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1、,Semiconductor Manufacturing TechnologyMichael Quirk&Julian Serda October 2001 by Prentice HallChapter 13 Photolithography:Surface Preparation to Soft Bake,2000 by Prentice Hall,Semiconductor Manufacturing Technologyby Michael Quirk and Julian Serda,Objectives,After studying the material in this cha
2、pter,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 steps to photoli
3、thography.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,including chemically
4、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.,Wafer Fabrication Process Flow,Used with permission from Advanced Micro Devices,Figure 13.1,Patterning ProcessPhotomaskReticleCritical Dimension
5、GenerationsLight SpectrumResolutionOverlay AccuracyProcess Latitude,Photolithography Concepts,Photomask and Reticle for Microlithography,Photograph provided courtesy of Advanced Micro Devices,Photo 13.1,Three Dimensional Pattern in Photoresist,Figure 13.2,Section of the Electromagnetic Spectrum,Figu
6、re 13.3,Important Wavelengths for Photolithography Exposure,Table 13.1,Importance of Mask Overlay Accuracy,Figure 13.4,Photolithography Processes,Negative ResistWafer image is opposite of mask imageExposed resist hardens and is insolubleDeveloper removes unexposed resistPositive ResistMask image is
7、same as wafer imageExposed resist softens and is solubleDeveloper removes exposed resist,Negative Lithography,Figure 13.5,Positive Lithography,Figure 13.6,Relationship Between Mask and Resist,Figure 13.7,Clear Field and Dark Field Masks,Figure 13.8,Eight Steps of Photolithography,Table 13.2,Eight St
8、eps of Photolithography,Figure 13.9,Photolithography Track System,Photo courtesy of Advanced Micro Devices,TEL Track Mark VIII,Photo 13.2,Vapor Prime,The First Step of Photolithography:Promotes Good Photoresist-to-Wafer AdhesionPrimes Wafer with Hexamethyldisilazane,HMDSFollowed by Dehydration BakeE
9、nsures Wafer Surface is Clean and Dry,Spin Coat,Figure 13.10,Soft bake,Characteristics 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
10、ut 30 SecondsOn a Hot PlateFollowed by Cooling Step on Cold Plate,Alignment and Exposure,Figure 13.11,Post-Exposure Bake,Required for Deep UV ResistsTypical Temperatures 100 to 110C on a hot plateImmediately after ExposureHas Become a Virtual Standard for DUV and Standard Resists,Photoresist Develop
11、ment,Figure 13.12,Hard Bake,A Post-Development Thermal BakeEvaporate Remaining SolventImprove Resist-to-Wafer AdhesionHigher Temperature(120 to 140C)than Soft Bake,Develop Inspect,Inspect to Verify a Quality PatternIdentify Quality Problems(Defects)Characterize the Performance of the Photolithograph
12、y ProcessPrevents Passing Defects to Other AreasEtchImplantRework Misprocessed or Defective Resist-coated WafersTypically an Automated Operation,Vapor Prime,Wafer CleaningDehydration BakeWafer PrimingPriming TechniquesPuddle Dispense and SpinSpray Dispense and SpinVapor Prime and Dehydration Bake,Ef
13、fect of Poor Resist Adhesion Due to Surface Contamination,Figure 13.13,HMDS Puddle Dispense and Spin,Figure 13.14,HMDS Hot Plate Dehydration Bake and Vapor Prime,Figure 13.15,The Purpose of Photoresist in Wafer Fab,To transfer the mask pattern to the photoresist on the top layer of the wafer surface
14、To protect the underlying material during subsequent processing e.g.etch or ion implantation.,Successive Reductions in CDs Lead to Progressive Improvements in Photoresist,Better image definition(resolution).Better adhesion to semiconductor wafer surfaces.Better uniformity characteristics.Increased p
15、rocess latitude(less sensitivity to process variations).,PhotoresistTypes of PhotoresistNegative Versus Positive PhotoresistsPhotoresist Physical PropertiesConventional I-Line PhotoresistsNegative I-Line PhotoresistsPositive I-Line PhotoresistsDeep UV(DUV)PhotoresistsPhotoresist Dispensing Methods,S
16、pin Coat,Types of Photoresists,Two Types of PhotoresistPositive ResistNegative ResistCD CapabilityConventional ResistDeep UV ResistProcess ApplicationsNon-critical LayersCritical Layers,Negative Versus Positive Resists,Negative ResistWafer image is opposite of mask imageExposed resist hardens and is
17、 insolubleDeveloper removes unexposed resistPositive ResistMask image is same as wafer imageExposed resist softens and is solubleDeveloper removes exposed resistResolution IssuesClear Field Versus Dark Field Masks,Photoresist Physical Characteristics,ResolutionContrastSensitivityViscosityAdhesionEtc
18、h resistanceSurface tensionStorage and handlingContaminants and particles,Resist Contrast,Figure 13.16,Surface Tension,Figure 13.17,Components of Conventional Photoresist,Figure 13.18,Negative Resist Cross-Linking,Figure 13.19,PAC as Dissolution Inhibitor in Positive I-Line Resist,Figure 13.20,Good
19、Contrast Characteristics of Positive I-line Photoresist,Figure 13.21,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
20、used with permission from USHIO Specialty Lighting Products,Figure 13.22,Chemically Amplified(CA)DUV Resist,Figure 13.23,Exposure Steps for Chemically-Amplified DUV Resist,Table 13.5,Steps of Photoresist Spin Coating,Figure 13.24,Automated Wafer Track for Photolithography,Figure 13.25,Photoresist Di
21、spense Nozzle,Figure 13.26,Resist Spin Speed Curve,Used with permission from JSR Microelectronics,Inc.,Figure 13.27,Soft Bake on Vacuum Hot Plate,Purpose of Soft Bake:Partial evaporation of photoresist solventsImproves adhesionImproves uniformityImproves etch resistanceImproves linewidth controlOptimizes light absorbance characteristics of photoresist,Figure 13.28,Solvent Content of Resist Versus Temperature During Soft Bake,Figure 13.29,Chapter 13 Review,Quality Measures362Troubleshooting363Summary364Key Terms364Review Questions364Equipment Suppliers Web Sites365References365,
