Introduction to Microfabrication

509 Pages·2010·34.089 MB·English

by  Sami Franssila

Introduction to Microfabrication
Introduction to Microfabrication, Second E dition Sami Franssila
© 2010 John Wiley & Sons, L td. ISBN: 978-0-470-74983-8
Introduction to Microfabrication
Second Edition
Sami Franssila
Professor of Materials Science at Aalto University
and Adjunct Professor of Micro- and Nanotechnology
at University of Helsinki, Finland
A John Wiley and Sons, Ltd., Publication
Thiseditionfirstpublished2010
©2010,JohnWiley&Sons,Ltd
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Franssila,Sami.
Introductiontomicrofabrication/SamiFranssila.–2nded.
p.cm.
Includesindex.
ISBN978-0-470-74983-8(cloth)
1. Microelectromechanicalsystems.2. Integratedcircuits.3. Semiconductorprocessing.4. Nanotechnology.
5. Microfabrication.I.Title.
TK7875.F732010
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2010010076
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Contents
PrefacetotheFirstEdition ix Polysilicon,OxideandNitrideThinFilms,Polymer
Films,AdvancedThinFilms,Exercises
PrefacetotheSecondEdition xiii
References andRelated Reading
Acknowledgements xv
6 Epitaxy 69
1 Introduction 1
Heteroepitaxy,EpitaxialDeposition,CVD
Substrates,ThinFilms,Processes, Dimensions,
Homoepitaxyof Silicon,Dopingof Epilayers,
Devices,MOSTransistor,CleanlinessandYield,
Measurement ofEpitaxialDeposition,Simulationof
Industries,Exercises
Epitaxy,Advanced Epitaxy,Exercises
Referencesand RelatedReading
References andRelated Reading
2 Micrometrology andMaterials
7 AdvancedThinFilms 77
Characterization 15
General FeaturesofThin-FilmProcesses, Film
MicroscopyandVisualization,Lateral and Vertical
Growthand Structure,Thin-FilmStructure
Dimensions,Optical Techniques,Electrical
Characterization,Surfacesand Interfaces,Adhesion,
Measurements, PhysicalandChemical Analyses,
Two-Layer Films,AlloysandDopedFilms,
Practical IssueswithMicrometrology,
MultilayerFilms,SelectiveDeposition,Reacted
MeasurementsEverywhere,Exercises
Films,SimulationofDeposition,ThicknessLimits
Referencesand RelatedReading ofThinFilms,Exercises
References andRelated Reading
3 Simulationof MicrofabricationProcesses 29
SimulatorTypes,Levelsof Simulation,The1D 8 PatternGeneration 93
Simulators,The2DSimulators,The3D Simulators, PatternGenerators,ElectronBeamLithography,
OtherSimulationNeedsinMicrofabrication, Laser PatternGenerators,PhotomaskFabrication,
Exercises PhotomaskInspection,Defectsand Repair,
Referencesand RelatedReading PhotomasksasTools,OtherPatternGeneration
Methods,Exercises
4 Silicon 35 References andRelated Reading
SiliconMaterialProperties,SiliconCrystalGrowth,
SiliconCrystalStructure,SiliconWaferingProcess, 9 OpticalLithography 103
Defectsand Non-IdealitiesinSiliconCrystals, LithographyProcessFlow,Resist Chemistry,Resist
AdvancedWafers, Exercises Application,Alignmentand Overlay,Exposure,
Referencesand RelatedReading ResistProfile,Resolution,ProcessLatitude,Basic
PatternShapes, LithographyPractice, Photoresist
5 Thin-FilmMaterialsandProcesses 47 Stripping,Exercises
ThinFilmsvs.BulkMaterials,Physical Vapor References andRelated Reading
Deposition,ChemicalVapor Deposition,PECVD:
Plasma-Enhanced CVD,ALD:AtomicLayer 10 AdvancedLithography 115
Deposition,Electrochemical Deposition(ECD), ProjectionOpticalSystems,ResolutionofProjection
OtherMethods,ThinFilmsOverTopography:Step OpticalSystems,Resists,Thin-FilmOpticsin
Coverage,Stresses,MetallicThinFilms, Resists,LithographyOver Steps,OpticalExtensions
vi Contents
ofOpticalLithography,Non-OpticalExtensionof 17 Bonding 191
OpticalLithography,LithographySimulation, BondingBasics, FusionBondingBlanketSilicon
LithographyTriangles,Exercises Wafers,AnodicBonding,MetallicBonding,
Referencesand RelatedReading AdhesiveBonding,Layer Transfer and Temporary
Bonding,Bondingof StructuredWafers, Bond
11 Etching 127 QualityMeasurements, BondingforPackaging,
EtchMechanisms, EtchingProfiles,AnisotropicWet Bondingat Large, Exercises
Etching,WetEtching,PlasmaEtching(RIE), Referencesand RelatedReading
IsotropicDryEtching,Etch Masks,Non-Masked
Etching,Multistepand MultilayerEtching,Etch 18 PolymerMicroprocessing 203
ProcessesforCommon Materials,IonBeam PolymerMaterials,PolymerThermal Properties,
Etching,EtchProcess Characteristics,Selecting Thick-ResistLithography,MoldingTechniques,
EtchProcesses, Exercises HotEmbossing,NanoimprintLithography,Masters
Referencesand RelatedReading forReplication,Processingon Polymers,Polymer
Bonding,PolymerDevices,Polymer Overview,
12 WaferCleaningandSurface Preparation 143
Exercises
ClassesofContamination,ChemicalWet Cleaning,
Referencesand RelatedReading
PhysicalWet Cleaning,Rinsingand Drying,Dry
Cleaning,ParticleRemoval,OrganicsRemoval,
19 GlassMicroprocessing 225
MetalRemoval,ContactAngle,SurfacePreparation,
Structureand PropertiesofGlasses, Glass
Exercises
Substrates,General ProcessingIssueswithGlasses,
Referencesand RelatedReading
GlassEtching,GlassBonding,GlassDevices,
SpecialtyGlasses,Exercises
13 Thermal Oxidation 153
Referencesand FurtherReading
Thermal OxidationProcess, Deal–GroveOxidation
Model,Oxidationof Polysilicon,OxideStructure,
20 AnisotropicWet Etching 237
Local OxidationofSilicon,Stressand Pattern
BasicStructureson <100>Silicon,Etchants,Etch
EffectsinOxidation,SimulationofOxidation,
MasksandProtectiveCoatings,EtchRateand Etch
Thermal Oxidesvs.otherOxides,Exercises
Stop,Front-SideProcessed Structures,Convex
Referencesand RelatedReading
CornerEtching,MembraneFabrication,
Through-WaferStructures,<110>Etching,<111>
14 Diffusion 165
SiliconEtching,Comparisonof<100>,<110>
DiffusionProcess, DiffusionMechanisms, Doping
and<111>Etching,Exercises
ofPolysilicon,DopingProfilesinDiffusion,
Referencesand RelatedReading
DiffusionApplications,Simulationof Diffusion,
Diffusionat Large, Exercises
21 DeepReactiveIonEtching 255
Referencesand RelatedReading
RIEProcess Capabilities,RIEProcess Physics
15 IonImplantation 173 andChemistry,Deep Etching,Combining
TheImplantationProcess, ImplantApplications, Anisotropicand IsotropicDRIE,Microneedlesand
ImplantDamage and DamageAnnealing,Toolsfor Nozzles,SidewallQuality,PatternSizeandPattern
IonImplantation,IonImplantationSimulation, DensityEffects, Etch Residuesand Damage, DRIE
ImplantationFurther,Exercises vs.Wet Etching,Exercises
Referencesand RelatedReading Referencesand RelatedReading
16 CMP:Chemical–Mechanical Polishing 181 22 WaferEngineering 271
CMPProcessand Tool,MechanicsofCMP, SiliconCrystals,Gettering,Wafer Mechanical
ChemistryofCMP,Non-IdealitiesinCMP, Specifications,EpitaxialWafers,SOI Wafers,
MonitoringCMPProcesses, Applicationsof CMP, BondingMechanics, Advanced Wafers,Variety of
CMPasaWhole,Exercises Wafers,Exercises
Referencesand RelatedReading Referencesand FurtherReading
Contents vii
23 SpecialProcesses andMaterials 283 Membranesand Bridges,Stiction,MultipleLayer
SubstratesotherthanSilicon,PatternGeneration, Structures,RotatingStructures,HingedStructures,
Patterning,Powder Blasting,Deposition,Porous CMOSWafers asSubstrates,Exercises
Silicon,MoldingwithLostMold,Exercises References andRelated Reading
Referencesand RelatedReading
30 MEMSProcess Integration 387
24 SerialMicroprocessing 299 SiliconMicrobridges,Double-SidedProcessing,
Focused IonBeam(FIB)Processing,Focused MembraneStructures,PiezoresistivePressure
ElectronBeam(FEB) Processing,Laser Direct Sensor,Tiltingand BendingThrough-WaferEtched
Writing,AFM Patterning,InkJetting,Mechanical Structures,NeedlesandTips,ChannelsandNozzles,
Structuring,Chemical and Chemomechanical BondedStructures,SurfaceMicromachining
MachiningScaled Down,Conclusions, CombinedwithBulkMicromachining,MEMS
Exercises Packaging,Microsystems,Exercises
Referencesand FurtherReading
References andRelated Reading
25 Process Integration 313
31 Process Equipment 409
TheTwoSidesoftheWafer,DeviceExample1:
BatchProcessing vs.SingleWafer Processing,
SolarCell,DeviceExample2: MicrofluidicSieves,
ProcessRegimes: TemperatureandPressure, Cluster
Wafer Selection,Masksand Lithography,Design
ToolsandIntegratedProcessing,Measuring
Rules,Resistors,DeviceExample3:PCRReactor,
FabricationProcesses, EquipmentFiguresofMerit,
DeviceExample4:IntegratedPassiveChip,
SimulationofProcessEquipment,ToolLifecycles,
ContaminationBudget,Thermal Processes,
CostofOwnership,Exercises
Metallization,PassivationandPackaging,
References andRelated Reading
Exercises
Referencesand RelatedReading
32 Equipment forHotProcesses 419
High-TemperatureEquipment:HotWallvs.Cold
26 MOSTransistorFabrication 329
Wall,FurnaceProcesses, RapidThermal
PolysiliconGateCMOS,PolysiliconGateCMOS:
Processing/RapidThermal Annealing,Furnacesvs.
10μmto1μmGenerations,MOSTransistor
Scaling,CMOSfrom0.8μmto65nm,Gate RTPSystems,Exercises
References andRelated Reading
Module,SOIMOSFETs, Thin-FilmTransistors,
IntegratedCircuits,Exercises
33 Vacuum andPlasmas 425
Referencesand RelatedReading
Vacuum Physicsand KineticTheory ofGases,
Vacuum Production,PlasmaEtching,Sputtering,
27 BipolarTransistors 347
ResidualGasIncorporationintoDepositedFilm,
FabricationProcess ofSBCBipolarTransistor,
PECVD,ResidenceTime,Exercises
AdvancedBipolarStructures,Lateral Isolation,
References andRelated Reading
BiCMOSTechnology,CostofIntegration,
Exercises
Referencesand RelatedReading 34 CVDandEpitaxyEquipment 433
DepositionRate,CVDRateModeling,CVD
28 MultilevelMetallization 357 Reactors,CVDwithLiquidSources,SiliconCVD
Two-LevelMetallization,Planarized Multilevel Epitaxy,EpitaxialReactors,ControlofCVD
Metallization,CopperMetallization,Dual Reactions,Exercises
Damascene Metallization,Low-k Dielectrics, References andRelated Reading
MetallizationScaling,Exercises
Referencesand RelatedReading 35 Cleanrooms 441
CleanroomConstruction,CleanroomStandards,
29 SurfaceMicromachining 369 CleanroomSubsystems,Environment,Safety and
SingleStructuralLayer Devices, Materialsfor Health(ESH),CleanroomOperatingProcedures,
SurfaceMicromachining,Mechanics of Mini-Environments,Exercises
Free-StandingFilms,CantileverStructures, References andRelated Reading
viii Contents
36 YieldandReliability 449 MaterialsChallenges,StatisticsandYield,Limitsof
YieldDefinitionsand Formulas,YieldModels, Scaling,Exercises
YieldRamping,Package Reliability,Metallization Referencesand RelatedReading
Reliability,DielectricDefectsand Quality,
StressMigration,DieYieldLoss, 39 MicrofabricationatLarge 485
Exercises New Devices,Proliferationof MEMS,
Referencesand RelatedReading Microfluidics,BioMEMS,Bondingand 3D
Integration,IC–MEMSIntegration,Microfabricated
37 Economicsof Microfabrication 457 DevicesforMicrofabrication,Exercises
Silicon,ICCostsand Prices,IC Industry,ICWafer Referencesand RelatedReading
Fabs,MEMSIndustry,Flat-PanelDisplayIndustry,
SolarCells,MagneticDataStorage,ShortTermand Appendix A Properties ofSilicon 499
LongTerm,Exercises
Referencesand RelatedReading Appendix B ConstantsandConversion
Factors 501
38 Moore’sLawandScalingTrends 469
FromTransistortoIntegratedCircuit,Historical Appendix C OxideandNitrideThickness
DevelopmentofICManufacturing,MOSScaling, byColor 503
DeparturefromPlanar BulkTechnology,
Memories,LithographyFuture,Moore’sLaw, Index 505
Preface to the First Edition
Microfabrication is generic: its applications include gate oxides today are thinner than the ultimate limits
integrated circuits, MEMS, microfluidics, micro-optics, conceived in the 1970s. And it is pedagogically better
nanotechnology and countless others. Microfabrication to show applications of CVD films before plunging into
is encountered in slightly different guises in all of these pressure dependence of deposition rate, and to discuss
applications: electroplating is essential for deep sub- metal film functionalities before embracing sputtering
micron IC metallization and for LIGA-microstructures; yieldmodels.
deep-RIE is a key technology in trench DRAMs and in In this book, another major emphasis is on materials.
MEMS; imprint lithography is utilized in microfluidics Materials are universal, and not outdated rapidly. New
where typical dimensions are 100μm, as well as in materialsare,ofcourse,beingintroducedallthetime,but
nanotechnology, where feature sizes are down to 10nm. the basic materials properties like resistivity, dielectric
This book is unique because it treats microfabrication in constant, coefficient of thermal expansion and Young’s
its own right, independent of applications, and therefore modulus must always be considered for low-k and
itcanbeusedinelectricalengineering,materialsscience, high-k dielectrics, SnO sensor films, diamond coatings
2
physicsand chemistryclasses alike. and 100μm-thick photoresists alike. Silicon, silicon
Instead of looking at devices, I have chosen to dioxide, silicon nitride, aluminium, tungsten, copper and
concentrate on microstructures on the wafer: lines photoresist will be met again in various applications:
and trenches, membranes and cantilevers, cavities and nitride is used not only in LOCOS isolation, but also in
nozzles, diffusions and epilayers. Lines are sometimes MEMSthermalisolation;aluminiumnotonlyservesasa
isolated and sometimes in dense arrays, irrespective of conductorinICsbutalsoasamirrorinMOEMS;copper
linewidths;membranes can be made by timed etching or isusedforICmetallizationandalsoasasacrificiallayer
byetchstop;source/draindiffusionscanbealignedtothe under nickel in metal MEMS; photoresist acts not only
gate in a mask aligner or made in a self-aligned fashion; asaphotoactivematerialbutalsoasanadhesiveinwafer
oxidationonaplanarsurfaceiseasy,buttheoxidationof bonding.
topographic features is tricky. The microstructure-view Devices are, of course, discussed but from the
of microfabrication is a solution against outdating: fabrication viewpoint, without thorough device physics.
alignment must be considered for both 100μm fluidic The unifying idea is to discuss the commonalities and
channels and 100nm CMOS gates, etch undercutting generic features of the fabrication processes. Resistors
target may be 10nm or 10μm, but it is there; dopants andcapacitorsservetoexemplifyconceptslikealignment
will diffuse during high temperature anneals, but the sequence and design rules, or interface stability. After
junction depth target may be tens of nanometres or tens basic processes and concepts have been introduced,
ofmicrometres. process integration examples show a wide spectrum of
A common feature of older textbooks is concentration full process flows: for example, solar cell, piezoresistive
on physics and chemistry: plasma potentials, boundary pressuresensor,CMOS,AFMcantilevertip,microfluidic
layers, diffusion mechanisms, Rayleigh resolution, out-of-plane needle and super-self-aligned bipolar
thermodynamic stability and the like. This is certainly transistor. Small process-sequence examples include,
a guarantee against outdating in rapidly evolving similarly,avarietyofstructures:replacementgate,cavity
technologies, but microfabrication is an engineering sealing, self-aligned rotors and dual damascene-low-k
discipline, not physics and chemistry. CMOS scaling optionsare amongtheothers.
trendshaveinfact been morereliablethanbasicphysics Older textbooks present microfabrication as a toolbox
and chemistry in the past 40 years: optical lithography of MEMS or as the technology for CMOS manufactur-
was predicted to be unable to print submicron lines and ing. Both approaches lead to unsatisfactory views on
x Preface totheFirstEdition
microfabrication. Ten years ago, chemical–mechanical are emphasized. Epitaxy, CVD, PVD, spin coating and
polishing was not detailed in textbooks, and five years electroplating are discussed, with resulting materials
ago discussion on CMP was included in multilevel propertiesand microstructureson thecentrestage, rather
metallization chapter. Today, CMP is a generic tech- than equipment themselves. Lithography and etching
nology that has applications in CMOS front-end device then follow. This order of presentation enables more
isolation and surface micromechanics, and is used to realisticexamplestobediscussed earlyon.
fabricate photonic crystals and superconducting devices. The basic steps in silicon technology, such as oxida-
Itthereforedeservesachapterofitsown,independentof tion, diffusion and ion implantation are discussed next,
actualorpotentialapplications.Similarly,wafercleaning followed by CMP and bonding. Moulding and stamp-
used to be presented as a preparatory step for oxidation, ing techniques have also been included. In contrast to
but it is also essential for epitaxy, wafer bonding and older books, and to books with CMOS device emphasis,
CMP. Device-view, be it CMOS or some other, limits thisbookisstrongin back-end steps,thinfilms, etching,
processes and materials to a few known practices, and planarizationandnovelmaterials.Thisreflectsthegrow-
excludesmanyimportantaspectsthatarefruitfulinother ing importanceof multilevelmetallization in ICsas well
applications. as the generic nature of etch and deposition processes,
Theaimofthebookisforthestudenttofeelcomfort- and their wide applicability in almost all microfabrica-
able both in a megafab and in a student lab. This means tionfields.Packagingisnotdealtwith,againinlinewith
that both research-oriented and manufacturing-driven as- wafer-level view of microfabrication. This also excludes
pects of microfabrication must be covered. In order to stereomicrolithographyandmanyminiaturizedtraditional
keep the amount of material manageable, many things techniqueslikemicroelectrodischargemachining.
have had to be left out: high density plasmas are men- Microfabricationisan engineeringdiscipline,and vol-
tioned,buttheemphasis ison plasmaprocessing ingen- ume manufacturing of microdevices must be discussed.
eral; KOH and TMAH etching are both described, but Discussions on process equipment have often been
commonalitiesratherthandifferencesareshown;imprint bogged by the sheer number of different designs: should
lithographyandhotembossingarediscussedbutpolymer the students be shown both 13.56MHz diode etcher,
rheology is neglected; alternatives to optical lithography triode, microwave, ECR, ICP and helicon plasmas, and
arementioned,butdiscussedonlybriefly.Emphasisison should APCVD, LPCVD, SA-CVD, UHV-CVD and
common and conceptual principles, and not on the latest PECVD reactors all be presented? In this book, the
technologies, which hopefully extends the usable life of process equipment discussion is again tied to structures
thebook. that result on wafers, rather than in the equipment per
se: base vacuum interaction with thin-film purity is
discussed; the role of RTP temperature uniformity on
Structure of the Book
wafer stresses is considered; and surface reaction versus
transport controlled growth in different CVD reactors is
The structure of this book differs from the traditional
analysed. Cleanroom technology, wafer fab operations,
structure in many ways. Instead of discussing individ-
yield and cost are also covered. Moore’s law and other
ualprocessstepsatlengthfirstandputtingfullprocesses
trends expose students to some current and future issues
together in the last chapter, applications are presented
inmicrofabricationprocesses,materialsandapplications.
throughoutthebook.Thechaptersonequipmentaresep-
In many cases, treatment has been divided into two
arated from the chapters on processes in order to keep
chapters: for example, Chapter 5 treats thin film basics,
the basic concepts and current practical implementations
andChapter7dealswithmoreadvancedtopics.Lithogra-
apart.
phyandetchinghavebeendividedsimilarly.Thisenables
The introduction covers materials, processes, devices
short or long course versions to be designed around the
and industries. Measurements are presented next, and
book. The figures from the book are available to teach-
more examples of measurement needs in microfabrica-
ers via the Internet. Please register at Wiley for access
tion are presented in almost every chapter. A general
www.wileyeurope.com/go/microfabrication.
discussion of simulation follows, and more specific
simulationcasesarepresentedinthechaptersthatfollow.
Materials of microfabrication are presented next: Advice to Students
silicon and thin films. Silicon crystal growth is shortly
covered but from the very beginning, the discussion Thisbookisanintroductorytext.Basicuniversityphysics
centres on wafers and structures on wafers: therefore, and chemistry suffices for background.Materialsscience
silicon wafering process, and resulting wafer properties andelectronicscourseswillofcoursemakemanyaspects