Investigation of silicon-on-insulator materials and devices for VLSI and special-device applications

161 Pages·1991·5.2 MB·English

by  Chen, Hung-Sheng, 1961-

INVESTIGATIONOFSILICON-ON-INSULATORMATERIALSAND
DEVICESFORVLSIANDSPECIAL-DEVICEAPPLICATIONS
BY
HUNG-SHENGCHEN
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAIN
PARTIALFULFILLMENTOFTHEREQUIREMENTS
FORTHEDEGREEOFDOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1991
ACKNOWLEDGEMENTS
Iwish toexpress mysincereappreciation to thechairman ofmycommittee,
ProfessorShengS.Li,forhisguidance,encouragement,andsupportthroughoutthe
courseofthisresearch. IwouldalsoliketothankProfessorsDorotheaE.Burk,Gys
Bosman, Robert M. Fox,andTimothyJ. Andersonforservingonmysupervisory
committee.
Iamgratefulto Dr. WadeA. Krullat IbisTechnology Corp. forsupplying
devices for my measurements and explaining the processing detailofthe various
devices. ThanksareextendedtomycolleaguesFrederickT.Brady,Yi-NanLin,and
AndrewTzengfortheirhelpfuldiscussionsandencouragements.
Iamgreatlyindebtedtomyparentsandwifefortheirloveandsupportduring
thearduousroadofcompletingmyDoctorofPhilosophydegree.
Finally,thefinancialsupportoftheFloridaHighTechnologyandIndustryCoun-
cil,RADC/HansconAFB,andHarrisCorp. isgratefullyacknowledged.
i
TABLEOFCONTENTS
Page
ACKNOWLEDGEMENTS
i
ABSTRACT v
CHAPTER
1 INTRODUCTION 1
1.1Silicon-On-InsulatorTechnology 1
1.2PreparationofSIMOXWafers 2
1.3IntegratedCircuitandNovel-DeviceApplications 3
1.3.1MilitaryIntegratedCircuitApplications 4
1.3.2High-VoltageIntegratedCircuitApplications 5
1.3.3SubmicronCMOSApplications 5
1.3.4Novel-DeviceApplications 7
1.4SynopsisofChapters 8
2 DETERMINATIONOFGENERATIONLIFETIMEPROFILEIN
THINSEMICONDUCTORFILMS 12
2.1Introduction 12
2.2CurrentsinReverse-Biasedp-nJunction 12
2.3Theory 14
2.3.1EvaluationofGenerationLayerWidth 14
2.3.2GenerationLifetimeProfileTechnique 16
2.4ResultsandDiscussion 17
2.5Conclusion 21
3 AMODELFORANALYZINGTHEINTERFACEPROPERTIES
OFASEMICONDUCTOR-INSULATOR-SEMICONDUCTOR
STRUCTURE:CAPACITANCEANDCONDUCTANCE
TECHNIQUES
3.1Introduction 31
ii
3.2SmallSignalEquivalentCircuits 32
3.3ExtractionofInterfaceStateParameters 34
3.3.1CapacitanceMethod 34
3.3.2ConductanceMethod 35
3.4CouplingofSurfacePotentials 37
3.5DeterminationofSurfacePotentialVersusGateBias 40
3.6DeterminationoftheSISCapacitorParameters 41
3.7ResultsandDiscussion 42
3.8Conclusion 45
4 AMODELFORANALYZINGTHEINTERFACEPROPERTIES
OFASEMICONDUCTOR-INSULATOR-SEMICONDUCTOR
STRUCTURE:TRANSIENTCAPACITANCETECHNIQUES 63
4.1Introduction 63
4.2Bias-ScanDLTSTechnique 64
4.2.1CarrierDynamicsoftheSISCapacitor 65
4.2.2Bias-ScanDLTSAnalysis 67
4.3C-tandTemperature-ScanDLTSTechniques 72
4.3.1DecouplingattheF/OandS/OInterfaces 72
4.3.2C-VandC-tAnalysis 72
4.3.3Temperature-ScanDLTSAnalysis 74
4.4Conclusion 76
5 INTERFACESTATECHARACTERIZATIONINSMALL
GEOMETRYMOSFET’S 95
5.1Introduction 95
5.2MOSFETEquivalentCircuits 96
5.3StaticandDynamicTransconductanceofMOSFET’s 98
5.4ExtractionofInterfacePropertiesfromtheTransconductance 100
5.4.1High-FrequencyTransconductanceMethod 100
5.4.2Low-FrequencyTransconductanceMethod 101
5.4.3High-LowFrequencyTransconductanceMethod 102
5.4.4DynamicTransconductanceMethod 103
5.5ResultsandDiscussion 103
5.6Conclusion 105
6 DESIGNCONSIDERATIONSFORYIELDENHANCEMENT
OFSOIMOSFET’S 116
6.1Introduction 116
6.2StatisticalAnalysisofThresholdVoltage 117
6.2.1ThresholdVoltageofBulkMOSFET 118
m
6.2.2
ThresholdVoltageofThin-FilmSOIMOSFET 118
6.3ResultsandDiscussion 119
6.3.1VariationofOxideThickness 119
6.3.2VariationofDopingConcentration 120
6.3.3VariationofChannelLength 122
6.3.4VariationofFilmThickness 122
6.3.5VariationofTemperature 123
6.4DesignConsiderations 123
6.5Conclusion 125
7 SUMMARYANDCONCLUSIONS 138
REFERENCES 144
BIOGRAPHICALSKETCH 152
IV
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
INVESTIGATIONOFSILICON-ON-INSULATORMATERIALSAND
DEVICESFORVLSIANDSPECIAL-DEVICEAPPLICATIONS
By
Hung-shengChen
May1991
Chairman: ShengS.Li
MajorDepartment:ElectricalEngineering
Thisworkdealswiththecharacterization,modeling,anddesignconsiderations
ofsilicon-on-insulator(SOI)materialsanddevicesforVLSIandspecial-deviceappli-
cations. Itconsistsoftwoparts. Inthefirstpart,severalelectricalcharacterization
techniquesaredescribedthatuseteststructuressuchasdiode,capacitor,andMOS-
FETforevaluatingthefilmand interfacepropertiesofSOImaterialsanddevices.
Inthesecondpart,designconsiderationsforenhancingtheproductionyieldinSOI
VLSIcircuitsarediscussed.
UsingtheSOIdiodeasatestvehicle,wedevelopadifferentialtechniquethat
uses the reverse biased current-voltage and capacitance-voltage measurements for
determiningthegenerationlifetimeprofileinthethinsemiconductorfilm. Toeval-
uatethetopsiliconfilmand theinterfacepropertiesoftheSOIsubstrate, wede-
velopageneralizedmodelforelectricalcharacterizationofasemiconductor-insulator-
semiconductor(SIS)capacitorusingstatic,dynamic,andtransientcapacitanceand
conductancemethods. Byintroducing a couplingfactor, theconventional metal-
oxide-semiconductorcapacitortheoryismodifiedandappliedtoanalyzetheprop-
ertiesoftwo Si/SiC>2 interfaces (i.e.,film/buriedoxideand substrate/buriedoxide
interfaces)ofaSIScapacitor. Inaddition,wehavealsodevelopedseveralmethods
forthecharacterizationofinterfacestatesinasmallgeometryMOSFEToperatingin
thelinearregion. Interfacestatedensitiesdeterminedbythehigh-andlow-frequency
transconductancemeasurementsforbothbulkandSOIMOSFETsarepresented.
TheproductionyieldofVLSIcircuitsisinvestigatedbyexaminingthestatistical
variationofthethresholdvoltageinducedbyrandomdistributeddeviceparameters.
Theanalysisrevealsthatthin-filmSOIMOSFETislesssensitivetoinherentfluc-
tuations indeviceparameters. Design considerationsinminimizingthestatistical
thresholdvoltagevariationinSOIMOSFETsarediscussed. Byproperlychoosing
thegatematerial,filmthickness,andchanneldopingdensity,enhancementofpro-
ductionyieldcanbeexpectedforhighperformanceSOIVLSIcircuits.
vi
CHAPTER
1
INTRODUCTION
1.1Silicon-On-InsulatorTechnology
Thesilicon-on-insulator(SOI)technologieshavebeenunderrapiddevelopment
inthepastfewyears. TheSIMOX-based(SeparationbyIMplantationofOXygen)
SOImaterialoffers new promiseasleadingtechnologyforhigh-density, radiation-
hard,andhigh-performanceintegratedcircuits(ICs). TheusefulSOIpropertiesare
basedontheuniquecapabilityoftotalelectricalisolationofsilicon areas andthe
reductionofjunctionareas. ThepotentialadvantagesofSOItechnologyoverbulk
siliconforadvancedMOSdevicesarenumerous. Theyincludehigherspeed,lower
dynamicpowerconsumption,greaterpackingdensity,increasedtransientradiation
tolerance,integrationofbipolarandCMOSdevicesonthesamechip,and,forCMOS,
freedomfromlatchup.
HighqualitySOImaterialisrequiredinordertoachievethepotentialforthis
techniqueinICfabrication. ThereareseveralmethodsformakingSOIlayers,but,
atpresent,threetechniquesaregenerallybelievedtoholdthemostpromise. These
are (i) ion implantation ofoxygen below the silicon surface, (ii) recrystallization
ofpolysilicondepositedonathermallygrownoxide,and (iii)waferbonding. The
useofahigh-doseoxygenionimplantation,commonlyknownasSIMOX,isoneof
themajorcontendersforSOItechnology. SIMOXwafer,unlikeotherSOIwafers,
has theadvantagethat thematerialformation is simplyan additional step in an
ICfabricationprocess-ionimplantation,furnaceannealing,andepitaxialgrowth.
It isaconventional silicon-based technology, and thefabricationofSIMOX-based
1
2
circuits uses processing steps similar to those used in the conventional IC manu-
facturing. AlthoughresearchcontinuesonbothSIMOXandrecrystallization-based
SOI,SIMOXappearstobemorecompatiblewithconventionalICfabricationpro-
cesses than recrystallization-based SOI. Therefore, SIMOX has been moreheavily
investigatedanddevelopedthantherestofSOItechnologies.
1.2PreparationofSIMOXWafers
ASIMOXwaferispreparedbyimplantingasiliconwaferwithoxygenionsat
150-200keVandtoaniondoseoftypically1.2-2.4 x 1018/cm2(Fig. 1.1). Thedose
usedfor this processis about 100 times larger than anyother implant doseused
in semiconductorprocessing. This dosetranslates intoaverylongimplant time.
Evenwiththehighest-currentimplanter,whichdelivers100mAofbeamcurrent,the
oxygenimplantrequiresabout6-7hourstoimplanttwenty-five4” wafers[1]. The
temperatureduringimplantisveryimportantsinceinsitudynamicannealingmust
occuratthesurfaceofthewafer. Thewaferistypicallyheatedto400°Corhigher
duringtheionimplantationprocess. Ahighwafertemperatureensuresthatthefilm
retainsitscrystallinityduringthehigh-doseimplantationprocess[2].
Withsuchanextremeimplantsituation,severalothermattersbecomeimpor-
tant. Oneisthemetalliccontaminationintroducedduringtheimplant. Sinceoxygen
ions areveryreactive, structuresinsidetheimplanterthat canbeexposedtothe
ionizedoxygenmustbepassivated,usuallybycoatingwithquartzorsilicon. Never-
theless,somemetalliccontaminationispresentwithallimplanters,butthedoseand
currentareusuallymuchsmaller,andthecontaminationtendstoscalewithdose.
EarlySIMOXwaferwasfoundtohaveveryhighdensity(1x1017/cm3)ofthecom-
ponentsofstainless,copper, carbon, andaluminum. Thecontaminationhasbeen
reducedabouttwoordersofmagnitudebycarefulcontaminationcontrolinthelater
versionoftheoxygenimplantsystem[1],
3
Afteroxygenimplantation,thewaferistypicallyannealedabove1150°Cinan
inertambient. Thehigh-temperatureannealrepairsthedamageintroducedduring
implantationandallowsexcessoxygeninthesurfacesiliconlayertoout-diffuse,in-
creasingthedielectricstrengthoftheburiedoxidelayer. Afterimplantationand
anneal, thesurfacesiliconlayeristypically 100-300nmthick. Ifathickersilicon
layerisrequiredforICfabrication,anepitaxiallayercanbegrownbyconventional
epitaxialtechniques.
Thetwotypesofdefectswhicharedominantinthetopsiliconfilmfollowedthe
high-temperature annealingare precipitates and threading dislocations. Although
precipitatescanbeeasilyremovedbydissolutionduringhigh-temperatureannealing,
the threading dislocations once formed are exceedingly stable and are essentially
impossibletoremovebythermalannealingalone[3]. Twodifferentapproachescan
beidentifiedtoavoidthegenerationofthreadingdislocationsduringannealing: (i)
sequentialimplantationandannealingofsubstoichiometricdosesofoxygen,which
has been found tobeeffectivein reducingthedislocation density bylimitingthe
maximumprecipitatesizeattainedduringtheearlystagesofannealing[4],and(ii)
formationofabandoforderedoxideprecipitatestoreducethestressinthisregion
andtoconfinethedislocationstoanarrowregionabovetheburiedoxidesothatthey
canberemovedastheprecipitatesareincorporatedintotheburiedoxide[5],
Mostoftheimplantedinsulatorlayersareformedbyoxygenimplantation,how-
ever it is also possible to create a buried insulator layer by implanting nitrogen.
Nitrogenhastheadvantageinthatalowerdoseisrequiredtocreatetheinsulator,
sothatthesiliconfilmwillbedamagedless. Thecompetingeffectsthatmakethe
implantednitrogenapproachmoredifficult includeanarrowwindowofdosesthat
areusefulandpossibleadverseeffectsofresidualnitrogeninthesiliconlayer[1], A
veryattractiveapproachistheuseofbothoxygenandnitrogenimplantstoforma
buriedoxynitride.