NAND Flash Memory Technologies

Foreword xi Preface xv Acknowledgments xvii About the Author xix 1 Introduction 1 1.1 Background, 1 1.2 Overview, 8 References, 10 2 Principle of NAND Flash Memory 17 2.1 NAND Flash Device and Architecture, 17 2.1.1 NAND Flash Memory Cell Architecture, 17 2.1.2 Peripheral Device, 19 2.2 Cell Operation, 21 2.2.1 Read Operation, 21 2.2.2 Program and Erase Operation, 21 2.2.3 Program and Erase Dynamics, 28 2.2.4 Program Boosting Operation, 31 2.3 Multilevel Cell (MLC), 34 2.3.1 Cell Vt Setting, 34 References, 35 3 NAND Flash Memory Devices 37 3.1 Introduction, 37 3.2 LOCOS Cell, 40 3.2.1 Conventional LOCOS Cell, 40 3.2.2 Advanced LOCOS Cell, 40 3.2.3 Isolation Technology, 43 3.2.4 Reliability, 46 3.3 Self-Aligned STI Cell (SA-STI Cell) with FG Wing, 48 3.3.1 Structure of SA-STI Cell, 48 3.3.2 Fabrication Process Flow, 50 3.3.3 Characteristics of SA-STI with FG Wing Cell, 53 3.3.4 Characteristics of Peripheral Devices, 57 3.4 Self-Aligned STI Cell (SA-STI Cell) without FG Wing, 59 3.4.1 SA-STI Cell Structure, 59 3.4.2 Fabrication Process, 60 3.4.3 Shallow Trench Isolation (STI), 61 3.4.4 SA-STI Cell Characteristics, 64 3.5 Planar FG Cell, 66 3.5.1 Structure Advantages, 66 3.5.2 Electrical Characteristics, 68 3.6 Sidewall Transfer Transistor Cell (SWATT Cell), 69 3.6.1 Concept of the SWATT Cell, 70 3.6.2 Fabrication Process, 71 3.6.3 Electrical Characteristics, 74 3.7 Advanced NAND Flash Device Technologies, 77 3.7.1 Dummy Word Line, 77 3.7.2 The P-Type Floating Gate, 82 References, 89 4 Advanced Operation for Multilevel Cell 93 4.1 Introduction, 93 4.2 Program Operation for Tight Vt Distribution Width, 94 4.2.1 Cell Vt Setting, 94 4.2.2 Incremental Step Pulse Program (ISPP), 95 4.2.3 Bit-by-Bit Verify Operations, 98 4.2.4 Two-Step Verify Scheme, 99 4.2.5 Pseudo-Pass Scheme in Page Program, 102 4.3 Page Program Sequence, 104 4.3.1 Original Page Program Scheme, 104 4.3.2 New Page Program Scheme (1), 107 4.3.3 New Page Program Scheme (2), 108 4.3.4 All-Bit-Line (ABL) Architecture, 111 4.4 TLC (3 Bits/Cell), 113 4.5 QLC (4 Bits/Cell), 115 4.6 Three-Level (1.5 Bits/Cell) NAND flash, 119 4.7 Moving Read Algorithm, 122 References, 123 5 Scaling Challenge of NAND Flash Memory Cells 129 5.1 Introduction, 129 5.2 Read Window Margin (RWM), 130 5.2.1 Assumption for Read Window Margin (RWM), 131 5.2.2 Programmed Vt Distribution Width, 135 5.2.3 Vt Window, 137 5.2.4 Read Window Margin (RWM), 139 5.2.5 RWM Vt Setting Dependence, 140 5.3 Floating-Gate Capacitive Coupling Interference, 142 5.3.1 Model of Floating-Gate Capacitive Coupling Interference, 142 5.3.2 Direct Coupling with Channel, 145 5.3.3 Coupling with Source/Drain, 148 5.3.4 Air Gap and Low-k Material, 149 5.4 Program Electron Injection Spread, 153 5.4.1 Theory of Program Electron Injection Spread, 153 5.4.2 Effect of Lower Doping in FG, 158 5.5 Random Telegraph Signal Noise (RTN), 161 5.5.1 RTN in Flash Memory Cells, 161 5.5.2 Scaling Trend of RTN, 166 5.6 Cell Structure Challenge, 170 5.7 High-Field Limitation, 171 5.8 A Few Electron Phenomena, 175 5.9 Patterning Limitation, 178 5.10 Variation, 179 5.11 Scaling impact on Data Retention, 183 5.12 Summary, 185 References, 186 6 Reliability of NAND Flash Memory 195 6.1 Introduction, 195 6.2 Program/Erase Cycling Endurance and Data Retention, 198 6.2.1 Program and Erase Scheme, 198 6.2.2 Program and Erase Cycling Endurance, 200 6.2.3 Data Retention Characteristics, 203 6.3 Analysis of Program/Erase Cycling Endurance and Data Retention, 210 6.3.1 Program/Erase Cycling Degradation, 210 6.3.2 SILC (Stress-Induced Leakage Current), 216 6.3.3 Data Retention in NAND Flash Product, 219 6.3.4 Distributed Cycling Test, 222 6.4 Read Disturb, 224 6.4.1 Program/Erase Scheme Dependence, 224 6.4.2 Detrapping and SILC, 229 6.4.3 Read Disturb in NAND Flash Product, 234 6.4.4 Hot Carrier Injection Mechanism in Read Disturb, 235 6.5 Program Disturb, 238 6.5.1 Model of Self-Boosting, 238 6.5.2 Hot Carrier Injection Mechanism, 244 6.5.3 Channel Coupling, 248 6.6 Erratic Over-Program, 250 6.7 Negative Vt shift phenomena, 253 6.7.1 Background and Experiment, 253 6.7.2 Negative Vt Shift, 254 6.7.3 Program Speed and Victim Cell Vt Dependence, 256 6.7.4 Carrier Separation in Programming Conditions, 260 6.7.5 Model, 262 6.8 Summary, 263 References, 266 7 Three-Dimensional NAND Flash Cell 273 7.1 Background of Three-Dimensional NAND Cells, 273 7.2 BiCS (Bit Cost Scalable Technology) / P-BiCS (Pipe-Shape BiCS), 276 7.2.1 Concept of BiCS, 276 7.2.2 Fabrication Process of BiCS, 278 7.2.3 Electrical Characteristics, 279 7.2.4 Pipe-Shaped BiCS, 285 7.3 TCAT (Terabit Cell Array Transistor)/V-NAND (Vertical-NAND), 289 7.3.1 Structure and Fabrication Process of TCAT, 289 7.3.2 Electrical Characteristics, 292 7.3.3 128-Gb MLC V-NAND Flash Memory, 294 7.3.4 128-Gb TLC V-NAND Flash Memory, 296 7.4 SMArT (Stacked Memory Array Transistor), 298 7.4.1 Structural Advantage of SMArT, 298 7.4.2 Electrical Characteristics, 301 7.5 VG-NAND (Vertical Gate NAND Cell), 302 7.5.1 Structure and Fabrication Process of VG-NAND, 302 7.5.2 Electrical Characteristics, 305 7.6 Dual Control Gate--Surrounding Floating Gate Cell (DC-SF Cell), 308 7.6.1 Concern for Charge Trap 3D Cell, 308 7.6.2 DC-SF NAND Flash Cells, 309 7.6.3 Results and Discussions, 313 7.6.4 Scaling Capability, 317 7.7 Advanced DC-SF Cell, 317 7.7.1 Improvement on DC-SF Cell, 317 7.7.2 MCGL Process, 319 7.7.3 New Read Scheme, 319 7.7.4 New Programming Scheme, 325 7.7.5 Reliability, 329 References, 329 8 Challenges of Three-Dimensional NAND Flash Memory 335 8.1 Introduction, 335 8.2 Comparison of 3D NAND Cells, 336 8.3 Data Retention, 339 8.3.1 Quick Initial Charge Loss, 339 8.3.2 Temperature Dependence, 342 8.4 Program Disturb, 343 8.4.1 New Program Disturb Modes, 343 8.4.2 Analysis of Program Disturb, 345 8.5 Word-Line RC Delay, 350 8.6 Cell Current Fluctuation, 353 8.6.1 Conduction Mechanism, 353 8.6.2 VG Dependence, 358 8.6.3 Random Telegraph Noise (RTN), 360 8.6.4 Back-Side Trap in Macaroni Channel, 363 8.6.5 Laser Thermal Anneal, 366 8.7 Number of Stacked Cells, 368 8.8 Peripheral Circuit Under Cell Array, 370 8.9 Power Consumption, 371 8.10 Future Trend of 3D NAND Flash Memory, 374 References, 376 9 Conclusions 381 9.1 Discussions and Conclusions, 381 9.2 Perspective, 384 References, 385 Index 389