Materials, Process and Production Equipment Considerations to Achieve High-Yield MicroLED Mass-Production

Transcription

1 Materials, Process and Production Equipment Considerations to Achieve High-Yield MicroLED Mass-Production Francois J. Henley April 10,

2 Agenda MicroLED Displays: the next display tech Benefits and Challenges Considerations to achieve high-quality, high-yield microled displays MicroLED Source Substrate Growth Template MOCVD microled growth & device formation MicroLED Test/Inspection EL (or PL?) functional test Color Measurement Assembly Technology Selection of effective mass-transfer technologies supporting mass-production Connection Technology A comprehensive solution to µled manufacturing EPI, Test, Mass-Transfer & Interconnect Conclusions 2

3 New Technologies can be Daunting at First How did THIS look in the early days? They ll be millions made. In every home. Color too. Not very believable. 3

4 Then in the early 90s. Active-Matrix TFT-LCD Displays Many elements, large process size High cost and low performance/yield at first. 4

5 Photon Dynamics (PDI) => Orbotech => KLA-Tencor TFT-LCD Flat-Panel Display Test Company F. Henley PDI Founder, VP Engineering, President, COO/CTO 1986 to 1997 Developed Voltage Imaging TFT Array Test Source: Photon Dynamics, Inc. 5

6 Next Display Evolution: Micro-LEDs LCD Many elements Relatively expensive Uses LED backlight with 6x brightness loss Micro-LED Direct light emission Relatively inexpensive Brighter, less power Flexible display capable Color options are broad Color LEDs Blue LEDs with phosphors How to mass-produce? About 87% market share of a US$117B display market (2017) 6

7 Micro-LED Benefits 7

8 Micro-LED Display Technology Large Display & Microdisplay Cellphones, Tablets, Laptops, Monitors, TVs, etc. AR/VR Microdisplays 8

9 MicroLED Manufacturing Process - Simplified AM-Plate (xt+yc) Driver IC Mounting Mass-Transfer Micro-LEDs Laminate µled Preparation : Well developed by the TFT-LCD industry uled placement and connection on a backplane is key manufacturing issue 9

10 Simplified MicroLED Manufacturing Process Flow AM-Plate (xt+yc) Driver IC Mounting Mass-Transfer Micro-LEDs MicroLED Connection EPI Substrate MOCVD Processing µled Testing KGD Generation Laminate : Well developed by the TFT-LCD industry MicroLED EPI substrate and MOCVD processes are not optimized for uled MicroLED functional testing methods are not well developed Mass-transfer tool and processes are not well developed and generally incompatible with other steps Connection technology dependent on specific MicroLED design and assembly method 10

11 Major MicroLED Manufacturing Steps 1. Source Substrate & MOCVD: MicroLED Quality EQE, brightness & color uniformity 2. Functional Test PL or EL? 2. Color Measurement Individual MicroLED or spot measurement? 3. Assembly Technology utilizing high-yield mass-transfer processes 4. Connection Technology Allowing rapid and reliable MicroLED connections 11

12 MicroLED Manufacturing Process Yield MicroLED defect rate must be less than 1/20*#pixels for 95% yield For 4k UHD TV, this is 0.002ppm Post-assembly MicroLED defect rate is calculated as: Where D test = Defect rate of in-process microled test (false positive binning) D sub = Defect rate caused by substrate defects (~ 10ppm) D EPI = Defect rate caused by EPI & LED processing (~ ppm) D assy = Defect rate of mass-transfer/assembly process (depends on method, can be ~ 0) D cnct = Defect rate of connection process (depends on method, can be ~ 0) D = D test (D sub +D EPI ) + D assy + D cnct Overall yield: Y=D pixels 12

13 MicroLED Formation Process 13

14 MicroLED Performance Scaling Challenges Higher efficiency/eqe, yield Need for higher material quality and uniformity Better efficiency at low-injection conditions How to achieve good scaling EQE/uniformity performance? Process (microled device design, lower sidewall recombination) GaN Material Quality (TDD & ABC parameter) 10µm x 10µm (HVPE GaN) ~1 dislocations/pixel 10µm x 10µm (GaN-Sapphire) ~100 dislocations/pixel. Higher Quality GaN can improve EQE, uniformity But Too expensive Maximum 100mm Cannot be scaled => Layer-Transfer engineered substrate technology can help 14

15 Introducing QMAT QMAT Inc., Santa Clara, CA USA Maker of III-V engineered substrates GaN and GaAs layer-transfer capability Able to support R&D and substrate manufacturing Licensee and owner of over 100 US patents 15

16 MicroLED Compatible EPI Template (Ex. Beam-Addressed Release Approach) Bright-Field TEM Test and beam release enhancement layers can simplify manufacturing The EPI substrate can become the print head Local, softer LLO process Major reduction in process steps, handling and cost Ablation process supports fast BAR assembly 16

17 MicroLED Compatible EPI Template (Ex. Beam-Addressed Release Approach) LED Device Source Substrate MOCVD processing is fairly standard GaN-GaN growth eliminates sub-processes The EPI substrate can become the print head Substrate is ready for uled fabrication 17

18 QMAT & MicroLEDs QMAT enables higher microled device efficiency, yield and uniformity 1. QMAT Engineered LED-device growth substrates (2 to 8 ) GaN-based substrates Colored LED substrates 2. Higher quality material for enhanced EQE Enhanced uniformity Higher Yield Longer battery life 3. Integrated structures to enhance microled functions Easier microled device removal Design for testability 6 GaAs on Sapphire with Integrated Layers 18

19 MicroLED Performance Sensitive to GaN Quality iphone7/8 (~0.02 A/cm 2 ) VR Goggles iwatch (0.04 A/cm 2 ) 15 Laptop 55 HDTV 100 Projection TV MicroLED Display Battery Life is Key SID 2017 Paper 25-4 (CEA-LETI) 10µm x 10µm (QMAT GaN) ~1 dislocations/pixel. 10µm x 10µm (GaN-Sapphire) ~100 dislocations/pixel Extrapolation Source: Soraa 19

20 MicroLED Performance Sensitive to GaN Quality iphone7/8 (~0.02 A/cm 2 ) VR Goggles iwatch (0.04 A/cm 2 ) 15 Laptop 55 HDTV 100 Projection TV MicroLED Display Battery Life is Key 10µm x 10µm (QMAT GaN) ~1 dislocations/pixel. Brightness Nonuniformity A Parameter Variations Sidewall Recombination 10µm x 10µm (GaN-Sapphire) ~100 dislocations/pixel Extrapolation Source: Soraa 20

21 How QMAT EPI Templates enhance MicroLED manufacturing AM-Plate (xt+yc) Driver IC Mounting Mass-Transfer Micro-LEDs 3 MicroLED Connection EPI Substrate MOCVD Processing 1 µled Testing KGD Generation 2 Laminate 1. Lowers Substrate Cost and EPI Processing 2. Allows design for testability 3. Allows design for enhanced printability 4. Higher manufacturing yield & better display uniformity, higher efficiency/longer battery life 4 21

22 MicroLED Test Process 22

23 Test Options and Strategy Functional test is crucial when MicroLED yield is less than % Blind printing will lower yield to ~0 Need fast EL wafer-level functional test for every microled device Preferably at target injection current density (A/cm 2 ) Binning capable Generate Know Good Die (KGD) file to drive the mass-transfer equipment Can PL work? Slow (~ 30 for 6 ) PL to EL functionality correlation is suspect Color test is also necessary but at what resolution? Propose that spot checking over wafer will be sufficient MicroLED Source Substrate MicroLED Device Matrix (ex. 10um device, 6 => 100M MicroLEDs) PL MicroLED Image (EtaMax) 6 x 6 Color Measurement EL Array MicroLED Functional Test Image (36 measurements, not 100M!) (Tesoro Scientific) Data Courtesy of Tesoro Scientific, Inc. 23

24 < 50µm Lateral Micro-LED Functional Test Example Lateral device with << 50µm emission area Lateral microled Device Micro-LED Functional Test System Support Substrate Emission area MicroLED Array Tesoro Scientific, Inc. Functional Test Image Sub-10µm to mm size LED device test capable All substrate size capable Lateral and vertical devices High-throughput to generate a KGD datafile Testing across range of LED current density Binning, thresholding, yield statistics 24

25 < 50µm Lateral Micro-LED Functional Test Example Lateral device with << 50µm emission area Lateral microled Device Micro-LED Functional Test System Support Substrate Emission area MicroLED Array Tesoro Scientific, Inc. Functional Test Image Data Courtesy of Tesoro Scientific, Inc. 25

26 Lateral Micro-LED Functional Test Example Lateral device with << 50µm emission area Data Courtesy of Tesoro Scientific, Inc. 26

27 KGD Testing Key to High-Yield MicroLED Manufacturing Allows high-yield mass-transfer EPI wafer-level binning, sort and test opportunity Lateral LED example is < 3-4 nines Proves need for KGD production test Data Courtesy of Tesoro Scientific, Inc. Source: Adapted from X-Celeprint 27

28 Why in-process Functional Test If D test is sufficiently low, the overall yield will be dominated by assembly and connection steps These steps are equipment and method dependent and can also be aided by more inspection D = D test (D sub +D EPI ) + D assy + D cnct ~0 28

29 EL vs PL Concurrent PL/EL Measurement PL EL Image PL EL Image Data Courtesy of Tesoro Scientific, Inc. 29

30 EL vs PL First Integrated PL/EL Measurement PL Image EL Image EL testing contains more functional information PL test shows some correlation => certain defects show up in PL and EL More defects detected when measured in EL mode PL shows good, but EL shows non-functional Same for partial microled functionality Data Courtesy of Tesoro Scientific, Inc. 30

31 In-Process Test: Preliminary Learnings In-process test can effectively eliminate the substrate material & microled EPI/microLED process defects But D test must be very low no false positives For 4k UHD: 0.002ppm from 1000ppm means D test < 2ppm EL test can in principle achieve this PL may have too many false positives (high D test ) caused by classes of defects not able to be classified as failures 31

32 MicroLED Mass-Transfer Process 32

33 Pick and Place Technology Older Technology Not Able To Meet Requirements 100M cellphones (HDTV Resolution) 1x10 8 phones x 6x10 6 sub-pixels/phone = 6x10 14 sub-pixels/year (!) Problem 1 (Throughput & Scalability) Using pick and place at 60k uleds/20 seconds & 6000 hrs/year-equipment Need > 9,000 mass-transfer systems (!) Source: X-Celeprint 33

34 Pick and Place Technology Older Technology Not Able To Meet Requirements Problem 2 (Yield/Rework) Blind printing will cause major rework cost and expense No selection of good/bad die Bad die Bad die Adapted from SID 2017 paper

35 Reality Check Making 100 Million µled Cellphones/Year Problem 2 (Yield/Rework) Blind printing will cause major rework cost and expense Need 7 Nines for > 10% yield on 4k UHD. Yield with Test Source: Adapted from X-Celeprint Blind printing just cannot work without major post rework or dual redundancy Better approach is only to transfer Known Good Die (KGD) KGD approaches can theoretically use source substrates with low yields to make 100% good displays 35

36 What does MicroLED manufacturing require? MicroLED manufacturing requires a systems solutions approach Reason is that high-yield microled print methods cannot work without a substrate, EPI and test strategy to support Zero-ppm printing MicroLED manufacturing requires three new key steps for success: 1. High-yield substrate & compatible EPI process supporting testing and printing strategies 2. Wafer-level functional test methods that can generate a KGD (Known Good Die) defect file 3. Fast printing method that use the KGD file for error free Zero ppm printing 36

37 MicroLED Compatible EPI Template (Ex. Beam-Addressed Release Approach) Test Enhancement Layer(s) Source Substrate Target Substrate Transfer Release Layer(s) Test and beam release enhancement layers can simplify manufacturing The EPI substrate can become the print head Local, softer LLO process Major reduction in process steps, handling and cost 37

38 MicroLED Compatible EPI Template (Ex. Beam-Addressed Release Approach) Test Enhancement Layer(s) Beam Source Substrate Target Substrate Transfer Release Layer(s) Test and beam release enhancement layers can simplify manufacturing The EPI substrate can become the print head Local, softer LLO process Major reduction in process steps, handling and cost 38

39 Zero-ppm BAR Mass-Transfer Tool Basic Specifications: KGD driven beam addressing no bad die transferred 100KHz to MHz beam pulsing Method can support > 1B microleds/hour throughput Able to efficiently fabricate cellphones to large TVs 65 4k UHD TACT time (25M sub-pixels): < HD cellphone TACT time (6M sub-pixels): < 1.5 Data Courtesy of Tesoro Scientific, Inc. 39

40 BAR Mass-Transfer Method Pixel Area (Target) µled array (Source) 40

41 BAR Mass-Transfer Method 41

42 BAR Mass-Transfer Method 42

43 BAR Mass-Transfer Method 43

44 BAR Mass-Transfer Method 44

45 MicroLED Interconnect Process 45

46 MicroLED Device Structure Vertical or lateral structure will drive approaches, complexity Placement Accuracy ΔX, ΔY, Δθ at full speed Scalability What works at 50µm+ may not work at sub-10µm Repairability Important for early microled designs but should be designed out Contact Complexity Key Considerations for MicroLED Interconnects 1-side (lateral) vs 2-sided contacting scheme (vertical) Possible need for a secondary assembly system & intermediate transfer plate Can the mass-transfer equipment perform the interconnect directly on the target substrate? If not, a 1:1 type transfer equipment will connect (solder?) the devices with heat (ex. roll-roll masstransfer with heat capability) 46

47 Conclusions How to change this.. To this..? 47

48 Systems Approach to µled Manufacturing All Other Steps are Developed EPI Substrate MicroLED Fabrication High-quality GaN & Internal Layer(s) Testability Printability Enhanced µled performance Design to support test and printing Enhance µled manufacturing & performance MicroLED Functional Test MicroLED Zero-ppm Mass-Transfer MicroLED Interconnect Functional test for Zero-ppm µled manufacturing 100% EL functional test => Generate KGD defect file Spot color measurement Use Zero-ppm print methods Fast (> M µled/hr) Uses KGD defect files Can transfer to final backplane or temporary 1:1 plate Use compatible high-yield interconnect technologies Vertical MicroLED is more scalable May require a 1:1 secondary print system 48

49 Proposed Solution for uled Manufacturing AM-Plate (xt+yc) Driver IC Mounting Mass-Transfer Micro-LEDs MicroLED Connection EPI Substrate MOCVD Processing µled Testing KGD Generation Laminate QMAT Inc. => MicroLED Device Substrate Test & Mass-Transfer Equipment The EPI substrate can become the print head Integrated layers enhance test and mass-transfer New test and mass-transfer technologies make µled massproduction capable Compatible with high-yield interconnect technologies * Photon Dynamics Inc., Microtronic Inc. (representative models only - actual systems in development by other companies) 49

50 Thank You! QMAT, Inc Walsh Ave. Santa Clara, CA (408)