fab well.pdf
-
Upload
praveenbanthi -
Category
Documents
-
view
240 -
download
0
Transcript of fab well.pdf
-
7/28/2019 fab well.pdf
1/64
CMOS LAB MANUAL
2011
Author:MatthewLeone
ToddKaiser
MontanaStateUniversity
Rev2 December2010CMO
SLA
BMA
NUAL
This manual was designed for use with the Montana Microfabrication
FacilityatMSU.TheintentionofthemanualistoprovidelabusersandMSU
students with a complete description of the methods used to fabricate
CMOSdeviceson4inchsiliconsubstrates.
SpecialThanksto:
AndyLingley
PhilHimmer
-
7/28/2019 fab well.pdf
2/64
SUPPLIERS
UniversityofMinnesotaNanoFabricationCenter(NFC):Photomaskswww.nfc.unm.edu
VirginiaSemiconductor:SiliconSubstrates
www.virginiasemi.com
ELCATInc.:SiliconSubstrates
www.elcat.com
JTBaker:ChemicalSupplies
www.mallbaker.com/default.asp
TechnicalGlassProductsInc:Quartzware
www.technicalglass.com
KurtJLeskerCompany:EvaporationFilaments
www.lesker.com
MSUChemstore:Labware/ChemicalSupplies
www.chemistry.montana.edu/chemstores
SigmaAldrich:ChemicalSupplies
www.sigmaaldrich.com
SPISupplies:WaferTweezers
http://www.2spi.com/spihome.html
GasesPlus:PressurizedGasTanks
www.gasesplus.com (406)3889109
-
7/28/2019 fab well.pdf
3/64
ThehightemperatureprocessstepsforuseinEE407labsthisyeararelistedhere.
wetoxidation 1000C 180min
Nwelldiffusion 825C 50minN2/25minO2
drivein 1000C 4hr/8hrW/&W/Ooxide
wetoxidation 1000C 90min
N+diffusion 850C 20min
wetoxidation 1000C 90min
P+diffusion 950C 20min
drivein 1000C 60min
wetoxidation 1000C 30min
dryoxidation 1000C 60min
-
7/28/2019 fab well.pdf
4/64
NOTES/RECOMMENDATIONSFROMTHEAUTHOR:
Previousfabricationattemptshavebeenmetwithmixedsuccess.Inmostcasesthelargechanneled
NMOStransistors,resistorsanddiodesfunctionedproperly.However,insomecasesthethresholdvoltagewas
negative,indicatingadepletionmodedeviceandperhapsinappropriatedopantlevels,butthediffusiontimesand
temperaturesshowednoassociation.Inmanycases,thesmallerchanneldevicesfailedtofunctionandexhibited
shortcircuitbehavior.
ThePMOSdevices,includingresistors,transistorsanddiodesnearlyalwaysfailed.Numerousreasons
werethoughttoexplainforthefailurebutnonehavebeenprovenasthecause.Themostobviousreasonfor
failuremayjustbeaninappropriatedopinglevelofeithertheNwellorP+devices.Thedopantconcentrations
mayhavebeenshiftedduetosegregationeffectsduringoxidegrowthorthermalcycles.Orthefailuremaybe
causedfrompoorelectricalcontacttothediffusedregions,perhapsathinfilmofBSGoroxidewasactingasa
barrierbetweenthealuminumanddiffusedsilicon.TypicallyafterBorondeposition,theresultingBSGfilmneeds
tobeetchedlongerthannecessarytoremovethermalSiO2. Ifinsufficientlyetched,theBorondopedregionswill
appearblueishandiftestedwiththeNanospecor4prointprobewillindicateoxideispresent.Thissituationhas
beenencounteredinpreviousfabricationattempts.
FrommyexperienceandreadingsIwouldrecommendtryingthefollowingmodifiedfabricationsequence.
Iftheprocesscannotbemadesuccessfulbymodifyingetchtimesordiffusionschedules,Iwouldrecommend
shiftingtheprocessfromanNwellonPtypesubstratetoaPwellonNtypesubstrate.Otheruniversitieshave
incorporatedthistypeofCMOSfabricationwithsuccessfulresults.
MatthewLeone
MontanaStateUniversity
2007
RecommendedCMOSProcess:Oxidation(wet): 1000C 90min
NwellPredeposition: 800C 20minOxidation(wet) 1050C 60min
NwellDrivein: 1050C 300min
N+S/DPredeposition: 850C 20min
Oxidation(wet): 1000C 60min
P+S/DPredeposition: 950C 20min
Oxidation(dry): 1050C 45min
LongOxideEtchin6:1BOEtoremoveBSGandSiO2fromvias.
-
7/28/2019 fab well.pdf
5/64
How to use this manual
14week Overview
Themanualisbrokenupintoweeklysegmentscontainingmultiplesections:Goals,Equipment,Parameters,
MethodsandResults.Eachweekasetofprocessgoalsispresentedtotheuseralongwithalistofequipmentand
themethodsusedtoachievethosegoals.Theparameterssegmentisdevotedtoprocessdependentparameters
specifictothefabricationmethodsusedthatweek.Theparametersarecolorcodedtocorrespondtoaspecific
processmethod.Themethodssectiondescribestheprocessesusedwithinthatweektoachievethedesiredgoals.
Themethodsarenumberedtocorrespondtoaprocessgoal.Theresultsectionisleftblankforuserstorecordthe
resultsofthatweeksprocesses.
Introduction&Oxidation Week1
Photolithography&Etching(Nwell) Week2
Cleaning&Diffusion(N) Week3
Documenting,Cleaning&Oxidation Week4
Photolithography&Etching(N+Source/Drain) Week5
Cleaning&Diffusion(N+) Week6
Documenting,Cleaning&Oxidation Week7
Photolithography&Etching(P+Source/Drain) Week8
Cleaning&Diffusion(P+) Week9
Documenting,Cleaning&Oxidation Week10
Photolithography&Etching(Vias) Week11
Cleaning&AluminumEvaporation Week12
Photolithography,Etching(Pads)&Documenting Week13
Probing&Testing Week14
-
7/28/2019 fab well.pdf
6/64
Introduction & Oxidation Week 1
OxidationParameters
Temperature(C) Time(minutes) Type(wetordry) N2/O2Flow BubblerSetting1000 180 Wet 7/9 40
EQUIPMENT:
WaferScribe JANDEL4pointProbeStation
RCAtanks(Optional) MODULABOxidationFurnace
GOALS:
1. Familiarize studentswith the cleanroomlayout,equipment,safetyandprocedure.
2.
Present
an
overview
of
the
MEMS
fabrication process and variousprocessing techniques (i.e.photolithography,etching,etc)
3. CharacterizethewafersubstratesandIDindividualwafers
4. RCAclean(Optionalfornewwafers)5. Oxidation(Fieldoxide)
PARAMETERS
-
7/28/2019 fab well.pdf
7/64
Methods:
1.CleanRoomEtiquette
Thelabemploysmanyhazardouschemicalsand
processes.Thesafetyofthelabstudentsandusersisthe
number one priority when participating in the lab.
Follow all gowning and safety procedures outlined by
thelabTA.Tomaintain the integrityofthewafersand the
equipment, adhere to the process descriptions and
detailsprovidedbythelabTA.
Themostcommonreasonawaferwillnotmake
it to the end of the fabrication sequence, is poor
handling.Thewafershouldbehandledwith thewafer
tweezersandwithgreatattention.Limitthehandlingof
the wafer with gloved hands to the edges and only
duringnecessarycircumstances.Never touch thewafer
with a bare hand and never touch the center of thewafer,evenwithglovedhands.
When processing in the cleanroom, sources of
contaminationareanotherfactorwhichmay inhibitthe
successofthefabrication.Therefore,donottalknextto
the wafers, keep the lid to the wafer box closed and
lastly,donothastilymoveaboutthecleanroomanddo
notgetinahurrytofinishaprocess.Whenalabstudent
getsinahurryitcreatesasituationwithagreaterlikely
hood of breaking a wafer or damaging a piece of
equipment.
Week1
-
7/28/2019 fab well.pdf
8/64
Methods:
2.ProcessOverview:
TheCMOSdevicesarefabricatedusingcommon
bulk silicon processing techniques. The sequence is a
simple set of repeating steps including oxidation,
etching,diffusion,cleaningandpatterning.Anoverview
of the sequence is shown to the right (Figure 1). Thefabrication portion of the lab should take roughly
thirteenweekstocomplete,withthefinalweekdevoted
totesting.
Alayoutofthedieisshowninthebottomright
(Figure2).Amore completedescriptionof thedevices
foundon thedie is foundat theendof thedocument
undertheDieLayoutsection.
Documenteverything seenanddone inaclean
room lab notebook. Record all measureable quantities
and procedures and any deviations. It is important torecord every detail which may help explain device
failuresoranomalies.
3.WaferCharacterizationandID:Semiconductorsubstrates,referredtoaswafers,
caneasilybeordered through retailersandcustomized
forspecificapplications.Thewafersusedforthelabare
100mmindiameter,52525mthick,,singleside
polished,single
crystal
silicon,
doped
with
boron
(Ptype)
toaresistivityof120 /cm.
Asimpletesttodetermine ifthesubstrate isP
typeorNtypesiliconisknownastheHotProbeTest.
Using a DMM and a soldering iron, heat the positive
probe of the DMM for several minutes with the
soldering iron. Make sure the DMM is set to measure
mV. Place both probe tips, positive and
negative(ground) to the wafer surface. If the DMM
indicatesapositivevoltagethesubstrateisNtype,ifthe
voltage is negative the substrate is Ptype. This testshouldbeaccurateuptoaresistivityof1000 /cm.
Week1Figure1Overviewofthefabricationsequence.
Figure 2 Microscope picture of the die layout. A more detaileddescriptionofthelayoutisfoundattheendofthisdocument.
-
7/28/2019 fab well.pdf
9/64
Methods:
3.WaferCharacterizationandID:
ContinuedThebulkresistivity(cm)isdeterminedbyfirst
acquiringthesheetresistivity (/) ofthewafersusing
theJANDEL 4pointProbe Stationand thenmultiplying
thisvaluebythewaferthicknessandacorrectionfactor.
SeetheJANDELmanual fordetailsonusingthe4point
probe.
Tokeep trackof individualwafers,a scribecan
be used to mark the back of the wafer with an
identificationmark,typicallyanumberorletter.
Proceedby lightlypressing the tipof thescribe
againstthesurfaceofthewaferandwithasfewstrokes
aspossiblescribeasectionnumberandwafernumber.
Scribingshouldbedoneasclosetotheedgeaspossible
tolimittheeffectonfabricateddevices.
5.Oxidation:GrowingSiO2
(CheckParameterssectionfordetails)
The goal of the first oxidation run is to grow
enoughsilicondioxide(SiO2)roughlya0.5mthickfilm,
tomaskthesubsequentdiffusion.
Tooxidize,insertthewafers intotheMODULAB
oxidationfurnaceusing thequartz rodandquartzboat
(seeFigure4).Thereshouldbetwodummywafers,oneat the front of the boat and another at the rear, to
maintainuniformityacross theboat.Ramp the furnace
to 600C before the removing the quartz boat and
loading the wafers. Prior to the temperature reaching
400C, turnon thenitrogen topurge the furnace.Also,
set the potentiometer on the bubbler if performing a
wet oxidation (which we are). Once the wafers are
loadedand inplaceat thecenterof the furnace, ramp
the furnace to the desired temperature. When the
desiredtemperatureisreachedstartthetimer,stopthenitrogenflowandturnontheoxygen.Aftertheallotted
time, ramp the furnace down to 600C, pull the boat,
remove thewafers,and set themaside to cool.When
finished, turn the furnace to 0C and turn off the
nitrogenwhenthetemperaturedropsbelow400C.
Week1Figure3Scribingthesurfaceofawaferusingasteeltippedscribe.
Figure 4 A student using a quartz rod to insert wafers into theoxidationfurnace.
-
7/28/2019 fab well.pdf
10/64
SheetResistance(/)&Resistivity(cm):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week1
-
7/28/2019 fab well.pdf
11/64
Photolithography & Etching (Nwell) Week 2
EQUIPMENT:
Nanospec
BREWERspincoaterandhotplate
SHIPLEY1813positivephotoresist ABMContactMaskAligner
MF319developer
TeflonCassette
6:1BOE
GOALS:
1. Measure the thickness of the SiO2 withtheNanospec.
2.
Photolithography(Mask
#1
Nwell)
3. Hardbake4. EtchSiO2
PARAMETERS:
Spincoat&SoftbakeParameters
SpinProgram
Speed(RPM)
Time(seconds)
Ramp(RPM/s)
DispenseType
(automaticormanual)
SoftbakeProgram
Temperature(C)
Time(minutes)
#9 5250 30 20000 Manual(static)
#2 115 2
Exposure&DevelopmentParameters(MASK#1)
MaskOrientation(writingtoward
orawayfromuser)
WaferOrientation(flattotheleftorthe
right)
UVIntensityChannelB(mW/cm2)
UVDose(J/cm2)
ExposureTime(seconds)
DevelopmentTime(seconds)
Away Left 30 ~135 4.5 3060HardbakeParameters
HardbakeProgram Temperature(C) Time(minutes)#2 115 2
SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask6:1 900 5* Shipley1813Photoresist
-
7/28/2019 fab well.pdf
12/64
Methods:
1.MeasuringtheSiO2thickness:
The thickness of the freshly grown silicon
dioxide layer is measured with the Nanospec. Choose
theappropriatefilmtypeduringthepromptsandusea
blank wafer as reference. Measure the thickness at
several different points on the wafer to monitoruniformity and determine a maximum film thickness.
AlsonotethatthethicknessoftheSiO2determinesthe
color of the wafer, therefore, color can be used to
approximate film thicknessesand identifyanomalies in
film.Forreference,theNanospecpromptsformeasuring
SiO2thicknessare:
Iswavelength480nm? Y (ifnot,typeNandvalue)
Databankoption? N
Refrindexoption? N
Switchtoprinter? N
Enterfilmtype: 1SiO2
Enterobjlens: 1=10x
2.PhotolithographywithMask#1(Nwell):
Spincoating&Softbaking
(CheckParameterssectionfordetails)
The goal of the photolithography step is to
transfer patterns from the mask set to the wafer
surface.Photoresist,whichisaUVsensitivechemical,is
patterned by selectively exposing certain regions with
UV light. Photoresist isalso chemically resistant to the
SiO2etchant,hydrofluoricacid(alsoreferredtoasBOE);
therefore itisusedtomask,orblock,selectportionsof
the SiO2 from being etched. The first patterns
transferred to thewaferaretheNwells,whichwillact
asasubstrateforthePMOSdevices.
Beginby
using
the
BREWER
spin
coater
tospin
a
thin film (~1um) ofSHIPLEY1813photoresistonto the
topside of the wafer. Next, transfer the wafer to the
adjacenthotplateandsoftbaketoremovesolventsand
hardenthe resist.Agoodcoatingofphotoresistwillbe
barely visible to the naked eye and have a minimal
numberofstreaksorblotches(seeFigure7).Ifthereare
alargenumberofdefects,solventclean,dehydrate,and
tryrespinningmorephotoresist.
Week2Figure5StudentsusingtheNanospectomeasuretheSiO2thickness.
Figure6ViewfromtheNanospeceyepiece,theedgeoftheoctagonshouldbeinfocusforpropermeasurement.
Figure 7 Wafers that have been spun with photoresist and exhibitsignsofapoorcoatingi.e.streaking,blotchinessandcolorgradients
-
7/28/2019 fab well.pdf
13/64
Methods:
2.PhotolithographywithMask#1(Nwell):
Exposure&Development(CheckParameterssectionfordetails)
Proceed by patterning the photoresist with
Mask #1. Start by loading the mask onto the ABM
contactaligner mask stage. Turn the maskvac on andraisethemaskstage.Carefully, loadthewaferontothe
substratechuckandorient itsuchthattheplane
(wafer flat) is to the left and running straight up and
down. Turn on the substratevac to lock the wafer in
placeand lower the chuck toavoidhitting the contact
mask. Next, lower the mask stage and raise the
substrate chuck up to meet the mask, fringe lines will
become visible as the wafer and mask come into
contact.Alignthemaskto thewaferusing themarkers
on the sides of the wafer (no alignment for the first
photolithography step). Turn on the contactvac to
removeanyairgapbetweenmaskandwafer.Adjustthe
exposuretimeandchannelsettingthenexpose.Remove
the wafer by turning off the contactvac, lowering the
substratechuck,raisingthemaskframe,andturningoff
thesubstratevac.TransferthewafertoadishofMF319
developer(afaintoutlineofthefeaturescanbeseenat
this point), submerge the wafer in MF319 and gently
swirl for 3060 seconds until the exposed resist is
completelydissolved. Ifdonecorrectly there shouldbe
nophotoresist left inthenwellregions. Ifthere is (see
Figure8),resubmergethewaferintheMF319developer
foradditional time. Ifunsuccessful,usea solvent clean
to strip the photoresist, dehydrate and respin again.
When finished, pour the used MF319 into the MF319
wastecontainerlocatedunderthesolventbenchnextto
thephotoresist.
Week2
3.Hardbaking:
(CheckParameterssectionfordetails)
Hardbaking is the final step in the
photolithography sequence, but to emphasize its
importanceitgetsitsownheading.Thegoalofthehard
bake istoremoveanyremainingsolventsand/orwaterfromtheresist.Ithasbeenobserved,thatwithouthard
baking, thephotoresistexhibitsadhesionproblemsand
frequentlydelaminatesfromthesurfaceduringetching.
Hardbakingisverysimilartosoftbakingandfollowsthe
sameprocedure.Loadawaferontoahotplateforaset
timeattheappropriatetemperature.
Figure 8 A microscope picture of a patterned feature afterdevelopment in MF319. The color gradient indicates that thephotoresist was not completely removed during the development.
Thewafer shouldbedeveloped for longeror redonewitha longerexposure.
Figure 9 Several features indicating photoresist adhesionproblemsafteretchingSiO2.ThecolorgradientshowsataperedSiO2etchafterthephotoresistdelaminated.
-
7/28/2019 fab well.pdf
14/64
Methods:
4.EtchingtheSiO2:
(CheckParameterssectionfordetails)ThegoaloftheSiO2etchistoremovethesilicon
dioxide from the exposed regions in the photoresist.
SilicondioxideisetchedwithBOE(BufferedOxideEtch)
which is a combination of hydrofluoric acid andbuffering chemicals to stabilize the reaction. BOE is
highlyselectivetosilicondioxidesothephotoresistwill
notbeetched.
ThisstepshouldbecarriedoutbythelabTAfor
safetyreasons.BeginbyloadingthewafersintoaTeflon
cassettewithequal spacingbetweenwafers.Using the
handle, submerge the cassette in 6:1 BOE for the
appropriateamountoftimeoruntiltheexposedSiO2is
completely removed. To determine if the SiO2 is
completely removed, check the regions for color (see
Figure 10) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Figure 10 An example of micromasking with features that wereetchedbuthadundevelopedphotoresistmaskingtheetch.Thebluecolor indicatesthatSiO2stillremainsoverthosefeatures.Thewhitecolor is bare silicon. Micromasking can usually be solved with adescumetch(dryO2plasmaetch)beforeetchinginBOE.
Week2Figure11AprofilometermeasurementinreferencetoFigure10.Thedataindicatesthatasmallamount(250nm)ofSiO2remainsinetchedwindows.ThisSiO2willinhibitthefollowingdiffusion.
-
7/28/2019 fab well.pdf
15/64
RESULTS: Week2
SiO2Thickness( ):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
-
7/28/2019 fab well.pdf
16/64
Cleaning & Diffusion (N) Week 3
EQUIPMENT:
Acetone,Methanol,Isopropyl
MODULABPhosphorousDiffusion
Furnace PHOSPLUSTP250PhosphorousSources
RCACleanTanks
PARAMETERS:
RCACleanParameters
PiranhaSolution PiranhaEtchTime(minutes)
BOEsolution BOEEtchTime(seconds)
IonicClean IonicCleanEtchTime
(minutes)3:1
H2O2:H2SO4
10 6:1 10 6:1:1H2O:H2O2:HCl
10
PhosphorousDiffusionParameters(Nwell)
BoronSource Temperature(C) Time(minutes) N2FlowPHOSPLUSTP250 900 20 7
DriveinParameters(Nwell)
BoronSource Temperature(C) Time(minutes) N2FlowNone 1000 600 7
GOALS:
1. FullWaferClean(Solvent&RCA)2. PhosphorusDiffusion
-
7/28/2019 fab well.pdf
17/64
Methods:
1.WaferCleaning:
(CheckParameterssectionfordetails)The wafers need to be cleaned to remove
photoresist,andanypossible sourcesofcontamination
beforebeingplacedinahightemperaturefurnace.
To remove the photoresist a solvent clean isperformed.Beginbyplacinganevaporatingdishonthe
solventbench to catch solvent waste. Rinse the wafer
with acetone using the squirt bottle, and follow with
methanol and isopropyl. The acetone will remove the
photoresist and the methanol and isopropyl with
remove any acetone residue. Rinse the wafers in DI
wateranddrywithanitrogengun.Whenfinishedpour
thesolventwasteintotheSolventWasteContainer.
To removepossible sourcesofcontaminationa
modifiedRCAcleanisperformed.TheRCAcleanconsists
of rinsing the wafers in three chemical solutions. The
first isamixtureofsulfuricacidandhydrogenperoxide
known as Piranha etch. The piranha etch will remove
any organic material. The second mixture is a simple
BOE solutionwhichwill stripanynativeoxide thathas
accumulated on the wafer surface. The third and final
solutionisdesignedtoremoveanyheavymetalions,itis
a mixture of hydrochloric acid, water and hydrogen
peroxide.Thissolutionisreferredtoasionicclean
This step shouldalsobe carriedoutby the lab
TA. Load thewafers intoaTeflon cassette transfer the
cassettebetweentheRCAsolutionsuntilthecleaningis
complete.Rinse thewafersandcassette inabucketof
DIwaterthenpulleachwaferandrinseanddrybyhand.
Figure 12 Wafers submerged in Piranha Etch to remove organiccontaminates.
Week3
6.PhosphorousDiffusion:
(CheckParameterssectionfordetails)
Thegoalof thephosphorousdiffusion is to flip
the polarity of the Ptype substrate in the Nwells. In
other words, the diffusion will create Ntype silicon
areasonthewafer.TheseNwellsorTUBSwillactasthesubstrateforthePMOSdevices.
The diffusion is modeled as a solidsolubility
limiteddiffusion followedbyseveraldriveinsteps.The
expectedresistivitycanbederivedfromthismodeland
verifiedwiththePHOSPLUSdatasheet.
TodiffuseNtype (Phosphorous)material,ramp
theMODULABPhosphorousDiffusion Furnace to600C
andsetthenitrogenflow.Removethequartzboatwith
the solid, white, PHOSPLUS TP250 sources already in
place. Load the siliconwafersnext to the sourceswith
thepatternedsidefacingasource(seeFigureB). Insert
thequartzboat to the centerof the furnaceand ramp
the furnace to the desired temperature. When the
desiredtemperatureisreachedstartthetimer.Afterthe
allottedtime,rampthefurnacedownto600C,pullthe
quartzboatandremovethewafersandsetthemaside
tocool.Whenfinished,turnthefurnaceto0Candturn
off the nitrogen when the temperature drops below
400C.
FigureBAnillustrationofhowthewafersareloadedintothequartz
boatnexttothediffusionsources.
-
7/28/2019 fab well.pdf
18/64
RESULTS: Week3
RESULTS:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
-
7/28/2019 fab well.pdf
19/64
Documenting, Cleaning & Oxidation Week 4
EQUIPMENT:
OpticalMicroscope 6:1BOE
Tefloncassette JANDEL4pointProbeStation RCACleantanks MODULABOxidationFurnace CANONDigitalCamera
PARAMETERS:
GOALS:
1. Take pictures using the microscope anddigitalcamera.
2.
Stripthe
SiO2
&PSG
3. Obtain 4point probe measurements ofthediffusion
4. RCAclean5. Oxidation
SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask6:1 900 5* none
RCACleanParameters
PiranhaSolution PiranhaEtchTime(minutes)
BOEsolution BOEEtchTime(seconds)
IonicClean IonicCleanEtchTime
(minutes)3:1
H2O2:H2SO4
10 6:1 10 6:1:1
H2O:H2O2:HCl
10
OxidationParameters
Temperature(C) Time(minutes) Type(wetordry) N2/O2Flow BubblerSetting1000 90 Wet 7/9 40
-
7/28/2019 fab well.pdf
20/64
Methods:
1.TakingPictures:
With the first diffusion completed, the wafers
nowhaveobservablefeatures.Fromthispoint,onegoal
of the lab is to document the fabrication progress by
takingpicturesof the surfaceof thewaferas itmoves
through the sequence. Begin by using the opticalmicroscopeandCANONdigitalcameratotakeapicture
ofthediffusedNwell(showninFigure13)
Figure13AdiffusedNwell.Theaddeddopantscreatethedifferentcolor.
4.StrippingtheSiO2andPSG:
(CheckParameterssectionfordetails)Preparethewafersurfaceforthenextoxidation
bycompletelyremovingalltheSiO2andPSG.
REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1
BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor
(see Figure 9) and hydrophobicity. When the etch iscomplete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week4Figure 14 A lab TA handling acids at the rinse sink with full acidprotectionclothing.Notethefacemask,apron,andchemicalgloves.
3.DiffusionMeasurements:
There is a large diffused rectangle/square test
region. This region is used to measure the sheet
resistivity associated with the phosphorus Nwell
diffusion (seeFigure16nextpage).Use theJANDEL4
point probe to measure the sheet resistivity of the
diffusion.Startbyraisingtheprobearm,uncappingthe
tipandplacingthewaferonthestage.Aligntheprobes
over the test region and lower the arm into contact.
Start the testbyusinga small current, roughly100nA,and increment the current until the sheet resistivity
stabilizes.ConsulttheJANDEL4pointprobemanualfor
furtherassistance.Themeasuredsheetresistivityshould
correspond to the value foundon this PHOSPLUS data
sheet for the appropriate time and temperature (see
Figure17nextpage).
Figure15AstudentusingtheJANDEL4pointprobetodocumentthesheetresistivityofthediffusion.
-
7/28/2019 fab well.pdf
21/64
Methods:Figure16Anoutlineofthewaferdiffusiontestregions.Thearea inpinkisdiffusedasN andshouldbetestedwiththe4pointprobe.
Figure 17 A graph from the PhosPlus datasheet illustrating therelationship between diffusion time, temperature and sheetresistivity. The graph should be used to verify sheetresistivitymeasurements.
Week4
4.RCACleaning:
(CheckParameterssectionfordetails)REPEAT: To remove possible sources of
contaminationamodifiedRCA clean isperformed.The
RCA clean consists of rinsing the wafers in three
chemicalsolutions:Piranhaetch,BOE,Ionicclean.ThisstepshouldbecarriedoutbythelabTAfor
safety. Load the wafers into a Teflon cassette transfer
the cassette between the RCA solutions until the
cleaning iscomplete.Rinsethewafersandcassette ina
bucketofDIwater thenpulleachwaferand rinseand
drybyhand.
5.Oxidation:GrowingSiO2
(CheckParameterssectionfordetails)Thegoalofthesecondoxidationrunisthesame
asthefirst:growenoughsilicondioxide(SiO2)roughlya
0.5mthickfilm,tomaskthesubsequentdiffusion.
REPEAT: To oxidize, insert the wafers into the
MODULAB oxidationfurnace using the quartz rod and
quartzboat(seeFigure4).Thereshouldbetwodummy
wafers,oneatthefrontoftheboatandanotheratthe
rear, tomaintainuniformityacross theboat.Ramp the
furnace to 600Cbefore the removing thequartzboat
and loading the wafers. Prior to the temperaturereaching 400C, turn on the nitrogen to purge the
furnace.Also, set the potentiometer on the bubbler if
performing a wet oxidation (which we are). Once the
wafers are loaded and in place at the center of the
furnace, ramp the furnace to thedesired temperature.
When the desired temperature is reached start the
timer, stop the nitrogen flow and turnon theoxygen.
Aftertheallottedtime,rampthefurnacedownto600C
(or0C if finishedwith furnace),pull theboat, remove
the wafers, and set them aside to cool. When thetemperature drops below 400C the nitrogen can be
turnedoff.
-
7/28/2019 fab well.pdf
22/64
SheetResistance(/)&Resistivity(cm):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week4
-
7/28/2019 fab well.pdf
23/64
Photolitho & Etching(N+ Source/Drain) Week 5
EQUIPMENT:
Nanospec
BREWERspincoaterandhotplate
SHIPLEY1813positivephotoresist ABMContactMaskAligner
MF319developer
TeflonCassette
6:1BOE
PARAMETERS:
Spincoat&SoftbakeParameters
SpinProgram
Speed(RPM)
Time(seconds)
Ramp(RPM/s)
DispenseType
(automaticormanual)
SoftbakeProgram
Temperature(C)
Time(minutes)
#9 5250 30 20000 Manual(static)
#2 115 2
Exposure&DevelopmentParameters(MASK#2)
MaskOrientation(writingtoward
orawayfromuser)
WaferOrientation(flattotheleftorthe
right)
UVIntensityChannelB(mW/cm2)
UVDose(J/cm2)
ExposureTime(seconds)
DevelopmentTime(seconds)
Away Left 30 ~135 4.5 3060HardbakeParameters
HardbakeProgram Temperature(C) Time(minutes)#2 115 2
SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask6:1 900 5* Shipley1813Photoresist
GOALS:
1. Measure the thickness of the SiO2 layerwiththeNanospec.
2.
Photolithography
(Mask#2N+Source/Drain)3. Hardbake4. EtchSiO2
-
7/28/2019 fab well.pdf
24/64
Methods:
1.MeasuringtheSiO2thickness:
Measure the thicknessof the silicondioxideat
several different points on the wafer using the
Nanospec. For reference, the Nanospec prompts for
measuringSiO2thicknessare:
Iswavelength480nm? Y (ifnot,typeNandvalue)
Databankoption? N
Refrindexoption? N
Switchtoprinter? N
Enterfilmtype: 1SiO2
Enterobjlens: 1=10x
2.PhotolithographywithMask#2(N+S/D):
Spincoating
&
Soft
baking
(CheckParameterssectionfordetails)
The second mask contains the features for the
NMOSsourcesanddrains.
REPEAT:BeginbyusingtheBREWERspincoater
tospinathinfilmofSHIPLEY1813photoresistontothe
topside of the wafer. Next, transfer the wafer to the
adjacenthotplateandsoftbaketoremovesolventsand
hardenthe resist.Agoodcoatingofphotoresistwillbe
barely visible to the naked eye and have a minimal
numberofstreaksorblotches(seeFigure7).Ifthereare
alargenumberofdefects,solventclean,dehydrate,and
tryrespinningmorephotoresist.
Figure18StudentsandprofessorlookingonasawaferisalignedandexposedattheABMcontactaligner.
Week5
2.PhotolithographywithMask#2(N+S/D):
Exposure&Development(CheckParameterssectionfordetails)
Proceed by patterning the photoresist with
Mask#2.
REPEAT:Load themaskonto theABM contactalignermaskstage.Turn themaskvaconandraisethe
maskstage.Carefully,loadthewaferontothesubstrate
chuckandorientitsuchthattheplane(waferflat)
istotheleftandrunningstraightupanddown.Turnon
the substratevac to lock thewafer inplaceand lower
thechucktoavoidhittingthecontactmask.Next,lower
themaskstageandraisethesubstratechuckuptomeet
themask, fringe lineswillbecome visible as thewafer
andmaskcomeintocontact.Alignthemasktothewafer
usingthemarkersonthesidesofthewafer.Turnonthe
contactvac to remove any air gap between mask and
wafer. Adjust the exposure time and channel setting
then expose. Remove the wafer by turning off the
contactvac, lowering the substrate chuck, raising the
mask frame,andturningoffthesubstratevac.Transfer
thewafer toadishofMF319developer (a faintoutline
ofthefeaturescanbeseenatthispoint),submergethe
waferinMF319andgentlyswirlfor3060secondsuntil
the exposed resist is completely dissolved. If done
correctly there should be no photoresist left in the
diffusion contact regions (see Figure 8). If there is,
resubmerge the wafer in the MF319 developer for
additional time. If unsuccessful, use a solvent clean to
strip the photoresist, dehydrate and respin again.
When finished, pour the used MF319 into the MF319
wastecontainerlocatedunderthesolventbenchnextto
thephotoresist.
-
7/28/2019 fab well.pdf
25/64
Methods:
3.Hardbaking:
(CheckParameterssectionfordetails)
REPEAT: It has been observed, that without
hardbaking,thephotoresistexhibitsadhesionproblems
and frequently delaminates from the surface during
etching. Hardbaking is very similar to softbaking andfollows the same procedure. Load a wafer onto a
hotplateforasettimeattheappropriatetemperature.
4.EtchingtheSiO2:
(CheckParameterssectionfordetails)REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor
(see Figure 9) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week5
-
7/28/2019 fab well.pdf
26/64
SiO2Thickness( ):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week5
-
7/28/2019 fab well.pdf
27/64
Cleaning & Diffusion (N+) Week 6
EQUIPMENT:
RCATanks
Acetone,Methanol,Isopropyl
PhosphorousDiffusionFurnace PHOSPLUSTP250PhosphorousSources
TeflonCassette
PARAMETERS:
RCACleanParameters
PiranhaSolution PiranhaEtchTime(minutes)
BOEsolution BOEEtchTime(seconds)
IonicClean IonicCleanEtchTime
(minutes)3:1
H2O2:H2SO4
10 6:1 10 6:1:1H2O:H2O2:HCl
10
BoronDiffusionParameters(N+)
BoronSource Temperature(C) Time(minutes) N2Flow
PHOSPLUSTP250 900 60 7
GOALS:
1. FullWaferClean(Solvent&RCA)2. PhosphorousDiffusion
-
7/28/2019 fab well.pdf
28/64
Methods:
1.WaferCleaning:
(CheckParameterssectionfordetails)The wafers need to be cleaned to remove
photoresist,andanypossible sourcesofcontamination
beforebeingplacedinahightemperaturefurnace.
REPEAT: To remove the photoresist a solventcleanisperformed.Beginbyplacinganevaporatingdish
on the solventbench tocatch solventwaste.Rinse the
wafer with acetone using the squirt bottle, and follow
withmethanol and isopropyl. The acetonewill remove
the photoresist and the methanol and isopropyl with
remove any acetone residue. Rinse the wafers in DI
wateranddrywithanitrogengun.Whenfinishedpour
thesolventwasteintotheSolventWasteContainer.
REPEAT: To remove possible sources of
contaminationamodifiedRCA clean isperformed.This
stepshouldbecarriedoutbythelabTA.Loadthewafers
intoaTefloncassettetransferthecassettebetweenthe
RCA solutionsuntil the cleaning is complete.Rinse the
wafers and cassette in a bucket of DI water then pull
eachwaferandrinseanddrybyhand,
6.PhosphorousDiffusion:
(CheckParameterssectionfordetails)
The goal of the phosphorous diffusion is tocreatehighlydopedNtypesilicontoactasthesources
anddrainsoftheNMOStransistors.
REPEAT: To diffuse Ntype (Phosphorous)
material, ramp the MODULAB Phosphorous Diffusion
Furnaceto600Candsetthenitrogenflow.Removethe
quartz boat with the solid, white, PHOSPLUS TP250
sourcesalreadyinplace.Loadthesiliconwafersnextto
the sources with the patterned side facing a source.
Insert thequartzboat to thecenterof the furnaceand
rampthefurnacetothedesiredtemperature.Whenthedesiredtemperatureisreachedstartthetimer.Afterthe
allottedtime,rampthefurnacedownto600C(or0Cif
finishedwithfurnace),pullthequartzboatandremove
the wafers and set them aside to cool. When the
temperature drops below 400C the nitrogen can be
turnedoff.
Week6
-
7/28/2019 fab well.pdf
29/64
RESULTS:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week6
-
7/28/2019 fab well.pdf
30/64
Documenting, Cleaning & Oxidation Week 7
PARAMETERS:
SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask
6:1 900 5* noneRCACleanParameters
PiranhaSolution PiranhaEtchTime(minutes)
BOEsolution BOEEtchTime(seconds)
IonicClean IonicCleanEtchTime
(minutes)3:1
H2O2:H2SO4
10 6:1 10 6:1:1H2O:H2O2:HCl
10
OxidationParameters
Temperature(C) Time(minutes) Type(wetordry) N2/O2Flow BubblerSetting1000 90 Wet 7/9 40
GOALS:
1. Take pictures using the microscope anddigitalcamera
2.
Stripthe
SiO2
and
PSG
3. Obtain 4point probe measurements ofthediffusion
4. RCAclean5. Oxidation
EQUIPMENT:
OpticalMicroscope CANONDigitalCamera
6:1BOE TeflonCassette JANDEL4pointProbeStation RCATanks MODULABOxidationFurnace
-
7/28/2019 fab well.pdf
31/64
Methods:
1.TakingPictures:
Use theOpticalMicroscopeandCANONDigital
Camera to takepicturesof thediffusedNMOS sources
anddrains.
Figure19DiffusedNMOSsourcesanddrains.
2.StrippingtheSiO2andPSG:
(CheckParameterssectionfordetails)Preparethewafersurfaceforthenextoxidation
bycompletelyremovingalltheSiO2andPSG.
REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1
BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor
(see Figure 9) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week7
3.DiffusionMeasurements:
Use theJANDEL 4pointprobe to measure the
sheetresistivityoftheN+andNwelldiffusions(Referto
Figure21forthelocationofthediffusedareas).Consult
theJANDEL4pointprobemanualforfurtherassistance.
Themeasured sheet resistivityof theN+ region shouldcorrespond to the value found on the PhosPlus data
sheet(seeFigure20).
Figure 20 A graph from the PhosPlus datasheet illustrating therelationship between diffusion time, temperature and sheetresistivity.
Figure21Anoutlineofthewaferdiffusiontestregions.Thearea inpinkisthefreshlydiffusedN+regionandshouldbetestedwiththe4pointprobe.
-
7/28/2019 fab well.pdf
32/64
Week7
5.Oxidation:GrowingSiO2
(CheckParameterssectionfordetails)
Thegoaloftheoxidationrunistogrowenough
silicondioxide(SiO2)roughlya0.5mthickfilm,tomask
thesubsequentdiffusion.
REPEAT: To oxidize, insert the wafers into theMODULAB oxidationfurnace using the quartz rod and
quartzboat(seeFigure4).Thereshouldbetwodummy
wafers,oneatthefrontoftheboatandanotheratthe
rear, tomaintainuniformityacross theboat.Ramp the
furnace to 600Cbefore the removing thequartzboat
and loading the wafers. Prior to the temperature
reaching 400C, turn on the nitrogen to purge the
furnace.Also, set the potentiometer on the bubbler if
performing a wet oxidation (which we are). Once the
wafers are loaded and in place at the center of the
furnace, ramp the furnace to thedesired temperature.
When the desired temperature is reached start the
timer, stop the nitrogen flow and turnon theoxygen.
Aftertheallottedtime,rampthefurnacedownto600C
(or0C if finishedwith furnace),pull theboat, remove
the wafers, and set them aside to cool. When the
temperature drops below 400C the nitrogen can be
turnedoff.
Methods:
4.RCACleaning:
(CheckParameterssectionfordetails)REPEAT: To remove possible sources of
contaminationamodifiedRCA clean isperformed.The
RCA clean consists of rinsing the wafers in three
chemicalsolutions:Piranhaetch,BOE,Ionicclean.ThisstepshouldbecarriedoutbythelabTAfor
safety. Load the wafers into a Teflon cassette transfer
the cassette between the RCA solutions until the
cleaningiscomplete.Rinsethewafersandcassette ina
bucketofDIwater thenpulleachwaferand rinseand
drybyhand.
-
7/28/2019 fab well.pdf
33/64
SheetResistance(/)&Resistivity(cm):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week7
-
7/28/2019 fab well.pdf
34/64
Photolitho & Etching (P+ Source/Drain) Week 8
PARAMETERS:
Spincoat&SoftbakeParameters
Spin
Program
Speed
(RPM)
Time
(seconds)
Ramp
(RPM/s)
Dispense
Type(automaticor
manual)
Softbake
Program
Temperature
(C)
Time
(minutes)
#9 5250 30 20000 Manual(static)
#2 115 2
Exposure&DevelopmentParameters(MASK#3)
MaskOrientation(writingtoward
orawayfromuser)
WaferOrientation(flattotheleftorthe
right)
UVIntensityChannelB(mW/cm2)
UVDose(J/cm2)
ExposureTime(seconds)
DevelopmentTime(seconds)
Away Left 30 ~135 4.5 3060
HardbakeParametersHardbakeProgram Temperature(C) Time(minutes)
#2 115 2SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask6:1 900 5* Shipley1813Photoresist
EQUIPMENT:
Nanospec BREWERspincoaterandhotplate
SHIPLEY1813positivephotoresist ABMContactMaskAligner MF319developer 6:1BOE TeflonCassette
GOALS:
1. Measure the thickness of the SiO2 layerwiththeNanospec
2.
Photolithography
(Mask#3P+Source/Drain)3. Hardbake4. SiO2Etch
-
7/28/2019 fab well.pdf
35/64
Methods:
1.MeasuringtheSiO2thickness:
Measure the thicknessof the silicondioxideat
several different points on the wafer using the
Nanospec. For reference, the Nanospec prompts for
measuringSiO2thicknessare:
Iswavelength480nm? Y (ifnot,typeNandvalue)
Databankoption? N
Refrindexoption? N
Switchtoprinter? N
Enterfilmtype: 1SiO2
Enterobjlens: 1=10x
2.PhotolithographywithMask#3(P+S/D):
Spincoating
&
Soft
baking
(CheckParameterssectionfordetails)
The third mask contains the features for the
PMOSsourcesanddrains.
REPEAT:BeginbyusingtheBREWERspincoater
tospinathinfilmofSHIPLEY1813photoresistontothe
topside of the wafer. Next, transfer the wafer to the
adjacenthotplateandsoftbaketoremovesolventsand
hardenthe resist.Agoodcoatingofphotoresistwillbe
barely visible to the naked eye and have a minimal
numberofstreaksorblotches(seeFigure7).Ifthereare
alargenumberofdefects,solventclean,dehydrate,and
tryrespinningmorephotoresist.
Figure22AstudentusingtheABMmaskalignertoalignMask#3.
Week8
2.PhotolithographywithMask#3(P+S/D):
Exposure&Development(CheckParameterssectionfordetails)
Proceed by patterning the photoresist with
Mask#3.
REPEAT:Load themaskonto theABM contactalignermaskstage.Turn themaskvaconandraisethe
maskstage.Carefully,loadthewaferontothesubstrate
chuckandorientitsuchthattheplane(waferflat)
istotheleftandrunningstraightupanddown.Turnon
the substratevac to lock thewafer inplaceand lower
thechucktoavoidhittingthecontactmask.Next,lower
themaskstageandraisethesubstratechuckuptomeet
themask, fringe lineswillbecome visible as thewafer
andmaskcomeintocontact.Alignthemasktothewafer
usingthemarkersonthesidesofthewafer.Turnonthe
contactvac to remove any air gap between mask and
wafer. Adjust the exposure time and channel setting
then expose. Remove the wafer by turning off the
contactvac, lowering the substrate chuck, raising the
mask frame,andturningoffthesubstratevac.Transfer
thewafer toadishofMF319developer (a faintoutline
ofthefeaturescanbeseenatthispoint),submergethe
waferinMF319andgentlyswirlfor3060secondsuntil
the exposed resist is completely dissolved. If done
correctly there should be no photoresist left in the
diffusion contact regions (see Figure 8). If there is,
resubmerge the wafer in the MF319 developer for
additional time. If unsuccessful, use a solvent clean to
strip the photoresist, dehydrate and respin again.
When finished, pour the used MF319 into the MF319
wastecontainerlocatedunderthesolventbenchnextto
thephotoresist.
-
7/28/2019 fab well.pdf
36/64
Methods:
3.Hardbaking:
(CheckParameterssectionfordetails)
REPEAT: It has been observed, that without
hardbaking,thephotoresistexhibitsadhesionproblems
and frequently delaminates from the surface during
etching. Hardbaking is very similar to softbaking andfollows the same procedure. Load a wafer onto a
hotplateforasettimeattheappropriatetemperature.
4.EtchingtheSiO2:
(CheckParameterssectionfordetails)REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor
(see Figure 9) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week8
-
7/28/2019 fab well.pdf
37/64
SiO2Thickness( ):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week8
-
7/28/2019 fab well.pdf
38/64
Cleaning & Diffusion (P+) Week 9
PARAMETERS:
RCACleanParameters
PiranhaSolution PiranhaEtchTime(minutes)
BOEsolution BOEEtchTime(seconds)
IonicClean IonicCleanEtchTime
(minutes)3:1
H2O2:H2SO4
10 6:1 10 6:1:1
H2O:H2O2:HCl
10
BoronDiffusionParameters(DIFFUSEDCONTACTS)
BoronSource Temperature(C) Time(minutes) N2FlowBORONPLUSGS139 1000 120 7
DriveinParameters(DIFFUSEDCONTACTS)
BoronSource Temperature(C) Time(minutes) N2Flownone 1000 60 7
EQUIPMENT:
Acetone,Methanol,Isopropyl RCATanks
BoronDiffusionFurnace BORONPLUSGS139BoronSources
GOALS:
1. FullWaferClean(Solvent&RCA)2. BoronDiffusion
-
7/28/2019 fab well.pdf
39/64
Methods:
1.WaferCleaning:
(CheckParameterssectionfordetails)The wafers need to be cleaned to remove
photoresist,andanypossible sourcesofcontamination
beforebeingplacedinahightemperaturefurnace.
REPEAT: To remove the photoresist a solventcleanisperformed.Beginbyplacinganevaporatingdish
on the solventbench tocatch solventwaste.Rinse the
wafer with acetone using the squirt bottle, and follow
withmethanol and isopropyl. The acetonewill remove
the photoresist and the methanol and isopropyl with
remove any acetone residue. Rinse the wafers in DI
wateranddrywithanitrogengun.Whenfinishedpour
thesolventwasteintotheSolventWasteContainer.
REPEAT: To remove possible sources of
contaminationamodifiedRCA clean isperformed.This
stepshouldbecarriedoutbythelabTA.Loadthewafers
intoaTefloncassettetransferthecassettebetweenthe
RCA solutionsuntil the cleaning is complete.Rinse the
wafers and cassette in a bucket of DI water then pull
eachwaferandrinseanddrybyhand,
6.BoronDiffusion:
(CheckParameterssectionfordetails)
The goal of the boron diffusion is to createhighly doped Ptype silicon to act as the sources and
drainsofthePMOStransistors.
REPEAT: To diffuse Ptype (Boron) material,
ramptheLindbergBlueBoronDiffusionFurnaceto600C
andsetthenitrogenflow.Removethequartzboatwith
thesolid,white,BORONPLUSGS139sourcesalready in
place. Load the siliconwafersnext to the sourceswith
thepatternedsidefacingasource.Insertthequartzboat
tothecenterofthefurnaceandrampthefurnacetothe
desired temperature.When thedesired temperature isreached start the timer. After the allotted time, ramp
the furnace down to 600C (or 0C if finished with
furnace), pull the quartz boat and remove the wafers
and set them aside to cool. When the temperature
dropsbelow400Cthenitrogencanbeturnedoff.
Week9
-
7/28/2019 fab well.pdf
40/64
RESULTS:
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week9
-
7/28/2019 fab well.pdf
41/64
Documenting, Cleaning & Oxidation Week 10
PARAMETERS:
SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask6:1 900 5* Shipley1813Photoresist
RCACleanParameters
PiranhaSolution PiranhaEtchTime(minutes)
BOEsolution BOEEtchTime(seconds)
IonicClean IonicCleanEtchTime
(minutes)
3:1H2O2:H2SO4
10 6:1 10 6:1:1H2O:H2O2:HCl
10
OxidationParameters
Temperature(C) Time(minutes) Type(wetordry) N2/O2Flow BubblerSetting1000 30 Wet 7/9 N/A
OxidationParameters
Temperature(C) Time(minutes) Type(wetordry) N2/O2Flow BubblerSetting1000 60 Dry 7/9 N/A
EQUIPMENT:
OpticalMicroscope CANONDigitalCamera
JANDEL4pointprobe RCAtanks MODULABOxidationFurnace
GOALS:
1. Take pictures with microscope andcamera
2.
StripSiO2 and
BSG
3. 4pointprobe3. RCAclean4. DryOxidation
-
7/28/2019 fab well.pdf
42/64
Methods:
1.TakingPictures:
Use theOpticalMicroscopeandCANONDigital
Camera to takepicturesof thediffused PMOS sources
anddrains.
Figure23DiffusedPMOSandNMOSsourcesanddrains.
2.Stripping
the
SiO2
and
PSG:
(CheckParameterssectionfordetails)Preparethewafersurfaceforthenextoxidation
bycompletelyremovingalltheSiO2andPSG.
REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1
BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor(see Figure 9) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week10
3.DiffusionMeasurements:
Use the 4point probe to measure the sheet
resistivityof theP+,N+andNwelldiffusions (Refer to
Figure25forthelocationofthediffusedareas).Consult
theJANDEL4pointprobemanualforfurtherassistance.
Themeasured sheet resistivityof theP+ region shouldcorrespond to the value found on the BoronPlus data
sheet(seeFigure24).
Figure24GraphfromtheBoronPlusdatasheet.
-
7/28/2019 fab well.pdf
43/64
Methods:
1.TakingPictures:
Use theOpticalMicroscopeandCANONDigital
Camera to takepicturesof thediffused PMOS sources
anddrains.
Figure16CompletedType2piezoresistors.
2.Stripping
the
SiO2
and
PSG:
(CheckParameterssectionfordetails)Preparethewafersurfaceforthenextoxidation
bycompletelyremovingalltheSiO2andPSG.
REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1
BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor(see Figure 9) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week10
5.DryOxidation:GrowingSiO2
(CheckParameterssectionfordetails)
Thegoalof the fourthoxidation run is togrow
the gate oxide. The oxide thickness should be
approximately 700 thick. The method of oxidation
differs from theprevious runs, theoxidewillbegrownwithdryO2.
REPEAT: To oxidize, insert the wafers into
oxidationfurnaceusingthequartzrodandquartzboat.
Thereshouldbetwodummywafers,oneatthefrontof
theboatandanotherattherear,tomaintainuniformity
acrosstheboat.Ramp the furnace to600Cbefore the
removing thequartzboatand loading thewafers.Prior
tothetemperaturereaching400C,turnonthenitrogen
to purge the furnace. Load the wafers and insert the
quartzboat to thecenterof the furnaceand ramp the
furnace to thedesired temperature.When thedesired
temperature is reached start the timer, stop the
nitrogenflowandturnontheoxygen.Aftertheallotted
time,rampthefurnacedownto600C(or0Ciffinished
withfurnace),pulltheboat,removethewafers,andset
themasidetocool.
Methods:Figure25Anoutlineofthewaferdiffusiontestregions.Thearea inpink is diffused as P+. Test each area with the 4point probe andrecordthefinalsheetresistivities.
4.RCACleaning:
(CheckParameterssectionfordetails)REPEAT: To remove possible sources of
contaminationamodifiedRCA clean isperformed.The
RCA clean consists of rinsing the wafers in three
chemicalsolutions:Piranhaetch,BOE,Ionicclean.
ThisstepshouldbecarriedoutbythelabTAfor
safety. Load the wafers into a Teflon cassette transfer
the cassette between the RCA solutions until the
cleaningiscomplete.Rinsethewafersandcassette ina
bucketofDIwater thenpulleachwaferand rinseand
drybyhand.
-
7/28/2019 fab well.pdf
44/64
SheetResistance(/)&Resistivity(cm):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES: Ashortwetoxidationwasaddedalongwithanothermaskingstep.
Thegateoxidemask(GOX)removesthefieldoxidewherethegateoxideistobegrown
andgeneratesthealignmentmarksforthecontactmask. Inthepastthisstepwas
removedtoexpeditetheprocesssothatitcouldbefinishedbytheendoftheterm.WenowstartonWeek#2withthesubstratesalreadyoxidizedtoallowfortheextra
processingstepsnow.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
RESULTS: Week10
-
7/28/2019 fab well.pdf
45/64
Photolithography & Etching (Vias) Week 11
PARAMETERS:
Spincoat&SoftbakeParameters
Spin
Program
Speed
(RPM)
Time
(seconds)
Ramp
(RPM/s)
Dispense
Type(automaticor
manual)
Softbake
Program
Temperature
(C)
Time
(minutes)
#9 5250 30 20000 Manual(static)
#2 115 2
Exposure&DevelopmentParameters(MASK#4)
MaskOrientation(writingtoward
orawayfromuser)
WaferOrientation(flattotheleftorthe
right)
UVIntensityChannelB(mW/cm2)
UVDose(J/cm2)
ExposureTime(seconds)
DevelopmentTime(seconds)
Away Left 30 ~135 4.5 3060
HardbakeParametersHardbakeProgram Temperature(C) Time(minutes)
#2 115 2SiO2EtchParameters*for4,2004,500 thickSiO2layer
BOEconcentration SiO2EtchRate(/min) Approx.EtchTime(minutes) EtchMask6:1 900 5* Shipley1813Photoresist
EQUIPMENT:
Nanospec BREWERspincoaterandhotplate
SHIPLEY1813positivephotoresist ABMContactMaskAligner MF319developer 6:1BOE TeflonCassette
GOALS:
1. Measure the thickness of the SiO2 layerwiththeNanospec
2.
Photolithography(Mask
#4
Vias)
3. Hardbake4. SiO2Etch
-
7/28/2019 fab well.pdf
46/64
Methods:
1.MeasuringtheSiO2thickness:
Measure the thicknessof the silicondioxideat
several different points on the wafer using the
Nanospec. For reference, the Nanospec prompts for
measuringSiO2thicknessare:
Iswavelength480nm? Y (ifnot,typeNandvalue)
Databankoption? N
Refrindexoption? N
Switchtoprinter? N
Enterfilmtype: 1SiO2
Enterobjlens: 1=10x
2.PhotolithographywithMask#4(Vias):
Spincoating
&
Soft
baking
(CheckParameterssectionfordetails)
Thefourthmaskcontainsthefeaturesofthevia
etch. The vias are holes in the SiO2 which allow the
aluminumpadstocontactthediffusedsiliconsurface.
REPEAT:BeginbyusingtheBREWERspincoater
tospinathinfilmofSHIPLEY1813photoresistontothe
topside of the wafer. Next, transfer the wafer to the
adjacenthotplateandsoftbaketoremovesolventsand
hardenthe resist.Agoodcoatingofphotoresistwillbe
barely visible to the naked eye and have a minimal
numberofstreaksorblotches(seeFigure7).Ifthereare
alargenumberofdefects,solventclean,dehydrate,and
tryrespinningmorephotoresist.
Week11
2.PhotolithographywithMask#4(Vias):
Exposure&Development(CheckParameterssectionfordetails)
Proceed by patterning the photoresist with
Mask#4.
REPEAT:Load themaskonto theABM contactalignermaskstage.Turn themaskvaconandraisethe
maskstage.Carefully,loadthewaferontothesubstrate
chuckandorientitsuchthattheplane(waferflat)
istotheleftandrunningstraightupanddown.Turnon
the substratevac to lock thewafer inplaceand lower
thechucktoavoidhittingthecontactmask.Next,lower
themaskstageandraisethesubstratechuckuptomeet
themask, fringe lineswillbecome visible as thewafer
andmaskcomeintocontact.Alignthemasktothewafer
usingthemarkersonthesidesofthewafer.Turnonthe
contactvac to remove any air gap between mask and
wafer. Adjust the exposure time and channel setting
then expose. Remove the wafer by turning off the
contactvac, lowering the substrate chuck, raising the
mask frame,andturningoffthesubstratevac.Transfer
thewafer toadishofMF319developer (a faintoutline
ofthefeaturescanbeseenatthispoint),submergethe
waferinMF319andgentlyswirlfor3060secondsuntil
the exposed resist is completely dissolved. If done
correctly there should be no photoresist left in the
diffusion contact regions (see Figure 8). If there is,
resubmerge the wafer in the MF319 developer for
additional time. If unsuccessful, use a solvent clean to
strip the photoresist, dehydrate and respin again.
When finished, pour the used MF319 into the MF319
wastecontainerlocatedunderthesolventbenchnextto
thephotoresist.
-
7/28/2019 fab well.pdf
47/64
Methods:
3.Hardbaking:
(CheckParameterssectionfordetails)
REPEAT: It has been observed, that without
hardbaking,thephotoresistexhibitsadhesionproblems
and frequently delaminates from the surface during
etching. Hardbaking is very similar to softbaking andfollows the same procedure. Load a wafer onto a
hotplateforasettimeattheappropriatetemperature.
4.EtchingtheSiO2:
(CheckParameterssectionfordetails)REPEAT:This step shouldbe carriedoutby the
lab TA for safety reasons.Beginby loading the wafers
into a Teflon cassette with equal spacing between
wafers.Using thehandle, submerge thecassette in6:1BOE for the appropriate amount of time or until the
exposedSiO2iscompletelyremoved.Todetermineifthe
SiO2 iscompletely removed,checkthe regions forcolor
(see Figure 9) and hydrophobicity. When the etch is
complete,removethecassetteandrinsethewafersina
bucket of DI water. Pull the cassette from the rinse
bucketandrinseanddryindividualwaferswithDIwater
andnitrogengun.
Week11
-
7/28/2019 fab well.pdf
48/64
SiO2Thickness( ):
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
NOTES/CHANGES:
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________________________________________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
____________________________________