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Hybrid bonding methods for lower temperature 3 d integration 1


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* Overview of primary 3D bonding processes
* Mechanics of metal bonding options
* Mechanics for hybrid bond materials
* Process requirement comparisons
* Equipment requirements for hybrid bond processes

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Hybrid bonding methods for lower temperature 3 d integration 1

  1. 1. Hybrid Bonding Methods for Lower Temperature 3D Integration James Hermanowski October 2010
  2. 2. 2 Overview Overview of primary 3D bonding processes Mechanics of metal bonding options Mechanics for hybrid bond materials Process requirement comparisons Equipment requirements for hybrid bond processes Summary
  3. 3. 3 Expanding CE (consumer electronics) market drives the Semiconductor innovation Push for integration Reduction in power consumption Smaller form factor Image sensors and memory stacking (for mobile applications) are two mass volume applications for TSVs with close time-to-market 1980‘s1950‘s Today Enabling new devices 3D Integration: Stacking for Higher Capacity
  4. 4. 4 Fusion / Adhesive Bonding Lithography, Adhesive Bonding CMOS ImageSensor CMOS Image Sensor Integration (BSI) CMOS Image Sensor Packaging Wafer Level Optics Assembly Imprinting, UV Bonding Kodak / Intel / Samsung Memory Stacking DRAM FLASH NAND Metal to Metal Bonding Fusion bonding Adhesive Bonding SUSS Equipment for 3D Packaging
  5. 5. 5 3D IC Process Sequence Variations A&C B&D E F G H I Lithography Temp. Bonding Aligning and Bonding (Permanent) Source: Phil Garrou, MCNC 2008 Test
  6. 6. 6 3D IC Process Sequence Variations "face-up" Bond (metal bonding)TSV from back (vias first)Wafer Thinning (temp. handle)No TSVI TSV from front (vias last)"face-up" Bond (all methods)Wafer Thinning (temp. handle)No TSVH TSV from back (vias last)Wafer Thinning (on 3D stack)"face-down" Bond (all methods)No TSVG "face-up" Bond (metal bonding)Wafer Thinning (temp. handle)TSV from front (vias first)No TSVF Wafer Thinning (on 3D stack)"face-down" Bond (metal bonding)TSV from front (vias first)No TSVE Wafer Thinning (on 3D stack)"face-down" Bond (metal bonding)BEOL TSV (vias first)D "face-up" Bond (metal bonding)Wafer Thinning (temp. handle)BEOL TSV (vias first)C Wafer Thinning (on 3D stack)"face-down" Bond (metal bonding)FEOL TSV (vias first)B "face-up" Bond (metal bonding)Wafer Thinning (temp. handle)FEOL TSV (vias first)A Step #3Step #2Step #1IC WaferProcess
  7. 7. 7 Logic to Logic Stacking using Cu-Cu Metal to Metal 3D Technology at the 300mm Wafer to Wafer Level SOURCE: Intel Developers ForumSOURCE: Intel Developers Forum
  8. 8. 8 Stacked Memory Modules using Cu-Cu Metal to Metal 3D Method SOURCE: Intel Developers Forum
  9. 9. 9 3D Structure using Wafer Level Cu-Cu Bonding
  10. 10. 10 Silicon Direct Bonded 3D Chip to Wafer Example DBI employs a chemo-mechanical polish to expose metal patterns embedded in the silicon-oxide surface of each chip. When the metal connection points of each chip are placed in contact using the company's room-temperature die- to-wafer bonding technology, the alignment is preserved, as opposed to other bonding techniques that apply heat or pressure that can result in misalignment. The oxide bonds create high bond energy between the surfaces, which brings the metal contact points close to each other to form effective electrical connections between chips after a 350°C anneal.
  11. 11. 11 RPI/Albany Nanotech and IBM, Freescale Approach using BCB
  12. 12. 12 Preparation for Cu-BCB Hybrid Bonding 1. Cu on Device Layer on Si 2. Pattern Cu (this gives larger vias) 3. Coat w/ BCB 4. Planarize/Expose Cu Nails
  13. 13. 13 Preparation for Cu-SiO2 Hybrid Bonding 1. Oxide on Device Layer on Si 4. Planarize to Cu Nails 2. DRIE Etch Via holes 3. Fill Via holes w/ Cu
  14. 14. 14 Requirements for Diffusion Bonding Proper materials system: Rapid Diffusion at Low Temperature Same crystal structure best Minimal size difference High Solubility High mobility and small activation energy Diffusion Barriers to protected regions High Quality films - No contamination or oxide layer for metals Intimate Contact between surfaces Process Variables Heat Pressure Gas Ambient Process Vacuum levels
  15. 15. 15 Complete Solid Solubility • Both Cu and Ni are FCC crystals • ρ(Cu)=8.93 gm/cm3 • ρ(Ni)=8.91 gm/cm3 • Lattice Spacing a0(Cu)=3.6148Å • Lattice Spacing a0(Ni)=3.5239Å Copper (Cu) - Nickel (Ni) αα liqliq CuCu NiNi
  16. 16. 16 Microstructure Development Interface Properties 1. Generally retain elastic properties of noble metals. 2. Resistivity usually obeys Vegard’s rule - linear with % atomic concentration of mix. 3. Full layer diffusion not needed. 4. Adhesion layers may be needed for initial substrate deposition process. 5. Diffusion barrier may be incorporated with adhesion layer to prevent diffusion into substrate. 6. Wetting agents between A & B layers assists in initialization of diffusion. Silicon Silicon Metal A (Ni) Metal B (Cu) Fully mixed with
  17. 17. 17 Diffusion Bonding 1. The mechanical force of the bonder establishes intimate contact between the surfaces. Some plastic deformation may occur. 2. During heating the atoms migrate between lattice sites across the interface to establish a void free bond. RMS <2-5 nm required. 3. Vacancies and grain boundaries will exist in final interface area. Hermeticity is nearly identical to a bulk material.
  18. 18. 18 Diffusion Pathways in Crystals: Poly vs Single Single CrystallineFine Grain Poly- Crystalline Dsurface > Dgrain.boundary > Dbulk Course Grain Poly- Crystalline
  19. 19. 19 Type A Kinetics: Rapid Bulk Diffusion Rates In Type A kinetics the lattice diffusion rates are rapid and diffusion profiles overlap between adjacent grains. gbgb gbgb gbgbgbgbbulk bulk bulk
  20. 20. 20 In type B kinetics the grain boundary is isolated between grains. Behavior mimics bulk diffusion. Diffusion is by both grain boundaries and bulk atomic motion. Dominate pathways are related to grain size and density. Type B Kinetics: Normal Bulk Diffusion w/ GB Effect gbgb gbgb gbgbgbgbbulk bulk bulk
  21. 21. 21 In Type C kinetics the lattice diffusion rate is insignificant and all atomic transport is dominated by grain boundary diffusion only For example room temperature diffusion. Type C Kinetics: Insignificant Bulk Diffusion gbgb gbgb gbgbgbgbbulk bulk bulk
  22. 22. 22 6 4 2 0 -6 -4 -2 6 4 2 0 -6 -4 -2 2 40 6 8 10 12 6 4 2 0 -6 -4 -2 2 40 6 8 10 12 Log[1/g.s.(cm)] Log ρd (cm-2) Log ρd (cm-2) Log[1/g.s.(cm)] T/Tm = 0.3T/Tm = 0.4 T/Tm = 0.6 T/Tm = 0.5 gbgb gbgbgbgb gbgb ll ll ll ll dddd dd dd • Regimes of grain size (g.s.) and dislocation density ρd over which (l) lattice diffusion, (gb) grain boundary diffusion of (d) dislocation diffusion is the dominate mechanism for atomic motion. • All data is normalized to the melting point and applies for a thin film fcc metal at steady state. • Shaded area is typical of thin film dislocation density 108 to 1012 lines/cm2. Low Temperature Diffusion Relies on Defects
  23. 23. 23 Metal Bonding Options Reaction Type Metal † Bond Temp Oxidizes CMOS Compatible Cu-Cu >350°C No Yes Au-Au >300°C Yes No Al-Ge >419°C No Yes Au-Si >363°C Yes No Au-Ge >361°C Yes No Au-Sn >278°C No No Cu-Sn >231°C No Yes † Eutectic bonds are done ~15°C above the listed eutectic tempereature. Diffusion bonds lower limit expressed. Diffusion Eutectic CMOS compatibility –barrier layers are often used to prevent metal migration to the CMOS structure.
  24. 24. 24 Key Unique Requirements for Metal Bonds Surface roughness is important to allow the metal surfaces to come into intimate contact, especially for diffusion bonding Metal oxide formation can prevent strong bond formation Preventive actions and process controls need to be established Force requirements are much tougher Structural issues with bond chamber will become much more apparent during metal bonding For example, the chamber shape may change with the application of high heat and force causing unbonded areas to form in the devices Temperature controls will be pushed harder To obtain the tighter overlay possible with metal bonding, it is important to control both wafers to tight temperature tolerances To prevent oxide formation, it is more desireable to load wafers at lower temperatures into the bond chamber
  25. 25. 25 Gold-Gold bond at 300°C for 30 min. Au layer is 350nm, Cr is 50nm thick 0.5μm AuAu AuAu CrCr CrCr SiSi SiSi InterfaceInterface 0.5μm AuAu AuAu CrCr CrCr SiSi SiSi InterfaceInterface Surface roughness is important to maintain intimate contact and good bonds.
  26. 26. 26 Thin (400nm) Cu/Cu bonds at 300°C for 30 min. 1μm Si Si Cu Cu Interface Interface 1μm1μm Si Si Cu Cu Interface Interface Ultra smooth surfaces allow better molecular intermixing and deliver good bond quality
  27. 27. 27 Common Polymer Material Choices Company Dow Toray Sumitomo Sumitomo Dow Corning HD-Micro HD-Micro MicroChem Trade Name Cyclotene PWDC-1000 CRC-8000 CRX 2580P WL-5000 HD-2771 HD-3003XP SU8 Material BCB PI PBO PI Silicone PI PI Epoxy PhotoPatternable Both Negative Positive Positive Yes Yes Negative Yes Negative Both Negative Residual Stress (MPa) 28 28 60 <6.4 Moisture Uptake (%) 0.23 0.6 0.3-0.9 0.06 ~0.2 >1.0 0.08% Coefficient of Thermal Expansion (ppm/°C) 52 36 51 100 <236 42 124 52 Glass Transistion Temperature (°C) >350 295 294 188 50-55 Cure Temperature (°C) 210-250 250+ 320 200 <250 >350 220 95 Dielectric Constant 2.65 2.9 2.65 <3.3 3 3.4 Modulus (GPa) 2.9 2.9 2.9 1.6 0.15-0.335 2.7 2.4 4 Thermal Stability (%loss at 350C/1hr) 2 <1 5 <6 <1 <1 Shrinkage During Cure (%) 2.5 <2 40-50 <0.04% Minimum Thickness (µm) 1 3 3 10 2 4 1 5 Storage Temperature (°C) -15 4 -15 r.t. or -18 Shelf Life (mos.) 6 6 6 12 @ -18C
  28. 28. 28 BCB Phase Diagram: Tailored Solutions Liquid Solid • Control of bond kinetics allows interface to become more or less compliant to device layers and structures. • Control of phase transformation and gaseous byproducts happens during both the pre-cure and the final bond process. 65°C 100°C 125°C 150°C 175°C
  29. 29. 29 Hybrid Cu/BCB Bonds Sample # Lx Ly Rx Ry 92 -1.45 -0.75 -0.55 0.40 Benefits to maintaining alignment while bonding metal with BCB as a supporting layer and interlayer dielectric
  30. 30. Equipment for Permanent & Temporary Bonding for 3D Integration
  31. 31. 31 Permanent Bonding Cu-Cu Bonding Polymer / Hybrid Bonding Fusion Bonding Temporary Bonding/De-bonding capability Thermoplastics Process (eg. HT10.10) 3M WSS Process Dupont / HD Process Thin Materials AG (TMAT) Process Total Process Flexibility for 3D Applications XBC300 Standardized Platform
  32. 32. 32 XBC300 Configuration Examples SC300 For adhesive coating Module 3 PL300 (TMAT) Laser module DB300 Tape on frame LF300 SC300 for cleaning (optional) Temporary Bonding De-bonding
  33. 33. 33 True Modular Design
  34. 34. 34 True Modular Design
  35. 35. 35 True Modular Design
  36. 36. 36 True Modular Design True Modular Design Lowers investment risk Ideal for changing technology requirements Lowers COO Small footprint, high throughput
  37. 37. 37 BA300UHP Aligner CB300 Bonder CP300 Cool Plate SC300 Spin Coater PL300T Surface Prep LF300 Low Force Bonder DB300 Debonder Temporary Bonding Permanent Bonding CL300 Wafer Cleaning PL300 Plasma Activation Process Flexibility: Complete Line of Process Modules
  38. 38. 38 Permanent Bonding Configurations BA300UHP Aligner CB300 Bonder CP300 Cool Plate Fusion Bond Configuration Cu-Cu and Polymer Bond Configuration* BA300UHP Aligner (if alignment with keys required) PL300 Plasma Activation CL300 Wafer Cleaning *Optional Die to Wafer Collective Bonding
  39. 39. 39 Permanent Bond Configurations BA300UHP Bond Aligner – submicron alignment accuracy CB300 Bond Chamber – temperature & force uniformity CP300 Cool Plate – controlled cool rate *Optional Die to Wafer Collective Bonding Cu-Cu and Polymer Bond Configuration*
  40. 40. 40 Sub Micron Alignment Accuracy Path to 350nm PBA for Cu-Cu bonding Path to 150nm PBA for Fusion bonding ISA alignment mode for face to face alignment Allows smaller via diameters and higher via densities Built in Wedge Error Compensation (WEC) to make upper and lower wafers parallel prior to alignment Eliminates wafer shift during wafer clamping Closed loop optical tracking of mechanical movements Void free bonding in the BA with RPP™ Patent pending RPP™ creates an engineered bond wave for propagation Eliminates need for bond module BA300UHP Bond Aligner Module
  41. 41. 41 Fusion Bonding in the BA300UHP Wafers are loaded and vacuum held against SiC chucks Chucks and the vacuum or pressure, that can be controlled between the chuck and the backside of the wafer, “engineers” the shape of the bonding surface The chucks are used to align and bring the wafers into contact The chucks are also used to engineer the bond wave from center to edge using RPP (Radial Pressure Propagation). Click icon for RPP Presentation XBC300 Wafer Bonder RPP (Radial Pressure Propagation) in the BA300UHP Aligner Module
  42. 42. 42 Si C Chuck & Tool Fixture (Patent Pending) Transports aligned pair from BA300 to CB300 Delivers reproducible submicron alignment capabilities Maintains wafer to wafer alignment throughout all process and transfer steps No exclusion zone required for clamping Maintains alignment accuracy through temperature ramp Chuck CTE matches Si CTE Increases throughput by reduction of thermal mass
  43. 43. 43 CB300 Bond Chamber Module Production Requirement Closed Bond Chamber Contamination Free Open chamber lid introduces air- turbulence and particles into bond chamber Uniform heat Open chamber lid causes temperature gradient between the front and back 3 Post Superstructure takes force, not bond chamber Chamber lid is the structural force carrying element in clam shell design– this causes force distortion Safety Opening chamber lid exposes user to high temperatures
  44. 44. 44 CB Chamber Force Uniformity Excellent Force Uniformity Within ±5% pressure uniformity Patented Pressure Column Technology for up to 90kN of bond force Load Cell Verification Bond Force options Standard: 3kN to 60kN High Force Option: 3kN to 90kN Traditional PistonTraditional Piston Bond- Interface SUSS Pressure Column TechnologySUSS Pressure Column Technology
  45. 45. 45 CB Chamber Thermal Design Superior Thermal Performance Within ±1.5% temperature uniformity Fast ramp (to 30°C/min) and cool rate (to 20°C/min) Matched top and bottom stack assemblies Perfect symmetry Multi-zone, vacuum-isolated heaters Dramatically reduces hot spots and burnouts Eliminates edge effects
  46. 46. 46 CB Chamber Structural Design Best-in-Class Post Bond Alignment ±1.5µm post bond alignment for metal bonds Rigid superstructure Solid alignment stability High planarity silicon carbide chucks Maintains long term planarity for superior post-bond alignment accuracy
  47. 47. 47 CP300 Cool Plate Module Fixture and wafer cooling Unclamp, unload, and optional fixture load Queuing and buffer station for fixtures and wafers
  48. 48. 48 CL300 Wafer Cleaning Module for Fusion Bonding Wet spin process for wafer cleaning Twin ultrasonic head IR Assisted Drying NH4OH chemistry Simultaneous clean, mechanical align and bond two wafers Bond initiation integrated into CL300 Closed process chamber for maximum particle protection Rated for particle sizes down to 100nm Design based on CFD (computational fluid dynamic) modeling Example of KLA data w/ no adders down to 100nm CFD modeling of chamber
  49. 49. 49 PL300 Plasma Activation Module for Fusion Bonding Cleaning & surface conditioning for fusion bonding Simple operation with plasma activation times in <30 seconds Enables high bond strength at low annealing temperatures Vacuum chamber based plasma system Uniform glow plasma Power supply options for frequency and power level Ex: 100kHz/300W; 13.56MHz; 2.4GHz Automatic tuning Input gases with up to 4 MFCs Radially designed high conductance plenum and vacuum system
  50. 50. 50 Summary Metal, fusion and hybrid bond processes have been reviewed Hybrid bond processes require mixture of metal bond processing with either oxide bonding or polymer bond process modules Tool flexibility is important Metal hybrid bonding processes are being implemented as the next generation solution Although metal hybrid bonding processes have many advantages over other approaches they also require much more from the process equipment For example much more stringent specs for force and thermal control Process equipment proven to satisfy these requirements has been presented