Sige Heterojunction Bipolar Transistors

SiGe HBTs is a hot topic within the microelectronics community because of its applications potential within integrated circuits operating at radio frequencies. Applications range from high speed optical networking to wireless communication devices. The addition of germanium to silicon technologies to form silicon germanium (SiGe) devices has created a revolution in the semiconductor industry. These transistors form the enabling devices in a wide range of products for wireless and wired communications. This book features: SiGe products include chip sets for wireless cellular handsets as well as WLAN and high-speed wired network applications Describes the physics and technology of SiGe HBTs, with coverage of Si and Ge bipolar transistors Written with the practising engineer in mind, this book explains the operating principles and applications of bipolar transistor technology. Essential reading for practising microelectronics engineers and researchers. Also, optical communications engineers and communication technology engineers. An ideal reference tool for masters level students in microelectronics and electronics engineering.

Professor Ashburn has worked as an industrial engineer, a consultant and a university professor and has accumulated a wealth of practical knowledge for incorporation in this book.

Preface

xiii

Physical Constants and Properties of Silicon and Silicon-Germanium

xvii

List of Symbols

xix

1 Introduction

1

(12)

1.1 Evolution of Silicon Bipolar Technology

1

(2)

1.2 Evolution of Silicon-Germanium HBT Technology

3

(2)

1.3 Operating Principles of the Bipolar Transistor

5

(5)

References

10

(3)

2 Basic Bipolar Transistor Theory

13

(14)

2.1 Introduction

13

(1)

2.2 Components of Base Current

13

(3)

2.3 Fundamental Equations

16

(3)

2.3.1 Assumptions

17

(2)

2.4 Base Current

19

(4)

2.4.1 Base Current in Shallow Emitters

20

(1)

2.4.2 Base Current in Deep Emitters

21

(1)

2.4.3 Recombination Current in the Neutral Base

22

(1)

2.5 Collector Current

23

(1)

2.6 Current Gain

24

(1)

2.7 Gummel Numbers

25

(2)

3 Heavy Doping Effects

27

(18)

3.1 Introduction

27

(1)

3.2 Majority and Minority Carrier Mobility

28

(4)

3.3 Bandgap Narrowing

32

(4)

3.4 Minority Carrier Lifetime

36

(3)

3.5 Gain and Heavy Doping Effects

39

(1)

3.6 Non-uniform Doping Profiles

40

(2)

References

42

(3)

4 Second-Order Effects

45

(26)

4.1 Introduction

45

(1)

4.2 Low Current Gain

46

(10)

4.2.1 Recombination via Deep Levels

46

(3)

4.2.2 Recombination Current in the Forward Biased Emitter/Base Depletion Region

49

(3)

4.2.3 Generation Current in a Reverse Biased pn Junction

52

(1)

4.2.4 Origins of Deep Levels in Bipolar Transistors

53

(3)

4.3 High Current Gain

56

(2)

4.4 Basewidth Modulation

58

(1)

4.5 Series Resistance

59

(2)

4.6 Junction Breakdown

61

(8)

4.6.1 Punch-through

62

(1)

4.6.2 Zener Breakdown

63

(1)

4.6.3 Avalanche Breakdown

64

(1)

4.6.4 Junction Breakdown in Practice

65

(1)

4.6.5 Common Base and Common Emitter Breakdown Voltages

65

(3)

4.6.6 Trade-off between Gain and BVCEO

68

(1)

References

69

(2)

5 High-frequency Performance

71

(22)

5.1 Introduction

71

(1)

5.2 Forward Transit Time TF

72

(4)

5.2.1 Components of TF

72

(1)

5.2.2 Base Transit Time

72

(2)

5.2.3 Emitter Delay

74

(1)

5.2.4 Collector/Base Depletion Region Transit Time

75

(1)

5.2.5 Emitter/Base Depletion Region Delay

76

(1)

5.3 Cut-off Frequency fT

76

(3)

5.4 Maximum Oscillation Frequency frnax

79

(1)

5.5 Kirk Effect

80

(4)

5.6 Base, Collector and Emitter Resistance

84

(3)

5.6.1 Base Resistance

84

(2)

5.6.2 Collector Resistance

86

(1)

5.7 Emitter/Base and Collector/Base Depletion Capacitance

87

(1)

5.8 Quasi-saturation

88

(2)

5.9 Current Crowding

90

(1)

References

91

(2)

6 Polysilicon Emitters

93

(28)

6.1 Introduction

93

(1)

6.2 Basic Fabrication and Operation of Polysilicon Emitters

94

(2)

6.3 Diffusion in Polysilicon Emitters

96

(4)

6.4 Influence of the Polysilicon/Silicon Interface

100

(1)

6.5 Base Current in Polysilicon Emitters

101

(3)

6.6 Effective Surface Recombination Velocity

104

(3)

6.7 Emitter Resistance

107

(1)

6.8 Design of Practical Polysilicon Emitters

108

(8)

6.8.1 Break-up of the Interfacial Oxide Layer and Epitaxial Regrowth

108

(3)

6.8.2 Epitaxially Regrown Emitters

111

(1)

6.8.3 Trade-off between Emitter Resistance and Current Gain in Polysilicon Emitters

112

(3)

6.8.4 Emitter Plug Effect and in situ Doped Polysilicon Emitters

115

(1)

6.9 pnp Polysilicon Emitters

116

(2)

References

118

(3)

7 Properties and Growth of Silicon-Germanium

121

(28)

7.1 Introduction

121

(1)

7.2 Materials Properties of Silicon-Germanium

122

(5)

7.2.1 Pseudomorphic Silicon-Germanium

122

(1)

7.2.2 Critical Thickness

123

(2)

7.2.3 Band Structure of Silicon-Germanium

125

(2)

7.3 Physical Properties of Silicon-Germanium

127

(3)

7.3.1 Dielectric Constant

127

(1)

7.3.2 Density of States

127

(1)

7.3.3 Apparent Bandgap Narrowing

128

(1)

7.3.4 Minority Carrier Hole Mobility

129

(1)

7.4 Basic Epitaxy Theory

130

(6)

7.4.1 Boundary Layer Model

133

(2)

7.4.2 Growth Modes

135

(1)

7.5 Low-Temperature Epitaxy

136

(3)

7.5.1 In situ Hydrogen Bake

136

(1)

7.5.2 Hydrogen Passivation

137

(1)

7.5.3 Ultra-clean Epitaxy Systems

138

(1)

7.6 Comparison of Silicon and Silicon-Germanium Epitaxy

139

(2)

7.7 Selective Epitaxy

141

(4)

7.7.1 Faceting and Loading Effects

143

(2)

References

145

(4)

8 Silicon-Germanium Heterojunction Bipolar Transistors

149

(18)

8.1 Introduction

149

(1)

8.2 Bandgap Engineering

150

(2)

8.3 Collector Current, Base Current and Gain Enhancement

152

(1)

8.4 Cut-off Frequency

153

(1)

8.5 Device Design Trade-offs in a SiGe HBT

154

(1)

8.6 Graded Germanium Profiles

155

(3)

8.6.1 Design Equations for a Graded Germanium Profile

156

(2)

8.7 Boron Diffusion in SiGe HBTs

158

(5)

8.7.1 Parasitic Energy Barriers

158

(2)

8.7.2 Factors Influencing Boron Diffusion in Si and SiGe

160

(2)

8.7.3 SiGe:C-Reduction of Boron Diffusion by Carbon Doping

162

(1)

8.8 Strain Relaxation and Strain Compensated Si1-x-yGexCy

163

(1)

References

164

(3)

9 Silicon Bipolar Technology

167

(24)

9.1 Introduction

167

(2)

9.2 Buried Layer and Epitaxy

169

(3)

9.3 Isolation

172

(4)

9.4 Selective Implanted Collector

176

(2)

9.5 Double-polysilicon, Self-aligned Bipolar Process

178

(5)

9.6 Single-polysilicon Bipolar Process

183

(1)

9.7 BiCMOS Process

184

(2)

9.8 Complementary Bipolar Process

186

(1)

References

187

(4)

10 Silicon-Germanium Heterojunction Bipolar Technology

191

(20)

10.1 Introduction

191

(2)

10.2 Differential Epitaxy Silicon-Germanium HBT Process

193

(5)

10.2.1 Polysilicon Nucleation Layer

195

(1)

10.2.2 Self-aligned Emitter for the Differential Epitaxy HBT

196

(2)

10.3 Selective Epitaxy Silicon-Germanium HBT Process

198

(2)

10.4 Silicon-Germanium-Carbon HBT Process

200

(1)

10.5 Silicon-Germanium HBT Process Using Germanium Implantation

201

(2)

10.6 Radio Frequency Silicon-Germanium BiCMOS Process

203

(5)

References

208

(3)

11 Compact Models of Bipolar Transistors

211

(28)

11.1 Introduction

211

(1)

11.2 Ebers-Moll Model

212

(2)

11.3 Non-linear Hybrid-π Model

214

(2)

11.4 Modelling the Low-current Gain

216

(2)

11.5 AC Non-linear Hyhrid-π Model

218

(2)

11.6 Small-signal Hyhrid-rπ Model

220

(2)

11.7 Gummel-Poon Model

222

(3)

11.8 The SPICE Bipolar Transistor Model

225

(8)

11.8.1 Collector Current and Base Current

226

(1)

11.8.2 Forward Transit Time

226

(3)

11.8.3 Base Resistance

229

(1)

11.8.4 Collector Resistance

230

(1)

11.8.5 Emitter Resistance

231

(1)

11.8.6 Emitter, Collector and Substrate Capacitances

232

(1)

11.8.7 Additional Parameters

233

(1)

11.9 Limitations of the SPICE Bipolar Transistor Model

233

(1)

11.10 VBIL Model

234

(2)

11.11 Mextram Model

236

(2)

References

238

(1)

12 Optimization of Silicon and Silicon-Germanium Bipolar Technologies

239

(18)

12.1 Introduction

239

(1)

12.2 ECL and CML Propagation Delay Expressions

240

(2)

12.3 Calculation of Electrical Parameters

242

(2)

12.4 Gate Delay Estimation

244

(2)

12.5 Optimization Procedure

246

(1)

12.6 Optimization of Silicon Bipolar Technology

246

(5)

12.7 Optimization of Silicon-Germanium HBT Technology

251

(4)

References

255

(2)

Index

257

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Sige Heterojunction Bipolar Transistors

Summary

Author Biography

Table of Contents

Supplemental Materials