Micro and Nano Fabrication: Tools and Processes

Micro and Nano

Fabrication

Hans H. Gatzen · Volker Saile · Jürg Leuthold

Tools and Processes

Micro and Nano Fabrication

Hans H. Gatzen • Volker Saile

Jürg Leuthold

Micro and Nano Fabrication

Tools and Processes

With a Foreward and an Introduction by Richard S. Muller

123

Hans H. Gatzen

Center for Production Technology, Institute

for Micro Production Technology

Leibniz Universität Hannover

Garbsen

Germany

Volker Saile

KIT Division 5, Physics and Mathematics

Karlsruhe Institute of Technology

Eggenstein-Leopoldshafen

Germany

Jürg Leuthold

Institute of Electromagnetic Fields

ETH Zurich

Zurich

Switzerland

ISBN 978-3-662-44394-1 ISBN 978-3-662-44395-8 (eBook)

DOI 10.1007/978-3-662-44395-8

Library of Congress Control Number: 2014948737

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Foreward

After nearly half a century during which progress in building microsystems was

overwhelmingly focused on advances in the production of electronic elements—

mainly advances in integrated circuits, a new era has emerged. In this era, micro￾systems embrace new challenges that handle a diversity of signals, typically many

of which are nonelectrical. These systems, broadly identified as microelectrome￾chanical systems (MEMS) or nanoelectromechanical systems (NEMS), have a wide

range of applications in fields such as industrial controls, transportation, informa￾tion processing, biomedical devices, as well as many others. Especially noteworthy

is the development of MEMS/NEMS for applications in the new major product area

comprised of sophisticated mobile systems that are capable of being Wi-Fi-linked to

“cloud-based” communication and computing systems. This area is already a heavy

consumer of MEMS for accelerometers, gyros, and ground-position sensing.

Forthcoming are MEMS for health-monitoring and therapy, and for many more

applications. Invention and development in this area will occupy MEMS creators

for decades. It is, indeed, an exciting, highly fruitful time to begin work in this field!

By the end of 2012, the value of MEMS production on the world scale totaled

approximately 12 billion dollars (US) and growth of production was 11 %. These

numbers exhibit clearly that there is great opportunity for skilled performers in

MEMS design. It will be necessary to master designs that call for new materials and

processes. As history has shown, the chances of success in these endeavors are

strongly advanced by study of relevant established technology. This philosophy has

guided the authors in their choices and emphasis of topics in this book.

The authors have made use of their many years of working on MEMS and

NEMS to make clear where we are and how we got there. They have chosen topics

that will inspire and inform you, the reader, about the plentiful challenges and

opportunities in this field.

v

Having begun research and teaching in integrated circuits in the early 1960s,

followed with early work in what is now called MEMS at the end of the 1960s, I

have a strong bond with the field and with many of its major contributors. My wish

for you, the reader, mirrors the wish that has guided the authors: may this book help

you to find enthusiasm, fulfillment, and success in MEMS.

Berkeley, California, Fall 2013 Richard S. Muller

vi Foreward

Preface

Microelectromechanical systems (MEMS) and nanoelectromechanical systems

(NEMS) are miniaturized devices, quite often with a transducer function, and with

the smallest structural dimensions of 100 µm or 100 nm, respectively. Due to the

small dimensions, the production technology applied is rather different from that of

macroscopic systems. Processes often are more similar to those used in the semi￾conductor industry, without, however, reaching even closely this industry’s process

standardization.

This book is intended for the university student, technician, engineer, manager,

or scientist who would like to expose herself or himself to the field of MEMS and

NEMS fabrication. While the main emphasis is on technology, the book also

provides theoretical background on selected subjects, allowing a better under￾standing of physical and chemical technological basics.

As an introduction, Chap. 1 presents a brief look into the history of MEMS

(contributed by Richard S. Muller, UC Berkeley). Chapter 2 examines the nature of

Vacuum Technology. Chapters 3 and 4 discuss Deposition and Etching Technol￾ogies, respectively, two of the key technologies of micro and nano fabrication.

Chapter 5 covers Doping and Surface Modification technologies. Chapter 6 confers

on the third key technology: pattern transfer by Lithography. Chapter 7 presents a

unique technology for fabricating high aspect ratio microparts closely related to

lithography: LIGA. Chapter 8 discusses Nanofabrication by Self-assembly. Chapters

9 and 10 present Enabling Technologies: Wafer Planarization and Bonding as well

as Contamination Control by cleaning and production in a cleanroom. Chapter 11

concludes the book with a MEMS fabrication sample.

vii

Acknowledgments

Writing a technological book like this one draws on a multitude of resources. My

coauthors and I would like to acknowledge valuable contributions. A very

important part was access to the literature, which was expertly provided by the

German National Library of Science and Technology—University Library Han￾nover both for digital and (often quite rare) “paper” literature.

We are particularly grateful that a person so influential to the development of

microelectromechanical systems (MEMS) as Prof. Richard S. Muller, co-founder

of the Berkeley Sensor and Actuator Center (BSAC) at UC Berkeley, followed our

request to write a Foreward for this book and also to provide us with his view of the

historic perspectives of MEMS. We considered his latter contribution so valuable

that we chose to use it as our Introduction (Chap. 1). We further would like to thank

numerous persons in the industry and in research facilities for sharing with us

insight into micro and nano fabrication processes and the operation of respective

equipment and in particular: Niclas Mika and Rutger Voets, ASML, Veldhoven,

The Netherlands; Michael Sättler, Frank Schäfer, Jan Peter Stadler, and Heiko

Stahl, Robert Bosch GmbH, Reutlingen, Germany; Eric Pabo, EVG, Ft. Collins,

Colorado; David Fowler, Marvell Nanofabrication Laboratory, UC Berkeley,

Berkeley, California; Dennis Hollars, MiaSolé, Santa Clara, California (now

retired); Gabi Grützner, Jan Jasper Klein, Arne Schleunitz, Christine Schuster, Karl

Pfeiffer, Marko Vogler, and Anja Voigt, micro resist technology, Berlin, Germany;

Joachim Schulz, Microworks, Eggenstein-Leopoldshafen, Germany; Susie Wil￾liams, Oxford Instruments Plasma Technology, Bristol, UK; Karin Braun, Süss

MicroTec, Garching, Germany; and Johannes Hartung, von Ardenne, Dresden,

Germany.

At the IMT, Karlsruhe Institute of Technology, we are indepted to Dieter Maas

and Uwe Köhler, for providing us with detailed insight into tools and processes in

their cleanroom, Dieter Maas and Markus Breig for taking photographs, Timo

Heneka for preparing test specimens, Paul Abaffi for taking SEM micrographs, and

Peter J. Jakobs for providing insight into e-beam resists. We would like to express

thanks to Johann Schuardt for expertly drawing most of the pictures in the book, as

ix

well as Angelika Olbrich from the IPQ at the Karlsruhe Institute of Technology and

Claudia Hössbacher from the IFH, ETH Zurich for creating the rest.

Likewise, at the Leibniz Universität Hannover we would like to show appreci￾ation to Jürgen Becker and Veronika Gladilova at the IMPT for sharing equipment

and process information, Marc Christopher Wurz and Tom Creutzburg for pro￾viding pictures of the IMPT cleanroom, and in particular to Jasmin Scheerle for

demonstrating the use of cleanroom garment. We further would like to thank Fritz

Schulze Wischeler at the LNQE for equipment information at this facility.

We additionally would like to show gratitude to H. Jörg Osten, MBE, and

Jürgen Caro, PCI, both Leibniz Universität Hannover, for sharing their respective

course materials on semiconductor technology and self-organization of materials.

Furthermore, to Jürgen Caro we are particularly indebted for patiently and

instantaneously answering numerous chemical questions, suggesting chemical etch

processes, and subjecting Chap. 8 on Nanofabrication by Self-assembly to a critical

review. We would like to thank Youry Fedoryshyn, IFH, ETH Zurich, for a review

of Chap. 2 and Christine Ruffert, IMPT Hannover for reviewing the whole man￾uscript, providing detailed process information on the fab sample presented in

Chap. 11 as well as helping with choosing exercise questions. Lastly, we are

indebted to the team of Petra Jantzen, Mayra Castro, and Judith Hinterberg at

Springer for guiding this project to completion.

As the lead author, it is my privilege to extend special thanks to the IMT at the

Karlsruhe Institute of Technology for providing me with an office in Karlsruhe for

the duration of the project, allowing me to work on the book both in Hanover and

Karlsruhe. Furthermore, I am particularly indebted to my wife Carmen C. Gatzen,

who carefully proofread the whole manuscript repeatedly. Nevertheless, I am

responsible for residual errors. I also would like to express my gratitude to her for

providing administrative support and, last but not least, for offering an occasional

word of encouragement. Also, I acknowledge professional computer support from

Dieter Gutjahr and Oliver Klein, IMT Karlsruhe and Piriya Taptimthong, IMPT

Hannover, as well as software support from my son Matthias M. Gatzen, Baker

Hughes, Celle Technology Center.

Hanover, Germany, Spring 2014 Hans H. Gatzen

x Acknowledgments

Contents

1 Introduction—MEMS, a Historical Perspective .............. 1

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Vacuum Technology .................................. 7

2.1 Introduction into Vacuum Technology. . . . . . . . . . . . . . . . . . 7

2.1.1 Importance of Vacuum Technology for Processing

and Characterization . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.2 Historical Overview . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.3 Vacuum Technology Basics . . . . . . . . . . . . . . . . . . . 11

2.2 Gas Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.2.1 Kinetic Gas Behavior . . . . . . . . . . . . . . . . . . . . . . . 14

2.2.2 Ideal and Real Gas . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3 Gas Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.3.1 Flow Regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.3.2 Viscous Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.3.3 Molecular Flow and Transition Regime . . . . . . . . . . . 23

2.4 Vacuum Systems—Overview . . . . . . . . . . . . . . . . . . . . . . . . 24

2.4.1 Vacuum Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.4.2 Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.5 Roughing Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.5.1 Rotary Vane Pump . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.5.2 Rotary Piston Pump . . . . . . . . . . . . . . . . . . . . . . . . 28

2.5.3 Roots Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.5.4 Diaphragm Pump . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.6 High Vacuum Pumps I—Kinetic Transfer Pumps . . . . . . . . . . 31

2.6.1 Diffusion Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.6.2 Turbomolecular Pump . . . . . . . . . . . . . . . . . . . . . . . 33

2.6.3 Turbomolecular Drag Pump . . . . . . . . . . . . . . . . . . . 35

2.7 High Vacuum Pumps II—Entrapment Pumps . . . . . . . . . . . . . 36

2.7.1 Cryogenic Pumps I—Cryopump . . . . . . . . . . . . . . . . 36

2.7.2 Cryogenic Pumps II—Meissner Trap. . . . . . . . . . . . . 39

xi

2.7.3 Getter and Sputter Ion Pumps. . . . . . . . . . . . . . . . . . 40

2.8 Vacuum Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

2.8.1 Elastomer Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

2.8.2 Metal Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.9 Vacuum Measurement and Analysis . . . . . . . . . . . . . . . . . . . 43

2.9.1 Introduction into Pressure Measurement. . . . . . . . . . . 43

2.9.2 Direct-Reading Pressure Gauges . . . . . . . . . . . . . . . . 44

2.9.3 Indirect-Reading Gauges—Thermal Conductivity

Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

2.9.4 Indirect-Reading Gauges—Ionization Gauges . . . . . . . 48

2.9.5 Flow Meter and Mass Flow Controller . . . . . . . . . . . 49

2.9.6 Residual Gas Analysis (RGA) . . . . . . . . . . . . . . . . . 50

2.10 Desorption and Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2.10.1 Gas Release from Solids . . . . . . . . . . . . . . . . . . . . . 53

2.10.2 Leaks and Leak Detection . . . . . . . . . . . . . . . . . . . . 56

2.11 Vacuum Pump Applications . . . . . . . . . . . . . . . . . . . . . . . . . 57

2.11.1 Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

2.11.2 Examples of Vacuum Systems Used in Research . . . . 58

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

3 Deposition Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

3.1 Introduction and Historic Background . . . . . . . . . . . . . . . . . . 65

3.1.1 The Origins of Thin-Film Technology . . . . . . . . . . . . 65

3.1.2 Introduction into Deposition . . . . . . . . . . . . . . . . . . . 66

3.2 Thermal Physical Vapor Deposition (Thermal PVD) . . . . . . . . 67

3.2.1 Introduction into Thermal PVD

and Historic Overview. . . . . . . . . . . . . . . . . . . . . . . 67

3.2.2 Evaporation Process Theory . . . . . . . . . . . . . . . . . . . 68

3.2.3 Evaporation Hardware and Process . . . . . . . . . . . . . . 81

3.2.4 Molecular Beam Epitaxy (MBE). . . . . . . . . . . . . . . . 88

3.2.5 Pulsed Laser Deposition (PLD). . . . . . . . . . . . . . . . . 93

3.3 Plasma and Arc Physical Vapor Deposition

(Plasma/Arc PVD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

3.3.1 Introduction and History . . . . . . . . . . . . . . . . . . . . . 94

3.3.2 Plasma Physics. . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

3.3.3 Physics of Sputtering. . . . . . . . . . . . . . . . . . . . . . . . 106

3.3.4 Sputtering Hardware and Process . . . . . . . . . . . . . . . 116

3.3.5 Ion Beam Deposition (IBD) . . . . . . . . . . . . . . . . . . . 120

3.3.6 Cathodic Arc Plasma and Filtered Cathodic

Arc Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

3.4 Hybrid PVD Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

3.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

3.4.2 Ion Beam Assisted Evaporation . . . . . . . . . . . . . . . . 124

xii Contents

3.5 Chemical Vapor Deposition (CVD)-Like Processes . . . . . . . . . 125

3.5.1 Introduction into CVD-Like Processes

and Historic Overview. . . . . . . . . . . . . . . . . . . . . . . 125

3.5.2 Reaction Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

3.5.3 Thermodynamics of CVD . . . . . . . . . . . . . . . . . . . . 130

3.5.4 Gas Transport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

3.5.5 Film Growth Kinetics . . . . . . . . . . . . . . . . . . . . . . . 140

3.5.6 Thermal CVD—Reactors and Processes. . . . . . . . . . . 147

3.5.7 Plasma-Enhanced Chemical Vapor Deposition

(PECVD)—Reactors and Processes . . . . . . . . . . . . . . 150

3.5.8 Laser-Induced Chemical Vapor

Deposition (LCVD). . . . . . . . . . . . . . . . . . . . . . . . . 154

3.5.9 CVD Gas Safety and Analysis . . . . . . . . . . . . . . . . . 155

3.5.10 Atomic Layer Deposition (ALD). . . . . . . . . . . . . . . . 156

3.6 Physical-Chemical Hybrid Processes . . . . . . . . . . . . . . . . . . . 164

3.6.1 Activated Reactive Evaporation (ARE) . . . . . . . . . . . 164

3.6.2 Reactive Sputtering . . . . . . . . . . . . . . . . . . . . . . . . . 165

3.7 Liquid-Phase Deposition by Spin-Coating, Spray-Coating,

and Dip-Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

3.7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

3.7.2 Spin-Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

3.7.3 Spray-Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

3.7.4 Dip-Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

3.8 Solgel Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

3.8.1 Solgel Process Basics . . . . . . . . . . . . . . . . . . . . . . . 174

3.8.2 Solgel Process Example. . . . . . . . . . . . . . . . . . . . . . 175

3.9 Electrochemical and Chemical Reaction Deposition. . . . . . . . . 176

3.9.1 Electrochemical Deposition . . . . . . . . . . . . . . . . . . . 176

3.9.2 Chemical Deposition: Electroless Plating . . . . . . . . . . 189

3.9.3 Electrophoretic Deposition (EPD) . . . . . . . . . . . . . . . 190

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

4 Etching Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

4.1 Etching Technologies Basics . . . . . . . . . . . . . . . . . . . . . . . . 205

4.1.1 Introduction into Etching . . . . . . . . . . . . . . . . . . . . . 205

4.1.2 History of Etching . . . . . . . . . . . . . . . . . . . . . . . . . 207

4.2 Wet-Chemical Etching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

4.2.1 Wet-Chemical Etching Processes . . . . . . . . . . . . . . . 208

4.2.2 Wet-Chemical Etching of Single Crystal Silicon . . . . . 211

4.2.3 Etching of Insulators and Dielectrics . . . . . . . . . . . . . 231

4.2.4 Etching of Conductors. . . . . . . . . . . . . . . . . . . . . . . 232

4.3 Dry Etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

4.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

4.3.2 Physical Etching . . . . . . . . . . . . . . . . . . . . . . . . . . . 235

Contents xiii

4.3.3 Chemical Dry Etch . . . . . . . . . . . . . . . . . . . . . . . . . 249

4.3.4 Physical–Chemical Processes . . . . . . . . . . . . . . . . . . 255

4.4 Mechanical and Mechanical–Chemical Etching. . . . . . . . . . . . 264

4.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

4.4.2 Powder Blasting . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

4.4.3 Gas Cluster Ion Beam (GCIB) Technology . . . . . . . . 265

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

5 Doping and Surface Modification . . . . . . . . . . . . . . . . . . . . . . . . 273

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

5.1.1 The Importance of Doping and Surface

Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

5.1.2 History of Doping and Surface Modification . . . . . . . 273

5.2 Introduction into Doping . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

5.2.1 Electrical Conductivity in Solids . . . . . . . . . . . . . . . . 275

5.2.2 Semiconductor Properties and Doping of Silicon. . . . . 276

5.3 Doping by Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

5.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

5.3.2 Dopant Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . 278

5.3.3 Theoretical Description of Diffusion . . . . . . . . . . . . . 279

5.3.4 Atomistic Model of Diffusion. . . . . . . . . . . . . . . . . . 282

5.3.5 Diffusion Furnace and Process . . . . . . . . . . . . . . . . . 284

5.4 Doping by Implantation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

5.4.1 Introduction into Implantation. . . . . . . . . . . . . . . . . . 288

5.4.2 Implantation Science . . . . . . . . . . . . . . . . . . . . . . . . 289

5.4.3 Ion Implanter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

5.4.4 Rapid Thermal Processing (RTP) . . . . . . . . . . . . . . . 299

5.5 Doping Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

5.5.1 MEMS Applications . . . . . . . . . . . . . . . . . . . . . . . . 300

5.5.2 Wafer Technology Applications . . . . . . . . . . . . . . . . 301

5.6 Thermal Oxidation of Silicon . . . . . . . . . . . . . . . . . . . . . . . . 302

5.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

5.6.2 General Properties of SiO2 . . . . . . . . . . . . . . . . . . . . 303

5.6.3 Oxidation Mechanisms . . . . . . . . . . . . . . . . . . . . . . 303

5.6.4 Oxidation Equipment and Process . . . . . . . . . . . . . . . 307

5.6.5 Applications of Thermal SiO2. . . . . . . . . . . . . . . . . . 309

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310

6 Lithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

6.1 Overview and Historic Development . . . . . . . . . . . . . . . . . . . 313

6.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

6.1.2 Historic Development . . . . . . . . . . . . . . . . . . . . . . . 315

6.2 Mask-Based Lithography I—Optical Lithography . . . . . . . . . . 317

6.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

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6.2.2 Optical Lithography Process Sequence. . . . . . . . . . . . 318

6.2.3 Optical Basics of Lithography I—Exposure

Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

6.2.4 Optical Basics of Lithography II—Physical

Limitations of Optics. . . . . . . . . . . . . . . . . . . . . . . . 329

6.2.5 Selected Photolithography Tools and Processes. . . . . . 346

6.2.6 Advanced Semiconductor Lithography Processes . . . . 355

6.3 Mask-Based Lithography II: X-Ray Lithography

(XRL) Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

6.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

6.3.2 XRL Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364

6.3.3 XRL Mask Fabrication . . . . . . . . . . . . . . . . . . . . . . 366

6.4 Direct Write Lithography . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

6.4.1 Laser Lithography. . . . . . . . . . . . . . . . . . . . . . . . . . 367

6.4.2 E-Beam Lithography . . . . . . . . . . . . . . . . . . . . . . . . 371

6.5 Scanning Probe-Based Lithography . . . . . . . . . . . . . . . . . . . . 374

6.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374

6.5.2 AFM-Based Nanoscratch Lithography . . . . . . . . . . . . 374

6.5.3 Dip-Pen Nanolithography (DPN) . . . . . . . . . . . . . . . 375

6.6 Nanofabrication by Replication and Pattern Transfer . . . . . . . . 376

6.6.1 Nanoimprint Lithography (NIL) . . . . . . . . . . . . . . . . 376

6.6.2 Soft Lithography. . . . . . . . . . . . . . . . . . . . . . . . . . . 377

6.7 Photoresist and Ink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

6.7.1 Aggregate State Alternatives . . . . . . . . . . . . . . . . . . 380

6.7.2 UV Resists, Soluble When Cured . . . . . . . . . . . . . . . 381

6.7.3 UV Resists, Non-soluble When Cured: SU-8 . . . . . . . 383

6.7.4 Two-Photon Absorption Resists . . . . . . . . . . . . . . . . 384

6.7.5 X-Ray, E-Beam, and EUV Resists . . . . . . . . . . . . . . 385

6.7.6 Nanoimprint Resists . . . . . . . . . . . . . . . . . . . . . . . . 387

6.7.7 Inks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389

7 LIGA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

7.2 LIGA Infrastructure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

7.2.1 Challenge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

7.2.2 Synchrotron Radiation Source . . . . . . . . . . . . . . . . . 398

7.2.3 Electrochemical Deposition Capabilities. . . . . . . . . . . 400

7.2.4 Replication Capabilities . . . . . . . . . . . . . . . . . . . . . . 401

7.3 LIGA Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401

7.3.1 Mask Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . 401

7.3.2 X-Ray Lithography Process . . . . . . . . . . . . . . . . . . . 403

7.3.3 Mold Insert Fabrication by Electrodeposition . . . . . . . 404

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7.3.4 Replication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405

7.4 Direct LIGA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405

7.5 LIGA and Direct LIGA Production Samples . . . . . . . . . . . . . 405

7.5.1 LIGA Production Sample: Microspectrometer. . . . . . . 405

7.5.2 Direct LIGA Product Samples: Escapement Parts . . . . 406

7.6 LIGA and HARMST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408

8 Nanofabrication by Self-Assembly . . . . . . . . . . . . . . . . . . . . . . . . 409

8.1 Introduction and Historic Background . . . . . . . . . . . . . . . . . . 409

8.1.1 Top–Down and Bottom–Up Nanofabrication . . . . . . . 409

8.1.2 Historic Background . . . . . . . . . . . . . . . . . . . . . . . . 410

8.2 Self-Assembly Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

8.2.1 Introduction into Self-Assembly . . . . . . . . . . . . . . . . 411

8.2.2 Chemical, Physical, and Colloidal Self-Assembly . . . . 411

8.2.3 Static and Dynamic Self-Assembly . . . . . . . . . . . . . . 412

8.2.4 Co-Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413

8.2.5 Hierarchical Self-Assembly . . . . . . . . . . . . . . . . . . . 413

8.2.6 Directed (or Guided) Self-Assembly—Basics . . . . . . . 414

8.2.7 The Role of Defects in Self-Assembly. . . . . . . . . . . . 414

8.3 Self-Assembled Monolayers (SAMs) . . . . . . . . . . . . . . . . . . . 415

8.4 Directed Self-Assembly—Mechanisms. . . . . . . . . . . . . . . . . . 416

8.4.1 Surface Topography . . . . . . . . . . . . . . . . . . . . . . . . 416

8.4.2 Surface Wetting . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

8.5 Nanosystem Building Blocks—Examples. . . . . . . . . . . . . . . . 418

8.5.1 DNA Scaffolds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

8.5.2 Carbon Nanotubes (CNTs) . . . . . . . . . . . . . . . . . . . . 419

8.5.3 Block Copolymers . . . . . . . . . . . . . . . . . . . . . . . . . 420

8.5.4 Porous Alumina . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422

9 Enabling Technologies I—Wafer Planarization and Bonding . . . . 425

9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

9.2 Wafer Planarization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426

9.2.1 Planarization Challenge . . . . . . . . . . . . . . . . . . . . . . 426

9.2.2 History of CMP in the Semiconductor Industry . . . . . 427

9.2.3 CMP Equipment and Consumables . . . . . . . . . . . . . . 429

9.2.4 CMP Process and Issues . . . . . . . . . . . . . . . . . . . . . 436

9.2.5 CMP Applications . . . . . . . . . . . . . . . . . . . . . . . . . 437

9.3 Wafer Bonding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

9.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

9.3.2 Anodic Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

9.3.3 Silicon Fusion Bonding . . . . . . . . . . . . . . . . . . . . . . 443

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