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Hummerru 6.2
User'sManual
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1 Sputtercoating:a brieftechnicalbackground
6.2,it is usefulto knowabout
Beforeyouunpack,set up andoperateyourHummer@
works. lt isn'tabsolutely
necessary
that
sputtercoatingandhowyournewinstrument
you readthischapter.However,
your
herewillhelpyou understand
the information
Hummerandoperateit better.
lntroduction
producesan image.
ln electronmicroscopy
floodingelectrons
overa specimen
Typically,specimens
are poorelectrical
examinedin an electronmicroscope
conductors
andwillaccumulate
a negativechargefromthe electronflood. Thischarge
distortsthe image.To minimize
and producethe bestimages,specimens
distortion
shouldhavea conductive
surface.Evensamplesthataresomewhatconductive
will
producea betterimageif theirconductive
produce
will
a betterimageif their
conductivity
is increased.
Coatingthe specimen
withmetal,usuallya precious
metalsuchas gold,palladium
or
an alloyof thetwo can increasesurfaceconductivity.
lf appliedcorrectly,
the coating
won'timpairresolution
or surfacedetail.Severalcoatingtechniques
havebeen
developedandare routinelyusedin preparing
samplesfor electronmicroscopy,
Two
commontechniques
are evaporative
coatingandsputtercoating.
Evaporativecoating
Evaporative
coatinginvolvessublimation
of a metalat hightemperature
and high
vacuum.The metalvapor"sprays"
the specimen,
adhering
to any exposedsurfaces.
Thistechniqueis directional,
andan irregular-shaped
specimenmayneedto be tilted
and rotatedto be totallycovered.Sincethe metalis hot,somespecimens
can be
damaged.Further,sincemetalparticlesizeand coatingthicknessare hardto control,
the resultsheavilydependon operator
skill,technique
andcare.
Sputtercoating
Sputtercoating,usedin AnatechHummers,
is a coldprocessin whichionsimpacting
a
metalsourcedislodgemetalatoms.Theatomsdispersethroughout
the process
chamberin a waythatadequately
coatsirregular-shaped
specimens
withouttiltingor
rotatingthem. Sincethe atomsare cool,thereis no thermaldamage.
ln contrastto the "spray''
of relatively
largeclumpsof metalin the evaporative
process,
sputtering
processthatcloudsof metalatoms.Thisallowsthe uniformity
is microscopic
andthicknessof sputtercoatingsto be easilycontrolled.In general,sputtering
produceshighqualityand repeatable
coatingscompared
process.
to the evaporative
Sputtercoatingprovidestwo additional
benefits.First,sputtering
is donein a "soft"
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and
usingsmall,reliable
canbe obtained
vacuumof 50 to 70 millitorr.Suchpressure
highvacuum
pumps,in contrast
to the costlyandelaborate
mechanical
inexpensive
coating
efficiently
Second,
sputter
coating.
pumpsystemsrequiredfor evaporative
usesmaterialto achievea desiredthickness.Sputtercoatingis muchmoreefficient
coating-andresultsin a lowerannualpreciousmetalcost.
thanevaporative
Hummerfundamentals
specimens:
Plate,Etch
Hummerproductsoperatein threemodesusefulfor preparing
of
and maintenance
and Plasma.Thesehavea commonelement-the creation
phenomenon
is
used
in
each
and
how
it
this
plasma.Thefollowing
sections
describe
processing
mode.
Plasmaproductionand use
(see
The natureof gas plasmasis describedin detailin numerousreferences
presented
hereavoids
bibliography
at the endof thischapter).Thediscussion
for workingwithplasmasand
detail,but providesampleinformation
unneededscientific
Anatechequipment.
Gasplasmamayformwhengas is exposedto an electricfield. lf the fieldis sufficiently
an electronor twoand becomeionized.The
strong,mostgas atomswillsurrender
comprise
the gasplasma,or plasma.
energeticelectrons
ionizedgasand liberated
partial
vacuumis usedto createplasma. The gas is ionized
Typically,
a noblegas in a
highvoltage.
in the fieldproducedby a hazardously
lonizedgas'atomsare heavy,but initiallyhavekineticenergy.However,theirkinetic
throughthefield.Withhighkineticenergy,someof
energybuildsas theyaccelerate
metalsurface,or spuffersource,and
the ionswillsmashintoa negative-charged
adhere
dislodgemetalsatoms.Thesemetalatomscanfloataroundandwill eventually
to a specimen.
electrons
movein the oppositedirection.
Whileionsmoveto the source,energetic
and causeit to heat. Biological
Unfortunately,
the lattercan hit the specimen
polymersor anyspecimens
thatare heat-sensitive
can be affectedand
specimens,
whenobservedin an electronmicroscope.
distortedby this heating,leadingto artifacts
problemsby usinga magnetlocatedwithin
AnatechHummersalleviateelectron-heating
willbe divertedawayfromit by the
the source.Electronsmovingtowardthe specimen
magnetic
field.
To furthercontrolelectrons;
the specimenstage.This
a darkspaceshieldsurrounds
groundedshieldattractselectrons,
whichmayhaveescapedthe effectof the magnetic
field. The shieldand magnetworktogetherto keepthe specimenand stagecool.
Sputtering
materialfromthe metalsource.
describes
the processof dislodging
Sputtering
rafe specifies
the amountof sourcematerialremovedper unittime. Spuffer
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per minute,is the rateat whicha
as angstroms
coatingrafe,usuallyexpressed
rateincreases,
and
material,Whenthe sputtering
specimenis coveredby sputtered
of
souring
will
more
atoms
be
there
since
rateincreases,
thenthe sputter-coating
materialfloatingaround.
Manydifferentgasescanbe usedfor sputtering.Argonis typicallyusedbecauseit
price.Nitrogenis usedless
rateandhasa reasonable
promotesa highersputtering
rate.
and
thus
a lowersputter-coating
produces
rate
sputtering
a
lower
it
oftenbecause
can
Hummers
argon.
Anatech
Nitrogengas producesa sputter
' coatingratehalfthatof
onlybe usedwithinertgases.
PlateMode-toplatea specimenwith a metal
AnatechHummersproduceplasmafor platingin a chamberwitha negative-charged
stage(onwhichthe specimensits)at the
sourceat the top anda positive-charged
by a vacuumpump,andthe
bottom.DuringPlateMode,the chamberis evacuated
valve.
leak
The plasmaformswhena high
gas
adjustable
through
an
operating enters
towardthe source
voltageis appliedbetweenthe sourceand stage. lonsaccelerate
highervoltagewillproduce
to thevoltageapplied.ln general,
withenergy;proportional
the sputterrateandthe current.
moreions,whichincreases
Etch Mode-toremovematerialfrom a specimen
ln EtchMode,the polarityof the stageandtargetare reversed.DuringEtchMode,ions
surface(similarto metalatomsbeing
willdislodgematerialfromthe specimen's
dislodged
fromthe sputtersourceduringPlateMode).Materialis etchedfromthe
rateachievedin PlateMode.
slowerthanthe sputtering
specimensubstantially
heatingof the specimen.
Additionally,
EtchModecausesconsiderable
the sourcecan be contaminated
by
lf etchingcontinues
too long(overtwo minutes),
"back-sputtered"
fromthe specimen.To avoidcontaminatinga precious
material
metalsourceduringprolongedetching,replaceit with the aluminumetch ring.
withthe DigitalThickness
Monitor(DTM),always
Also,if yourHummeris equipped
removethe DTMcrystalbeforeusing Etch Mode. Handlethe DTMcrystal
carefully-don'tget fingerprints
on the crystalor debrisinsidethe crystalcan.
PlasmaMode-tocleana specimen
andetchingof metals,ceramics,
Plasmaprocessing
is usedforashing,cleaning
glasses,organicsandcomposite
materials.In contrastto Plateand EtchModes,which
current.The resultingplasmais
usedirectcurrent,PlasmaModeusesalternating
sufficiently
energetic
to removesmallamountsof organicor volatilecontaminants
from
of organicspecimens.
specimen
surfaces,
andfor cross-linking
An exposureof abouttwo minutesin PlasmaModebeforeplatingimprovesscanning
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electron
microscope
images.In particular,
thistreatment
helpsreduceaccumulation
of
contamination
causedby the electronbeam.Transmission
grids
electronmicroscope
processed
in PlasmaModearemorehydrophilic.
lf plasmaprocessing
continues
too long(overtwo minutes),
the sourcecan be
"back-sputtered"
contaminated
by material
fromthe specimen.To avoid
contaminating
a preciousmetalsourceduringprolongedetching,replaceit with
the aluminumetch ring.
Also,if yourHummeris equipped
withthe DigitalThickness
Monitor(DTM),always
removethe DTMcrystal beforeusing Etch Mode. Handlethe DTMcrystal
carefully-don'tgetfingerprints
on the crystalor debrisinsidethe crystalcan.
PulseMode-to improveprocessuniformityand reducespecimenheating
Anyof the threeHummermodesdescribedabovecan be operatedin a repeatedonpattern,calledPulseMode. Duringcontinuous
off-on-off
sputtercoating,deposited
material
tendsto aggregate
in discrete
areas,called"islands".
PulseModehelps
reduceislandsize.Also,PulseModehelpsminimize
specimen
heating.Withminimal
heating,however,overallprocesstimeincreases
for a givencoatingthickness.
Hummerhigh voltagesafety
All Hummersareequippedwithinterlocks
or softwaresafeguards
to preventhigh
voltagefrombeinggeneratedunlessthe top plateis closedandthe chamberis under
vacuum.Thetop plateinterlock
is mountednearthe hinge.Thevacuuminterlock
is
set so the highvoltageis disabledwhenthe chamberis ventedand is enabledwhen
the chamberis evacuated.Theseinterlocksare importantsafetyfeatures-don,t
overridethem.
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Bibliography
ThinFitmProcesses,editedby JohnL. Vossenand WernerKern. AcademicPress,
NewYork,1978.
:
t
:
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NewYork,
byG.CarterandJ. S. Colligon.Am. Elsevier,
So/rds,
IonBombardmentof
1968.
by M. Kaminsky.Academic
on Metal Surfaces,
Atomicand lonic lmpactPhenomena
Press,NewYork,1965.
editedby L. l. Maisseland R. Glang. McGrawHandbookof the ThinFilm Technology,
by L. l. Maisselandby G. K. WehnerandG. S.
Hill,NewYork,1970.Seearticles
Anderson.
J. C. Kellyand
and TheirApplicationgby P. D.Townsend,
lon lmplantation,Sputtering
N. E. W. Hartley.AcademicPress,NewYork,1976.
;
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etchor plasmaprocessusingthe instructions
in the nextchapter.
lf youare notplanning
to processspecimens
now,closethe mainprocessgasvalveat
thetank.
3 Operatingyour Hummer6.2
Thischaptercontains
the primaryoperating
instructions
forthe Hummer@
6.2. How
youwantto processyourspecimens
determines
whereyou needto go in thischapter:
.
To plateyourspecimens,
go to the instructions
startingon this page.
.
To etchyourspecimens,
go to the instructions
startingon page19.
.
To plasmayourspecimens,
go to the instructions
startingon page23.
Afteryou becomefamiliarwiththeseprocesses,
you can usethe operatingsummaries
in Appendix
A.
Gettingreadyto plate
1. Set MainPowerSwitchoff.
2' Movethe top plateto itsfullyopenposition.Removethe glassdeposition
chamber.
3. Installa sputtersource(usually
gold/palladium
or gold):
cAUTloN:Alwayshandlethe sputtersourcewithlint-free,
powoer
free gloves.Barefingerswillcontaminate
the sputtersource.
a' Findthe threeholeson the backof the sputtersource.Lineup theseholeswith
the threebananaplugsin the top plate.
b. Positionthe sputtersourceoverthe bananaplugs. Gentlyandfirmlypressthe
sputtersourceintoplace.
To removethe sputtersource,slidethe hookedendof the sputtersource
extractorbetweenthe sputtersourceandthe magnetcover. Rotatethe extractor
to engagethe sputterringneara,bananaplug,thenpullit out about1110inch(2
mm). Movetheextractor
to anotherspotnearanotherbananaplugandpull
again.RepeatneareachbananaplugwhileholdingyourotherhandoVerthe
sputtersource(to preventit fromfallingwhenit pullsfree).
4. Placespecimens
on the stage.The holesin the stageaccommodate
standardSEM
stubs,whichare usefulforholdingsmallspecimens.
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5. Installthe glassdeposition
chamber
on the bottomplate.
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6. Gentlylowerthetop plate. Listenfor the "click"of the highvoltageinterlock
switch.
(lf the interlock
plasmacannotbe generated.)
switchis notactuated,
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7. Openthe mainprocessgasvalveat thetank. Setthe secondstageof the gas
regulator
to 5-6psi(35,000-41,000
N/m2or 35-41kPa).
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CAUTION:
Highergas pressure
candamagethe FineGasControl
Valveandcangivethe appearance
of a leak.
CAUTION:Argondisplacesair. Provideadequateventilation
when usingthe
H u mme r.
8. Decideon a platingtime. Coating
thickness
depends
on plasmavoltageand
current,vacuumlevel,processgas,sputtersourcematerialand otherfactors.The
timeyou selectis a matterof judgement,
basedon yourexperience
andevaluation
of previousspecimens.You are encouraged
to experiment
to developa feelfor the
platingtimesthatare appropriate
for yourspecimens
andoperatingconditions.This
set of operating
conditions
is a goodstartingpoint:
!
Variable
Value
Sputtersourcematerial
Processgas
Chamber
vacuum
VoltageControl
Plasmacurrent
Platingtime
Gold/palladium
or gold
Argon
60-80millitorr
Position
8.5
15 milliamps
2 minutes
Coatingratesshownin the graph(on nextpage)providesomeadditional
guidelines
for
platingtime.
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Hummer 6.2 approximatesputter coating rates
Conditions:
Processgas
C h a mb e va
r cuum
Voltagecontrol
P l a smacu rr ent
Argon
70 + 10 m illitor r
Position8.5
15 m illiamps
Rales for your specimenswill vary according to the
Specific conditionspresent during each run.
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Plating
1. Followinstructions
in Geffingreadyto plate,above.
2. Set the operatingcontrolsas follows:
Control
Set to
Main PowerSwitch
VoltageSwitch
VoltageControl
Gas On/Off Switch
Manual/AutoSwitch
Pulse
Mode Switch
off
off
0
off
Manual
off
Plate
CAUTION:Do notturnthe modeswitchwhiletheVoltage
switchis on. Failure
to complycoulddamagethe powersupplyor cause
bod
3. Turnthe MainPowerSwitchon.
1. Flushthe chamber
withprocess
gas:
a. Allowthe vacuumto reach30 millitorr.
b. Turnthe Gas On/OffSwitchon.
c. Allowthe vacuumto riseto 200 millitorr.Adjustthe FineGasControlValveas
needed.
d. Turn the Gas On/OffSwitchoff.
e. Allowthe vacuumto reach30 millitorr.
f. Repeatthis steps4.a.to 4.e.two moretimes.
5. Turnthe GasOn/OffSwitchon. Adjustthe FineGas ControlValvefor a vacuumof
40 to 60 millitor.
6. Whenthe vacuumhasstabilized
at 40 to 60 millitorr,
turnthe VoltageSwitchon.
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on the Current
about'15milliamps
to achieve
7. TurntheVoltageControlclockwise
Meter.
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of watervapor,atmospheric
adhesion
dueto molecular
fluctuate
if sputtersource
gasesandsolvents.Vacuumwillalsofluctuate
is notclean.
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NOTE:lf the plasmadoes not appear,makecertainthe Manual/Auto
Switchis in the ManualPosition.
8. Alternatelyadjustthe Fine Gas ControlValveand the VoltageControlto achieve
of 15 milliampscurrentat 60 to B0 millitorr.
stableconditions
theVoltageControlshould
havestabilized,
NOff: Whenconditions
of current'
readbetweenabout8 and 9 for 15 milliamps
IF
or
. VoltageControl< 4 andcurrent= 15 milliamps,
. VoltageControl=8'9 andcurrent> 35 milliamps,
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THEN
. Shutdownthe system( seestep11 ) and
. Go to Chapter5, Troubleshooting,
andcarryoutthe
3.
for SymPtom
recommendations
9. lf you wantautomatictiming:
a. Set the Manual/AutoSwitchto Auto.
b. Set the Timerto the desiredtime. (The plasmawill automaticallystop afterthe
time you set.)
10. lf you want pulseoperation,set the PulseSwitchon. (Rememberthatduringpulse
mode,the plasmais on only halfthe time. Adjustyour manualor automatictime
accordingly.)
11. When desiredplatingtime has been reached,shutdownthe system:
a. Set VoltageControlto O.
b. Turn VoltageSwitchoff.
c. Turn Gas On/OffSwitch off.
Switchto Manual(if automatictimingwas used).
d. Turn Manual/Auto
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e. TurnthePulseSwitchoff (ifPulseModewasused).
t
f. TumMainPowerSwitchoff.
g. Allowthesystemto ventto theatmosphere
(about1 to 2 minutes).
f--'
Ir",
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glasschamber
12. Opentopplate,remove
andremove
specimens.
lf youarenotplanning
to processmorespecimens,
closethemainprocess
----- gas
e- vatveat
thetank.
For abbreviatedplatinginstructions,see AppendixA.
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Hummer6.2
summary
Plating--operating
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1.
2.
3.
4.
5.
MainPoweroff.
lnstallsputtersource.
on stage.
Putspecimens
Installglasschamberandlowertopplate.
Set operatingcontrols:
Set to
Control
off
Main PowerSwitch
off
VoltageSwitch
0
VoltageControl
off
Gas On/OffSwitch
Manual
Manual/AutoSwitch
off
Pu l se
Plate
Mode Switch
6. MainPoweron.
7. Flushchamber
withprocessgasthreetimes.
8. Stabilizevacuumat 40 to 60 millitorr.
9. Gas OniOffSwitchon. VoltageSwitchon.
of 15 milliamps
10.AdjustFineGasControlandVoltageControlfor stableconditions
at 60 to 80 millitor.
Switchto
timing:setTimerto desiredtimeand set Manual/Auto
11. Forautomatic
Auto.
12. Forpulseoperation:
set PulseSwitchon.
shutdownsystem:
13. Whendesiredplatingtimehasbeenreached,
a. VoltageControlto O.
b. VoltageSwitchoff.
c. Gas OnlOffSwitchoff.
d. Manual/Auto
Switchto Manual.
e. PulseSwitchoff.
f. MainPoweroff.
g. Allowsystemto ventto atmosphere.
14. Removespecimens.
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Afterprocessing
all yourspecimens:
. Turnoff processgas mainvalveat tank.
. Cleandeposition
chambercomponents.
granted
to copythispage.
@1993,
AnatechLtd. Permission
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