Wafer-Level Integrated Systems : Implementation Issues

From the perspective of complex systems, conventional Ie's can be regarded as "discrete" devices interconnected according to system design objectives imposed at the circuit board level and higher levels in the system implementation hierarchy. However, silicon monolithic circuits have progressed to such complex functions that a transition from a philosophy of integrated circuits (Ie's) to one of integrated sys­ tems is necessary. Wafer-scale integration has played an important role over the past few years in highlighting the system level issues which will most significantly impact the implementation of complex monolithic systems and system components. Rather than being a revolutionary approach, wafer-scale integration will evolve naturally from VLSI as defect avoidance, fault tolerance and testing are introduced into VLSI circuits. Successful introduction of defect avoidance, for example, relaxes limits imposed by yield and cost on Ie dimensions, allowing the monolithic circuit's area to be chosen according to the natural partitioning of a system into individual functions rather than imposing area limits due to defect densities. The term "wafer­ level" is perhaps more appropriate than "wafer-scale". A "wafer-level" monolithic system component may have dimensions ranging from conventional yield-limited Ie dimensions to full wafer dimensions. In this sense, "wafer-scale" merely represents the obvious upper practical limit imposed by wafer sizes on the area of monolithic circuits. The transition to monolithic, wafer-level integrated systems will require a mapping of the full range of system design issues onto the design of monolithic circuit.

1. Introduction and Overview.- 1.1 Device vs System Scaling.- 1.2 Major Implementation Issues.- 1.2.1 Reconfiguration Mechanisms.- 1.2.2 Architecural Reconfiguration Issues.- 1.2.3 Defects vs Failures.- 1.2.4 Yield Models.- 1.2.5 Fault Modeling.- 1.2.6 Testing.- 1.2.7 Reconfiguration Algorithms.- 1.2.8 WSI Packaging.- 1.3 ESPRIT 824 WSI Program.- References.- 2. Interconnect Issues.- 2.1 Physical Interconnect Hierarchy.- 2.2 Recursive vs Non-Recursive Interconnect Links.- 2.3 On-Chip Interconnect Lengths.- 2.4 Inter-Chip Connection Lengths.- 2.5 Electrical Models of Interconnection Lines.- 2.6 Minimum Line Capacitance.- 2.7 Scaling of On-Chip Interconnections.- 2.8 Chip-to-Board Interconnect Discontinuity.- 2.9 Comparison of Packaging Schemes.- 2.10 Clock Distribution and Clock Skew.- References.- 3. Fabrication Defects.- 3.1 Substrate defects.- 3.1.1 The “perfect” crystal and Intrinsic Defects.- 3.1.2 Crystal growth and defects.- 3.1.3 Dislocations and stacking faults.- 3.1.4 Gettering for low defect density active regions.- 3.1.5 Wafer flatness distortions.- 3.2 Lithography-induced defects.- 3.2.1 Photoresists-induced defects.- 3.2.2 Resist pattern exposure.- 3.2.3 Mask-to-mask alignment errors.- 3.3 Thin Film Defects.- 3.3.1 Metal line defects.- 3.3.2 Dielectric defects.- 3.3.3 Interlayer vias/contacts.- References.- 4. Reliability and Failures.- 4.1 Failure rate modeling.- 4.1.1 Failure Rate Measures.- 4.1.2 Analytic models.- 4.2 General reliability of IC’s.- 4.2.1 Bathtub reliability rate curve.- 4.2.2 Models for thermally activated failures.- 4.2.3 Oxide breakdown.- 4.2.4 Oxide wearout.- 4.2.5 Hot electron injection induced failure.- 4.3 Failure due to metal electromigration.- 4.4 Failure rates under MOS dimensional and voltage scaling laws.- References.- 5. Yield models and Analysis.- 5.1 General yield models.- 5.2 Early yield models.- 5.3 General IC yield models.- 5.4 VLSI yield models based on yield observations.- 5.5 Defect size distributions and critical areas.- 5.6 Yield simultion in VLSI CAD tools.- 5.7 Appendix.- References.- 6. Fault Modeling.- 6.1 General fault modeling issues.- 6.2 Definitions.- 6.3 Stuck-at faults and weak 0/1 faults.- 6.4 “Stuck” transistor faults.- 6.5 Bridging faults.- 6.6 Metastability in latches and flip-flops.- References.- 7. General testing techniques.- 7.1 General Test issues.- 7.1.1 Manufacturing defect testing.- 7.1.2 In-service testing.- 7.1.3 General purpose vs special purpose testing.- 7.2 Scan path test design.- 7.3 LSSD-based Test Methodologies.- 7.4 Pseudorandom test pattern generators.- 7.5 Test response compression.- 7.5.1 General test response analysis schemes.- 7.5.2 Counting response analysis.- 7.5.3 Signature analysis.- 7.5.4 Parallel data signature analysis.- References.- 8. Function-Specific Testing.- 8.1 Memory testing.- 8.1.1 General memory organization.- 8.1.2 Functions requiring fault models.- 8.1.3 Memory cell array fault models.- 8.1.4 Decoder logic fault models.- 8.1.5 Read/write logic fault models.- 8.1.6 Memory test algorithms.- 8.2 Built-in testing of regular arrays.- 8.2.1 Testing linear iterative arrays.- 8.2.2 C-testable array multipliers.- 8.2.3 Recomputing with shifted operands.- 8.2.4 Algorithm-based fault tolerance.- 8.3 Testable programmable logic arrays.- 8.3.1 Physical and logical fault models.- 8.3.2 Design for testable PLA’s.- References.- 9. Physical Restructuring.- 9.1 General Restructuring Techniques.- 9.2 Laser “zapping” for memory repair.- 9.3 Electronically field-programmable anti-fuses.- 9.4 Laser-assisted chemical processing.- 9.4.1 General laser-enhanced chemical processing.- 9.4.2 General applications.- 9.4.3 Laser-assisted chemical processing for interconnect restructuring.- 9.5 Focussed ion beams for restructuring.- 9.6 Electron beam restructuring.- 9.7 Restructurable VLSI program.- 9.7.1 Laser vertical links.- 9.7.2 Laser diffused link.- 9.7.3 Software tools for RVLSI.- References.- 10. Programmable Electronic Reconfiguration Switches.- 10.1 General switching issues.- 10.1.1 Area overhead.- 10.1.2 General delay issues.- 10.1.3 Comparison of physical and electronic reconfiguration.- 10.2 Reconfigurable processors.- 10.3 WASP (The WAfer-scale Systolic Processor).- 10.4 Representative switch configurations.- 10.5 Non-lattice reconfiguration switch organizations.- References.- 11. Formal Models of Reconfiguration.- 11.1 Introduction.- 11.2 Probabilistic bounds: Linear arrays.- 11.2.1 General results on fault distributions.- 11.2.2 Patching method.- 11.2.3 The minimum spanning tree method of Leighton and Leiserson.- 11.2.4 The minimum spanning tree method of Greene and Gamal.- 11.3 Probabilistic bounds: 2-dimensional arrays.- 11.3.1 Tree-of-meshes algorithm.- 11.3.2 Divide and conquer method.- 11.4 The Diogenes approach of Rosenberg.- 11.5 Self-reconfiguration algorithms.- 11.6 Spare roow/column allocation algorithms.- References.- 12. Silicon Wafer Hybrids.- 12.1 Introduction.- 12.2 Wafer transmission module.- 12.2.1 WTM technology.- 12.2.2 3-D wafer-stacks.- 12.2.3 Performance issues.- 12.3 AVP modules.- 12.4 Programmable hybrid wafer circuits.- 12.5 MicroChannel cooling and chip attachment.- 12.6 Microwave performance issues.- 12.7 Chip Templates.- 12.8 Other Silicon Circuit Board Studies.- 12.8.1 Self-Aligned Solder Bump Chip Attachment.- 12.8.2 Stacked Wafer Modules.- References.- 13. Optical Interconnections.- 13.1 optical interconnects.- 13.1.1 Electronic On-Chip Data Rates.- 13.1.2 Electronic Interconnection Energy Burdens.- 13.1.3 Energy Burden of Optical Links.- 13.1.4 Energy Burden of Wafer-to-Wafer Interconnections.- 13.2 Optical Interconnect Components.- 13.2.1 Optical Transmission Medium.- 13.2.2 Optical “Connectors”.- 13.2.3 Optical Sources and Detectors.- References.