Fundamentals of Ultra-Thin-Body MOSFETs and FinFETs

228 Pages·2013·3.75 MB·English

by  Fossum J.G., Trivedi V.P.

Fundamentalsof Ultra-Thin-BodyMOSFETs and FinFETs
Understand the theory, design, and applications of thetwo principal candidates for the
nextmainstreamsemiconductor-industrydevicewiththisconciseandclearguidetoFD/
UTBtransistors.
Thisbook
* DescribesFD/SOIMOSFETsand3-DFinFETsindetail
* Covers short-channel effects, quantum-mechanical effects, and applications of UTB
devicestofloating-bodyDRAMandconventionalSRAM
* Provides design criteria for nanoscale FinFET and nanoscale thin- and thick-BOX
planarFD/SOIMOSFETtohelpreducetechnologydevelopmenttime
* ProjectspotentialnanoscaleUTBCMOSperformances
* Containsend-of-chapterexercises
For professional engineers in the CMOS IC field who need to know about optimal
nonclassicaldevicedesignandintegration,thisisamust-haveresource.
Jerry G. Fossum is Distinguished Professor Emeritus of Electrical and Computer
Engineering at the University of Florida, Gainesville, and a Fellow of the IEEE. He
won the IEEE/EDS J. J. Ebers Award in 2004 for “outstanding contributions to the
advancementofSOICMOSdevicesandcircuitsthroughmodeling.”
Vishal P. Trivedi is a Member of the Technical Staff and a Distinguished Innovator at
FreescaleSemiconductor,Inc.,andaSeniorMemberoftheIEEE.
“The future of CMOS technology lies in replacing the classical, bulk MOSFET with
new transistor structures such as the FinFET and ultra-thin body MOSFET. Those
with asolidbackgroundinclassicalMOSdevicetheorywillfindhere anauthoritative
andcomprehensivetreatmentofthefinalfrontierinCMOStechnology.”
MarkLundstrom,DonandCarolScifresDistinguishedProfessorofElectricaland
ComputerEngineering,PurdueUniversity
“Avaluablevolumeonthedesignandmodelingofsilicon-on-insulatorandmultiple-gate
MOSFETsbyapioneerandexpertonthesubject.”
YuanTaur,UniversityofCaliforniaatSanDiego
“Thisispreciselythebookeverybodyintheadvancednano-CMOSworldwantedtosee
out ASAP. Timely, brilliant and most useful - written by a Master (VT) and his own
formerMaster(JF).Alifeexperienceiscondensedanddistilledtoprovidethenecessary
ingredients needed for understanding the physics mechanisms and for pursuing with
transistor modeling and circuit design. The book is primarily addressed to specialists,
engineers and graduate students. This is not a romantic novel about SOI and FinFET
affair;itissolidstuffwhereadvancedconcepts,strongaffirmationsandlotsofpractical
equationsdonotleavespaceforscientificdust.”
SorinCristoloveanu,CNRS,Grenoble,France
“ThisisatimelybookaboutSOIMOSFETsandFinFETswrittenbyoneoftheleading
authoritiesinthefieldandhisformerstudent.SinceFinFETshavestartedbeingimple-
mentedbyvariouscompaniesinproduction,thereisaneedforclearunderstandingofthe
designtrade-offsofsuchdevices.Prof.Fossum,whohasdoneseminalworkonmodel-
ingSOIMOSFETssincethe1980s,providesaclearelucidationofthephysicsofthese
devices. Graduate students, faculty and industrial practitioners should benefit from the
pedagogyinthisbook.”
SanjayBanerjee,UniversityofTexasatAustin
Fundamentals of Ultra-Thin-Body
MOSFETs and FinFETs
JERRY G. FOSSUM
UniversityofFlorida,Gainesville
VISHAL P. TRIVEDI
FreescaleSemiconductor,Arizona
UniversityPrintingHouse,CambridgeCB28BS,UnitedKingdom
PublishedintheUnitedStatesofAmericabyCambridgeUniversityPress,NewYork
CambridgeUniversityPressispartoftheUniversityofCambridge.
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©CambridgeUniversityPress2013
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Firstpublished2013
PrintingintheUnitedKingdombyTJInternationalLtd.PadstowCornwall
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Fossum,JerryG.,1943–
Fundamentalsofultra-thin-bodyMOSFETsandFinFETs/JerryG.Fossum,Vishal
P.Trivedi.
pages cm
ISBN978-1-107-03041-1(hardback)
1. Metaloxidesemiconductorfield-effecttransistors. 2. Integratedcircuits–Verylargescale
integration. I. Title.
TK7871.99.M44F67 2013
621.38150284–dc23
2013013370
ISBN978-1-107-03041-1Hardback
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Contents
Preface pagevii
Tableofphysicalconstants ix
Listofsymbols x
Listofacronyms xv
1 Introduction 1
1.1 UltimatenanoscaleCMOS 3
1.1.1 PlanarFD/SOIMOSFET 5
1.1.2 FinFET 5
1.2 Briefoverviewofthebook 9
2 UniquefeaturesofUTBMOSFETs 13
2.1 Long-channelthresholdvoltage 15
2.1.1 Thedepletionapproximation 15
2.1.2 Reviewoftheclassicalcharge-couplingmodel 16
2.1.3 Nonclassicalmodel 17
2.1.4 Applications 22
2.1.5 Generalizedchargecoupling 23
2.2 Quantum-mechanicaleffectsonV 25
t
2.3 Short-channeleffectsonV 31
t
2.3.1 Modeling 31
2.3.2 SCEcontrol 33
2.4 Random-dopanteffectonV 35
t
2.5 AdjustmentofV 36
t
2.5.1 S/Ddoping-dependentV 37
t
2.5.2 SensitivityandRDFanalyses 41
2.6 Current–voltagecharacteristics 42
2.6.1 Classicalcurrentformalismwithbulkinversion 42
2.6.2 Quantizationand2-Ddensityofstates 53
2.6.3 Bulk-inversioneffects 63
2.6.4 Carriermobility 67
2.7 Gate-source/drainunderlap 78
2.7.1 Effectivechannellength 78
2.7.2 ImpactofS/Ddopingprofile 84
vi Contents
2.7.3 Insightsfromoptimized18nmDGFinFETs 87
2.7.4 Fringecapacitance 89
2.8 Charge/capacitancedynamics 93
2.9 Floating-bodyeffects 94
2.9.1 TransientBJTeffect 95
2.9.2 FD/UTBfloating-bodyDRAM 96
Exercises 100
3 PlanarfullydepletedSOIMOSFETs 103
3.1 WhythinBOX? 103
3.1.1 FieldfringinginthickBOX 104
3.1.2 BenefitsofBOX-thicknessscaling 106
3.1.3 ChallengeswiththinBOX 107
3.2 Basicanalysesofscalinganddesign 109
3.2.1 2-DeffectsintheUTB 109
3.2.2 V controlviaUTBdoping? 115
t
3.2.3 V andSCEcontrolwithgatework-functionengineering 116
t
3.3 InsightsondesignandscalabilitywiththinBOX 120
3.3.1 Thin-BOXFD/SOICMOSdesignspace 121
3.3.2 LPversusHPdesign 124
3.3.3 GeneralinsightsonGP/biasdesignforvariableV 132
t
Exercises 136
4 FinFETs 138
4.1 Triple-ordouble-gate? 138
4.1.1 Effectsoffin-UTBdoping 139
4.1.2 Effectsofbulkinversion 141
4.1.3 Thepragmaticchoice 149
4.2 DGFinFETs 149
4.2.1 BulkSiversusSOI 150
4.2.2 SDGversusADG 154
4.2.3 Potentialspeedsuperiority 160
4.2.4 PragmaticFinFETdesign 165
4.3 TheITFET:ahybridoption 171
4.4 Independent-gateFinFET 173
4.5 SRAMapplication 176
4.5.1 V modulationviaunderlap 176
t
4.5.2 Celldesignandperformance 179
Exercises 186
AppendixUFDG 188
References 200
Index 208
Preface
Thecomputerrevolution(i.e.,faster,smaller,andcheapercomputers),andthetechnol-
ogies it has enabled (e.g., the Internet, laptops, smart phones), have been driven by
continuedsize-scalingoftheCMOStransistorsintheconstituentintegratedcircuits(ICs,
e.g.,themicroprocessor)ofthecomputer.Thisscaling,whichhasdoubledthetransistor
density on the CMOS IC chip about every two years, has been achieved by simply
ratioingthedimensionsandrelatedparametersofthebasic,classicaltransistorstructure
(i.e.,theplanarsingle-gateMOSFETinbulksiliconorpartiallydepletedSOI)(Taurand
Ning,2009)asimprovementsinlithographyenabledreducedminimumfeaturesize.The
CMOS devices have now become so small (e.g., gate lengths are 30–40nm) that this
straightforwardscalingisnolongerpossible,mainlybecauseoffundamentallimitations
inreliabledopingoftheclassicalMOSFET.Thus,continuedCMOSscalingwillrequire
a new, nonclassical transistor structure with ultra-thin body (UTB) that avoids these
limitations.ThefirstconcreteevidenceofthetransitiontoaUTBtransistorstructureis
IntelCorporation’sadoptionofthe“trigatetransistor”(orFinFET)(Authetal.,2012)for
22nmCMOStechnologyandbeyond.
This book details the fundamental physics of silicon-based UTB MOSFETs,
overviews their designs, with links to the process integration, and projects potential
nanoscale UTB-CMOS performance. The presentations are facilitated by the
authors’ process/physics-based compact model for double-gate MOSFETs, UFDG
(Appendix). This book is suitable as a textbook for a one-semester graduate or senior-
undergraduate university course, as well as for a fundamental guide to optimal non-
classicaldevicedesignandintegrationforprofessionalengineersintheCMOSICfield.
The prerequisites are good backgrounds in basic semiconductor device physics (e.g.,
as in Sze and Ng (2007)) and in fundamentals of classical bulk-Si MOSFETs (Taur
and Ning, 2009). In fact, this book is intended to be a supplementary text for the
latterbook.
TheauthorsacknowledgetheSOI-relatedworksofmanycolleagues,whichprovided
thebasesofmuchofthisbook.SpecialthanksaregiventoProfessorFossum’sformer
Ph.D. students who so contributed: Shishir Agrawal, Duckhyun Chang, Meng-Hsueh
Chiang, Jin-Young Choi, Siddharth Chouksey, Murshed Chowdhury, Lixin Ge,
Keunwoo Kim, Seung-Hwan Kim, Srinath Krishnan, Hyung-Kyu Lim, Zhichao Lu,
MarioPelella,DongwookSuh,SuryaVeeraraghavan,GlennWorkman,Ji-WoonYang,
PingYeh,WeiminZhang,andZhenmingZhou;andtoLeoMathewwhohasprovidedus
viii Preface
“theoretical guys” with invaluable technological insights for so many years. We also
thankMalgorzataJurczakandimecforprovidingthemicroscopyimagesonthefrontand
backcoversofthebook.
Wearealsogratefultoourfamilies.ProfessorFossumespeciallythankshiswife,Mary
Fossum,forunrelentingsupportofhis“SOIobsessions.”Dr.Trivediespeciallythanks
his parents (Pareexit and Hansa Trivedi), brother (Vaibhav), sister-in-law (Krushangi),
andniece(Eesha)fortheirconstantlove,care,andsupport.