FABRICATION OF GaAs DEVICES

Transcription

1 FABRICATION OF GaAs DEVICES by Albert G. Baca and Carol I. H. Ashby Sandia National Laboratories Albuquerque, NM, USA

2 CONTENTS Acknowledgment Abbreviations xiii 1 Introduction to GaAs devices Scope of this book GaAs materials Types of GaAs devices Electronic devices Photonic devices A brief history of GaAs devices History of GaAs electronic devices History of GaAs photonic devices Applications of GaAs devices Photonic device applications Electronic device applications 15 References 19 2 Semiconductor properties, growth, characterisation and processing techniques Chapter scope Semiconductor properties Energy levels and band structure in semiconductors Charged carriers in semiconductors Carrier transport and continuity equations Bulk crystal growth Methods of crystal growth Substrate properties and device requirements Epitaxy Molecular beam epitaxy Metal-organic chemical vapour deposition Material characterisation Light-based techniques Electron beam techniques 49 vii xv

3 2.5.3 Ionic techniques Electrical characterisation Processing techniques Back end processing and analysis Backside processing, die Separation and packaging Reliability Failure analysis Conclusion 66 References 67 Cleaning and passivation of GaAs and related alloys Chapterscope Cleaning and native oxide removal Removal of organic and metal ion contaminants Removal of native oxide Regrowth of native oxide Passivation of GaAs Electronic properties of the GaAs surface Chalcogenide passivation: S and Se Passivation for improved semiconductor regrowth Passivation for improved contact metallisation Special oxide passivations Dielectric passivations: PECVD and ECR SiN x and SiO x N y Conclusion 114 References 114 Wet etching and photolithography of GaAs and related alloys Chapterscope Mechanism of wet etch processes Rates and profiles Diffusion control Reaction-rate control Aging of etching Solution Practical wet etching Photoresist issues Basic wet etches Acidic wet etches Metal etches 135 vin

4 4.5 Compositional selectivity GaAs versus AlGaAs selectivity Selectivity versus other materials Effects of doping type Electrolytic effects in wet etching Effects of defects and damage Conclusion 144 References Dry etching of GaAs and related alloys Chapter scope Comparison of wet and dry etching Overview of dry etching processes Ion-beam etching (IBE) and ion effects in other plasma processes Chemical dry etching Plasma etching at very low ion energies Conventional reactive ion etching (RIE) Halogen-based plasmas for RIE Alkane-based plasmas for RIE High-density plasma etching (HDPE) Reactive-ion-beam etching (RIBE) and chemically assisted ion-beam etching (CAIBE) General issues for dry etching Etch uniformity Damage from dry etching Resists and their behaviour in dry etching processes Advantages of Ar addition Methods for end-point determination Plasma diagnostics for trouble-shooting Chamber cleaning issues Effect of Chamber materials Conclusion 177 References Ohmic contacts Chapter scope Principles of ohmic contacts Definitions Physics of ohmic contact formation Metallurgy of ohmic contact formation Fabrication and testing of ohmic contacts Fabrication of ohmic contacts Measurements of ohmic contacts 191 ix

5 6.4 Ohmic contacts to n-type GaAs GeAuNi ohmic contacts Limited Au contacts for improved thermal stability Ohmic contacts to heavily doped surfaces Refractory metals and contacts based on reducing the surface bandgap Ohmic contacts to p-type GaAs Conclusion 201 References Schottky contacts Chapterscope Physics and characterisation of Schottky contacts Physics of Schottky contacts Interfacial properties of Schottky contacts Fabrication of Schottky contacts Basic recessed gate fabrication Self-aligned Schottky gates Schottky gate structures Electrical characteristics of GaAs Schottky contacts Reliability of GaAs Schottky contacts Conclusion 227 References Field effect transistors Chapterscope Field effect transistor basics Field effect transistor tutorial Field effect transistor Performance and reliability issues Field effect transistor structures and materials Overview of field effect transistor fabrication Doping FETs Isolation of FETs Source and drain ohmic contacts Gate metal contacts Passivation Degradation of FETs Definition and characterisation of hot electrons 257 x

6 8.8.2 Hot electron degradation Other types of degradation Conclusion 265 References Heterojunction bipolar transistors Chapter scope HBT basics Bipolar transistor tutorial Other GaAs HBT Performance and reliability issues HBT device structure and material issues Overview of HBT fabrication MESA etching for GaAs-based HBTs Emitter mesa etch Base mesa etch Collector mesa etch Ohmic contacts for GaAs-based HBTs Emitter metal ohmic contacts Base metal ohmic contacts Collector metal ohmic contacts Passivation of GaAs-based HBTs Ledge passivation Dielectric passivation Sulphur passivation Variations on HBT processing Reliability of HBTs Conclusions 303 References Wet oxidation for optoelectronic and MIS GaAs devices Chapter scope Mechanism of wet oxidation processes Chemistry of wet and dry oxidation of AlGaAs Electronic consequences of oxidation processes Rates and profile evolution Al-mole-fraction effects Layer thickness effects Proximity enhancement effect Wet oxidation of other materials Miscellaneous observations Practical wet oxidation 319 xi

7 10.5 Applications in optoelectronic devices Structural issues for oxide VCSELs Defect-related issues for optoelectronic devices Applications in electronic GaAs devices Problems with wet and dry oxidation for MIS devices GaAs-on-insulator applications Conclusion 326 References 327 Glossary 329 Index 347 xn