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BY2ICHARD&9ANDA -ICHAEL(EYNE...
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$EMYSTIFYING#HIPMAKING
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$EMYSTIFYING#HIPMAKING
BY2ICHARD&9ANDA -ICHAEL(EYNES AND!NNE+-ILLER
.EWNESISANIMPRINTOF%LSEVIER #ORPORATE$RIVE 3UITE "URLINGTON -! 53! ,INACRE(OUSE *ORDAN(ILL /XFORD/8$0 5+ #OPYRIGHTÚ %LSEVIER)NC!LLRIGHTSRESERVED .OPARTOFTHISPUBLICATIONMAYBEREPRODUCED STOREDINARETRIEVALSYSTEM OR TRANSMITTEDINANYFORMORBYANYMEANS ELECTRONIC MECHANICAL PHOTOCOPYING RECORDING OROTHERWISE WITHOUTTHEPRIORWRITTENPERMISSIONOFTHEPUBLISHER 0ERMISSIONSMAYBESOUGHTDIRECTLYFROM%LSEVIERS3CIENCE4ECHNOLOGY2IGHTS $EPARTMENTIN/XFORD 5+PHONE FAX E MAILPERMISSIONS ELSEVIERCOMUK9OUMAYALSOCOMPLETEYOURREQUESTON LINEVIA THE%LSEVIERHOMEPAGEHTTPELSEVIERCOM BYSELECTINGh#USTOMER3UPPORTvANDTHEN h/BTAINING0ERMISSIONSv 2ECOGNIZINGTHEIMPORTANCEOFPRESERVINGWHATHASBEENWRITTEN %LSEVIERPRINTSITSBOOKSONACID FREEPAPERWHENEVERPOSSIBLE ,IBRARYOF#ONGRESS#ATALOGING IN 0UBLICATION$ATA !PPLICATIONSUBMITTED "RITISH,IBRARY#ATALOGUING IN 0UBLICATION$ATA !CATALOGUERECORDFORTHISBOOKISAVAILABLEFROMTHE"RITISH,IBRARY )3". &ORINFORMATIONONALL.EWNESPUBLICATIONS VISITOUR7EBSITEATWWWBOOKSELSEVIERCOM 0RINTEDINTHE5NITED3TATESOF!MERICA
Contents Foreword
........................................................................................................... xi... ............................................................................................. xiii
Acknowledgments
.............................................................................................. .................................................................................. . . Chapter 1: IC Fabrication Overview....................................................................... Section 1 : Introduction ...........................................................................................
About the Authors What’s on the CD-ROM?
1.1 Integrated Circuits .............................................................. 1.2 The Semiconductor Industry ...................... Section 2: Support Technologies
............................... ...............................
.............................................................................
xv
..
XVII
1 3
3 6 7
2.1 Crystal Growth and Wafer Preparation ......................................... . . 2.2 Contamination Control ...................................................... ............................... 8 2.3 Circuit Design and Mask Making .............. ............................. 10 2.4 Process Diagnostics and Metrology ...................................................................... 12 Section 3: Integrated Circuit Fabrication
...............................................................
3.1 Layering ................................................................................................................ 3.2 Patterning .............................................................................................................. 3.3 Doping .................................................................................................................. 3.4 Process Control and In-line Monitoring ............................................................... Section 4: Test and Assembly
................................................................................
4.1 Electrical Tests ..................................................................................................... 4.2 Die Separation ....................................................................................................... 4.3 Die Attach and Wire Bonding ............................................................................... 4.4 Encapsulation ........................................................................................................ 4.5 Final Test ............................................................................................................... Section 5: Summary .............................................................................................. Chapter 2: Support Technologies .........................................................................
......................................................................................... .........................................................................
Section 1 : Introduction . . Section 2: Contamination Control
2.1 Why Control Contamination? ............................................ ............................. ........................................... 2.2 Contamination Sources ..............................
V
13
13 18 21 22 25
25 25 25 26 26 27
29 31 33
33 35
Contents
2.3 The Cleanroom .................. ....................................................... Section 3: Crystal Growth and Preparation ...................................................... ......................................... ion .................................... ......................................... 3.3 Czochralski Silicon Growth ...................................................... 3.4 Shaping, Grinding. Cutting Polishing ......................... 3.5 Final Inspection and Shipping ............................... ......................................... Section 4: Circuit Design 4.1 Introduction ........................ ....................................................... 4.2 Product Definition and Ne duct Plan ......................... ......................................... 4.3 The Design Team ...................................................
.............................
.............................................
.....................................
4.4 The Design Process ................................................ ......................................... 4.5 Design Verification and Tapeout ........................................................................... Section 5: Photomask and Reticle Preparation...................................................... 5.1 Introduction ........................................................................................................... 5.2 Reticle Substrate Preparation ................................................................................ 5.3 Pattern Transfer ..................................................................................................... 5.4 Inspection and Defect Repair ................................................................................
................................................................................... ......................................................................................... .................................................................................... ..................................................................................
Chapter 3: Forming Wells
Section 1 : Introduction Section 2: Initial Oxidation Section 3: Photolithography 3.1 Introduction ........................ ....................................................... 3.2 Coat (Spin) ............. ...................................................... ............................. 3.3 Exposure (Step) ...................................................... ......................................... 3.4 Develop ..................................................... ..................................................... 3.5 After Develop Inspect (ADI) .......................................................... Section 4: Ion Implantation
................................................................................... Chapter 4: Isolate Active Areas (Shallow Trench Isolation) ..................................... Section 1: Introduction to Shallow Trench Isolation............................................... Section 2: Pad Oxide Growth ................................................................................ Section 3: Silicon Nitride Deposition ................................................................... Section 4: Photolithography for Photo/Etch........................................................ Section 5: Hard Mask Formation Using Plasma Etch ...........................................
41 42
47 49 53 55 57 59 59 59 60 61 63 65 71 79
a3 a4 87
93 95 99 101 105 107 5.1 Hard Mask Overview .......................................................................................... 107 109 5.2 Plasma Etch Overview ........................................................................................ 5.3 Etch Chemistry: Silicon Dioxide and Silicon Nitride ......................................... 114 Section 6: Form Trenches in Silicon with Plasma Etch.......................................... 119 Section 7: Fill Trenches with Silicon Dioxide ........................................................ 121 Section 8: Chemical Mechanical Polishing (CMP) to Remove Excess Dioxide .......123
vi
Contents Section 9:W e t Etch Removal o f Silicon N i t r i d e and Pad Oxide
............................ Chapter 5: Building the Transistors.................................................................... Section 1 : Introduction ....................................................................................... Section 2:Thin Film Formation ...........................................................................
......................................... 2.1 Gate Dielectric Oxidation .. 2.2 Polycrystalline Silicon (Poly) Deposition .................................................. 2.3 Nitride Cap Deposition ...................................................... Section 3: Poly Gate Formation........................................................................... ......................................... 3.1 Photoresist Patterning ........ 3.2 Plasma Etch .........................................................................................................
127 129 131 137 137
143 143 144 Section 4: Source/Drain Formation ..................................................................... 147 4.1 Introduction ......................................................................................................... 147 4.2 Shallow Implant .................................................................................................. 149 4.3 Spacer Formation ................................................................................................ 149 4.4 High-Dose Implant ............................................................................................. 151 4.5 Anneal ................................................................................................................. 151 .. Section 5: Salicide Formation .............................................................................. 153 5.1 Sputter Cobalt .................................................................................................... 155 5.2 RTP Reaction Forming Silicide .......................................................................... 155 5.3 Strip Residual Cobalt .......................................................................................... 156 156 5.4 Anneal the Silicide ..............................................................................................
.................................................................. ....................................................................................... ............................................................
Chapter 6: First Level Metallization Section 1 : Introduction Section 2: N i t r i d e and Oxide Depositions . . .. 2.1 Nitride Deposition .............................................................. ......................................... 2.2 Oxide Deposition ........................... Section 3: C M P Planarization Section 4:Photo/Etch for Contact Holes 4.1 Contact Hole Photolithography ......................................... ......................................... 4.2 Contact Etch ................................... Section 5:Tungsten Plug Process 5.1 Deposit Ti/TiN Barrier/Glue Layers ..........................................................
................
........................................................ ............................................................
164 167 169
........................................................
170 173
..........
5.2 Tungsten CVD .................................................................................................... 5.3 Tungsten CMP .................................................................................................... Section 6 : Low-lc Dielectric Process
157 159 163
.....................................................................
6.1 Deposit Low-k Dielectric Film ........................................................................... 6.2 Trench Photolithography and Etch ..................................................................... Section 7: Copper First Level Interconnection Process ......................................... 7.1 TdTaN Barrier Layer Deposition ....................................................................... 7.2 Sputter Copper (Cu) ............................................................................................
vii
174 176 177 177 180 183 183 185
Contents
7.3 Electroplate Copper (Cu) ......................................... ........................... 7.4 Copper CMP .......................................................................................................
........................... Section 1 : Introduction ....................................................................................... Section 2: Deposit Barrier Layer and lntermetal Dielectric ................................... Section 3: Dual Damascene Process ....................................................................
Chapter 8: Multilevel M e t a l Interconnects and Dual Damascene
3.1 Introduction ......................................................................................................... 3.2 Via Photo/Etch .................................................................................................... 3.3 Trench Photo/Etch ............................................................................................... 3.4 Deposit Barrier Layers ........................................................................................ 3.5 Sputter Copper .................................................................................................... 3.6 Electroplate Copper ............................................................................................ 3.7 CMP to Remove Excess Copper ......................................................................... 3.8 Deposit S i c Barrier Layer .................................................................................. 3.9 Build Additional Layers ......................................................................................
............................................................................ ....................................................................
Section 4: Form Bonding Pads Section 5: Final Passivation Process
185 186
i89 191 195 197
197 198 199 200 200 200 201 202 202 203 205
5.1 Deposit Final Passivation .................................................................................... 205 5.2 Photo/Etch for Bonding Pads .............................................................................. 205 Chapter 8: Test and Assembly
...........................................................................
....................................................................................... ......................................................................
Section 1 : Introduction Section 2: Wafer and Chip Testing
2.1 In-line Parametric Test ........................................................................................ 2.2 Wafer Sort (Probe) .............................................................................................. 2.3 Final Functional Test ...........................................................................................
.....................................................................
Section 3: Assembly and Packaging
3.1 Die Separation ..................................................................................................... 3.2 Die Attach and Bond Pad Connection ................................................................ 3.3 Encapsulation ......................................................................................................
207 209 211
211 212 213 215
215 216 218
........................................................................... Introduction ....................................................................................................... Section 1 : Atoms and Molecules .........................................................................
219
1.1 The Atom ............................................................................................................ 1.2 Molecules ............................................................................................................ 1.3 Organic Molecules ..............................................................................................
223 226 227
Appendix A: Science Overview
Section 2: Gases
.................................................................................................
2.1 Facts about Gases ................................................................................................ 2.2 Ions ...................................................................................................................... 2.3 Plasma ................................................................................................................. 2.4 Free Radicals .......................................................................................................
...
Vlll
221 223
229
229 230 230 231
Contents
2.5 Excited States ...................................................................................................... Section 3: Chemistry
...........................................................................................
...............................................................
3.3 Plasma Etch Chemistry ....................................................................................... Section 4: Solids
.................................................................................................
231 233
233 235 237
4.1 Conductors and Insulators . 4.2 Semiconductors .................. ........................................................................... 238 4.3 pn Junctions ........................................................................................................ 239
...............................................
241
5.1 Electric Charges and Fields 5.2 Electric Current ................................................................................................... 5.3 Magnetic Field ....................................................................................................
242 243
Section 5: Electricity, Electric and Magnetic Fields
Appendix B: Plasma Etch Supplement to Chapter 4 .............................................
......................................................................... .....................................................
Section 1 : Plasma Etcher Theory Section 2: Plasma Etch Process Requirements
Bibliography
....................................................................................................
Index ..............................................................................................................
245 247 249
251 253
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&OREWORD
7ELCOME4HISISTHESTORYOFHOWTHEVASTMAJORITYOFINTEGRATEDCIRCUITSARE MADECALLTHEMhCOMPUTERCHIPS vIFYOULIKE ALTHOUGHAHOSTOFOTHERELECTRONIC COMPONENTSAREMADEINMUCHTHESAMEWAY%VERYONEWHOISCURIOUSABOUTHOW SUCHTINY YETPOWERFUL DEVICESAREMADEWILLENJOYTHESTORY4HISBOOKWILLALSO SERVEASAVALUABLEUPDATETOTHOSEWHOMAYBEUNAWAREOFHOWDRASTICALLYTHESTATE OF THE ARTPROCESSESHAVECHANGEDINRECENTYEARS 4HEMOSTGLAMOROUSANDEXPENSIVE PARTOFTHECHIPMAKINGPROCESSISTHEFOCUS OFTHISBOOK!CHIPWILLBEBUILTEACHSTEPISDESCRIBED INORDER UNTILTHEWHOLECHIP ISCOMPLETED FROMTHEDESIGNPHASE TOGROWINGTHESILICONINGOTS TOTHElNALTESTING OFTHEPACKAGEDPART 4HEBUILDINGOFACHIPISAFASCINATINGPROCESSTHATWILLCERTAINLYIMPRESSAND ASTONISHEVERYONEWHOISNEWTOTHESTORYORWHOISOUTOFTOUCHWITHCURRENT PROCEDURES2EADON
XI
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!CKNOWLEDGMENTS
4HEAUTHORSAREVERYGRATEFULTOTHESEWONDERFULFOLKSWHOHELPEDMAKETHISPROJECT ASUCCESS+ATY9ANDAAND2OBERT,AINOF4 2AM 2OD'ROSSAT3TUDIO $AVID #RAVENOF,AM2ESEARCH#ORPORATION 0ATTY#IMLOV :AHARES h!NOTHER!RTIST vAND +AREN-OORE ANDTHEANALYSTSAT6,3)2ESEARCH
XIII
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!BOUTTHE!UTHORS
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XVII
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)NTRODUCTION )N#HAPTER YOUWILLLEARN v 7HATARESUPPORTTECHNOLOGIES v (OWTHEMANUFACTURINGENVIRONMENTISKEPTCLEAN v (OWSILICONWAFERSAREMADE v (OWANINTEGRATEDCIRCUITISDESIGNED v (OWTHECHIPDESIGNISTRANSFERREDTOTHEMANUFACTURINGLINE $ElNITION3UPPORT4ECHNOLOGIESARETHEANCILLARYORSUPPORTOPERATIONSTHATARECRITI CALTOTHEINTEGRATEDCIRCUITMANUFACTURINGPROCESS #HAPTER3ELECTIONOF4OPICS 4O SIMPLIFY THE ORGANIZATION OF THIS TEXT SOME TOPICS ARE INCLUDED IN THE SUPPORTTECHNOLOGIESCHAPTEREVENTHOUGHTHEYARENOTTECHNICALLYPROVIDING SUPPORTTOTHEMANUFACTURINGPROCESSBUTARE RATHER APRINCIPALPARTOFIT 4HEREASONFORTHATCHOICEISTOREINFORCETHEFOCUSOFTHISBOOK WHICHISTHE ACTUALFABRICATIONOFTHEINTEGRATEDCIRCUITS3OEVENTHOUGHTHECHIPCOULD NEVERBEMANUFACTUREDWITHOUTlRSTBEINGDESIGNED THEDISCUSSIONOFTHE DESIGNPROCESSISFOUNDIN#HAPTER
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#HAPTER&ORMING7ELLS $ElNITION$IELECTRICISTHENAMEOFASUBSTANCETHATSTRONGLYRESISTSTHEmOWOFELEC TRICALCURRENTANINSULATOR3ILICONDIOXIDEISAMEMBEROFTHISFAMILYOFMATERIALS $ElNITION4HERMAL/XIDEISSILICONDIOXIDE3I/ PRODUCEDBYTHETHERMALOXIDA TIONOFSILICON 0URPOSE4HERMALOXIDEISADIELECTRIClLMANELECTRICALINSULATOR )TISUSEDINCHIP STRUCTURESTHATINSULATECONDUCTORS MASKIMPLANTSANDETCHESANDPERFORMSOTHER PROTECTIVEFUNCTIONS $ISCUSSION 4HEMATERIALPROPERTIESOFTHERMALOXIDEAREEXTREMELYUNIFORM CHEMICALLYCONSISTENT ANDREPRODUCIBLE4HISHIGHQUALITYlLMPERFORMSCRITICALFUNCTIONSONTHECHIPAND WILLBEDISCUSSEDLATER !SILICONDIOXIDElLMCALLEDNATIVEOXIDEWILLFORMNATURALLYONSILICONWHENITIS EXPOSEDTOTHEAIRBUTINTHATCASEONLYAVERYTHIN NONUNIFORMLAYERFORMS4HETHER MALOXIDATIONPROCESSPRODUCESAVERYUNIFORMlLMWITHTHEPRECISELYCONTROLLABLE THICKNESSANDMATERIALPROPERTIESNEEDEDINCHIPFABRICATIONTECHNOLOGY 4HE"ASIC#HEMICAL2EACTION 3I/m3I/ SILICONANDOXYGENFORMSILICONDIOXIDE 7HAT#OLORISTHE7AFER /NEOFTHEINTERESTINGTHINGSABOUTTHETHINlLMSONTHEWAFERISTHEIRCOLOR VARIATION-ANYOFTHElLMSDEPOSITEDONTHEWAFERARETRANSPARENT$IFFER ENTTHICKNESSESOFlLMSANDSTACKEDlLMSCAUSETHEWAFERTOCHANGECOLOR THROUGHOUT THE PROCESS 0HOTORESIST CAN PRODUCE A BEAUTIFUL RAINBOW OF COLORUNFORTUNATELY INTHISCASE ITISUSUALLYASIGNALTHATSOMETHINGHAS GONEWRONG )N THE EARLY YEARS OF THE INDUSTRY THE MACHINES NEEDED TO MEASURE ALL OF THEVARIETIESOFlLMTHICKNESSESREQUIREDFORCHIPMAKINGHADNOTYETBEEN INVENTED3OTHElLMTHICKNESSWASCHECKEDAFTEROXIDATIONORDEPOSITIONBY HOLDINGTHEWAFERUPTOACOLORCHARTHANGINGONTHEWALLCLOSETOTHETOOL 4HEOPERATORHADTOBEABLETOCOMPARETHEWAFERCOLORTOTHEEXAMPLES SHOWNONTHECHARTTODETERMINETHElLMTHICKNESS3OMEOFTHETEXTSFOUND INTHEBIBLIOGRAPHYCONTAINATABLELISTINGTHECOLORSOFVARIOUSlLMSBASED ONTHEIRTHICKNESS
)NITIAL/XIDATION !&AMILIAR%XAMPLE 2USTISTHEPRODUCTOFACHEMICALREACTION)RONOXIDIZESORhRUSTSvINTHE PRESENCEOFOXYGENANDMOISTURE LEAVINGACOATINGOFIRONOXIDE&E/ ON THESURFACEOFTHEIRON3IMILARLY THEPROCESSOFOXIDIZINGTHESILICONWAFER LEAVESACOATINGOF3I/COVERINGTHEWAFER 7HEN CHARCOAL IS BURNED AN OXIDATION REACTION IS TAKING PLACE TOO 4HE FUELISPRIMARILYCOMPOSEDOFCARBON WHICHREACTSWITHOXYGENINTHEAIRTO FORMGASEOUSOXIDES CARBONMONOXIDE#/ ANDCARBONDIOXIDE#/ 4HE REACTIONISEXOTHERMICITGIVESOFFHEAT ALLOWINGTHEPRODUCTIONOFESSENTIAL HAMBURGERSANDHOTDOGS
)TISINTERESTINGTONOTETHATTHEEASEWITHWHICHASILICONDIOXIDElLMCANBE FORMEDONSILICON ASWELLASITSELECTRICALPROPERTIESANDSTABILITYWEREIMPORTANT FACTORSINTHERAPIDTRANSITIONFROMGERMANIUMTOSILICONINTHEEARLYYEARSOFTHE SEMICONDUCTORINDUSTRY/XIDEALSOHASOTHERADVANTAGEOUSPROPERTIESLIKETHEABILITY TOBLOCKTHEIMPLANTATIONOFDOPANTS WHICHWILLBEDISCUSSEDLATER 3ILICONDIOXIDEISACTUALLYAVERYFAMILIARSUBSTANCEITISTHEPRINCIPALCOMPO NENTOFGLASSANDSEVERALOTHERITEMSMENTIONEDINTHENEXTSIDEBAR"OTHhOXIDEvAND hGLASSvAREINDUSTRYSLANGTERMSFORSILICONDIOXIDE !NOTHER&AMILIAR%XAMPLE 3ANDISPERHAPSTHEMOSTFAMILIAREXAMPLEOFNATURALLYOCCURRINGSILICONDIOX IDE-UCHOFTHESANDINTHEWORLDISPRINCIPALLYCOMPOSEDOFSILICONDIOXIDE SOMEOFQUITEHIGHPURITY!NOTHERCOMMON NATURALLYOCCURRINGFORMOF3I/ ISQUARTZ ASINGLECRYSTALFORM!NIMPORTANTINDUSTRIALPRODUCTIShQUARTZ GLASS vSOMETIMESMADEBYMELTINGHIGHPURITYQUARTZCRYSTALSBUTALSOCAN BEPRODUCEDTODAYFROMMELTINGVERYHIGHPURITYSYNTHETICSILICONDIOXIDE 1UARTZGLASSISWIDELYUSEDINHIGHTEMPERATUREENVIRONMENTSINCLUDINGMANY APPLICATIONSINTHESEMICONDUCTORINDUSTRY4HETHERMALOXIDElLMGROWNON SILICONWAFERSISCHEMICALLYSIMILARTOQUARTZGLASS 3EVERALGEMSTONES SUCHASOPALANDAMETHYST AREALSOFORMSOFSILICONDIOX IDE#OMMONBOTTLEANDWINDOWGLASSESAREABOUTSILICONDIOXIDE
$IELECTRICMATERIALSARETHECOMPLEMENTTOCONDUCTINGMATERIALSTHATALLOWTHE CREATIONOFELECTRICALCOMPONENTSINTHECIRCUIT3EVERALDIELECTRICMATERIALSARENEEDED TOMAKECHIPSANDEACHWILLBEEXPLAINEDASITISENCOUNTERED
#HAPTER&ORMING7ELLS 4HECRITICALVALUEOFOXIDEISTHATITISAHARD STABLEDIELECTRIC3INCEELECTRICAL CIRCUITSAREBEINGBUILTONTHECHIP ITWILLCERTAINLYBENECESSARYTOSEPARATECONDUCT INGMATERIALSFROMEACHOTHERWITHANINSULATORTOAVOIDANELECTRICALSHORT2ECALLTHAT THECHIPISBUILTINLAYERS ANDINSULATINGLAYERSSEPARATECONDUCTINGLAYERSASREQUIRED BYANYELECTRICALCIRCUIT$IELECTRICSALSOFORMTHESEPARATINGMEDIUMBETWEENTHE PLATESOFACAPACITORANDPLAYACRITICALROLEINTHEFUNCTIONOFTHETRANSISTORSANDOTHER COMPONENTSONTHECHIP 4HEELECTRICALPROPERTIESOFOXIDEAREIMPORTANT BUTITHASOTHERUSESTOO)TMAY SERVEASANIMPLANTMASK BLOCKINGTHEPATHOFDOPANTPARTICLESTHATARESHOTATTHE WAFERINANIONIMPLANTERDISCUSSEDLATERINTHISCHAPTER !NOTHERIMPORTANTUSEISAS ANETCHMASK PROTECTINGPORTIONSOFAlLMFROMATTACKBYETCHANTCHEMICALS 7HATFUNCTIONISTHEOXIDECOATINGPERFORMINGATTHISPOINTINTHEPROCESS $ElNITION4HE!CTIVE!REAISTHEREGIONONTHESURFACEOFTHEWAFERWHERETHETRAN SISTORSTHEhACTIVEDEVICESvWILLBEBUILT)TMUSTBEKEPTASFREEASPOSSIBLE FROMCONTAMINATIONANDDAMAGE +EY0OINT4HEINITIALOXIDEISAPROTECTIVECOATING!LTHOUGHTHElLMCOVERSTHE WHOLECHIP THEFOCUSOFITSUSEISINTHEhACTIVEAREAv $ElNITION3ACRIlCIAL/XIDEISTHECOMMONNAMEFORATHERMALOXIDETHATWILLBE REMOVEDLATERINTHEPROCESS3ACRIlCIALOXIDESAREUSEDASPROTECTIVELAYERSOR OCCASIONALLYTOREMOVECONTAMINANTSFROMTHESILICONSURFACE4HEINITIALOXIDA TIONSTEPPRODUCESASACRIlCIALOXIDETHATISETCHEDOFFAFTERTHEWELLSHAVEBEEN FORMED 4HEINITIALOXIDEALSOINmUENCESTHEAMOUNTOFDOPANTENTERINGTHEWAFERFROM THEIMPLANTER4HETHICKNESSISCAREFULLYCONTROLLEDSOTHATTHEDEGREEOFSCREENINGIS PREDICTABLEANDUNIFORM !NOTHERIMPORTANTFUNCTIONOFTHEINITIALOXIDEISTOPREVENThKNOCK ONvOFSURFACE CONTAMINANTS ANEFFECTWHERETHEIMPACTINGIONSFROMTHEIMPLANTERPUSHUNWANTED IMPURITIESINTOTHESILICONCRYSTALWHERETHEYCANMOVEAROUNDANDDAMAGETHE TRANSISTORS 4HE)MPLANTER &OR CLARIlCATION IT SHOULD BE MENTIONED THAT THE IMPLANTER IS A PARTICLE ACCELERATORTHATSHOOTSCHARGEDPARTICLESATTHEWAFER DRIVINGTHEMINTOTHE SURFACE4HEDETAILSOFIMPLANTATIONWILLBEDISCUSSEDIN3ECTION
)NITIAL/XIDATION 4HE/XIDATION0ROCESS $ElNITION4HERMAL/XIDATIONOF3ILICONISTHEHIGHTEMPERATUREREACTIONOFTHE SILICONWAFERWITHOXYGEN WATERVAPOR ANDORNITROGENOXIDES4HISISUSUALLYTHE lRSTOPERATIONTOBEPERFORMEDONTHEWAFERSINTHEFAB 0URPOSE4OFORMTHERMALOXIDE SILICONDIOXIDEPRODUCEDBYDIRECTOXIDATIONOF SILICONATHIGHTEMPERATURE 0ROCESSGASESFLOW DOWNOVERWAFERS
&IGURE /XIDATION&URNACE 6ERTICAL4UBE&URNACE
%LECTRICALLY HEATEDFURNACE
1UARTZ GLASS TUBE
7AFERCARRIER RAISEDINTOFURNACE
1UARTZ'LASS CHAMBER
&IGURE 2APID4HERMAL0ROCESSOR 0ROCESS 'ASES
7AFER
"ANKSOF HIGH INTENSITYLAMPS
$ISCUSSION 4HISOXIDEMAYHAVEOTHERNAMES SUCHASSACRIlCIALOXIDEORPADOXIDE ANDCANDO SEVERALTHINGS DEPENDINGUPONTHEPROCESS3OMEOFTHESPECIlCSWILLBEDISCUSSEDIN THISANDSUBSEQUENTSECTIONS
#HAPTER&ORMING7ELLS )NITIAL/XIDATION0ROCESS&LOW &URNACEOXIDATION )NSPECTION !WETCLEANPRECEDESMOSTlLMGROWTHSORDEPOSITIONSTEPS5SINGVARIOUS COMBINATIONSOFACIDS BASES OXIDIZERSAND$)WATER SURFACECONTAMINANTS AREREMOVED 4HETEMPERATUREISVERYHIGHDURINGTHEMAJORITYOFTHEOXIDATIONOROTHERlLM DEPOSITIONOPERATIONSUNWANTEDCHEMICALIMPURITIESCANMOVEAROUNDINTHE WAFERTOPOINTSWHERETHEYWOULDRUINMANYTRANSISTORS4HEPHENOMENONIS CALLEDDIFFUSION WHICHISTHEENERGETICVIBRATIONOFTHEATOMSINTHECRYSTALAS WELLASTHEEXPANDEDDIMENSIONSOFTHECRYSTALATHIGHTEMPERATURECREATEAN ENVIRONMENTWHERESTRAYATOMSWILLBEMOVEDAROUNDINTHECRYSTALLATTICE
$ISCUSSION 4HERMALOXIDATIONINATUBEFURNACEISDONEBYPLACINGTHEWAFERSINTHEFURNACEWHILE ITISmUSHEDWITHGAS OFTENNITROGEN TODISPLACETHEAIR4HENOXYGENORWATERVAPOR ISINTRODUCEDWHILEHEATINGTHEWAFERSTO TYPICALLY SOMEWHEREINTHERANGEOF# TO# DEPENDINGONTHEPROCESSREQUIREMENTS!FURNACEOXIDATIONREQUIRESTHAT THEWAFERSBEPLACEDINSPECIALTEMPERATURE RESISTANTHOLDERSCALLEDBOATS WHICHARE SLOWLYINSERTEDINTOTHEFURNACE"ATCHESOFORMOREWAFERSAREPROCESSEDATTHE SAMETIME4HEFURNACEISHEATEDBYELECTRICALRESISTANCEHEATERS4HESLOWHEATING ANDCOOLINGOFTHEWAFERSTEMPERATURERAMPING ISCRITICALTOTHEPROCESSTOAVOID THERMALSHOCKWHICHWOULDWARPTHEWAFERSANDDAMAGETHECRYSTALSTRUCTURE3OME PROCESSINGCYCLESAREQUITELONGANDOFTENWAFERSATOPPOSITEENDSOFTHEFURNACEDIS PLAYSOMEVARIATIONINlLMCHARACTERISTICS !NOTHERTYPEOFHIGHTEMPERATURETOOLISCALLEDARAPIDTHERMALPROCESSOR240 4HE240ISAhSINGLE WAFERvSYSTEM MEANINGTHATITPROCESSESONLYONEWAFERATA TIME4HEWAFERISRAPIDLYHEATEDWITHHIGH INTENSITYLAMPS4HEPROCESSGASES INTHIS CASEOXYGENORWATERVAPOR AREINTRODUCEDWHENTHEWAFERREACHESTHEPRESCRIBED TEMPERATURE!FTERTHElLMISGROWN THELAMPSAREEXTINGUISHEDANDTHEPROCESSGASES ARETURNEDOFF7ATER COOLEDWAFERPLATENSORAmOODOFNITROGENGASMAYBEUSEDTO HELPRAPIDLYCARRYHEATAWAYFROMTHEWAFER!TYPICAL240SYSTEMWILLHEATTHEWAFER TO#ANDCOOLITBACKDOWNTOROOMTEMPERATUREINLESSTHANONEMINUTE 4HEISSUEOFTHROUGHPUTISVERYIMPORTANTINTHEMANUFACTURINGENVIRONMENT !LARGENUMBEROFWAFERSMUSTBEPROCESSEDINAGIVENAMOUNTOFTIMEINORDERTO
)NITIAL/XIDATION MINIMIZECOSTS4HECOMPETITIONBETWEENBATCHPROCESSORSANDSINGLE WAFERPROCES SORSHASALWAYSBEENlERCE NOTONLYBECAUSEOFTHROUGHPUTBUTALSOTHEMANYOTHER IMPORTANTPROCESSSPECIlCATIONS!NINTERESTINGVARIETYOFBOTHOFTHESETYPESOF PROCESSOR ASWELLASSOMEINNOVATIVECROSS BREEDSTHATCOMBINEASPECTSOFBOTH ARE FOUNDINFABSTODAY 4HERMAL"UDGET 4HERMALBUDGETISTHETERMTHATREFERSTOTHEAMOUNTOFHEATENERGYTHATTHE WAFERWILLTOLERATEDURINGTHEENTIREPROCESS4HEDEVICESBEINGBUILTONTHE WAFERWILLNOTTOLERATEHIGHTEMPERATURESLATERINTHEPROCESS&OREXAMPLE WHENMETALISDEPOSITEDONTHEWAFERLATERINTHEPROCESSTHATMETALWILL DEFORMORREACTWITHITSSURROUNDINGMATERIALSATONLYAFEWHUNDREDDEGREES #ELSIUS4HERMALOXIDEISGROWNATABOUT##LEARLY ITWILLNOTBEPOS SIBLETOGROWANOXIDEONTHEWAFERAFTERMETALHASBEENDEPOSITEDWITHOUT RUININGTHEDEVICES4EMPERATURELIMITATIONSWILLBEPOINTEDOUTTHROUGHOUT OURDISCUSSION
)NSPECTION $URINGTHEINSPECTIONPHASEOFTHEPROCESS MEASUREMENTSAREMADETOSEETHATTHE lLMTHICKNESSISCORRECTACCORDINGTOTHEDESIGNSPECIlCATIONSFORTHECHIP4HETERM hINSPEC vISINDUSTRYSLANGFORAPROPERLYDONEPROCESSINGSTEP4HEDEPOSITIONSTEPS REQUIREVERYCLOSEADHERENCETOlLMTHICKNESSANDCROSS WAFERTHICKNESSUNIFORMITY SPECIlCATIONS !NEXAMPLEOFTHEINITIALOXIDETHICKNESSUSEDFORSOMESTATE OF THEART#-/3 DEVICESISNANOMETERS WHICHMAYALSOBEEXPRESSEDAS!NGSTROMS $ElNITION/NE!NGSTROMª ALSOCALLEDTHE!NGSTROMUNIT IS¾nMETERSIN LENGTHONETEN BILLIONTHOFAMETER ORONETEN THOUSANDTHOFAMICRON)TMAY ALSOBEEXPRESSEDASONETENTHOFANANOMETER2ECALLTHATANANOMETERIS¾n METERSORONEBILLIONTHOFAMETER 4HE!NGSTROM5NIT 4HE!NGSTROMUNITISNAMEDAFTER!NDERS*!NGSTRM A3WEDISHPHYSICIST !TlRSTGLANCE ITSEEMSTOBEACUMBERSOMEANDANNOYINGUNITOFMEASURE BECAUSEITISINCONSISTENTWITHTHESTANDARDIZEDUNITSOFMEASURE LIKETHE MICRONANDNANOMETER ALLOFWHICHARESPACEDTHREEORDERSOFMAGNITUDE APARTTHATIS THENEXTSMALLERUNITISTHOFTHELARGERONEDIVIDETHE MILLIMETERINTOPARTSANDEACHONEISAMICRONINLENGTH
#HAPTER&ORMING7ELLS (OWEVER THE!NGSTROMUNITHASSPECIALPHYSICALMEANINGTHERADIIOFALL ATOMSAREAPPROXIMATELYONEORTWO!NGSTROMUNITS!CCORDINGTOTHE3AR GENT 7ELSH0ERIODIC4ABLE THELARGESTATOMICRADIUSIS&RANCIUMATª THE SMALLESTIS.EONATª)TISESPECIALLYMEANINGFULFORCHIPMAKINGSINCE THElLMSDEPOSITEDONTHEWAFERAREEXTREMELYTHIN4HISFACTISILLUSTRATEDIN THEDISCUSSIONOFTHE'ATE$IELECTRIClLMFOUNDIN#HAPTER
)MPORTANT&ILM#HARACTERISTICS 4HICKNESS4HEEXACTOXIDElLMTHICKNESSISSPECIlEDSOTHATTHEIMPLANTATION SCREENINGEFFECTOFTHEOXIDEISCONSISTENTFROMWAFER TO WAFERANDBATCH TO BATCH WHILESTILLPROVIDINGENOUGHPROTECTIONTOTHEUNDERLYINGSILICON 5NIFORMITY4HEWAFERWILLHAVEMANYINDIVIDUALCHIPSONITANDTHEGOALIS FOREACHONETOOPERATEIDENTICALLY&ORTHATTOHAPPEN THECROSS WAFERlLM THICKNESSMUSTBEKEPTWITHINTIGHTLIMITS !STHEREADERMIGHTEXPECT ALARGENUMBEROFPRODUCTWAFERSISNOTCOMMIT TEDTOAPROCESSINGTOOLWITHOUTDOUBLE CHECKINGTHATITISWORKINGPROPERLY 4HESETESTSAREPERFORMEDONATIMETABLETHATVARIESFROMFAB TO FAB BUT MONITORINGTHETOOLSISANECESSITY3OMEOFTHECOMMONNAMESFORTHESE WAFERSARETESTWAFERS PILOTWAFERSORMONITORWAFERS)TISNOTNECESSARYFORTHIS DISCUSSIONTOINCLUDETHEPROCEDURESINVOLVEDWITHTHESEWAFERS3UFlCETOSAY THATTHEYAREPROCESSEDINTHESTANDARDMANNER INSPECTED MEASUREDANDIF ALLISWELL THENLARGEBATCHESOFPRODUCTARECOMMITTEDTOTHETOOL
3%#4)/.
0HOTOLITHOGRAPHY )NTRODUCTION $ElNITION,ITHOGRAPHYISAPRINTINGPROCESS $ElNITION0HOTOLITHOGRAPHYISAPRINTINGPROCESSTHATUSESPHOTOGRAPHICTECHNIQUES TOTRANSFERAPATTERNFROMAPHOTOMASKORRETICLETOACOATINGOFPHOTOSENSITIVE MATERIAL CALLEDPHOTORESIST ONTHEWAFERSURFACE $ElNITION0HOTORESISTRESIST ISALIGHT SENSITIVEPLASTICMATERIALTHATISDISSOLVEDIN ASOLVENTTOFORMASOLUTION4HERESISTISDISPENSEDONTOTHEWAFERINTHEFORMOF ALIQUID THENSTABILIZEDSOLIDIlED BYABAKINGSTEPTHATALSOAFFECTSTHEPHOTOSEN SITIVITYANDSOLUBILITYINDEVELOPERSOLUTIONASDESCRIBEDLATERINTHISSECTION-OST PHOTORESISTISSENSITIVETOULTRAVIOLETLIGHT +EY0OINT4HEPROCESSOFWAFERPATTERNINGISNOWUNDERWAY"EFOREGETTINGINTOTHE DETAILSOFTHEPATTERNINGPROCESS TAKEALOOKAT&IGURE
&IGURE 0ATTERNED7AFER
#HAPTER&ORMING7ELLS 4OTHENAKEDEYE THEPATTERNEDWAFERLOOKSLIKEABUNCHOFSMALLSQUARESOR RECTANGLES(OWEVER WHENLOOKINGUNDERMAGNIlCATION THEREALDETAILSBECOMEVIS IBLE4HEPATTERNTHATISTRANSFERREDTOTHEWAFERISFOUNDONTHERETICLE2ECALLTHATTHE RETICLEMAYHAVETHEPATTERNFORONEDIEORMANYDIE DEPENDINGONTHEIRSIZEANDTHE SIZEOFTHEEXPOSURElELDOFTHEIMAGINGTOOLSTEPPER 4HETERMShDIEvANDhCHIPv AREUSEDINTERCHANGEABLYTHROUGHOUTTHISDISCUSSION/NERETICLEISREQUIREDFOREACH LAYERTHATNEEDSAMASKFORIMPLANTINGORETCHING4HEPATTERNFORMOSTLAYERSAPPEARS TOBEANUNCOMPLICATEDSETOFSQUARES LINESANDRECTANGLESONTHERETICLE)TISIMPRES SIVETHATTHESESIMPLEBITSCOMBINETOMAKESUCHASOPHISTICATEDDEVICE $IEVS$ICE 4HE PLURAL OF hDIEv IS hDICEv SEE ANY DICTIONARY (OWEVER USAGE IN THE INDUSTRYHASEVOLVEDAWAYFROMUSEOFTHEPLURALFORMANDhDIEvISCOMMONLY USEDFORBOTHSINGULARANDPLURAL
4HECOMPARATIVELYWIDESPACESBETWEENEACHDIEARECALLEDSCRIBELINESORSTREETS 4HESESPACESMUSTBERATHERWIDEBECAUSETHEDIEARECUTAPARTWITHADIAMONDSAW 4HEBLADEISMADEASTHINASPOSSIBLE BUTITISSTILLGIGANTICCOMPAREDTOTHEFEATURES ONTHECHIPSEE#HAPTER 0HOTOLITHOGRAPHY0ROCESS&LOW
#OAT3PIN A 3URFACE0REPARATION I 6ACUUMDEHYDRATIONBAKE II (-$3HEXAMETHYLDISILAZANE APPLICATION B 3PINRESISTAPPLICATION C 3OFTBAKE
%XPOSE3TEP $EVELOP A !PPLYDEVELOPERSOLUTION B 0OST DEVELOPRINSE !FTER$EVELOP)NSPECTION!$)
0HOTOLITHOGRAPHY 5LTRA 6IOLET,IGHT
'LASSPLATE #HROMEPATTERN 0HOTORESIST
%XPOSURE
3ILICON$IOXIDE 3ILICON7AFER
$EVELOPMENT
%TCH
3TRIP2ESIST
&IGURE 4HE7AFER0ATTERNING0ROCESS 4HE9ELLOW2OOM .OWWEENTERTHEYELLOWROOM3INCEPHOTORESISTISSENSITIVETOULTRAVIOLET56 LIGHT THEAREAOFTHEFABWHEREITISPROCESSEDMUSTBEFREEOF566ISIBLEOR WHITELIGHTTHATWEAREALLFAMILIARWITHCONTAINS56ATTHEHIGHFREQUENCY ENDTHEBLUEEND OFTHESPECTRUMSOITCANNOTBEUSEDTOILLUMINATETHE PHOTOLITHOGRAPHYPROCESSINGAREA#UTTINGOFFTHEUPPERENDOFTHESPECTRUM CHANGESTHECOLOROFTHELIGHTANDMAKESEVERYTHINGLOOKYELLOW 7HATWOULDHAPPENIFWHITELIGHTGOTINTOTHEPHOTOAREA.OONEWOULD KNOWTHEREWASAPROBLEMUNTILTHEWAFERSWEREPUTINTOTHEDEVELOPERSOLU TION!LLOFTHERESISTWOULDDISSOLVEINTHEDEVELOPERLEAVINGNOPATTERNON THEWAFER7HYDOESTHATHAPPEN2EADON
$ElNITION!N)MPLANT-ASKISAPATTERNCREATEDINPHOTORESISTOROTHERMASKING MATERIAL 0URPOSE!NIMPLANTMASKALLOWSTHEINTRODUCTIONOFDOPANTSFROMANIMPLANTERTO ENTERONLYTHESPECIlEDAREASOFTHEWAFER4HERESISTFORMSACOMPARATIVELY THICKLAYEROFPLASTICTHATABSORBSTHESPEEDINGIONSORNEUTRALSSOTHATTHEYARE UNABLETOREACHTHESURFACEOFTHESILICON $OPANTSAREUSEDTOCREATETHETRANSISTORSANDSOMEOFTHEELECTRICALCOMPONENTS OFTHECHIP4HEDOPANTSMUSTBEPLACEDPRECISELYINTHECORRECTAREASFORTHECOM PONENTSTOWORK
#HAPTER&ORMING7ELLS
#OAT3PIN 3URFACE0REPARATION 7HENTHEWAFERSARRIVEATPHOTOLITHOGRAPHYPHOTO THEYENTERALOWPRESSUREBAKE OVENANDARETREATEDTOAhSAUNAvOFHOT DRYNITROGENGASTODRIVEOFFANYMOISTURE 4HENHEXAMETHYLDISILAZANE(-$3 ISDISPENSEDINTOTHECHAMBERINVAPORFORM WHEREITCOATSTHEWAFERS4HE(-$3FORMSANIMPORTANThGLUELAYERvTHATENSURES THEPHOTORESISTWILLSTICKTOTHEWAFERS 3URFACEPREPARATIONISALWAYSAMAJORISSUEINCHIPMAKING7EWOULDBEINREAL TROUBLEIFTHELAYERSDIDNTSTICKTOEACHOTHER 2ESIST!PPLICATION 4HEPROCESSOFCOATINGTHETOPOFTHEWAFERWITHPHOTORESISTISSOMETIMESCALLEDSPIN SIMPLYBECAUSETHETOOLTHATPUTSONTHERESISTSPINSTHEWAFERAROUND4HETOOLHOLDS THEWAFERONASPINNINGVACUUMCHUCK4HERESISTISDISPENSEDONTOTHECENTEROF THEWAFERTHROUGHATUBEANDISIMMEDIATELYmUNGOFFSIDEWAYSBECAUSETHEWAFERIS SPINNINGATARATHERHIGHSPEED"ELIEVEITORNOT THATISTHEIDEA4HESPINSPEEDISTHE PRINCIPLEDETERMINANTOFTHETHICKNESSOFTHERESISTTHATISLEFTONTHEWAFERRESISTVIS COSITYISALSOANIMPORTANTTHICKNESSFACTORITISOFTENTHETHICKNESSOFPANCAKESYRUP ORENGINEOIL &IGURE SHOWSASPINNER
&IGURE 0HOTORESIST#OATER3PINNER
3OFT"AKE !FTERTHERESISTISAPPLIEDTOTHEWAFERSPIN ITGOESTOAHOTPLATEFORAhSOFT BAKEvAT ABOUT#-OSTOFTHESOLVENTISDRIVENOFF LEAVINGASTICKYSEMISOLIDTHATSERVES ASAKINDOFPHOTOGRAPHIClLM4HENTHEWAFERMOVESTOTHESTEPPERFOREXPOSURE
0HOTOLITHOGRAPHY
%XPOSURE3TEP $ElNITION%XPOSUREISTHEPROCESSOFSHININGULTRAVIOLETLIGHTONTOTHEWAFER4HE WAFERISEXPOSEDTOULTRAVIOLETLIGHTJUSTASTHElLMINACAMERAISEXPOSEDTOVIS IBLELIGHT 4HESTEPPERISANINCREDIBLYSOPHISTICATEDDEVICE4HENAMEhSTEPPERvCOMESFROM THEWAYTHEMACHINEPERFORMSITSJOBOFEXPOSINGTHEWAFERTO56LIGHT!SQUARE ORRECTANGULARREGIONOFAFEWSQUARECENTIMETERSISEXPOSEDATATIME4HESTEPPER PHYSICALLYMOVESORhSTEPSvTHEWAFERINPREPARATIONFORTHENEXTEXPOSURE 7ATCHINGTHEMACHINEINACTIONISFUN4HEWAFERISPOSITIONEDFORTHElRST EXPOSURE THESHUTTEROPENSFORASECONDORLESS ALLOWINGTHE56LIGHTTOSHINEONTHE WAFER4HENTHEWAFERISSUDDENLYMOVEDASHORTDISTANCEFOLLOWEDBYANOTHERmASH OFLIGHT4HEPROCESSCONTINUES STEPBYSTEP BACKANDFORTHACROSSTHEWAFERUNTILTHE ENTIRESURFACEISEXPOSED4HERECANBEAHUNDREDORMORESTEPSNEEDEDTOEXPOSEAN ENTIREWAFER 7HATISTRULYAMAZINGABOUTTHESTEPPERISTHEEXTREMEPRECISIONWITHWHICHIT MOVESTHEWAFERFOREACHEXPOSURE2EMEMBERTHATEACHLAYERREQUIREDTOMAKEA CHIPMUSTBEPLACEDEXACTLYONTOPOFTHELASTLAYEROREVERYTHINGWILLBEJUMBLEDUP ANDTHEDEVICESWILLNOTWORK4HETOLERANCEFORALIGNMENTOFTHEWAFERISMEASURED INNANOMETERSFORTODAYSDEVICES REQUIRINGTHEUSEOFLASERSTODETERMINETHEPOSITION OFTHEVACUUMCHUCKASSEMBLYTHATHOLDSTHEWAFER )NMOREFAMILIARTERMS THESTEPPERPOSITIONSTHEWAFERWITHATOLERANCEOFCLOSER THANOFTHETHICKNESSOFAHAIR4HATSPRECISION 4HESTEPPERISESSENTIALLYTAKINGAPICTUREOFTHERETICLE4HElLMINWHICHTHE PICTUREWILLBEDEVELOPEDISTHEPHOTORESISTONTOPOFTHEWAFER
&IGURE 2ETICLE 0ROJECTEDONTO7AFER
#HAPTER&ORMING7ELLS $ElNITION4HE%XPOSURE&IELDORSIMPLY THElELD ISTHEAREAONTHEWAFERSURFACE THATISEXPOSEDTO56LIGHTATEACHEXPOSURE4HEMAJORITYOFSTEPPERSINTODAYS STATE OF THE ARTFABSUSEASCANNINGTECHNIQUETHATSWEEPSTHELIGHTQUICKLYACROSS THElELD4HESETOOLSARECALLEDhSCANNERSvANDUSEASTEP AND SCANTECHNIQUE 4HETERMhmASHvISANOTHERSLANGTERMFORTHEEXPOSURElELDTHATAPPLIESTO STEPPERSTHATEXPOSETHEENTIREAREAOFINTERESTASIFACAMERASHUTTEROPENEDAND CLOSED4HISSTEPPERTECHNOLOGYDOMINATEDTHEINDUSTRYFORMANYYEARSANDISSTILLIN USETODAY 563OURCE
2ETICLE 82EDUCTION ,ENS
&IGURE 3TEPPER0RINTS)MAGEIN2ESIST
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3ALICIDE&ORMATION $ElNITION!3ILICIDEISACHEMICALCOMPOUNDMADEOFSILICONANDAMETAL 0URPOSE3ILICIDESHAVEBEENUSEDFORMANYYEARSBECAUSETHEYIMPROVETHECONDUC TIVITYOFTHEGATEELECTRODEANDREDUCETHECONTACTRESISTANCE SPEEDINGUPTHECHIP $ElNITION0OLYCIDEISTHENAMEOFASTACKOFTWOlLMS SILICIDEONPOLYSILICON $ISCUSSION 4HEUSEOFTHEPOLYCIDElLMSTACKGIVESTHEBESTOFBOTHWORLDS4HEPOLYGATEOXIDE INTERFACEISWELL UNDERSTOODANDROBUST4HEPOLYISEASYTOPROCESSANDTOLERATESHIGH TEMPERATURES"UTTHEPOLY EVENHEAVILYDOPED ISNOTANEXCEPTIONALLYGOODCONDUC TOR-ANYSILICIDESHAVERESISTIVITIESTHATAREMUCHLOWERTHANDOPEDPOLYTHEIRUSE WILLSIGNIlCANTLYINCREASECHIPSPEED!NDTHESILICIDEWILLTOLERATEHIGHTEMPERATURES ENCOUNTEREDINPROCESSING TOO $ElNITION3ALICIDEISTHESHORTNAMEFORSELF ALIGNEDSILICIDE)NTHISPROCESS THE SILICIDEMATERIALONLYFORMSINEXACTLYTHERIGHTPLACESINTHETRANSISTORS $ElNITION3PUTTERING ACOMMONTYPEOF0HYSICAL6APOR$EPOSITION06$ ISTHE PROCESSOFPHYSICALLYBOMBARDINGATARGETSOURCEWITHARGONIONS WHICHKNOCKOFF ATOMSFROMTHETARGET SOMEOFWHICHlNDTHEIRWAYTOTHEWAFERANDSTICKTOIT
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)NTRODUCTION )NTHISCHAPTER YOUWILLLEARN v 7HYBARRIERLAYERSARENEEDED v 4HEIMPORTANCEOFPLANARITY v #ONNECTINGTHETRANSISTORTOTHERESTOFTHECIRCUIT v -ETALLIZATIONTECHNOLOGY v 4HEIMPORTANCEOFLOW KDIELECTRICS /BJECTIVEOF&IRST,EVEL-ETALLIZATIONTOELECTRICALLYCONNECTTHESOURCE DRAINAND GATEELECTRODESOFEACHTRANSISTORTOOTHERELEMENTSOFTHECHIPCIRCUIT &IRST,EVEL-ETALLIZATION0ROCESS&LOW .ITRIDEANDOXIDEDEPOSITIONS
A 0%#6$3I.BARRIERLAYER
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+EY0OINTSINTHE&IRST,EVEL-ETALLIZATION0ROCESS "ARRIERLAYERSARENEEDEDTOPREVENTAVARIETYOFPROBLEMS !DHESIONORhGLUEvLAYERSAREUSEDFORMAKINGTHElLMSSTICKTOGETHER 0LANARIZATIONISREQUIREDBYPHOTOLITHOGRAPHYTECHNOLOGY 4UNGSTEN#6$ISREQUIREDTOlLLHIGHASPECTRATIOCONTACTHOLES ,OW KDIELECTRICMATERIALSAREREPLACINGDEPOSITEDOXIDEASTHEINTERMETAL DIELECTRIC)-$ #OPPERWIRINGFORINTERCONNECTIONSISREQUIREDFORSTATE OF THE ARTDEVICES %ACHOFTHESEPOINTSWILLBEEXPLAINEDINTHEAPPROPRIATESECTIONSOFTHISCHAPTER $ISCUSSION &IRSTLEVELMETALLIZATIONHASCHANGEDDRASTICALLYINRECENTYEARS4HISPROCESSINGSTEP ISDOMINATEDBYNEWTECHNOLOGYANDNEWMATERIALS &ORMANYYEARS ELECTRICALCONNECTIONSTOTHESOURCE DRAINANDGATEOFEACH TRANSISTORWEREMADEWITHALUMINUM THESAMEALUMINUMlLMTHATWASPATTERNED ANDETCHEDTOFORMTHEINTERCONNECTINGWIRINGBETWEENTHEDEVICESONTHECHIPS4HIS ALUMINUMTECHNOLOGYISSTILLWIDELYUSEDTODAYFOREARLIERGENERATIONCHIPS)NDEED MANYCHIPDESIGNSENJOYDECADESOFCONTINUEDUSESEE&IGURE !SDEVICEDIMENSIONSDECREASEDOVERTHEYEARS THEDEPTHOFTHEPNJUNCTIONALSO DECREASED7ITHSHALLOWERJUNCTIONS APROBLEMCALLEDJUNCTION SPIKINGAROSE7HEN
)NTRODUCTION ALUMINUMCOMESINCONTACTWITHSILICON SOMEOFTHESILICONWILLDISSOLVEINTHEALU MINUMTHISPHENOMENONFORMSWHATISCALLEDASOLIDSOLUTION4HEALUMINUMSILICON ALLOYWILL INTURN MOVEINTOTHEAREASVOIDEDOFSILICON7ITHSHALLOWPNJUNCTIONS THESEhSPIKESvCOULDBELONGENOUGHTOPENETRATETHROUGHTHEJUNCTION SHORTINGITOUT 4HESHORTSWILLPREVENTTHECHIPFROMOPERATING !LUMINUM 3ILICON DIOXIDE
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.ITRIDEAND/XIDE$EPOSITIONS .ITRIDE$EPOSITION $ElNITION!"ARRIER,AYERISAlLMORSTACKOFlLMSTHATACTSASABARRIERAGAINSTTHE DIFFUSIONOFATOMSORMOLECULESTHROUGHIT 0URPOSE"ARRIERLAYERSPERFORMAVARIETYOFFUNCTIONS&OREXAMPLE THEYCANBEUSED TOBLOCKSILICONATOMSFROMDISSOLVINGINALUMINUMTHEYWILLKEEPMOBILEION CONTAMINATIONFROMMIGRATINGTHROUGHTHECHIP PROTECTTHECOMPLETEDWAFERFROM AIRANDMOISTUREINTHEATMOSPHEREANDMAYALSOACTASAGLUETOHOLDTWOSTACKED lLMSTOGETHER $ISCUSSION 3ILICONNITRIDEISAWIDELYUSEDBARRIERLAYERANDISALSOINCORPORATEDINTOCOMBINA TIONSOFlLMSUSEDASBARRIERSORGLUELAYERS4HEUSEOFNITRIDEASAHARDMASKANDAN IMPLANTMASKHAVEBEENDISCUSSEDPREVIOUSLY)TISADIELECTRICMATERIALTHATISCRITICAL TOCHIPMAKING 4HECOMPLETEDCHIPSAREOFTENPROTECTEDBYABARRIEROF0%#6$SILICONNITRIDE 4HE0%#6$TECHNIQUEPRODUCESANITRIDELAYERCONTAININGALOTOFHYDROGEN UNLIKE THE,0#6$3I.DISCUSSEDEARLIERIN#HAPTER4HECHEMICALFORMULAFORTHISlLM ISOFTENWRITTENAS3I.4HE0%#6$NITRIDEISSTILLATOUGHDIELECTRICANDPERFECTLYCA PABLEOFDOINGTHEJOBOFABARRIERLAYER BUTMAYBEDEPOSITEDATALOWERTEMPERATURE )FNOTFORTHELOWERTEMPERATUREDEPOSITION ITCOULDNOTBEUSEDBECAUSETHEHIGHER TEMPERATUREMETHODWOULDCAUSEDESTRUCTIVECHEMICALANDMETALLURGICALREACTIONSIN THECHIPWIRING!FTERTHElRSTLEVELOFMETALWIRINGISINPLACE NOTEMPERATURESHIGHER THANABOUT#CANBEUSED
#HAPTER&IRST,EVEL-ETALLIZATION /NEOFTHEAPPLICATIONSFORBARRIERLAYERSCOMESFROMTHEUSEOFCOPPERTECHNOL OGYFORTHEMETALINTERCONNECTS4HEDANGEROFCOPPERCONTAMINATINGTHEDEVICESWILL BEDISCUSSEDINTHEUPCOMINGSECTIONONCOPPERDEPOSITION !NOTHERIMPORTANTTASKFORTHEBARRIERLAYERISTOKEEPTHEDOPANTSINTHEDOPED OXIDEFROMMIGRATINGINTOTHEUNDERLYINGLAYERSANDCHANGINGTHEDOPINGPROlLES REVIEW#HAPTER OFTHECONDUCTINGREGIONSOFTHETRANSISTORS4HENEXTLAYERTOBE DISCUSSEDINTHEPROCESSISOFTENADEPOSITEDOXIDEDOPEDWITHBORONANDPHOSPHO ROUS3OMEMOVEMENTOFDOPANTSFROMTHISLAYERINTOADJACENTREGIONSISPOSSIBLE &ORADISCUSSIONOFNITRIDEDEPOSITION REVIEW#HAPTER
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/XIDE$EPOSITION $ElNITION4HE0RE -ETAL$IELECTRIC0-$ ISTHETHICKINSULATINGLAYERDEPOSITEDTO COVERTHETRANSISTORSBEFORETHElRSTLEVELOFMETALWIRINGISFORMED 0URPOSE4HEPRE METALDIELECTRICPREVENTSELECTRICALSHORTSBETWEENTHECONDUCTING ELEMENTSOFTHETRANSISTORSANDTHEWIRESTHATCONNECTTHETRANSISTORSTOTHERESTOF THECIRCUIT)TISRELATIVELYTHICKTOREDUCEELECTRICALINTERACTIONBETWEENTHEWIRING ANDTHEDEVICESBELOW4HEPRIMARYCONCERNISPARASITICCAPACITANCETHETEN DENCYFORNEARBYCONDUCTORSTOINTERACTWHENTHEYARECARRYINGACURRENT0ARASITIC CAPACITANCEDELAYSTHETRANSMISSIONOFSIGNALSTHROUGHTHECIRCUITWIRINGITIS DISCUSSEDLATERINTHECHAPTER $ISCUSSION 4HEPRE METALDIELECTRICISA#6$OXIDETHATISDOPEDWITHPHOSPHOROUSORWITHBOTH BORONANDPHOSPHOROUS4HENAMESOFTHESElLMSAREPHOSPHOSILICATEGLASS03'
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#-00LANARIZATION $ElNITION0LANARIZATIONISTHEPROCESSOFMAKINGTHESURFACEOFTHEWAFERASmAT OR PLANAR ASPOSSIBLE 0URPOSE4HEBUMPSONTHESURFACEOFTHEWAFERCANBEROUGHLYASHIGHASTHEDEPTH OFFOCUSOFTHESTEPPERSINSTATE OF THE ARTTOOLS4HESTEPPERISUNABLETOLOOK DOWNATTHEWAFERSURFACEANDFOCUSONALLPOINTSOFTHEWAFERTOPRINTTHENEXT PATTERNINTHISCASE THECONTACTHOLES7ITHOUTPLANARIZATION THEHOLESATSOME POINTSONTHEWAFERWOULDBEOUTOFFOCUS RESULTINGINAPOORLYDElNEDPATTERN ORNOPATTERNATALLINTHERESISTMASK
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!PPENDIX"0LASMA%TCH3UPPLEMENTTO#HAPTER 4HEREAREMANYADDITIONALREQUIREMENTSSPECIlCTOPARTICULARAPPLICATIONS4HESE AREUSUALLYTHEHIGHESTPRIORITY4HEREFERENCESINTHE"IBLIOGRAPHYOFFERIDEASFOR FURTHERREADING
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#ROPPER 7ILLIAM( 'REAT0HYSICISTS4HE,IFEAND4IMESOF,EADING0HYSICISTS FROM'ALILEOTO(AWKING .EW9ORK /XFORD5NIVERSITY0RESS 3ZE 3- 0HYSICSOF3EMICONDUCTOR$EVICES 3ECOND%DITION *OHN7ILEY 3ONS (ALLIDAY $AVID 2OBERT2ESNICK AND*EARL7ALKER &UNDAMENTALSOF0HYSICS %XTENDED &IFTH%DITION *OHN7ILEY3ONS "ROWN 4HEODORE, AND(%UGENE,E-AY *R #HEMISTRYTHE#ENTRAL3CIENCE 0RENTICE (ALL )NC 4HE/XFORD!MERICAN$ICTIONARYAND,ANGUAGE'UIDE /XFORD5NIVERSITY0RESS 7OLF 3 -ICROCHIP-ANUFACTURING ,ATTICE0RESS 3ZE 3- 6,3)4ECHNOLOGY "ELL4ELEPHONE,ABORATORIES )NCORPORATED 'HANDHI 3ORAB+ 6,3)&ABRICATION0RINCIPLES 3ILICONAND'ALLIUM!RSENIDE *OHN7ILEYSONS )NC 3EMICONDUCTOR)NTEGRATED#IRCUIT&ABRICATION4ECHNIQUES &AIRCHILD #ORPORATION -ANOS $ENNIS- AND$ANIEL,&LAMM 0LASMA%TCHING!N)NTRODUCTION !CADEMIC0RESS )NC ,IEBERMAN -ICHAEL! AND!LLAN*,ICHTENBERG 0RINCIPLESOF0LASMA$IS CHARGESAND-ATERIALS0ROCESSING *OHN7ILEY3ONS )NC
"IBLIOGRAPHY #HAPMAN "RIAN 'LOW$ISCHARGE0ROCESSES 3PUTTERINGAND0LASMA%TCHING *OHN7ILEY3ONS )NC 2OSSNAGEL 3TEPHEN- *EROME*#UOMO AND7ILLIAM$7ESTWOOD (ANDBOOK OF0LASMA0ROCESSING4ECHNOLOGY &UNDAMENTALS %TCHING $EPOSITION AND3UR FACE)NTERACTIONS .OYES0UBLICATIONS (EYNES -ICHAEL AND!NNE+-ILLER )NTEGRATED#IRCUIT3YNOPSIS 4HIRD%DITION 3EMICONDUCTOR3ERVICES (EYNES -ICHAEL AND!NNE+-ILLER 3EMICONDUCTOR4ERMINOLOGYn'RAPHIC 'LOSSARYOF4ERMS &OURTH%DITION 3EMICONDUCTOR3ERVICES -AKINGTHE-ICROCHIP!TTHE,IMITS)))6IDEO4RAINING#OURSE 3EMICONDUCTOR 3ERVICES %VANS + !-ILLERAND06AN:ANT #LEANROOM4ECHNOLOGY-ANUAL 3ECOND %DITION 3EMICONDUCTOR3ERVICES 6AN:ANT 0ETER -ICROCHIP&ABRICATION &IFTH%DITION -C'RAW (ILL 'ISE 0ETER% "LANCHARD 2ICHARD 3EMICONDUCTORAND)NTEGRATED#IRCUIT&ABRI CATION4ECHNIQUES 2ESTON0UBLISHING#OMPANY )NC 6AN.OSTRANDS3CIENTIlC%NCYCLOPEDIA &IFTH%D ,ITTON%DUCATIONAL0UBLISH ING )NC #2$(ANDBOOKOF#HEMISTRYAND0HYSICS TH%D n #2#0RESS )NC 0LUMMER *AMES$ $EAL -ICHAEL$ 'RIFlN 0ETER" 3ILICON6,3)4ECHNOL OGY 0RENTICE(ALL )NC 4HE3EMICONDUCTOR0ICTURE$ICTIONARY $-$ATA )NC
)NDEX
3YMBOLS
#
($0 #6$
CHEMICALCOMPOUND CHEMICALMECHANICALPOLISHING#-0 CHEMICALVAPORDEPOSITION#6$ CHEMISTRY CLEANROOM #-/3DEVICES COMPLEMENTARYMETALOXIDESEMICONDUCTOR #-/3 COMPOUNDSEMICONDUCTORS COMPUTER AIDEDDESIGN#!$ CONTACTHOLE
! ACTIVATED ACTIVEAREA ADHESIONLAYER ADSORBED AFTERDEVELOPINSPECTION!$) !NGSTROM !NGSTROMUNIT ANNEAL SPIKE ANNEALING ASHING ASPECTRATIO ATOMICLAYERDEPOSITION!,$ AUTOMATEDMATERIALHANDLINGSYSTEMS!-(3
" BACK GRINDING BACK LAPPING BARRIERLAYER BINNING BIT BONDINGPADS BUNNYSUIT BYTE
$ DEIONIZEDWATER$)WATER DELAMINATEPEELOFF DEPLETIONREGION DESIGNENGINEER DESIGNRULES DESIGNRULECHECKS$2# DESIGNRULESETS DESIGNVERIlCATION DIE ATTACH DIE BONDING DIELECTRICS HIGH K LOW K DIFFUSION DOPANTS ACTIVATED
)NDEX N TYPE P TYPE DRYETCHING DUALDAMASCENE$$ DYNAMICRANDOMACCESSMEMORY$2!-
% EFmUENT ELECTRICCHARGE ELECTRICCURRENT ELECTRIClELD ELECTROCHEMICALDEPOSITION%#$ ELECTROMAGNET ELECTROMIGRATION ELECTRONICSGRADESILICON%'3 ELECTROPLATING ENCAPSULATION EPITAXIALSILICONEPI EXCITEDSTATE EXPOSURE EXPOSURElELD
& FABRICATIONAREA lELDEFFECTTRANSISTOR lNALTEST mIP CHIPBONDING mUID FOUNDRY FUNCTIONTEST
' GAS GATEDIELECTRIC GERMANIUM'E GETTER GLUELAYER
( HALOGENS HARDMASK HIGH KDIELECTRICS HIGH KGATEDIELECTRICS HIGHASPECTRATIOCONTACT(!2#
) )))n6SEMICONDUCTORS IMPLANTMASK INERTGASES INGOT INLINEPACKAGE INTEGRATEDCIRCUIT)# INTERLEVELDIELECTRIC),$ INTERMETALDIELECTRIC)-$ INVERSESQUARELAW INSPEC ISOTROPIC
* JUNCTION SPIKING
+ KISTHEDIELECTRICCONSTANT
, LATCH UP LAYOUTDESIGNER LAYOUTENGINEER LAYOUTVERSUSSCHEMATIC,63 LIGHTLYDOPEDDRAIN,$$ LIGHTEMITTINGDIODES,%$S LITHOGRAPHY LOGICENGINEER LOW KDIELECTRICS LOW KDIELECTRICMATERIALS LOWPRESSURE#6$,0#6$
MAGNETIClELD METALINTERCONNECTS METALOXIDESEMICONDUCTORlELDEFFECTTRANSISTOR -/3&%4 MICRON MICROPROCESSORS MIL SPEC MILITARYAPPLICATIONS MOLECULE MONITORWAFERS -OORES,AW
)NDEX .
2
N TYPE NATIVEOXIDE NEWPRODUCTPLAN.00 NOBLEGASES
RAPIDTHERMALPROCESSOR240 REACTANTS RECTIlER REENTRANTPROlLESUNDERCUTTING RESISTTRIMMING RETICLE
0 P TYPE PADOXIDE PARALLEL PLATECAPACITOR PARASITICCAPACITANCE PASSIVATION PELLICLES PHASE SHIFTMASK PHASE SHIFTMASKCHECK PHOTOLITHOGRAPHY PHOTOMASK PHOTORESISTRESIST RETICLE PHOTOMASKRETICLE PHOTORESISTRESIST PHOTORESISTASHING PURPOSE PHOTORESISTSTRIPPING PHYSICALVAPORDEPOSITION06$ PILOTWAFERS PLANARIZATION PLASMA PLASMAENHANCED#6$0%#6$ PLASMAETCH PLUG PNJUNCTION POLYCIDE POLYCRYSTALLINEPOLY POTENTIALDIFFERENCE PRE METALDIELECTRIC0-$ PROBE PRODUCTDElNITION PROTECTIVEPASSIVATION
1 QUARTZ QUARTZGLASS
3 SACRIlCIALOXIDE SALICIDE SCANNINGELECTRONMICROSCOPES3%- SCHEMATIC SCRIBELINE SCRUBBERS SELF ALIGNEDGATE SEMICONDUCTOR SHALLOWTRENCH SHALLOWTRENCHISOLATION34) SHEARINGSTRESS SIDEWALLPASSIVATION SILICA SILICIDES SILICON3I POLYCRYSTALLINEPOLY SINGLECRYSTAL SILICONDIOXIDE SILICONNITRIDENITRIDE SILICONONINSULATOR3/) SIMULATIONS SINGLECRYSTAL SOFTWAREENGINEERS SOLIDSTATEDEVICE SOURCEANDDRAIN SPACER SPECIlCATIONS SPIKEANNEAL SPIN ONDIELECTRIC3/$ SPIN ONGLASS3/' SPUTTERING STANDARDMECHANICALINTERFACE3-)& STATICRANDOMACCESSMEMORY32!- STEP AND REPEATREDUCTION PROJECTIONPRINTING STEP AND SCAN STEPPER
)NDEX STREET SUBSTRATE SURFACTANTS
4 TAPEOUT TAPEAUTOMATEDBONDING4!" TESTWAFERS THERMALBUDGET THERMALOXIDATIONOFSILICON THERMALOXIDE THROUGHPUT TRENCHETCH TRENCHlLLPROCESS
5 UNDERCUTTING
6 VERTICALLAMINARmOW6,& VIA
7 WAFERSORT WELL WELLDIFFUSION WELLDRIVE IN WETETCH
9 YELLOWROOM
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