1、 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaSemiconductor Manufacturing TechnologyMichael Quirk & Julian Serda October 2001 by Prentice HallChapter 13 Photolithography: Surface Preparation to Soft Bake 2000 by Prentice HallSemiconductor Manufacturing
2、Technologyby Michael Quirk and Julian Serda 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaObjectivesAfter studying the material in this chapter, you will be able to:1. Explain the basic concepts for photolithography, including process overview, critical
3、dimension generations, light spectrum, resolution and process latitude.2. Discuss the difference between negative and positive lithography.3. State and describe the eight basic steps to photolithography.4. Explain how the wafer surface is prepared for photolithography.5. Describe photoresist and dis
4、cuss 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, including chemically amplified resists.8. Explain how photoresist is applied in wafer manufacturing.9. Discuss the purpos
5、e of soft bake and how it is accomplished in production. 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaWafer Fabrication Process FlowImplantDiffusionTest/SortEtchPolishPhotoCompleted waferUnpatterned waferWafer startThin FilmsWafer fabrication (front-end
6、) Used with permission from Advanced Micro DevicesFigure 13.1 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda Patterning Process Photomask Reticle Critical Dimension Generations Light Spectrum Resolution Overlay Accuracy Process LatitudePhotolithography C
7、oncepts 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaPhotomask and Reticle for MicrolithographyPhotograph provided courtesy of Advanced Micro Devices4:1 Reticle1:1 MaskPhoto 13.1 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quir
8、k and Julian SerdaThree Dimensional Pattern in PhotoresistLinewidthSpaceThicknessSubstratePhotoresistFigure 13.2 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaSection of the Electromagnetic SpectrumVisibleRadio wavesMicro-wavesInfraredGamma raysUVX-raysf
9、 (Hz)1010101010101010101046810121416221820(m)420-2-4-6-8-14-10-1210101010101010101010365436405248193157ghiDUVDUVVUV (nm)Common UV wavelengths used in optical lithography.Figure 13.3 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaImportant Wavelengths for
10、Photolithography ExposureUV Wavelength(nm)WavelengthNameUV Emission Source436g-lineMercury arc lamp405h-lineMercury arc lamp365i-lineMercury arc lamp248Deep UV (DUV)Mercury arc lamp orKrypton Fluoride (KrF) excimer laser193Deep UV (DUV)Argon Fluoride (ArF) excimer laser157Vacuum UV (VUV)Fluorine (F2
11、) excimer laserTable 13.1 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaImportance of Mask Overlay AccuracyPMOSFETNMOSFETCross section of CMOS inverterTop view of CMOS inverterThe masking layers determine the accuracy by which subsequent processes can be
12、 performed. The photoresist mask pattern prepares individual layers for proper placement, orientation, and size of structures to be etched or implanted. Small sizes and low tolerances do not provide much room for error.Figure 13.4 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael
13、 Quirk and Julian SerdaPhotolithography Processes Negative Resist Wafer image is opposite of mask image Exposed resist hardens and is insoluble Developer removes unexposed resist Positive Resist Mask image is same as wafer image Exposed resist softens and is soluble Developer removes exposed resist
14、2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaNegative LithographyUltraviolet lightIslandAreas exposed to light become crosslinked and resist the developer chemical.Resulting pattern after the resist is developed.WindowExposed area of photoresistShadow o
15、n photoresistChrome island on glass maskSilicon substratePhotoresistOxidePhotoresistOxideSilicon substrateFigure 13.5 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaPositive LithographyFigure 13.6 photoresistsilicon substrateoxideoxidesilicon substratepho
16、toresistUltraviolet lightIslandAreas exposed to light are dissolved.Resulting pattern after the resist is developed.Shadow on photoresistExposed area of photoresistChrome island on glass maskWindowSilicon substratePhotoresistOxidePhotoresistOxideSilicon substrate 2001 by Prentice HallSemiconductor M
17、anufacturing Technologyby Michael Quirk and Julian SerdaRelationship Between Mask and ResistDesired photoresist structure to be printed on wafer WindowSubstrateIsland of photoresistQuartzChromeIslandMask pattern required when using negative photoresist (opposite of intended structure)Mask pattern re
18、quired when using positive photoresist (same as intended structure)Figure 13.7 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaClear Field and Dark Field MasksSimulation of contact holes(positive resist lithography)Simulation of metal interconnect lines(po
19、sitive resist lithography)Clear Field MaskDark Field MaskFigure 13.8 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaEight Steps of PhotolithographyTable 13.2 StepChapter1. Vapor prime132. Spin coat133. Soft bake134. Alignment and exposure145. Post-exposur
20、e bake (PEB)156. Develop157. Hard bake158. Develop inspect15 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaEight Steps of Photolithography8) Develop inspect5) Post-exposure bake6) Develop7) Hard bakeUV LightMask4) Alignment and ExposureResist2) Spin coat
21、3) Soft bake1) Vapor primeHMDSFigure 13.9 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaPhotolithography Track SystemPhoto courtesy of Advanced Micro Devices, TEL Track Mark VIIIPhoto 13.2 2001 by Prentice HallSemiconductor Manufacturing Technologyby Mic
22、hael Quirk and Julian SerdaVapor PrimeThe First Step of Photolithography: Promotes Good Photoresist-to-Wafer Adhesion Primes Wafer with Hexamethyldisilazane, HMDS Followed by Dehydration Bake Ensures Wafer Surface is Clean and Dry 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael
23、 Quirk and Julian SerdaSpin CoatProcess Summary:Wafer is held onto vacuum chuckDispense 5ml of photoresistSlow spin 500 rpmRamp up to 3000 to 5000 rpmQuality measures: time speed thickness uniformity particles and defectsVacuum chuckSpindle connected to spin motorTo vacuum pumpPhotoresist dispenserF
24、igure 13.10 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaSoft bakeCharacteristics of Soft Bake: Improves Photoresist-to-Wafer Adhesion Promotes Resist Uniformity on Wafer Improves Linewidth Control During Etch Drives Off Most of Solvent in Photoresist T
25、ypical Bake Temperatures are 90 to 100C For About 30 Seconds On a Hot Plate Followed by Cooling Step on Cold Plate 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaAlignment and ExposureProcess Summary:Transfers the mask image to the resist-coated waferActi
26、vates photo-sensitive components of photoresistQuality measures: linewidth resolution overlay accuracy particles and defectsUV light sourceMaskResistFigure 13.11 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaPost-Exposure Bake Required for Deep UV Resist
27、s Typical Temperatures 100 to 110C on a hot plate Immediately after Exposure Has Become a Virtual Standard for DUV and Standard Resists 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaPhotoresist DevelopmentProcess Summary:Soluble areas of photoresist are
28、dissolved 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 2001 by Prentice HallSemiconductor Manufacturing Technologyby M
29、ichael Quirk and Julian SerdaHard Bake A Post-Development Thermal Bake Evaporate Remaining Solvent Improve Resist-to-Wafer Adhesion Higher Temperature (120 to 140C) than Soft Bake 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaDevelop Inspect Inspect to V
30、erify a Quality Pattern Identify Quality Problems (Defects) Characterize the Performance of the Photolithography Process Prevents Passing Defects to Other Areas Etch Implant Rework Misprocessed or Defective Resist-coated Wafers Typically an Automated Operation 2001 by Prentice HallSemiconductor Manu
31、facturing Technologyby Michael Quirk and Julian SerdaVapor Prime Wafer Cleaning Dehydration Bake Wafer Priming Priming Techniques Puddle Dispense and Spin Spray Dispense and Spin Vapor Prime and Dehydration Bake 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian S
32、erdaEffect of Poor Resist Adhesion Due to Surface ContaminationFigure 13.13 Resist liftoff 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaHMDS Puddle Dispense and SpinPuddle formationSpin wafer to remove excess liquidFigure 13.14 2001 by Prentice HallSemi
33、conductor Manufacturing Technologyby Michael Quirk and Julian SerdaHMDS Hot Plate Dehydration Bake and Vapor PrimeWaferExhaustHot plateChamber coverProcess Summary:Dehydration bake in enclosed chamber with exhaustHexamethyldisilazane (HMDS) Clean and dry wafer surface (hydrophobic)Temp 200 to 250CTi
34、me 60 sec. Figure 13.15 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaThe Purpose of Photoresist in Wafer Fab To transfer the mask pattern to the photoresist on the top layer of the wafer surface To protect the underlying material during subsequent proce
35、ssing e.g. etch or ion implantation. 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaSuccessive Reductions in CDs Lead to Progressive Improvements in Photoresist Better image definition (resolution). Better adhesion to semiconductor wafer surfaces. Better
36、uniformity characteristics. Increased process latitude (less sensitivity to process variations). 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda Photoresist Types of Photoresist Negative Versus Positive Photoresists Photoresist Physical Properties Convent
37、ional I-Line Photoresists Negative I-Line Photoresists Positive I-Line Photoresists Deep UV (DUV) Photoresists Photoresist Dispensing MethodsSpin Coat 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaTypes of Photoresists Two Types of Photoresist Positive R
38、esist Negative Resist CD Capability Conventional Resist Deep UV Resist Process Applications Non-critical Layers Critical Layers 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaNegative Versus Positive Resists Negative Resist Wafer image is opposite of mask
39、 image Exposed resist hardens and is insoluble Developer removes unexposed resist Positive Resist Mask image is same as wafer image Exposed resist softens and is soluble Developer removes exposed resist Resolution Issues Clear Field Versus Dark Field Masks 2001 by Prentice HallSemiconductor Manufact
40、uring Technologyby Michael Quirk and Julian SerdaPhotoresist Physical Characteristics Resolution Contrast Sensitivity Viscosity Adhesion Etch resistance Surface tension Storage and handling Contaminants and particles 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Jul
41、ian SerdaResist ContrastPoor Resist ContrastSloped wallsSwellingPoor contrastResistFilmGood Resist ContrastSharp wallsNo swellingGood contrastResistFilmFigure 13.16 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaSurface TensionLow surface tension High sur
42、face tensionfrom low molecular from high molecular forces forcesFigure 13.17 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaComponents of Conventional PhotoresistAdditives: chemicals that control specific aspects of resist materialSolvent: gives resist it
43、s flow characteristicsSensitizers: photosensitive component of the resist materialResin: mix of polymers used as binder; gives resist mechanical and chemical propertiesFigure 13.18 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaNegative Resist Cross-Linki
44、ngAreas exposed to light become crosslinked and resist the developer chemical.Unexposed areas remain soluble to developer chemical.Pre-exposure- photoresistPost-exposure- photoresistPost-develop- photoresistUVOxidePhotoresistSubstrateCrosslinksUnexposedExposedSolubleFigure 13.19 2001 by Prentice Hal
45、lSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaPAC 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 developer chemical.Pre-exposure+ photoresis
46、tPost-exposure+ photoresistPost-develop+ photoresistUVOxidePhotoresistSubstrateSoluble resist ExposedUnexposedPACFigure 13.20 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaGood Contrast Characteristics of Positive I-line PhotoresistPositive Photoresist:S
47、harp wallsNo swellingGood contrastFilmResistFigure 13.21 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaDUV Emission Spectrum* Intensity of mercury lamp is too low at 248 nm to be usable in DUV photolithography applications. Excimer lasers, such as shown
48、on the left provide more energy for a given DUV wavelength. Mercury lamp spectrum used with permission from USHIO Specialty Lighting ProductsFigure 13.22 100806040200248 nmRelative Intensity (%)KrF laser emission spectrumEmission spectrum of high-intensity mercury lamp120100806040200200300 400 500 6
49、00Wavelength (nm)Relative Intensity (%)g-line436 nmi-line365 nmh-line405 nmDUV*248 nm 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian SerdaChemically Amplified (CA) DUV ResistResist exposed to light dissolves in the developer chemical.Unexposed resist remains c
50、rosslinked and PAGs are inactive.Pre-exposure+ CA photoresistPost-exposure+ CA photoresistPost-develop+ CA photoresistUVOxidePhotoresistSubstrateUnchanged ExposedUnexposedAcid-catalyzed reaction (during PEB)PAGPAGPAGPAGH+PAGPAGPAGH+H+PAGPAGFigure 13.23 2001 by Prentice HallSemiconductor Manufacturin
