Changes observed in characteristic of the focus and stigmation controls on the RAITH , User please report if they observed changes in control functions.
jwc at snf.stanford.edu
Wed Jun 14 18:39:10 PDT 2006
Greetings Raith Community:
Today when I came onto the system it was immediately apparent that the
typical response characteristic manipulating the controls for FOCUS and
less so the Stigmation controls has changed profoundly from my last
access on the system yesterday. In fact I have never seen it take so
much translation of the controls to change focus and orders of magnitude
more current is required to properly stigmate. (Note before that it was
less than 1 mm to go from stop to stop on the X-Y stigmation controls.
now it is five to ten mm!)
This indicated to me that the chamber and likely the lower end of the
column at the objective lens and pole piece have become severely
contaminated in an individual event. The upper column and gun section
seems to be maintaining good vacuum, but the big change in stigmation
characteristic is very worrisome.
I suspect that the RAITH system may have become contaminated with the
oily residues that we have been observing showing up on the VINOX
microscope. See my previous message on this topic.
In fact it may be an Ebeam Lab Raith User whom introduced oil or
silicon contaminated samples into the system yesterday evening.
All Users working on the tool are asked to be especially vigilant in not
placing samples into the system that are not fully baked and cured to
above 140 degrees C. Never allow any materials into the system
containing Wax, greases, silicon based lubricants and pump oils, krytox
fluoridated grease, adhesive tapes including carbon and copper tape. If
it isn't high vacuum compliant it doesn't go into the system. If
residues are on the backside of the sample it doesn't go into the system.
If it is not one of our standard resist materials it is not to go into
the system without my approval.
In the past on other SEM and Ebeam systems, we have observed spurious
contamination events from out gassing of resist and extended exposure of
resist under the Ebeam. In time this will coat up the Apertures, the
pole pieces, and the Objective lens with hydrocarbon residue resulting
in more and more current required to the properly align the gun and when
focusing and stigmating on a SEM image. This is what I would normally
observe as a SEM system extend beyond the normal PM interval for
cleaning, FE gun and aperture replacement... Some of those events were
recoverable and the systems returned to normal after a few days period
of time. But most of the time contamination like this can only be
addressed by a full column PM and an extended N2 Purge followed by a
several hundred hour long Gun Bake Out.
In reference to the superb resolution and outstanding EBL results we are
obtaining on the system since a new column was installed on this tool,
it would be unfortunate if just one careless user ruined the whole thing
for everyone by contaminating the column. I am hoping we will not have
to tear this column down to effect a repair. Users are requested to
report any changes they have observed when running the system recently.
Thank you for your support!
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