1 Device Physics 1
1.1 Semiconductors 1
1.1.1. Generation and Recombination 4
1.1.2. Extrinsic Semiconductors 6
1.1.3. Diffusion and Drift 9
1.2 PN Junctions 11
1.2.1. Depletion Regions 11
1.2.2. PNDiodes 13
1.2.3. Schottky Diodes 16
1.2.4. Zener Diodes 18
1.2.5. Ohmic Contacts 19
1.3 Bipolar Junction Transistors 21
1.3.1. Beta 23
1.3.2. I-V Characteristics 24
1.4 MOS Transistors 25
1.4.1. Threshold Voltage 27
1.4.2. I-V Characteristics 29
1.5 JFET Transistors 32
1.6 Summary 34
1.7 Exercises 35
2 Semiconductor Fabrication 37
2.1 Silicon Manufacture 37
2.1.1. Crystal Growth 38
2.1.2. Wafer Manufacturing 39
2.1.3. The Crystal Structure of Silicon 39
2.2 Photolithography 41
2.2.1. Photoresists 41
2.2.2. Photomasks and Reticles 42
2.2.3. Patterning 43
2.3 Oxide Growth and Removal 43
2.3.1. Oxide Growth and Deposition 44
2.3.2. Oxide Removal 45
2.3.3. Other Effects of Oxide Growth and Removal 47
2.3.4. Local Oxidation of Silicon (LOCOS) 49
2.4 Diffusion and Ion Implantation 50
2.4.1. Diffusion 51
2.4.2. Other Effects of Diffusion 53
2.4.3. Ion Implantation 55
2.5 Silicon Deposition and Etching 57
2.5.1. Epitaxy 57
2.5.2. Polysilicon Deposition 59
2.5.3. Dielectric Isolation 60
2.6 Metallization 62
2.6.1. Deposition and Removal of Aluminum 63
2.6.2. Refractory Barrier Metal 65
2.6.3. Silicidation 67
2.6.4. Interlevel Oxide, Interlevel Nitride, and Protective Overcoat 69
2.6.5. Copper Metallization 71
2.7 Assembly 73
2.7.1. Mount and Bond 74
2.7.2. Packaging 77
2.8 . Summary 78
2.9 Exercises 78
3 Representative Processes 80
3.1 Standard Bipolar 81
3.1.1. Essential Features 81
3.1.2. Fabrication Sequence 82
Starting Material 82
N-Buried Layer 82
Epitaxial Growth 83
Isolation Diffusion 83
Deep-N+ 83
Base Implant 84
Emitter Diffusion 84
Contact 85
Metallization 85
Protective Overcoat 86
3.1.3. Available Devices 86
NPN Transistors 86
PNP Transistors 88
Resistors 90
Capacitors 92
3.1.4. Process Extensions 93
Up-Down Isolation 93
Double-Level Metal 94
Schottky Diodes 94
High-Sheet Resistors 94
Super-Beta Transistors 96
3.2 Polysilicon-Gate CMOS 96
3.2.1. Essential Features 97
3.2.2. Fabrication Sequence 98
Starting Material 98
Epitaxial Growth 98
N-Well Diffusion 98
Inverse Moat 99
Channel Stop Implants 100
LOCOS Processing and Dummy Gate Oxidation 100
Threshold Adjust 101
Polysilicon Deposition and Patterning 102
Source/Drain Implants 102
Contacts 103
Metallization 103
Protective Overcoat 103
3.2.3. Available Devices 104
NMOS Transistors 104
PMOS Transistors 106
Substrate PNP Transistors 107
Resistors 107
Capacitors 109
3.2.4. Process Extensions 109
Double-Level Metal 110
Shallow Trench Isolation 110
Silicidation 111
Lightly Doped Drain (LDD) Transistors 112
Extended-Drain, High-Voltage Transistors 113
3.3 Analog BiCMOS 114
3.3.1. Essential Features 115
3.3.2. Fabrication Sequence 116
Starting Material 116
N-Buried Layer 116
Epitaxial Growth 117
N-Well Diffusion and Deep-N+ 117
Base Implant 118
Inverse Moat 118
Channel Stop Implants 119
LOCOS Processing and Dummy Gate Oxidation 119
Threshold Adjust 119
Polysilicon Deposition and Pattern 120
Source/Drain Implants 120
Metallization and Protective Overcoat 120
Process Comparison 121
3.3.3. Available Devices 121
NPN Transistors 121
PNP Transistors 123
Resistors 125
3.3.4. Process Extensions 125
Advanced Metal Systems 126
Dielectric Isolation 126
3.4 Summary 130
3.5 Exercises 131
4 Failure Mechanisms 133
4.1 ElectricalOverstress 133
4.1.1. Electrostatic Discharge (ESD) 134
Effects 135
Preventative Measures 135
4.1.2. Electromigration 136
Effects 136
Preventative Measures 137
4.1.3. Dielectric Breakdown 138
Effects 138
Preventative Measures 139
4.1.4. The Antenna Effect 141
Effects 141
Preventative Measures 142
4.2 Contamination 143
4.2.1. Dry Corrosion 144
Effects 144
Preventative Measures 145
4.2.2. Mobile Ion Contamination 145
Effects 145
Preventative Measures 146
4.3 Surface Effects 148
4.3.1. Hot Carrier Injection 148
Effects 148
Preventative Measures 150
4.3.2. ZenerWalkout 151
Effects 151
Preventative Measures 152
4.3.3. Avalanche-Induced Beta Degradation 153
Effects 153
Preventative Measures 154
4.3.4. Negative Bias Temperature Instability 154
Effects 155
Preventative Measures 155
4.3.5. Parasitic Channels and Charge Spreading 156
Effects 156
Preventative Measures (Standard Bipolar) 159
Preventative Measures (CMOS and BiCMOS) 162
4.4 Parasitics 164
4.4.1. Substrate Debiasing 165
Effects 166
Preventative Measures 167
4.4.2. Minority-Carrier Injection 169
Effects 169
Preventative Measures (Substrate Injection) 172
Preventative Measures (Cross-Injection) 178
4.4.3. Substrate Influence 180
Effects 180
Preventative Measures 180
4.5 Summary 183
4.6 Exercises 183
5 Resistors 185
5.1 Resistivity and Sheet Resistance 185
5.2 Resistor Layout 187
5.3 Resistor Variability 191
5.3.1. Process Variation 191
5.3.2. Temperature Variation 192
5.3.3. Nonlinearity 193
5.3.4. Contact Resistance 196
5.4 Resistor Parasitics 197
5.5 Comparison of Available Resistors 200
5.5.1. Base Resistors 200
5.5.2. Emitter Resistors 201
5.5.3. Base Pinch Resistors 202
5.5.4. High-Sheet Resistors 202
5.5.5. EpiPinch Resistors 205
5.5.6. Metal Resistors 206
5.5.7. Poly Resistors 208
5.5.8. NSD and PSD Resistors 211
5.5.9. N-Well Resistors 211
5.5.10. Thin-Film Resistors 212
5.6 Adjusting Resistor Values 213
5.6.1. Tweaking Resistors 213
Sliding Contacts 214
Sliding Heads 215
Trombone Slides 215
Metal Options 215
5.6.2. Trimming Resistors 216
Fuses 216
Zener Zaps 219
EPROM Trims 221
Laser Trims 222
5.7 Summary 223
5.8 Exercises 224
6 Capacitors and Inductors 226
6.1 Capacitance 226
6.1.1. Capacitor Variability 232
Process Variation 232
Voltage Modulation and Temperature Variation 233
6.1.2. Capacitor Parasitics 235
6.1.3. Comparison of Available Capacitors 237
Base-Emitter Junction Capacitors 237
MOS Capacitors 239
Poly-Poly Capacitors 241
Stack Capacitors 243
Lateral Flux Capacitors 245
High-Permittivity Capacitors 246
6.2 Inductance 246
6.2.1. Inductor Parasitics 248
6.2.2. Inductor Construction 250
Guidelines for lntegrating Inductors 251
6.3 Summary 252
6.4 Exercises 253
7 Matching of Resistors and Capacitors 254
7.1 Measuring Mismatch 254
7.2 Causes of Mismatch 257
7.2.1. Random Variation 257
Capacitors 258
Resistors 258
7.2.2. Process Biases 260
7.2.3. Interconnection Parasitics 261
7.2.4. Pattern Shift 263
7.2.5. Etch Rate Variations 265
7.2.6. Photolithographic Effects 267
7.2.7. Diffusion Interactions 268
7.2.8. Hydrogenation 270
7.2.9. Mechanical Stress and Package Shift 271
7.2.10. Stress Gradients 274
Piezoresistivity 274
Gradients and Centroids 275
Common-Centroid Layout 277
Location and Orientation 281
7.2.11. Temperature Gradients and Thermoelectrics 283
Thermal Gradients 285
Thermoelectric Effects 287
7.2.12. Electrostatic Interactions 288
Voltage Modulation 288
Charge Spreading 292
Dielectric Polarization 293
Dielectric Relaxation 294
7.3 Rules for Device Matching 295
7.3.1. Rules for Resistor Matching 296
7.3.2. Rules for Capacitor Matching 300
7.4 Summary 303
7.5 Exercises 304
8 Bipolar Transistors 306
8.1 Topics in Bipolar Transistor Operation 306
8.1.1. Beta Rolloff 308
8.1.2. Avalanche Breakdown 308
8.1.3. Thermal Runaway and Secondary Breakdown 310
8.1.4. Saturation in NPN Transistors 312
8.1.5. Saturation in Lateral PNP Transistors 315
8.1.6. Parasitics of Bipolar Transistors 318
8.2 Standard Bipolar Small-Signal Transistors 320
8.2.1. The Standard Bipolar NPN Transistor 320
Construction of Small-Signal NPN Transistors 322
8.2.2. The Standard Bipolar Substrate PNP Transistor 326
Construction of Small-Signal Substrate PNP Transistors 328
8.2.3. The Standard Bipolar Lateral PNP Transistor 330
Construction of Small-Signal Lateral PNP Transistors 332
8.2.4. High-Voltage Bipolar Transistors 337
8.2.5. Super-Beta NPN Transistors 340
8.3 CMOS and BiCMOS Small-Signal Bipolar Transistors 341
8.3.1. CMOS PNPTransistors 341
8.3.2. Shallow-Well Transistors 345
8.3.3. Analog BiCMOS Bipolar Transistors 347
8.3.4. Fast Bipolar Transistors 349
8.3.5. Polysilicon-Emitter Transistors 351
8.3.6. Oxide-IsolatedTransistors 354
8.3.7. Silicon-Germanium Transistors 356
8.4 Summary 358
8.5 Exercises 358
9 Applications of Bipolar Transistors 360
9.1 Power Bipolar Transistors 361
9.1.1. Failure Mechanisms of NPN Power Transistors 362
Emitter Debiasing 362
Thermal Runaway and Secondary Breakdown 364
Kirk Effect 366
9.1.2. Layout of Power NPN Transistors 368
The Interdigitated-Emitter Transistor 369
The Wide-Emitter Narrow-Contact Transistor 371
The Christmas-Tree Device 372
The Cruciform-Emitter Transistor 373
Power Transistor Layout in Analog BiCMOS 374
Selecting a Power Transistor Layout 376
9.1.3. Power PNP Transistors 376
9.1.4. Saturation Detection and Limiting 378
9.2 Matching Bipolar Transistors 381
9.2.1. Random Variations 382
9.2.2. Emitter Degeneration 384
9.2.3. NBLShadow 386
9.2.4. Thermal Gradients 387
9.2.5. Stress Gradients 391
9.2.6. Filler-Induced Stress 393
9.2.7. Other Causes of Systomatic Mismatch 395
9.3 Rules for Bipolar Transistor Matching 396
9.3.1. Rules for Matching Vertical Transistors 397
9.3.2. Rules for Matching Lateral Transistors 402
9.4 Summary 402
9.5 Exercises 403
10 Diodes 406
10.1 Diodes in Standard Bipolar 406
10.1.1. Diode-ConnectedTransistors 406
10.1.2. Zener Diodes 409
Surface Zener Diodes 410
Buried Zeners 412
10.1.3. Schottky Diodes 415
10.1.4. Power Diodes 420
10.2 Diodes in CMOS and BiCMOS Processes 422
10.2.1. CMOS Junction Diodes 422
10.2.2. CMOS and BiCMOS Schottky Diodes 423
10.3 Matching Diodes 425
10.3.1. Matching PN Junction Diodes 425
10.3.2. Matching Zener Diodes 426
10.3.3. Matching Schottky Diodes 428
10.4 Summary 428
10.5 Exercises 429
11 Field-Effect Transistors 430
11.1 Topics in MOS Transistor Operation 431
11.1.1. Modeling the MOSTransistor 431
Device Transconductance 432
Threshold Voltage 434
11.1.2. Parasitics of MOS Transistors 438
Breakdown Mechanisms 440
CMOS Latchup 442
Leakage Mechanisms 443
11.2 Constructing CMOS Transistors 446
11.2.1. Coding the MOS Transistor 447
Width and Length 448
11.2.2. N-Well and P-Well Processes 449
11.2.3. Channel Stop Implants 452
11.2.4. Threshold Adjust Implants 453
11.2.5. Scaling the Transistor 456
11.2.6. Variant Structures 459
Serpentine Transistors 461
Annular Transistors 462
11.2.7. Backgate Contacts 464
11.3 Floating-GateTransistors 467
11.3.1. Principles of Floating-Gate Transistor Operation 469
11.3.2. Single-Poly EEPROM Memory 472
11.4 The JFET Transistor 474
11.4.1. Modeling the JFET 474
11.4.2. JFETLayout 476
11.5 Summary 479
11.6 Exercises 479
12 Applications of MOS Transistors 482
12.1 Extended-Voltage Transistors 482
12.1.1. LDD and DDDTransistors 483
12.1.2. Extended-Drain Transistors 486
Extended-Drain NMOS Transistors 487
Extended-Drain PMOS Transistors 488
12.1.3. Multiple Gate Oxides 489
12.2 Power MOSTransistors 491
12.2.1. MOS Safe Operating Area 492
Electrical SOA 493
Electrothermal SOA 496
Rapid Transient Overload 497
12.2.2. Conventional MOS Power Transistors 498
The Rectangular Device 499
The Diagonal Device 500
Computation of RM 501
Other Considerations 502
Nonconventional Structures 503
12.2.3. DMOSTransistors 505
The Lateral DMOS Transistor 506
RESURF Transistors 508
The DMOS NPN 510
12.3 MOSTransistor Matching 511
12.3.1. Geometric Effects 513
Gate Area 513
Gate Oxide Thickness 514
Channel Length Modulation 515
Orientation 515
12.3.2. Diffusion and Etch Effects 516
Polysilicon Etch Rate Variations 516
Diffusion Penetration of Polysilicon 517
Contacts Over Active Gate 518
Diffusions Near the Channel 518
PMOS versus NMOS Transistors 519
12.3.3. Hydrogenation 520
Fill Metal and MOS Matching 521
12.3.4. Thermal and Stress Effects 521
Oxide Thickness Gradients 522
Stress Gradients 522
Thermal Gradients 522
12.3.5. Common-Centroid Layout of MOSTransistors 523
12.4 Rules for MOSTransistor Matching 528
12.5 Summary 531
12.6 Exercises 531
13 Special Topics 534
13.1 Merged Devices 534
13.1.1. Flawed Device Mergers 535
13.1.2. Successful Device Mergers 539
13.1.3. Low-Risk Merged Devices 541
13.1.4. Medium-Risk Merged Devices 542
13.1.5. Devising New Merged Devices 544
13.1.6. The Role of Merged Devices in Analog BiCMOS 544
13.2 Guard Rings 545
13.2.1. Standard Bipolar Electron Guard Rings 546
13.2.2. Standard Bipolar Hole Guard Rings 547
13.2.3. Guard Rings in CMOS and BiCMOS Designs 548
13.3 Single-level Interconnection 551
13.3.1. Mock Layouts and StickDiagrams 551
13.3.2. Techniques for Crossing Leads 553
13.3.3. Types of Tunnels 555
13.4 Constructing the Padring 557
13.4.1. Scribe Streets and Alignment Markers 557
13.4.2. Bondpads, Trimpads, and Testpads 558
13.5 ESD Structures 562
13.5.1. Zener Clamp 563
13.5.2. Two-Stage Zener Clamps 565
13.5.3. Buffered Zener Clamp 566
13.5.4. VCES Clamp 568
13.5.5. VECS Clamp 569
13.5.6. Antiparallel Diode Clamps 570
13.5.7. Grounded-Gate NMOS Clamps 570
13.5.8. CDM Clamps 572
13.5.9. Lateral SCR Clamps 573
13.5.10. Selecting ESD Structures 575
13.6 Exercises 578
14 Assembling the Die 581
14.1 Die Planning 581
14.1.1. Cell Area Estimation 582
Resistors 582
Capacitors 582
Vertical Bipolar Transistors 583
Lateral PNP Transistors 583
MOS Transistors 583
MOS Power Transistors 584
Computing Cell Area 584
14.1.2. Die Area Estimation 584
14.1.3. Gross Profit Margin 587
14.2 Floorplanning 588
14.3 Top-Level Interconnection 594
14.3.1. Principles of Channel Routing 594
14.3.2. Special Routing Techniques 596
Kelvin Connections 597
Noisy Signals and Sensitive Signals 598
14.3.3. Electromigration 600
14.3.4. Minimizing Stress Effects 603
14.4 Conclusion 604
14.5 Exercises 605
Appendices 607
A. Table of Acronyms Used in the Text 607
B. The Miller Indices of a Cubic Crystal 611
C. Sample Layout Rules 614
D. Mathematical Derivations 622
E. Sources for Layout Editor Software 627
Index 628