半导体工艺-复旦大学-蒋玉龙-Chapter13

Chapter13ContactandInterconnectionOutlineI.IncreasingimportanceofcontactandinterconnectionforVLSI/ULSITechnologyII.Advancedcontact&interconnectiontechnology---integrationofvariousthinfilmmaterialsandprocesstechniquesIII.ContactresistanceIV.Al/SiOhmiccontactandinterconnectV.CuinterconnectionbydamascenetechnologyVI.Silicide,PolycideandSalicideI.IncreasingimportanceofcontactandinterconnectionforVLSI/ULSITechnology‹RequirementsandproblemsofC&IforICProgress(1)HighSpeed:¾Lowinterconnectresistance¾Lowcontactresistance¾Lowparasiticcapacitance¾Problem:RC↑WTLRρ=TLWkCv0ε=(InterlevelC)WLTkCl0ε=(InterlineC)(Contactresistanceincreasesalsowithdevicescaling)(2)Highreliability¾Uniformmetal/Siinterface¾LowelectromigrationProblems:*Metal/Si:interdiffusion&interactionÆAl“Spiking”ÆContactfailure*Electromigration:ÆvoidformationÆinterconnectfailure(3)Highdensity¾Smallercontact,morenarrowmetalline¾MultilevelmetallizationA–ChipareaG–NumberofICgatesP–Metalpitch(linewidth+space)N–NumberofmetallevelsProblems:Increasingprocesscomplexity∴C&I–OneofthebottlenecksfordeepsubμICtechnology!NPGA3/2=YearofProduction200520062007200820092010201120122013DRAM½Pitch(nm)(contacted)807065575045403632MPU/ASICMetal1½Pitch(nm)(contacted)907868595245403632MPUPhysicalGateLength(nm)322825222018161413Numberofmetallevels111111121212121213Numberofoptionallevels–groundplanes/capacitors444444444Totalinterconnectlength(m/cm2)–Metal1andfiveintermediatelevels,activewiringonly[1]101912121439171220002222250028573125Multi-levelInterconnectpredictioninITRS-2006II.AdvancedContact&InterconnectionTechnology–Integrationofvariousthinfilmmaterialsandprocesstechniques1.VariousmaterialsforC&I‹ForearlyIC:Al‹Atmediumstage:(≥2-3μm)Al+DopedPoly-Si‹ForAdvancedVLSI/ULSI:(1)Highconductivemetal&itsalloy:Al,Al-Si,Al-Si-Cu,Cu(2)HeavilydopedpolySi:n+-Poly-Si,p+-Poly-Si(3)Refractorymetals:W,Ta...(4)Metalsilicide:TiSi2,CoSi2,PtSi,NiSi,WSi2(5)Othermetalalloyandcompound:TiN,WN…+Differentdielectricfilms:Inorganic:SiO2,PSG,BSG,BPSG,FSGOrganicpolymers2.Combinationofvariousprocessingtechnology(1)Self-alignedtechnology:9Self-alignedpoly-Sigateandpolycidegatetechnology9Self-alignedsilicidecontactandgatetechnology(salicide)(2)Diffusionbarriertechnology(3)MultilevelinterconnectionCMOS:0.5μm---3-4Levels;0.35μm---4-5Levels;130nm--8Levels;90nm--9;65nm—11;45nm-12;32nm-13;20nm-14Levels(byITRS-05)(4)LayeredmetallizationstructureSi(Al)/Contact(adhesion)layer/Diffusionbarrierlayer/Verticalinterconnection/Lateralinterconnection/Anti-reflection(capping)coating(5)Newmaterialsandprocesstechniquessupportingabovetechnologies‹TypicalcrosssectionofadvancedCMOSinterconnection‹AdvancedC&Itechnologydependson:¾Introductionofnewmaterials¾Integrationofnewprocessesandstructures3.Variousthinfilmdeposition,formationandetchingtechnologies¾Sputtering¾Evaporation¾CVD¾Solidstatereaction¾Reactiveionetching¾Selectiveetching(wet&dry)¾Planarizationtechniques:CMP;Etchingbackprocess4.Requirementsforgateelectrodeandinterconnectsmaterials:¾Lowresistivity¾Hightemperaturestability(~1000°C)¾Finelineetchingcapability¾Easytopassivation¾ChemicalstabilitytothecommonlyusedsolutionsinICprocess¾LowcontactresistancewithSi&metals¾ResistancetoElectromigration5.RequirementsforOhmicContacts¾Lowcontactresistivity¾Limitedinterfaceinteraction¾InterfaceuniformityandstabilityRCDelayTimeof1cminterconnectlineonSiO2(1μm)/SifordifferentmaterialsMaterialResistivity(μΩ·cm)Thickness(nm)RS(Ω/□)RC(ns/cm)Al2.72500.110.4Cu2.02500.080.3W82500.321.1Mo82500.321.1TiSi2152500.62.1CoSi2152500.62.1NiSi152500.62.1WSi2702502.89.7MoSi2~100250413.8TaSi2552502.27.6TiN5025026.9PolySi~10005002069III.ContactResistance‹TwotypesofMetal/Sicontacts¾Schottkycontactonn-Si¾Ohmiccontactonn+-Si‹ForND≤1017cm-3:CurrentflowbythermionicemissionA*:Richardsonconstant;ΦB:Barrierheight]1))[exp(/exp(2*−−=KTqVKTqTAJBφ‹Specificcontactresistance(Rc)¾IfΦB=0.85V→Rc=4.7×105Ω·cm2Φ=0.25V→Rc=4×10-7Ω·cm2Rc(onp-Si)Rc(onn-Si)‹ForND1019cm-3:Currentflowbycarriertunnelingε–Dielectricpermittivity;m*–EffectivemassofcarrierA–Constant¾Example:IfLowerRcisneededfordeepsub-μCMOS])[exp(*20cmKTqTqAKdJdVRBVc•Ω===φ)](*4exp[DBcNhmARφεπ≈26101cmRc•Ω×≈−Ω==→×−−100)10(1011246RμμΩ=×400:5.05.0Rμμ‹Totalresistanceofacontact:r=rs+rcrs–spreadingresistanceofsemiconductorundercontact(Ω)rc–contactresistance(Ω)Bothrs,rcdependondopingandcontactsize‹Typicalvalueoftotalresistanceforacontact:r≈10-100Ω/contact‹WithshrinkageofcontactsizelowerspecificcontactresistanceisrequiredIV.Al/SiOhmicContactandInterconnect1.Al--ExtensivelyusedinterconnectmaterialforIC¾No.3materialforSidevicesfabricationafterSi,SiO2‹LowResistivity:P≈2.7μΩ·cm‹CompatibilitywithSi&SiO2‹GoodadhesionwithSiO2duetoslightreactiontoformAl2O3atAl/SiO2interface‹MatureAlprocessingtechnology¾Deposition(evaporationÆsputtering)¾Etching(wetÆdry)2.Twoproblems(1)AlspikingAlmeltingpoint--660°CAl-SieutecticT--577°CAtT577°C:¾Highsolubility&diffusivityofSiinAl:Æ“Etching”ofSibyAlÆSi,AlinterdiffustionÆPitsinSisurfaceÆAl-SpikingÆpnjunctionfailure¾OrientationeffectofAlspiking9ASpikingismoresevereo