Handbook of Advanced Plasma Processing Techniques

Springer-Verlag Berlin Heidelberg GmbH ONLINE LlBRARY

Physics and Astronomy http://www.springer.de/phys/

R. J. Shul S. J. Pearton (Eds.)

Handbook of Advanced Plasma Proeessing Teehniques

With 413 Figures Including 10 in Color

i Springer

Dr. Randy J. Shul Sandia National Laboratories Dept. 1313, MS 0603 PO Box 5800 NM 87185 Albuquerque, USA

Professor Stephen J. Pearton University of Florida Dept. Mat. Sci. Eng. 132 Rhines Hali, PO Box 116400 FL 32611 Gainesville, USA

ISBN 978-3-642-63096-5 ISBN 978-3-642-56989-0 (eBook) DOI 10.1007/978-3-642-56989-0

Library of Congress Cataloging-in-Publication Data. Handbook of advanced plasma processing tech­niques / R.). Shul, S.). Pearton (eds.). p.cm. Includes bibliographical references and index. ISBN 3540667725 (alk. paper) 1. Plasma engineering. 2. Electronic circuits-Design and construction. 3. Plasma etching. 4. Plasma spraying. 1. Shul, R.). II. Pearton, S.). TA2020.H35 2000 621.044-dc21 00-038824

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Preface

Pattern transfer by dry etching and plasma-enhanced chemical vapor de­position are two of the cornerstone techniques for modern integrated cir­cuit fabrication. The success of these methods has also sparked interest in their application to other techniques, such as surface-micromachined sen­sors, read/write heads for data storage and magnetic random access memory (MRAM). The extremely complex chemistry and physics of plasmas and their interactions with the exposed surfaces of semiconductors and other materi­als is often overlooked at the manufacturing stage. In this case, the process is optimized by an informed "trial-and-error" approach which relies heavily on design-of-experiment techniques and the intuition of the process engineer. The need for regular cleaning of plasma reactors to remove built-up reaction or precursor gas products adds an extra degree of complexity because the interaction of the reactive species in the plasma with the reactor walls can also have a strong effect on the number of these species available for etching or deposition. Since the microelectronics industry depends on having high process yields at each step of the fabrication process, it is imperative that a full understanding of plasma etching and deposition techniques be achieved.

In this volume, we have enlisted experts in the field of plasma physics, plasma and process modeling, plasma diagnostics, plasma-induced damage and various applications such as creation of photomasks, Si MEMS, com­pound semiconductor etching, high-density plasma deposition and magnetic materials etching, to give detailed overviews of these topics. The coverage should appeal to process engineers, researchers in both industry and acad­emia and those entering the field who need a single-source review of particular subjects.

Albuquerque and Gainesville, February 2000

R.J. Shut S.J. Pearion

Contents

1 Some Fundamental Aspects of Plasma-Assisted Etching J.W. Coburn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 1

1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 The Evolution of Plasma Etching Equipment ................. 4

1.2.1 The "Barrel" Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.2 Planar and Cylindrical Diode Systems ................. 5 1.2.3 Planar Triode Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.2.4 Dual Frequency Planar Triode Systems. . . . . . . . . . . . . . . . . 9 1.2.5 Inductively Coupled Plasmas,

Wave Generated Plasmas, etc. ........................ 9 1.3 The Role of Ions in Reactive Ion Etching. . . . . . .. . . . . . . . . . . . .. 12

1.3.1 Ion-Assisted Gas-Surface Chemistry and the Resulting Etching Anisotropy. . . . . . . . . . . . . . . . .. 12

1.3.2 Mechanistic Aspects of Ion-Assisted Gas-Surface Chemistry 15 1.3.3 Other Factors That Influence Etching Anisotropy. . . . . . .. 18

1.4 The Influence of the Reactor Walls and Other Surfaces. . . . . . . .. 22 1.4.1 The Etching Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22 1.4.2 Polymer Deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 24 1.4.3 Surface-Catalyzed Atom-Atom Recombination. . . . . . . . .. 25

1.5 Ion Beam-Based Methods .................................. 27 1.6 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31

2 Plasma Fundamentals for Materials Processing J.E. Stevens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33

2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33 2.2 Single Particle Motion ..................................... 36 2.3 Collision Processes ........................................ 38 2.4 Velocity Distributions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 43 2.5 Sheaths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 45 2.6 Plasma Transport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51 2.7 Dielectric Properties ..................................... " 55 2.8 Plasma Sources for Thin Films Processing. . . . . . . . . . . . . . . . . . .. 57

2.8.1 Capacitive Sources .................................. 58

VIII Contents

2.8.2 High Density Sources .... . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59 2.8.3 Inductive Sources ................................... 60 2.8.4 ECR Sources ....................................... 61 2.8.5 2.8.6 2.8.7

Helicon Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wave Sources ...................................... . Downstream Sources ................................ .

References .................................................... .

3 Plasma Modeling

62 63 63 65

E. Meeks and P. Ho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 69

3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 69 3.2 Historical Perspective. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70 3.3 Plasma Modeling Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71

3.3.1 Well Mixed Reactor Models and Applications (O-D). . . . .. 73 3.3.2 One-Dimensional Models and Applications. . . .. . . . . . . . .. 76 3.3.3 Two-Dimensional Models and Applications. . .. . . . . . . . .. 79 3.3.4 Three-Dimensional Models and Applications. . . . . . . . . . .. 83 3.3.5 2-D and 3-D Profile Evolution Models and Applications.. 84

3.4 Chemical Reaction Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 84 3.4.1 Gas-Phase Kinetic and Transport Processes. . . . . . . . . . . .. 86 3.4.2 Surface Chemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 92 3.4.3 Reaction Mechanism Validation, Tuning, and Reduction.. 96 3.4.4 Sample Reaction Mechanism. . . . . . . . . . . . . . . . . . . . . . . . .. 98

3.5 Examples of Application of Plasma Modeling to Design or Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 103 3.5.1 Optimization of Plasma Cleaning Process

to Reduce Reactor Emissions ......................... 103 3.5.2 Optimization of Chemical Downstream Etch

Process Conditions ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 3.5.3 Reactor Design: Scaling-Up from 200 to 300mm Wafers .. 111 3.5.4 Mapping Pressure Gradients in Reactor Pump Port

and Inlet Regions ................................... 114 3.6 Future Directions of Plasma Modeling ....................... 114 References ..................................................... 117

4 Plasma Reactor Modeling M. Meyyappan ................................................. 123

4.1 Introduction .............................................. 123 4.2 Reactor Scale Model ....................................... 124

4.2.1 A Review of Various Approaches ...................... 124 4.2.2 Global Model ....................................... 125 4.2.3 Continuum Reactor Model ............................ 127 4.2.4 Hybrid Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 134

4.3 Feature Level Modeling ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 137

Contents IX

4.4 Database Needs ........................................... 141 4.5 Concluding Remarks ....................................... 141 References ..................................................... 143

5 Overview of Plasma Diagnostic Techniques G.A. Hebner, P.A. Miller, and J.R. Woodworth ..................... 145

5.1 Introduction .............................................. 145 5.2 Plasma Electrical Characterization .......................... 146

5.2.1 Electrical Diagnostics ................................ 146 5.2.2 Microwave Diagnostic Techniques ...................... 167 5.2.3 Ion-Energy Analyzers ................................ 171

5.3 Optical Diagnostic Techniques .............................. 177 5.3.1 Optical Emission .................................... 177 5.3.2 Optical Absorption Techniques ........................ 185 5.3.3 Laser-Induced Fluorescence ........................... 190 5.3.4 Negative Ion Photo detachment ........................ 197 5.3.5 Optogalvanic Spectroscopy ........................... 198 5.3.6 Thomson Scattering ................................. 199

References ..................................................... 200

6 Mass Spectrometric Characterization of Plasma Etching Processes C.R. Eddy, Jr ................................................... 205

6.1 Introduction .............................................. 205 6.2 Application to Fundamental Studies ......................... 208

6.2.1 Silicon/Fluorine ..................................... 209 6.2.2 Silicon/Chlorine ..................................... 210 6.2.3 Gallium Arsenide/Chlorine ........................... 211

6.3 Application in Etch Processing Reactors ..................... 212 6.3.1 General Description of Experiments .................... 212 6.3.2 IV-IV Semiconductors ............................... 212 6.3.3 III-V Semiconductors ................................ 219 6.3.4 II-VI Semiconductors ................................ 232 6.3.5 Metals and Perovskites ............................... 239 6.3.6 Issues in Application and Interpretation ................ 244

6.4 Summary and Future Directions ............................. 248 References ..................................................... 254

7 Fundamentals of Plasma Process-Induced Charging and Damage K.P. Giapis .................................................... 257

7.1 Introduction .............................................. 257 7.2 The Origin of Pattern-Dependent Charging ................... 260

7.2.1 Differences in Ion and Electron Angular Distributions .... 260

X Contents

7.2.2 Charging as a Result of Current Imbalance ............. 263 7.2.3 Electron Shading Effects ............................. 264

7.3 The Notching Effect ....................................... 268 7.3.1 Observations and Mechanisms ........................ 268 7.3.2 Phenomena that Influence Notching ................... 270 7.3.3 Results from Self-Consistent Charging Simulations ....... 275 7.3.4 Validation .......................................... 279

7.4 Other Profile Effects Influenced by Charging .................. 282 7.4.1 Reactive Ion Etching Lag ............................. 282 7.4.2 Microtrenching ...................................... 285

7.5 Gate Oxide Degradation ................................... 290 7.5.1 The Driving Force for Current Injection ................ 290 7.5.2 Tunneling Current Transients ......................... 292 7.5.3 The Influence of Electron and Ion Temperature ......... 295

7.6 Charging Reduction Methodology ........................... 300 7.7 Concluding Remarks ....................................... 303

7.7.1 Historical Perspective ................................ 303 7.7.2 Will Charging Problems Persist? ...................... 304

References ..................................................... 305

8 Surface Damage Induced by Dry Etching S.W. Pang ..................................................... 309

8.1 Introduction .............................................. 309 8.2 Surface Damage in Si ...................................... 309

8.2.1 Changes in Electrical Characteristics due to Dry Etching. 310 8.2.2 Defects Evaluated by Surface Analysis ................. 315 8.2.3 Modeling of Etch-Induced Damage .................... 319

8.3 Surface Damage in III-V Semiconductors ..................... 325 8.3.1 Damage Dependence on Etch Conditions ............... 326 8.3.2 Effects of Etch Time and Materials on Defect Generation. 335 8.3.3 Changes in Electrical and Optical Characteristics ........ 338

8.4 Damage Removal .......................................... 344 8.4.1 Wet Etching, Dry Etching, Thermal Annealing,

and Two-Step Etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 8.4.2 Passivation by Low-Energy Reactive Species ............ 353

8.5 Summary ................................................. 357 References ..................................................... 357

9 Photomask Etching D.J. Resnick ................................................... 361

9.1 Introduction .............................................. 361 9.2 Optical Lithography ....................................... 364

9.2.1 Photomask Basics ................................... 364 9.2.2 Chrome Photomasks ................................. 364

Contents XI

9.2.3 MoSi Photomasks ................................... 372 9.2.4 Phase Shift Mask Technology ......................... 379

9.3 X-Ray Lithography ........................................ 383 9.3.1 X-Ray Lithography Basics ............................ 383 9.3.2 Gold Absorber-Based Masks .......................... 385 9.3.3 Refractory Masks .................................... 388 9.3.4 Amorphous Refractory-Based Masks ................... 389 9.3.5 Thermal Characteristics of a Mask Etch Process ........ 395 9.3.6 Hard Mask Materials ................................ 400

9.4 SCALPEL ................................................ 402 9.4.1 SCALPEL Basics .................................... 402 9.4.2 SCALPEL Mask Blank Processing ..................... 404 9.4.3 SCALPEL Mask Pattern Transfer ..................... 405

9.5 EUVL ................................................... 407 9.5.1 EUVL Basics ....................................... 407 9.5.2 EUVL Masks ....................................... 408 9.5.3 EUV Mask Pattern Transfer .......................... 409

9.6 Ion Projection Lithography ................................. 411 9.6.1 Ion Projection Lithography Basics ..................... 411 9.6.2 IPL Masks ......................................... 411 9.6.3 IPL Mask Pattern Transfer ........................... 413

9.7 IPL Mask Distortion Issues ................................. 414 9.8 Conclusion ............................................... 415 References ..................................................... 416

10 Bulk Si Micromachining for Integrated Microsystems and MEMS Processing R.J. Shul and J.G. Fleming ...................................... 419

10.1 Introduction .............................................. 419 10.2 Etch Technologies ......................................... 421

10.2.1 Wet Chemical Etching ............................... 421 10.2.2 Plasma Etching ..................................... 421 10.2.3 Reactive Ion Etching ................................. 423 10.2.4 High-Density Plasma Etching ......................... 424 10.2.5 Deep Reactive Ion Etching ........................... 425

10.3 ECR Results .............................................. 426 10.3.1 ECR Experimental .................................. 427 10.3.2 ECR Process Parameters ............................. 427 10.3.3 ECR Process Applications ............................ 433

10.4 DRIE Results ............................................. 439 10.4.1 DRIE versus ICP Etch Comparison .................... 439 10.4.2 Etch Rates and Selectivity to Masking Materials ........ 441 10.4.3 Aspect Ratio Dependent Etching (ARDE) in DRIE ...... 445 10.4.4 Etch Selectivities .................................... 446

XII Contents

10.5 DRIE Applications ........................................ 448 10.5.1 Chemical Sensing Devices ............................ 448 10.5.2 Advanced Packaging ................................. 453 10.5.3 SOl DRIE Etching .................................. 455

10.6 Conclusions ............................................... 457 References ..................................................... 457

11 Plasma Processing of 111-V Materials C. Youtsey and I. Adesida ....................................... 459

11.1 Introduction .............................................. 459 11.2 Dry Etching Techniques .................................... 459

11.2.1 Ion Beam Etching ................................... 459 11.2.2 Reactive Ion Etching ................................. 462 11.2.3 High-Density Plasma Reactive Ion Etching ............. 464

11.3 Masking Materials and Methods ............................. 466 11.4 Dry Etching Chemistries ................................... 469 11.5 Dry Etching of GaAs and Related Materials .................. 474 11.6 Dry Etching of InP and Related Materials .................... 477 11. 7 Dry Etching of GaN and Related Materials ................... 483 11.8 Selective Dry Etching of III-V Materials ...................... 490

11.8.1 GaAs on AIGaAs .................................... 490 11.8.2 InGaAs on InA lAs ................................... 492 11.8.3 GaN on AIGaN ..................................... 493

11.9 Conclusion ............................................... 494 References ..................................................... 496

12 Ion Beam Etching of Compound Semiconductors G.A. Vawter ................................................... 507

12.1 Introduction .............................................. 507 12.2 Definitions ............................................... 507

12.2.1 Ion Beam Etching ................................... 507 12.2.2 Reactive Ion Beam Etching ........................... 508 12.2.3 Chemically Assisted Ion Beam Etching ................. 508 12.2.4 Sputter Yield ....................................... 510

12.3 Ion Sources ............................................... 510 12.4 Historic Development ...................................... 512 12.5 Grid Design, Beam Uniformity, and Divergence ............... 513 12.6 Brief Overview of Etching Kinetics and Chemistry ............. 515 12.7 Surface Quality and Etch Masking ........................... 518 12.8 RIBE Etch Technology ..................................... 522

12.8.1 RIBE of GaAs and AIGaAs ........................... 522 12.8.2 RIBE of InP ........................................ 526 12.8.3 RIBE of InGaAsP and InP ........................... 528 12.8.4 RIBE of AIGaInP, GalnP and AIGalnAs ............... 528

Contents XIII

12.8.5 RIBE of (Al,Ga)Sb, (In,Ga)Sb and InAsSb ............. 529 12.8.6 RIBE of GaP and GaN .............................. 530 12.8.7 RIBE of ZnSe and ZnS ............................... 530

12.9 CAIBE Etch Technology ................................... 530 12.9.1 CAIBE of GaAs ..................................... 531 12.9.2 CAIBE of AlGaAs ................................... 532 12.9.3 CAIBE oflnP and InGaAsP .......................... 533 12.9.4 CAIBE of AlGalnP and AlGalnAs .................... 534 12.9.5 CAIBE of (Al,Ga)Sb and InSb ........................ 535 12.9.6 CAIBE of (Al,Ga)N ................................. 535

12.10 Endpoint Detection ........................................ 535 12.11 Damage .................................................. 538 References ..................................................... 539

13 Dry Etching of InP Vias S. Thomas III and J.J. Brown .................................... 549

13.1 Introduction .............................................. 549 13.2 Past Difficulties in Obtaining High Rate Etching for InP ....... 553

13.2.1 High Bias CH4-based Etching of InP ................... 553 13.2.2 Elevated Temperature Cl-based Etching of InP .......... 554

13.3 High Density Plasma Sources for High InP Etch Rate .......... 554 13.3.1 Reduced Bias CH4-Based ECR Etching of InP .......... 555 13.3.2 Addition of Cl to CH4-Based ECR Etching of InP ....... 556 13.3.3 Low Temperature Cl-Based Etching ................... 556

13.4 Measurement of Plasma Heating for InP Etching .............. 557 13.4.1 Wafer Heating During High-Density Plasma Etching ..... 557 13.4.2 Impact of Plasma Heating for InP Etching .............. 560 13.4.3 Effects of Chamber Pressure and Wafer Temperature

on Etch Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563 13.5 Application to Via Hole Etching ............................. 564

13.5.1 Etch Mask and Etch Characteristics ................... 565 13.5.2 Etching Slot Vias Using a Photoresist Mask ............ 567 13.5.3 OES for Endpoint ................................... 569

13.6 Summary ................................................. 570 References ..................................................... 571

14 Device DaIllage During Low TeIllperature High-Density PlasIlla CheIllical Vapor Deposition J. Lee and F. Ren ............................................... 575

14.1 Introduction .............................................. 575 14.2 Experimental ............................................. 576 14.3 Results and Discussion ..................................... 579 14.4 Summary and Conclusions .................................. 601 References ..................................................... 602

XIV Contents

15 Dry Etching of Magnetic Materials K.B. Jung, H. Cho, and S.J. Peart on .............................. 607

15.1 Introduction .............................................. 607 15.2 Ion Milling ............................................... 608 15.3 Cl2-Based ICP Etching of NiFe and Related Materials ......... 609 15.4 Copper Dry Etching in Chi Ar .............................. 620 15.5 CO INH3 Etching of Magnetic Materials ...................... 628 15.6 ECR and ICP Etching of NiMnSb ........................... 635 15.7 Dry Etching of LaCaMnOx and SmCo ....................... 640 15.8 Summary and Conclusions .................................. 644 References ..................................................... 644

Subject Index . ............................................... 649

List of Contributors

I. Adesida Microelectronics Laboratories University of Illinois 208 N. Wright St. Urbana, IL 61801, USA

J.J. Brown Princeton University Princeton, NJ 08544, USA

H. Cho Department of Materials Science and Engineering P.O. Box 116400 University of Florida Gainesville, FL 32611, USA

J.W. Coburn 6122 Franciscan Way San Jose, CA 95120-4416, USA

C.R. Eddy, Jr. Boston University Electrial & Computer Engineering Department 8 Saint Marys Street Boston, MA 02215-2421, USA

J.G. Fleming Center for Compound Semicon­ductor Science and Technology MS 0603 Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185-0603, USA

K. Giapis Chemical Engineering 210-41 California Institute of Technology 1200 E. California Blvd. Pasadena, CA 91125 USA

G.A. Hebner Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185, USA

P.Ho Sandia National Laboratories Albuquerque, NM 87185-0601, USA

K.B. Jung Department of Materials Science and Engineering P.O. Box 116400 University of Florida Gainesville, FL 32611, USA

J. Lee Plasma-Therm, Inc. 10050 16th Street, North St. Petersburg, FL 33716, USA

E. Meeks Reaction Design, Inc. 440 Lusk Blvd. Scite D-209 San Diego, CA 9214, USA

XVI List of Contributors

M. Meyyappan NASA Ames Research Center Mail Stop 229-3 Moffett Field, CA 94035, USA

P.A. Miller Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185, USA

S.W. Pang University of Michigan Department of Electrical Engineering & Computer Science 2304 EECS Bldg. 1301 Beal A venue Ann Arbor, MI 48109-2122, USA

S.J. Pearton Department of Materials Science and Engineering P.O. Box 116400 University of Florida Gainesville, FL 32611, USA

F. Ren Department of Chemical Engineering P.O. Box 116005 University of Florida Gainesville, FL 32611, USA

D. Resnick Motorola, Inc. 2100 E. Elliot Road Tempe, AZ 85284, USA

R.J. Shul Center for Compound Semiconductor Science and Technology MS 0603 Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185-0603, USA

J.E. Stevens Microelectronics Development Laboratory Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185, USA

S. Thomas III Microelectronics Lab HRL Laboratories, LLC 3011 Malibu Canyon Road Malibu, CA 90265, USA

G.A. Vawter Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185-0603, USA

J .R. Woodworth Sandia National Laboratories P.O. Box 5800 Albuquerque, NM 87185, USA

c. Youtsey N anovation Technologies 1801 Maple Ave. Evanston, IL 60201, USA