Michaelquirk半導體制造技術(shù)第13章光刻氣相成底膜到軟烘課件

1、Semiconductor Manufacturing TechnologyMichael Quirk & Julian Serda October 2001 by Prentice HallChapter 13 Photolithography: Surface Preparation to Soft Bake 2000 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda 第1頁，共53頁。ObjectivesAfter studying the material in

2、 this chapter, you will be able to:1.Explain the basic concepts for photolithography, including process overview, critical dimension generations, light spectrum, resolution and process latitude.2.Discuss the difference between negative and positive lithography.3.State and describe the eight basic st

3、eps to photolithography.4.Explain how the wafer surface is prepared for photolithography.5.Describe photoresist and discuss photoresist physical properties.6.Discuss the chemistry and applications of conventional i-line photoresist.7.Describe the chemistry and benefits of deep UV (DUV) resists, incl

4、uding chemically amplified resists.8.Explain how photoresist is applied in wafer manufacturing.9.Discuss the purpose of soft bake and how it is accomplished in production. 第2頁，共53頁。Wafer Fabrication Process FlowImplantDiffusionTest/SortEtchPolishPhotoCompleted waferUnpatterned waferWafer startThin F

5、ilmsWafer fabrication (front-end) Used with permission from Advanced Micro DevicesFigure 13.1 第3頁，共53頁。Patterning ProcessPhotomaskReticleCritical Dimension GenerationsLight SpectrumResolutionOverlay AccuracyProcess LatitudePhotolithography Concepts 第4頁，共53頁。Photomask and Reticle for Microlithography

6、Photograph provided courtesy of Advanced Micro Devices4:1 Reticle1:1 MaskPhoto 13.1 第5頁，共53頁。Three Dimensional Pattern in PhotoresistLinewidthSpaceThicknessSubstratePhotoresistFigure 13.2 第6頁，共53頁。Section of the Electromagnetic SpectrumVisibleRadio wavesMicro-wavesInfraredGamma raysUVX-raysf (Hz)101

7、0101010101010101046810121416221820(m)420-2-4-6-8-14-10-1210101010101010101010365436405248193157ghiDUVDUVVUVl (nm)Common UV wavelengths used in optical lithography.Figure 13.3 第7頁，共53頁。Important Wavelengths for Photolithography ExposureTable 13.1 第8頁，共53頁。Importance of Mask Overlay AccuracyPMOSFETNMO

8、SFETCross section of CMOS inverterTop view of CMOS inverterThe masking layers determine the accuracy by which subsequent processes can be performed. The photoresist mask pattern prepares individual layers for proper placement, orientation, and size of structures to be etched or implanted. Small size

9、s and low tolerances do not provide much room for error.Figure 13.4 第9頁，共53頁。Photolithography ProcessesNegative ResistWafer image is opposite of mask imageExposed resist hardens and is insolubleDeveloper removes unexposed resistPositive ResistMask image is same as wafer imageExposed resist softens a

10、nd is solubleDeveloper removes exposed resist 第10頁，共53頁。Negative LithographyUltraviolet lightIslandAreas exposed to light become crosslinked and resist the developer chemical.Resulting pattern after the resist is developed.WindowExposed area of photoresistShadow on photoresistChrome island on glass

11、maskSilicon substratePhotoresistOxidePhotoresistOxideSilicon substrateFigure 13.5 第11頁，共53頁。Positive LithographyFigure 13.6 photoresistsilicon substrateoxideoxidesilicon substratephotoresistUltraviolet lightIslandAreas exposed to light are dissolved.Resulting pattern after the resist is developed.Sh

12、adow on photoresistExposed area of photoresistChrome island on glass maskWindowSilicon substratePhotoresistOxidePhotoresistOxideSilicon substrate第12頁，共53頁。Relationship Between Mask and ResistDesired photoresist structure to be printed on wafer WindowSubstrateIsland of photoresistQuartzChromeIslandMa

13、sk pattern required when using negative photoresist (opposite of intended structure)Mask pattern required when using positive photoresist (same as intended structure)Figure 13.7 第13頁，共53頁。Clear Field and Dark Field MasksSimulation of contact holes(positive resist lithography)Simulation of metal inte

14、rconnect lines(positive resist lithography)Clear Field MaskDark Field MaskFigure 13.8 第14頁，共53頁。Eight Steps of PhotolithographyTable 13.2 第15頁，共53頁。Eight Steps of Photolithography8) Develop inspect5) Post-exposure bake6) Develop7) Hard bakeUV LightMask4) Alignment and ExposureResist2) Spin coat3) So

15、ft bake1) Vapor primeHMDSFigure 13.9 第16頁，共53頁。Photolithography Track SystemPhoto courtesy of Advanced Micro Devices, TEL Track Mark VIIIPhoto 13.2 第17頁，共53頁。Vapor PrimeThe First Step of Photolithography:Promotes Good Photoresist-to-Wafer AdhesionPrimes Wafer with Hexamethyldisilazane, HMDSFollowed

16、by Dehydration BakeEnsures Wafer Surface is Clean and Dry 第18頁，共53頁。Spin CoatProcess Summary:Wafer is held onto vacuum chuckDispense 5ml of photoresistSlow spin 500 rpmRamp up to 3000 to 5000 rpmQuality measures:timespeedthicknessuniformityparticles and defectsVacuum chuckSpindle connected to spin m

17、otorTo vacuum pumpPhotoresist dispenserFigure 13.10 第19頁，共53頁。Soft bakeCharacteristics of Soft Bake:Improves Photoresist-to-Wafer AdhesionPromotes Resist Uniformity on WaferImproves Linewidth Control During EtchDrives Off Most of Solvent in PhotoresistTypical Bake Temperatures are 90 to 100C For Abo

18、ut 30 SecondsOn a Hot PlateFollowed by Cooling Step on Cold Plate 第20頁，共53頁。Alignment and ExposureProcess Summary:Transfers the mask image to the resist-coated waferActivates photo-sensitive components of photoresistQuality measures: linewidth resolutionoverlay accuracyparticles and defectsUV light

19、sourceMaskResistFigure 13.11 第21頁，共53頁。Post-Exposure BakeRequired for Deep UV ResistsTypical Temperatures 100 to 110C on a hot plateImmediately after ExposureHas Become a Virtual Standard for DUV and Standard Resists 第22頁，共53頁。Photoresist DevelopmentProcess Summary:Soluble areas of photoresist are d

20、issolved by developer chemicalVisible patterns appear on wafer- windows- islandsQuality measures:- line resolution- uniformity- particles and defectsVacuum chuckSpindle connected to spin motorTo vacuum pumpDevelop dispenserFigure 13.12 第23頁，共53頁。Hard BakeA Post-Development Thermal BakeEvaporate Rema

21、ining SolventImprove Resist-to-Wafer AdhesionHigher Temperature (120 to 140C) than Soft Bake 第24頁，共53頁。Develop InspectInspect to Verify a Quality PatternIdentify Quality Problems (Defects)Characterize the Performance of the Photolithography ProcessPrevents Passing Defects to Other AreasEtchImplantRe

22、work Misprocessed or Defective Resist-coated WafersTypically an Automated Operation 第25頁，共53頁。Vapor PrimeWafer CleaningDehydration BakeWafer PrimingPriming TechniquesPuddle Dispense and SpinSpray Dispense and SpinVapor Prime and Dehydration Bake 第26頁，共53頁。Effect of Poor Resist Adhesion Due to Surfac

23、e ContaminationFigure 13.13 Resist liftoff第27頁，共53頁。HMDS Puddle Dispense and SpinPuddle formationSpin wafer to remove excess liquidFigure 13.14 第28頁，共53頁。HMDS Hot Plate Dehydration Bake and Vapor PrimeWaferExhaustHot plateChamber coverProcess Summary:Dehydration bake in enclosed chamber with exhaust

24、Hexamethyldisilazane (HMDS) Clean and dry wafer surface (hydrophobic)Temp 200 to 250CTime 60 sec. Figure 13.15 第29頁，共53頁。The Purpose of Photoresist in Wafer FabTo transfer the mask pattern to the photoresist on the top layer of the wafer surfaceTo protect the underlying material during subsequent pr

25、ocessing e.g. etch or ion implantation. 第30頁，共53頁。Successive Reductions in CDs Lead to Progressive Improvements in PhotoresistBetter image definition (resolution).Better adhesion to semiconductor wafer surfaces.Better uniformity characteristics.Increased process latitude (less sensitivity to process

26、 variations). 第31頁，共53頁。PhotoresistTypes of PhotoresistNegative Versus Positive PhotoresistsPhotoresist Physical PropertiesConventional I-Line PhotoresistsNegative I-Line PhotoresistsPositive I-Line PhotoresistsDeep UV (DUV) PhotoresistsPhotoresist Dispensing MethodsSpin Coat 第32頁，共53頁。Types of Phot

27、oresistsTwo Types of PhotoresistPositive ResistNegative ResistCD CapabilityConventional ResistDeep UV ResistProcess ApplicationsNon-critical LayersCritical Layers 第33頁，共53頁。Negative Versus Positive ResistsNegative ResistWafer image is opposite of mask imageExposed resist hardens and is insolubleDeve

28、loper removes unexposed resistPositive ResistMask image is same as wafer imageExposed resist softens and is solubleDeveloper removes exposed resistResolution IssuesClear Field Versus Dark Field Masks 第34頁，共53頁。Photoresist Physical CharacteristicsResolutionContrastSensitivityViscosityAdhesionEtch res

29、istanceSurface tensionStorage and handlingContaminants and particles 第35頁，共53頁。Resist ContrastPoor Resist ContrastSloped wallsSwellingPoor contrastResistFilmGood Resist ContrastSharp wallsNo swellingGood contrastResistFilmFigure 13.16 第36頁，共53頁。Surface TensionLow surface tension High surface tension

30、from low molecular from high molecular forces forcesFigure 13.17 第37頁，共53頁。Components of Conventional PhotoresistAdditives: chemicals that control specific aspects of resist materialSolvent: gives resist its flow characteristicsSensitizers: photosensitive component of the resist materialResin: mix o

31、f polymers used as binder; gives resist mechanical and chemical propertiesFigure 13.18 第38頁，共53頁。Negative Resist Cross-LinkingAreas exposed to light become crosslinked and resist the developer chemical.Unexposed areas remain soluble to developer chemical.Pre-exposure- photoresistPost-exposure- photo

32、resistPost-develop- photoresistUVOxidePhotoresistSubstrateCrosslinksUnexposedExposedSolubleFigure 13.19 第39頁，共53頁。PAC as Dissolution Inhibitor in Positive I-Line ResistResist exposed to light dissolves in the developer chemical.Unexposed resist, containing PACs, remain crosslinked and insoluble to d

33、eveloper chemical.Pre-exposure+ photoresistPost-exposure+ photoresistPost-develop+ photoresistUVOxidePhotoresistSubstrateSoluble resist ExposedUnexposedPACFigure 13.20 第40頁，共53頁。Good Contrast Characteristics of Positive I-line PhotoresistPositive Photoresist:Sharp wallsNo swellingGood contrastFilmRe

34、sistFigure 13.21 第41頁，共53頁。DUV Emission Spectrum* Intensity of mercury lamp is too low at 248 nm to be usable in DUV photolithography applications. Excimer lasers, such as shown on the left provide more energy for a given DUV wavelength. Mercury lamp spectrum used with permission from USHIO Specialt

35、y Lighting ProductsFigure 13.22 100806040200248 nmRelative Intensity (%)KrF laser emission spectrumEmission spectrum of high-intensity mercury lamp120100806040200200300 400 500 600Wavelength (nm)Relative Intensity (%)g-line436 nmi-line365 nmh-line405 nmDUV*248 nm第42頁，共53頁。Chemically Amplified (CA) D

36、UV ResistResist exposed to light dissolves in the developer chemical.Unexposed resist remains crosslinked and PAGs are inactive.Pre-exposure+ CA photoresistPost-exposure+ CA photoresistPost-develop+ CA photoresistUVOxidePhotoresistSubstrateUnchanged ExposedUnexposedAcid-catalyzed reaction (during PE

37、B)PAGPAGPAGPAGH+PAGPAGPAGH+H+PAGPAGFigure 13.23 第43頁，共53頁。Exposure Steps for Chemically-Amplified DUV ResistTable 13.5 第44頁，共53頁。Steps of Photoresist Spin Coating3) Spin-off4) Solvent evaporation1) Resist dispense2) Spin-upFigure 13.24 第45頁，共53頁。Wafer Transfer SystemLoad stationTransfer stationVapor primeResist coatDevelop and rinseEdge-bead removalSoft bakeCool plateCool plateHard bakeWafer stepper (