1. MIT Lincoln Laboratory 3-D Kickoff 1 CLK 4/7/00 3D Circuit Integration Technology for Multiproject Fabrication 7 April, 2000 James Burns, Andy Curtis, Paul Davis, Andy Loomis, Jim Reinold, Keith Warner, Peter Wyatt, Craig L. Keast, keast@LL.mit.edu MIT Lincoln Laboratory Lexington MA, 02173

2. MIT Lincoln Laboratory 3-D Kickoff 2 CLK 4/7/00 Outline Background –Motivation for 3-D technology –Why Multiproject Fabrication? Leveraging the FDSOI CMOS technology base Current Status –Photodiode process development –3-D technology transfer –Wafer Aligner/Bonder purchase –3-D Via topologies Summary

3. MIT Lincoln Laboratory 3-D Kickoff 3 CLK 4/7/00 3-D Circuit Technology General Objective –Break away from the traditional 2-D-constrained Moore’s Law scaling trends by developing and demonstrating a robust, high density, vertical chip-to-chip interconnection technology and making it available to the DoD and research community through multiproject runs Program Description (Joint effort with TREX Enterprises) –Develop enabling technologies for 3-D integration Precision wafer-to-wafer overlay Low temperature wafer-to-wafer oxide bonding High density wafer-to-wafer electrical interconnects –Demonstrate the 3-D technology by fabricating a high definition 3-layer imaging module –Put in place infrastructure to allow for 3-D multiproject fabrication

4. MIT Lincoln Laboratory 3-D Kickoff 4 CLK 4/7/00 Motivation: 3-D Circuit Technology High Bandwidth  -Processors Mixed Material System Integration Large Focal Planes Exploiting Different Process Technologies Advanced Imaging Technologies SOI CMOS 3D Better circuit / interconnect ratio “Unrestricted” vertical interconnections between layers Low digital system power: P=CV 2 f

5. MIT Lincoln Laboratory 3-D Kickoff 5 CLK 4/7/00 3-D Interconnect Demonstration Vehicle (Fully Parallel 64 x 64 APS Imager with A/D Conversion) A/D Converter Circuits fabricated in 1-  m thick SOI CMOS Active Pixel Imaging Circuits fabricated in 10-  m thick SOI CMOS 6  m Metal 1 Pad Via Isolation Plan View

6. MIT Lincoln Laboratory 3-D Kickoff 6 CLK 4/7/00 3-D Process Flow Back Metal Interconnect Adhesive 5  m Imager Silicon Imager Metal-1 Imager Metal-2 A/D Metal-1 Deep Via Back Metal Deep Via Cross Sectional SEM

7. MIT Lincoln Laboratory 3-D Kickoff 7 CLK 4/7/00 Developing 3-D Multiproject Infrastructure Transfer to, enhance and stabilize all aspects of the 3-D fabrication process in Lincoln’s Microelectronics Laboratory –Initial program effort had different parts of the 3-D fabrication process being performed at three different locations Starting circuit layer fabrication: MIT Lincoln Laboratory Wafer transfer and bonding: Kopin Corporation 3-D via etch and metallization: Northeastern University Demonstrate 3-D circuit technology by fabricating a three-layer high definition imaging module Imaging Layer (layer 1) SOI CMOS signal processing (layer 3) SOI CMOS A/D Converter (layer 2) Backside illumination Thinned Bulk Si Wafer

8. MIT Lincoln Laboratory 3-D Kickoff 8 CLK 4/7/00 Motivation: 3-D Multiproject Fabrication Mainstream silicon technology continues to focus on 2-D centered technologies –This approach will probably continue for another ~10+ years unless something “revolutionary” happens –This is the low risk path, lots of inertia in the system Maximizing the potential of 3-D system architecture requires a new “thought process” –We need to get a group of talented individuals and/or teams thinking about the design/architecture issue as it relates to specialized DoD and potential commercial system needs –This thinking needs to be focused in the context of a realizable 3-D technology

9. MIT Lincoln Laboratory 3-D Kickoff 9 CLK 4/7/00 Motivation: 3-D Multiproject Fabrication (cont.) The 3-D Multiproject Fabrication model provides the vehicle to explore the potential of 3-D system integration across a broad research interest base –Putting in place a “user friendly” streamlined 3-D integration technology built upon Aggressive low power, high performance SOI CMOS technology Robust oxide-based wafer bonding technology Precision wafer-to-wafer alignment technology –Provides the opportunity to explore mixed function (MEMS, CMOS, CCD, etc.) and mixed material (Si, SiGe, GaAs, etc.) system integration Builds upon Lincoln Laboratory’s past Multiproject Run experience and core process technologies already in place and under development at the Laboratory

10. MIT Lincoln Laboratory 3-D Kickoff 10 CLK 4/7/00 FY98FY99FY02FY01FY00 MUMS2 Ship 7/15/98 Baseline 0.25  m SOI/CMOS MUMS3 Ship 6/14/99 MUMS4 Start 1/1/00 0.10  m SOI CMOS 0.175  m SOI/CMOS Low Power, High Performance FDSOI CMOS Roadmap MUMS3.5 Start 2/1/99 LVA1 Start 4/1/00 LVA2 Start 11/1/00 Low Voltage Analog Merged CCD/CMOS Integrated 3-D Microsystems DoD/R&T DoD/AS&T 3-D Stacking Technology Rad Hard 0.175  m SOI/CMOS DARPA/ARMY DoD/DTRA Damascene Waveguides 3-D Layer Stacking RF MEMS Precision-MCM-D FDSOI CMOS InGaAs Detectors Honeywell/LM

11. MIT Lincoln Laboratory 3-D Kickoff 11 CLK 4/7/00 Advanced Photodiode Development Current CMOS processes support diode fabrication but: –Leakage currents are too high for low noise photodiodes –Substrate doping too high for large depletion regions and high quantum efficiency We are developing an enhanced photodiode process for the 3-D effort based on existing Lincoln Laboratory photodiode technology Microns Photodiode Process Simulation

12. MIT Lincoln Laboratory 3-D Kickoff 12 CLK 4/7/00 3-D Technology Transfer Original program had process activities at: MIT-LL, NEU, and Kopin All of these process activities are now being integrated in the the MIT-LL Microelectronics Laboratory tool set –Wafer-to-wafer alignment and void-free bonding –3-D via etching –3-D via interconnect metallization 150-mm Diameter Wafer Pair (Bonded and Thinned)

13. MIT Lincoln Laboratory 3-D Kickoff 13 CLK 4/7/00 Wafer Aligner/Bonder Purchase 3-D Integration Program requires a precision wafer-to- wafer overlay and bonding system We have researched the currently available commercial tools –Barely satisfactory for the current 3-D mutiproject demonstration effort –Clearly unsatisfactory for commercial 3-D fabrication Technology exists to make the necessary system but there is currently no market demanding the capabilities of such a tool Wafer-to-Wafer Alignment (Bottom side referenced)

14. MIT Lincoln Laboratory 3-D Kickoff 14 CLK 4/7/00 3-D Via Topologies Currently designing a mask set which will serve as the “workhorse” for developing the robust 3-D interconnect technology –Supports 2 and 3-layer stacking –Allows for the investigation of both topside-up and flipped wafer stacking techniques –Investigates multiple layer-to-layer via interconnect topologies –Designed for automated electrical characterization Si wafer Glue M1 M2 M3 M1 M3 M2 M1 M3 M4 Deep vias Shallow vias W1 W2 W3

15. MIT Lincoln Laboratory 3-D Kickoff 15 CLK 4/7/00 –Follow-on multiproject effort is a collaboration between Lincoln Laboratory and a commercial technology transfer partner (TREX Enterprises) Transferring, while enhancing and streamlining, the 3-D technology into the MIT Lincoln Laboratory “commercial” tool set –Program demonstrator is a three-layer, high definition (1280 x 1024) imaging module –Goal is to make 3-D multiproject prototyping available in 2002 Summary Developing the technology base necessary for demonstrating a robust 3-D circuit interconnect technology Sample Image –Original demonstration program was a team effort with Northeastern University and Kopin Corporation 64 x 64 imager with A/D conversion (>4,000 3-D interconnects)