ie. no sudden accelerations of the hair 
across the surface.

These notes are derived from practical experience here at La Silla and from an 
application note put out by Tektronix. 

Good luck Larry .... Email if I can be of further help,

                                     Peter Moore.
                                     Detectors Lab,
                                     European Southern Observatory,
                                     La Silla,
                                     Chile.

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Thanks again to all for the information.
--

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Larry Gadallah				Internet: gadallah@wu2.wl.aecl.ca
AECL Research, Whiteshell 		DECnet:   WL::GADALLAHL
Computing Support 			Voice:    (204) 753-2311 x2603
UNIX Systems Analyst 			FAX:      (204) 753-2455
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-- 

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Larry Gadallah				Internet: gadallah@wu2.wl.aecl.ca
AECL Research, Whiteshell 		DECnet:   WL::GADALLAHL
Newsgroups: sci.astro