Micro and nano fabrication tools and processes

Center for Production Technology, Institutefor Micro Production Technology Leibniz Universität Hannover Garbsen Germany Volker Saile KIT Division 5, Physics and Mathematics Karlsruhe Ins

Micro and Nano Fabrication

Hans H Gatzen · Volker Saile · Jürg Leuthold

Tools and Processes

Tai ngay!!! Ban co the xoa dong chu nay!!!

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

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

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

Library of Congress Control Number: 2014948737

Springer Heidelberg New York Dordrecht London

© Springer-Verlag Berlin Heidelberg 2015

This work is subject to copyright All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer Permissions for use may be obtained through RightsLink at the Copyright Clearance Center Violations are liable to prosecution under the respective Copyright Law The use of general descriptive names, registered names, trademarks, service marks, etc in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.

While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made The publisher makes no warranty, express or implied, with respect to the material contained herein.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

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

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

microelectrome-chanical systems (MEMS) or nanoelectromemicroelectrome-chanical systems (NEMS), have a wide

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

“cloud-based” communication and computing systems This area is already a heavyconsumer of MEMS for accelerometers, gyros, and ground-position sensing.Forthcoming are MEMS for health-monitoring and therapy, and for many moreapplications Invention and development in this area will occupy MEMS creators

By the end of 2012, the value of MEMS production on the world scale totaledapproximately 12 billion dollars (US) and growth of production was 11 % Thesenumbers exhibit clearly that there is great opportunity for skilled performers inMEMS design It will be necessary to master designs that call for new materials andprocesses As history has shown, the chances of success in these endeavors arestrongly advanced by study of relevant established technology This philosophy hasguided 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 andNEMS to make clear where we are and how we got there They have chosen topicsthat will inspire and inform you, the reader, about the plentiful challenges and

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

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

Microelectromechanical systems (MEMS) and nanoelectromechanical systems(NEMS) are miniaturized devices, quite often with a transducer function, and with

small dimensions, the production technology applied is rather different from that ofmacroscopic systems Processes often are more similar to those used in the semi-

standardization

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

NEMS fabrication While the main emphasis is on technology, the book alsoprovides theoretical background on selected subjects, allowing a better under-standing of physical and chemical technological basics

Technol-ogies, respectively, two of the key technologies of micro and nano fabrication

unique technology for fabricating high aspect ratio microparts closely related to

concludes the book with a MEMS fabrication sample

vii

Writing a technological book like this one draws on a multitude of resources Mycoauthors and I would like to acknowledge valuable contributions A veryimportant part was access to the literature, which was expertly provided by the

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

of the Berkeley Sensor and Actuator Center (BSAC) at UC Berkeley, followed ourrequest to write a Foreward for this book and also to provide us with his view of thehistoric perspectives of MEMS We considered his latter contribution so valuable

numerous persons in the industry and in research facilities for sharing with usinsight into micro and nano fabrication processes and the operation of respectiveequipment and in particular: Niclas Mika and Rutger Voets, ASML, Veldhoven,

Stahl, Robert Bosch GmbH, Reutlingen, Germany; Eric Pabo, EVG, Ft Collins,Colorado; David Fowler, Marvell Nanofabrication Laboratory, UC Berkeley,

Pfeiffer, Marko Vogler, and Anja Voigt, micro resist technology, Berlin, Germany;Joachim Schulz, Microworks, Eggenstein-Leopoldshafen, Germany; Susie Wil-

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

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

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

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

and process information, Marc Christopher Wurz and Tom Creutzburg for viding pictures of the IMPT cleanroom, and in particular to Jasmin Scheerle fordemonstrating the use of cleanroom garment We further would like to thank FritzSchulze Wischeler at the LNQE for equipment information at this facility

course materials on semiconductor technology and self-organization of materials

instantaneously answering numerous chemical questions, suggesting chemical etch

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

man-uscript, providing detailed process information on the fab sample presented in

indebted to the team of Petra Jantzen, Mayra Castro, and Judith Hinterberg atSpringer for guiding this project to completion

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

the duration of the project, allowing me to work on the book both in Hanover andKarlsruhe Furthermore, I am particularly indebted to my wife Carmen C Gatzen,who carefully proofread the whole manuscript repeatedly Nevertheless, I amresponsible for residual errors I also would like to express my gratitude to her forproviding administrative support and, last but not least, for offering an occasionalword of encouragement Also, I acknowledge professional computer support fromDieter Gutjahr and Oliver Klein, IMT Karlsruhe and Piriya Taptimthong, IMPTHannover, as well as software support from my son Matthias M Gatzen, BakerHughes, Celle Technology Center

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

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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

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

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

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

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

9.3.4 Bond Alignment 447

9.3.5 Direct Wafer Bonding Applications 449

References 452

10 Enabling Technologies II—Contamination Control 455

10.1 Introduction 455

10.1.1 The Necessity for Cleanliness 455

10.1.2 Contamination Removal by Cleaning 456

10.1.3 Minimization of Contamination by Fabrication in a Clean Environment 457

10.2 Cleaning Technology 457

10.2.1 Cleaning—An Overview 457

10.2.2 Aqueous Cleaning 458

10.2.3 Solvent Cleaning 465

10.2.4 Mechanical Cleaning 467

10.2.5 Rinsing and Drying 468

10.2.6 Dry Cleaning Technology 471

10.3 Cleanroom Technology 472

10.3.1 Introduction and History 472

10.3.2 Cleanroom Classification Standards 474

10.3.3 Laminar Airflow 476

10.3.4 High Efficiency Air Filtration 477

10.3.5 Cleanroom 479

10.3.6 Local Clean Area Solutions 484

10.3.7 Cleanroom Staff 487

References 491

11 Device Fabrication—An Example 495

11.1 Introduction 495

11.2 Device Description 496

11.2.1 Magnetic Levitation Principle 496

11.2.2 Magnetic Levitation Microsystem Integration Concept 496

11.2.3 Stator 497

11.2.4 Traveler with Permanent Magnet 499

11.3 Photoresists 499

11.4 Mask Steps 499

11.4.1 Introduction 499

11.4.2 Stator Masks and Their Uses 500

11.4.3 Stator Wafer Level Mask Overlay 502

11.4.4 Traveler Mask 502

11.5 Process Steps 503

11.5.1 Coil System Fabrication 503

11.5.2 Traveler System Fabrication 508

11.5.3 Dicing, Component Evaluation, and System Integration 510

References 512

Index 513

Hans H Gatzenreceived a Ph.D equivalent in Mechanical Engineering from theRWTH Aachen in Aachen, Germany, and held various positions in the computerperipherals industry in Germany and the USA from 1973 to 1992 In 1992, hefounded the Institute for Microtechnology (IMT) at the Hanover University in

his retirement in 2010 He is a Fellow of the American Society of MechanicalEngineers (ASME) and a member of Acatech (National Academy of Science andEngineering)

Elektronen-Synchrotron DESY in Hamburg, Germany, until 1989 From 1989 to

1998, he served as the Director of the J Bennett Johnston, Sr., Center for AdvancedMicrostructures and Devices (CAMD), Baton Rouge, Louisana, USA Since 1998,

he is Professor of Microstructure Technology at the Karlsruhe Institute of nology (KIT) Currently, he serves as Head of the KIT Division 5, Physics andMathematics

plasmonics, integrated optics, and optical communications From 2004 to 2013 hewas a full Professor at the Karlsruhe Institute of Technology (KIT) in Germany and

xix

µCP Microcontact printing

xxi

CNF Cornell Nanoscale and Science Facility

HARMNST High aspect ratio micro and nanostructure technology

MEMS Microelectromechanical systems

sol-gel process Trademark of the Fraunhofer-Gesellschaft zur

RF Radio frequency

and diluted

UHV Ultrahigh vacuum

Introduction —MEMS, a Historical

Perspective

Richard S Muller

MEMS began to appear when researchers considered ways to reduce the sizes ofengineering devices and systems An important influence came from the recognition

of new possibilities to do this by using technology and designs that had, in the1930s, produced an electron microscope By the end 1930s, however, World War II

apparent A compelling urgency for miniaturization arose from the needs for robotic

progress made in robotic-control systems became a stimulant for space research, anarea brought into sharp focus at the newly founded Jet Propulsion Laboratory (JPL)

at the California Institute of Technology (Caltech)

It was on the Caltech campus that Physics Professor Richard Feynman in 1959

pointed out the extraordinary possibilities that would be afforded by building crosystems on the scale of the natural framework of the molecular arrays that form

enthusiastic readership Widespread extractions and references of the lecture hadled to its republication several times The original article was cited nearly 1,500

before the general introduction of a technology that could make practical use of the

“room at the bottom.” That technology, integrated circuits, was to appear as the newdecade, the 1960s, began

the appearance of the silicon integrated circuit (IC) The growth of MEMS, however,was very slow because researchers concentrated their attention on the expandingcapabilities and commercial products that could be developed in purely electronicintegrated systems The seminal MEMS advance referred to above was taken whenmechanical as well as electronic functions were collaboratively incorporated into a

© Springer-Verlag Berlin Heidelberg 2015

H.H Gatzen et al., Micro and Nano Fabrication,

DOI 10.1007/978-3-662-44395-8_1

1

new batch-fabricated solid-state device Researchers at the Honeywell CorporationLaboratory incorporated a thinned-silicon diaphragm into a silicon chip On the

piezoresistors were positioned in order to provide electrical signals responsive to

way became one of the earliest microelectromechanical systems products, and theycontinue to be produced in large quantities to the present day

This early example of building a microelectromechanical element inspired manyfollow-on developments Other research programs early in the 1960s focused on

This area was especially researched at RCA laboratories in New Jersey, where

were shown to have great importance in inventing a new class of devices, acoustic-wave transducers and resonators which have grown to be of very great

surface This was demonstrated at Bell Telephone Laboratories and used to enableautomatic bonding of electronic devices and circuits in a process that became

micro-beams using the vapor deposition of metals was dramatically shown in a

The decade of the 1970s saw intense focus on the development of more andmore complex integrated circuits exploiting the planar process and overwhelm-ingly making use of bipolar technology Solid-state device research was heavilyfocused on understanding and electrically stabilizing the interface between silicon

—which had been demonstrated as a research result in 1963 A perspective on thetravails that persisted for more than 10 years is the subject of an IEEE Spectrum

During the 1970s, fundamental research was underway at a number of locations

into geometrical shapes that could be suitable for mechanical or optical elements

An overview of these developments has been given in a review article presented at

etching to produce a micro-accelerometer, described in 1979, raised widespread

technology being used on single-crystal silicon was exploited both to produceoptical devices of high quality and to control the dimensions of fluidic chambers inhigh-quality ink-jet printing As more and more activity was begun in this area,researchers from disparate locations recognized that a new research area was being

born Through the efforts of Professor Wen Ko (Case Western Reserve University),

a new conference focused on this research area was convened in Boston in 1981and those present organized themselves so that the conference, called Transducers

1981 would recur at two-year intervals This pattern persists yet in 2014, and scores

of important results in the MEMS area have been reported in the conference digestsfor this series Also, in 1981, a much-cited paper describing the new focus of siliconfor mechanical as well as electrical structures was written by Kurt Petersen, then at

of its major growth period in the 1980s

The increased pulse of activity in the early 1980s led the US National ScienceFoundation (NSF) to sponsor workshops to explore research and open questions in

(July, 1987), Hyannis, Massachusetts, (November, 1987), and Princeton, NewJersey, (January, 1988) Panel members for this NSF project consisted of many ofthe most active researchers in micro sensors and actuators An early consideration

“Micromechatronics” had been applied several times The name chosen by the

signals in any domain: electrical, optical, mechanical, magnetic, fluidic, thermal etc

its acronym MEMS can be pronounced The choice of the term MEMS became fullydominant after it was accepted by IEEE and ASME to be used when, in 1992, these

with elements that inter-relate signals in any domain

made possible the fabrication of highly complex mechanisms and the introduction

of important new commercial areas for MEMS such as accelerometers for air-bag

field of engineering around the world In 1991, many papers and an extensive

through the 1990s led the US National Research Council, and National MaterialsAdvisory Board to carry out a study that focused on advanced materials and fab-rication methods for MEMS The report of this study, published by the US National

Academy of Engineering [19], provides a snapshot of the MEMSfield at the end of

fast growth rate in new research, in product development, and in impact on societyitself MEMS has become so big that a single list of seminal references is notfeasible Not only is this the case, but it is also true that the new facility of searching

Anyone seeking information can, and should, use a favorite search engine to gaindata tailored to whatever special interests are in her/his mind Google Scholar is anexample of powerful software that can be used in this way Access to Google Scholar

causing the query display to have that label Should the user then wish information,for example, about a particular MEMS researcher, he/she should simply type in the

October 6, 2013)

Other literary data mines, such as those set up for publications (Xplore for IEEE

select a publication type, e.g., books and ebooks, conference publications, journals

pub-lisher, for example The breadth of any search can be narrowed in many ways as is

publisher

References

1 Feynman RP (1960) There ’s plenty of room at the bottom Caltech Eng Sci 25:22

2 Feynman RP (1992) There ’s plenty of room at the bottom IEEE/ASME J Microelectromech Syst 1:60

3 Tufte ON, Chapman PW, Long D (1962) Silicon diffused element piezoresistive diaphragms.

J Appl Phys 33:3322

4 Weimer PK (1962) The TFT, a new thin- film transistor Proc IRE 50:1462

5 White RM, Voltmer FW (1965) Direct piezoelectric coupling to surface elastic waves Appl Phys Lett 7:314

6 Muller RS, Conragan J (1965) Transducer action in a metal-insulator-piezoelectric semiconductor triode Appl Phys Lett 6:83

7 Lepselter MP (1969) Semiconducting device including beam leads US patent 3,426,252, issued Feb 4, 1969 to Bell Laboratories

8 Nathanson HC, Newell WE, Wickstrom RA, Davis RA Jr (1967) The resonant gate transistor IEEE Trans Electr Devices 14:117

9 Riesenman MJ (1991) Wanlass ’s CMOS circuit IEEE Spectrum 28:5

10 Seidel H (1987) Crystalline semiconductor micromachining In: Transducers ’87, Record of the 4th international conference on solid-state sensors and actuators, Tokyo, p 120, IEE Japan

11 Roylance LM, Angell JB (1979) A batch-fabricated silicon accelerometer IEEE Trans Electr Devices ED-26, vol 12, p 1911

12 Petersen KE (1982) Silicon as a mechanical material Proc IEEE 20:420

13 Kaigham G, Jarvis J, William Trimmer W (eds) (1988) Small machines, large opportunities: a report on the emerging field of microdynamics National Science Foundation, Washington

14 Howe RT, Muller RS (1983) Polycrystalline silicon micromechanical beams J Electrochem Soc 130:1420

15 Payne RS, Sherman S, Lewis S, Howe RT (1995) Surface micromachining: from vision to reality to vision [accelerometer] In: IEEE 41st international solid-state circuits conference, 15 Feb 1995, p 164

16 Wise KD (1986) Integrated sensors: key to future VLSI systems IEEE Proc 6th sensor symposium, p 1

17 Muller RS, Howe RT, Senturia SD, Smith RL, White RM (1990) Microsensors Volume in the IEEE Press Selected Reprint Series, TK7870.M4575

18 Trimmer WS (ed) (1997) Micromechanics and MEMS, classic and seminal papers to 1990 IEEE Press, New York

19 Muller RS (ed) (1997) Microelectromechanical systems, advanced materials and fabrication methods NMAB-483, National Academy Press, Washington

Vacuum Technology

partial vacuum conditions, i.e., at pressures orders of magnitude below ambient

during their deposition Since the pressure in the vacuum chamber during a down passes through up to 13 orders of magnitude, it is not surprising that ratherdifferent gas flow conditions have to be mastered A look at gas properties and gasflow basics provides an essential understanding for these conditions A vacuumsystem reaching ultrahigh vacuum consists of a combination of at least two pumps,

pump-a roughing pump working in the viscous flow regime pump-and pump-a high-vpump-acuum pumpworking down to the molecular flow regime Typically, roughing pumps are dis-placement pumps, while high-vacuum pumps are either kinetic transfer pumps orentrapment pumps General vacuum issues covered are the vacuum seal, vacuummeasurement and analysis, as well as desorption and leaks A discussion of vacuumpump applications concludes this chapter

2.1 Introduction into Vacuum Technology

2.1.1 Importance of Vacuum Technology for Processing

and Characterization

A majority of processes for fabricating microelectromechanical systems (MEMS)and nanoelectromechanical systems (NEMS) are conducted under partial vacuumconditions, i.e., at pressures orders of magnitude below ambient atmospheric

atoms with a free path in a line-of-sight process, in which they are traveling directlyfrom a source to a substrate to be coated or etched During the travel, the atoms aresubject to collisions with gas molecules present in the process chamber If thenumber of collisions with these gas molecules is too large, the atoms lose a sub-stantial amount of their energy They then either would barely reach the target, with

© Springer-Verlag Berlin Heidelberg 2015

H.H Gatzen et al., Micro and Nano Fabrication,

DOI 10.1007/978-3-662-44395-8_2

7

no energy left for traveling to an appropriate position in a crystal structure (in case

transfer at the bombarded surface (in case of a physical etching process), tively The second reason is minimizing the impingement of air or other gas

What, strictly speaking, is vacuum? It is a space completely free of matter Such

a condition neither exists naturally on earth (and not even in outer space), nor is itachievable by technical means Absolute vacuum does not exist This was postu-lated even in the middle ages when it was stated that nature abhors vacuum (Latin:horror vacui) Therefore, an atmosphere with a pressure below ambient strictly

mentioned that, depending on the source, the names of vacuum regimes andboundaries between them occasionally vary

examples and their pressure ranges, varying from analysis applications to space

Institute of Technology (KIT) in Eggenstein-Leopoldshafen, Germany, whereatmospheric conditions are simulated under various pressure conditions

2.1.2 Historical Overview

pumps are not able to raise the water more than 10 m He concluded that the water

in a tube was pushed up by the ambient pressure of the atmosphere and not sucked

by vacuum He continued this work after Galilei had passed away and conducted anexperiment By using mercury, which is 13.5 times denser than water, he reasonedthe atmospheric pressure should only be able to push up the mercury 1/13.5 times

was closed at the bottom with mercury and covered the top with a plug Then he

Table 2.1 Vacuum phases

Degree of vacuum Pressure range

Rough 105> p > 102 750 > p > 7.5 × 10−1

Fine 102> p > 10−1 7.5 × 10 −1 > p > 7.5 × 10−4High 10−1> p > 10−5 7.5 × 10 −4 > p > 7.5 × 10−8

< p Source O’Hanlon [ 1 ], Umrath [ 2 ], Ohring [ 13 ]

Fig 2.1 Industrial vacuum usage (adapted from Umrath [ 2 ])

Fig 2.2 Karlsruhe Institute of Technology ’s AIDA (Aerosol Interaction and Dynamics in the Atmosphere) facility Pressure range: 102–10 5 Pa

placed the tube upside down in a bowl of mercury and removed the plug Mercurypoured out of the tube and a mercury column of approx 750 mm remained in the

vacuum In creating this experiment, Torricelli invented the mercury barometer

atmospheric pressure At the Reichstag in Regensburg in 1654, he showed that two

between them evacuated, could not be pulled apart by two teams of eight horses

Modern high-vacuum technology is considered to start in 1905 with the German

potential of a metal The contact potential is the potential an electron has to come when performing a transition from vacuum to the surface of a metal, a phe-

sides, in particular since Gaede systematically conducted research regarding nate vacuum pump principles, thereby inventing the molecular pump in 1912, thediffusion pump in 1915, and 1935 to utilize gas ballast on rotary vane pumps, which

Vacuum

Ambient atmosphere

2.1.3 Vacuum Technology Basics

2.1.3.1 Ideal Gas Law

For gases at not too high pressures and temperatures, there are rather simple

inversely with its pressure or, formulated differently, the product of volume andpressure is proportional to the mass m and a function of the (absolute) temperature T:

dis-covered in 1802 that for a constant pressure p, the volume V is a function of

p

Fig 2.4 Otto von Guericke ’s experiment (Sketch by Gaspar Schott [ 8 ])

Equations (2.1) and (2.2) may be combined and extended to

which represents the equation of state for ideal gases, also named ideal gas law

absolute temperature

Particularly valuable is the ideal gas equation in its molar form To get to it, we

constant with the value

The ratio m/M describes the number of moles ν present in volume V

2.1.3.2 Avogadro’s Number and Boltzmann’s Constant

According to the hypothesis of the Italian mathematical physicist Amadeo

for ideal gases a certain quantity of substance (containing a certain number ofmolecules) has an equal volume

or

The quotient of NA and R is Boltzmann’s constant kB, named after the Austrian

2.1.3.3 Particle Density

kinetic gas theory (see below), n is a function of the pressure p [Pa], Boltzmann’sconstant k [J/K], and the thermodynamic temperature T [K] For ideal gases, therelationship is as follows:

q

To conclude the vacuum technology basics, let us have a closer look at the pressure

(and therefore the force F always attacks at a right angle) given by

The partial pressure of a gas or vapor equals the pressure that a gas or vapor wouldexhibit if it were the sole constituent inside the container

2.2 Gas Properties

2.2.1 Kinetic Gas Behavior

closer look at how a pressure is created in a gas atmosphere and on a solid surface

in contact with the gas, respectively By doing so, we will also shed light on otherphenomena occurring in a gas atmosphere The kinetic theory of gases provides us

ideal gas is a reasonable approximation of a real gas, particularly at extreme dilution

In an ideal gas, there are no attractive or repulsive forces between gas molecules

diameters

The basics of the kinetic gas theory are as follows: gas consists of a large number

molecules

The gas molecules are in a continuous state of random motion without anypreference in direction Each molecule moves along a straight line, until it collideswith another molecule or the wall of the pressure vessel Due to the impact, itchanges its direction and continues on another straight path in another direction,

In the ideal gas, the gas molecules do not exert forces onto each other except forcollisions (i.e., the moment of contact) Collisions of gas molecules with each otherand with the wall are elastic The impact due to collisions with the wall generatesthe gas pressure

λ

Fig 2.5 Free path λ of gas

particles between collisions

2.2.1.1 Mean Free Path

The continuous elastic collisions and the accompanying exchange of kinetic energy

d0

σ

Fig 2.6 Atom diameter d 0

and scattering cross section σ

The equation for only one component direction is as follows (taking thex-direction as an example):

ffiffiffiffiffiffiffiffiffi2RTM

R1 0

r

ð2:18Þ

function f v ð Þ for various

temperatures T It also shows

the most probable velocity v p

As an example, let us calculate the arithmetic mean velocityv of air at 27 °C Wewill carry the dimensions, which is a good engineering practice for thermodynamiccalculations It will alert us to errors, if the unit for the value we are calculating isincorrect (e.g., anything but m/s for a velocity).

v ¼

ffiffiffiffiffiffiffiffiffi8RTpM

r:

Constants and values required are:

K kmol

We further need the relationship between the dimensions for force [N],

v ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi8

r

2.2.1.3 Pressure Creation

By now we have seen that the gas molecules traveling with a velocity v impinge on