Sputtering by Particle Bombardment II: Sputtering of Alloys and Compounds, Electron and Neutron Sputtering, Surface Topography

398 Pages·1983·7.54 MB·English

by  Rainer Behrisch (auth.)

Topics in Applied Physics Volume 25
Sputtering by elcitraP
Bombardment II
Sputtering of Alloys and Compounds,
Electron and Neutron Sputtering,
Surface Topography
Edited by R. Behrisch
With Contributions by
R. Behrisch G. Betz G. Carter .B Navingek
J. Roth B.M.U. Scherzer P.D. Townsend
G. K. Wehner J.L. Whitton
htiW 551 serugiF
Springer-Verlag
Berlin Heidelberg New York Tokyo 3891
Dr. Rainer Behrisch
tutitsnI-kcnalP-xaM ffir ,kisyhpamsalP EURATOM Association
D-8046 Garching ieb Mfinchen, Fed. Rep. of ynamreG
ISBN 3-540-12593-0 Springer-Verlag Berlin Heidelberg New York Tokyo
ISBN 0-387-12593-0 Springer-Verlag New York Heidelberg Berlin Tokyo
Library of Congress Cataloging in Publication Data. Main entry under title: Sputtering by particle bombardme:
(Topics in applied physics; v. 47, ). Includes bibliographical references and indexes. Contents: .1 Physi~
sputtering of single-element solids-v. 2. Sputtering of alloys and compounds, electron and neutron sputteril
surface topography. 1. Sputtering (Physics) 2. Solids- Effect of radiation on. 3. Surfaces (Physics) - Effect
radiation on. .1 Behrisch, Rainer. II. Andersen, Hans Henrik. IlI. Title: Particle bombardment. IV. Seri
QCI76.g.s72s68 81-4313
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Preface
Sputtering, or the erosion of the surface of a solid due to the impact of energetic
particles, is of considerable interest from the standpoint of understanding the
fundamental processes involved as well as for the many applications of
sputtering in science and technology. In three volumes of this Topics ni Applied
Physics series, an attempt has been made to collect and review the present
knowledge of sputtering phenomena. The first book, "Sputtering by Particle
Bombardment I" (TAP 47), gives an introduction to collisional sputtering
theory and a summary of the measured sputtering yields obtained for poly-
crystalline single-element solids and for some single crystals during bombard-
ment, primarily with noble gas and hydrogen ions. This second volume
emphasizes the sputtering of multicomponent systems, chemical and surface
effects, and sputtering by particles other than ions.
In most applications and practical situations, multicomponent solids are
sputtered. The major effects observed for such cases are preferential sputtering
and compositional changes in the surface layers. These processes are treated in
some detail in Chap. 2 of the present volume by G. Betz and G.K. Wehner
which includes a table summarizing the systems investigated to date.
If the incident ions interact chemically with the target atoms forming stable
compounds or volatile molecules, the sputtering yields may be decreased or
increased and generally show a strong dependence on temperature. The present
knowledge of these phenomena is treated by J. Roth in Chap. .3
Sputtering by electrons and photons is of importance in insulating materials
and has been investigated primarily in ionic crystals. The major effects occur
via excitation and ionization processes in the solids and are reviewed by
P. Townsend in Chap. 4. Such processes also occur during ion bombardment,
but have yet to be investigated in detail.
Neutron sputtering effects are usually small and thus difficult to measure.
This field is of interest in reactor technology and is reviewed in Chap. 5 by
R. Behrisch.
Ion implantation and nonuniform surface removal generally lead to a large
modification of the surface structure and topography. During bombardment
with medium to high-Z atoms, the surface topography is generally dominated by
erosion, as treated by G. Carter, B. Navin~ek, and J. L. Whitton in Chap. .6
For light ions and high energies, gas implantation and accumulation can lead to
blistering, flaking, and finally spongy structures, as shown by B. M. U. Scherzer
in Chap. .7
IV ecaferP
In the third volume, "Sputtering by Particle Bombardment III" the present
knowledge of the angular, energy, mass and charge state distributions of
sputtered particles will be presented and the large variety of applications for
the sputtering process will be outlined.
Writing such a book si not possible as a monograph, but only in col-
laboration with leading scientists in the different areas of sputtering research.
Each contribution represents the personal view of the authors, but an attempt
has been made to integrate the different styles and emphases of the contributions
in a coherent way also by including many internal cross references as well as
references to Vol. I (TAP 47), by applying a consistent symbol utilization, and
by providing a cumulative subject and author index.
A major difficulty in such a collaboration is appropriate timing and the
many delays which often cannot be avoided. I would particularly like to thank
Gottfried Wehner for persevering with his contribution which was originally
agreed to in the Hofbr~iuhaus in M/inchen.
I appreciate the kind support and patience of all the authors who contri-
buted to this book. I gratefully acknowledge, also, the help of several colleagues
through their critical comments, and Springer-Verlag for their pleasent collab-
oration. This book is intended to be the basis and stimulation for basic research
and applied work in this exciting field of physics.
Garching, July 3891 Rainer Behrisch
Contents
1. Introduction and Overview. By R. Behrisch . . . . . . . . . . . . 1
I. 1 Background . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Sputtering Yields . . . . . . . . . . . . . . . . . . . . . 2
1.3 Sputtering Investigations for Single-Element Solids ...... 3
1.4 Theoretical Models for Sputtering . . . . . . . . . . . . . . 4
1.5 Sputtering of Multicomponent Targets . . . . . . . . . . . . 5
1.6 Sputtering of Nonmetals . . . . . . . . . . . . . . . . 6
1.7 Neutron Sputtering . . . . . . . . . . . . . . . . . . . . 7
1.8 Surface Topography . . . . . . . . . . . . . . . . . . . 7
1.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . 8
References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2. Sputtering of Multicomponent Materials
By G. Betz and G.K. Wehner (With 25 Figures) . . . . . . . . . 11
2.1 Historical Review and Need for Data . . . . . . . . . . . . 12
2.1.1 Historical Remarks . . . . . . . . . . . . . . . . . 12
2.l.2 Applications . . . . . . . . . . . . . . . . . . . . 14
2.2 Basic Considerations . . . . . . . . . . . . . . . . . . . 51
2.2.1 Multicomponent Materials . . . . . . . . . . . . . . 51
2.2.2 Characterization of the Sputtering Process for
Multicomponent Materials . . . . . . . . . . . . . . 16
2.2.3 Definitions of Total, Partial, and Component Sputtering
Yield . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Single Phase Alloys and Compounds with Only Low Vapor
Pressure Components . . . . . . . . . . . . . . . . . . . 20
2.3.1 Experimental Methods . . . . . . . . . . . . . . . . 20
2.3.2 Surface Composition Changes Due to Ion Bombardment. 24
a) Dependence on Alloy Composition, Ion Energy, and
Mass . . . . . . . . . . . . . . . . . . . . . . 24
b) Models Predicting Surface Composition Changes . . 27
2.3.3 The Altered Layer Formed by Ion Bombardment .... 32
a) Experimental Results . . . . . . . . . . . . . . . 33
b) Temperature Dependence . . . . . . . . . . . . . 36
c) Altered Layer Models . . . . . . . . . . . . . . . 38
2.3.4 Component and Total Sputtering Yields . . . . . . . . 42
2.3.5 Angular Distribution of Sputtered Constituents ..... 45
VIII Contents
2.4 Oxides and Other Compounds with One High Vapor Pressure
Component . . . . . . . . . . . . . . . . . . . . . . . 48
2.4.1 Experimental Techniques . . . . . . . . . . . . . . . 48
2.4.2 Structural Changes Under Ion Bombardment . . . . . . 49
2.4.3 Compositional Changes Under Ion Bombardment .... 51
a) Mass Effects . . . . . . . . . . . . . . . . . . . 53
b) Bonding Effects . . . . . . . . . . . . . . . . . 53
c) Sputtering Via Electronic Processes . . . . . . . . . 55
2.4.4 Sputtering Yields . . . . . . . . . . . . . . . . . . 56
2.5 Multiphase Materials . . . . . . . . . . . . . . . . . . . 60
2.5.1 Ion Bombardment for Low and Medium Fluences .... 60
2.5.2 Ion Bombardment for High Fluences . . . . . . . . . . 63
2.5.3 Sputtering Yields . . . . . . . . . . . . . . . . . . 63
2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . 65
2.7 Tables . . . . . . . . . . . . . . . . . . . . . . . . . 67
References . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3. Chemical Sputtering. By J. Roth (With 30 Figures) . . . . . . . . 91
3.1 Identification of Chemical Effects . . . . . . . . . . . . . . 91
3.1.1 Formation of an Altered Surface Layer . . . . . . . . . 93
3.1.2 Definition . . . . . . . . . . . . . . . . . . . . . 94
3.1.3 Summary . . . . . . . . . . . . . . . . . . . . . . 96
3.2 Experimental Methods . . . . . . . . . . . . . . . . . . 97
3.2.1 Measurements of the Partial Sputtering Yield . . . . . . 97
a) Ionization and Mass Analysis . . . . . . . . . . . 98
b) Matrix Isolation . . . . . . . . . . . . . . . . . 100
3.2.2 Surface Analysis Combined with Mass Spectrometry . . 101
3.2.3 Measurement of the Energy Distribution of Sputtered
Particles . . . . . . . . . . . . . . . . . . . . . . 102
3.3 Trapping and Compound Formation of Implanted Ions .... 103
3.3.1 Chemical Trapping of Hydrogen . . . . . . . . . . . . 104
a) Metals . . . . . . . . . . . . . . . . . . . . . 104
b) Semiconductors and Carbon . . . . . . . . . . . . 106
c) Oxides . . . . . . . . . . . . . . . . . . . . . 107
3.3.2 Chemical Trapping of C, O, N . . . . . . . . . . . . 107
3.3.3 Implantation of F and CI . . . . . . . . . . . . . . . 108
3.4 Chemically Enhanced and Reduced Physical Sputtering .... 109
3.4.1 Sputtering Yield . . . . . . . . . . . . . . . . . . . t09
a) Sputtering with Reactive Ions . . . . . . . . . . . 109
b) Sputtering in a Reactive Atmosphere . . . . . . . . 111
3.4.2 Sputtered Species . . . . . . . . . . . . . . . . . . 113
a) Sputtered Molecular Ions . . . . . . . . . . . . . 311
b) Sputtered Neutral Molecules . . . . . . . . . . . . 114
3.5 Chemical Sputtering . . . . . . . . . . . . . . . . . . . 116
Contents IX
3.5.1 Experimental Observations . . . . . . . . . . . . . . 117
a) Temperature Dependence of the Sputtering Yield . ! 17
b) Observation of Volatile Sputtered Molecules ..... 120
c) Threshold Energy for Sputtering . . . . . . . . . . 121
d) Energy Distribution of Sputtered Particles . . . . . . 123
e) Selectivity . . . . . . . . . . . . . . . . . . . . 124
3.5.2 Activation and Inhibition of Chemical Sputtering .... 127
a) State of the Bombarded Surface . . . . . . . . . . 127
b) Influence of Small Impurity Concentrations ..... 130
c) Molecular State of Bombarding Ions . . . . . . . . 130
3.5.3 Mechanism of Chemical Sputtering . . . . . . . . . . 131
a) Thermodynamic Equilibrium Reaction of Hydrogen and
Carbon . . . . . . . . . . . . . . . . . . . . . 131
b) Kinetic Reaction Model for Thermal Atomic Hydrogen. 133
c) Erosion of Graphite by Energetic Hydrogen Ions . 138
References . . . . . . . . . . . . . . . . . . . . . . . . . . 141
. Sputtering by Electrons and Photons
By P. D. Townsend (With 18 Figures) . . . . . . . . . . . . . . 147
4.1 Ion and Electron Sputtering Mechanisms . . . . . . . . . . 147
4.2 Defect Formation and Sputtering of Insulators . . . . . . . . 151
4.3 Defects in Alkali Halides . . . . . . . . . . . . . . . . . 153
4.3.1 The Original Excitonic Mechanism . . . . . . . . . . . 154
4.3.2 Modifications to the Basic Model . . . . . . . . . . . 156
4.3.3 Recent Views on the Excitonic Mechanism . . . . . . . 158
4.4 Sputtering from Alkali Halides . . . . . . . . . . . . . . . 159
4.4.1 Halogen Sputtering from Alkali Halides . . . . . . . . 159
4.4.2 Alkali Atom Sputtering . . . . . . . . . . . . . . . 161
4.4.3 Alkali Halide Sputtering Patterns . . . . . . . . . . . 163
4.4.4 Correlation with Luminescence . . . . . . . . . . . . 164
4.4.5 Velocity of Ejected Particles . . . . . . . . . . . . . . 661
4.5 Surface Topography . . . . . . . . . . . . . . . . . . . 167
4.6 Silver Halides . . . . . . . . . . . . . . . . . . . . . . 169
4.7 Surface Erosion by Photons . . . . . . . . . . . . . . . . 170
4.7.1 Laser Damage and Sputtering . . . . . . . . . . . . . 170
4.7.2 Photon Assisted Thermal Decomposition . . . . . . . . 172
4.8 Near Threshold Events with Relativistic Electrons . . . . . . . 173
4.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . 176
References . . . . . . . . . . . . . . . . . . . . . . . . . . 176
5. Sputtering of Solids with Neutrons. By R. Behrisch (With 25 Figures). 179
5.1 Neutron Irradiation Effects . . . . . . . . . . . . . . . . 179
5.2 Sputtering Experiments with Neutrons . . . . . . . . . . . . 182
5.2.1 Neutron Sources . . . . . . . . . . . . . . . . . . 182
X Contents
5.2.2 Experimental Conditions . . . . . . . . . . . . . . . 185
a) Surface and Vacuum Conditions . . . . . . . . . . 185
b) Limitations of Collector Measurements . . . . . . . 187
c) Measurement of the Deposits on the Collectors .... 187
5.2.3 Measured Sputtering Yields . . . . . . . . . . . . . . 190
a) Sputtering Yields for Au and Nb . . . . . . . . . . 190
b) Sputtering Yields for Fe, V, Co (Cu, Mo, In, W) . 192
c) Sputtering Yield for Solids Containing Fissile Atoms . 193
5.2.4 Sputtered Material . . . . . . . . . . . . . . . . . . 195
a) Sputtered Atoms, Angular Distribution . . . . . . . 195
b) Microparticle Emission . . . . . . . . . . . . . . 196
5.2.5 Radioactive Primary Knockon Emission Yield . . . . . . 198
a) (n, ),~ Emission Yields, Thermal Neutron Sputtering . 199
b) Primary Knockon Emission by Fast Neutrons .... 200
c) Emission of Fission Fragments . . . . . . . . . . . 203
5.3 Theoretical Considerations . . . . . . . . . . . . . . . . . 203
5.3.1 Primary Knockon Atoms and Cascades in an Infinite Solid. 204
5.3.2 Sputtering Yields . . . . . . . . . . . . . . . . . . 208
a) Forward and Backward Sputtering . . . . . . . . . 208
b) Transverse Sputtering . . . . . . . . . . . . . . . 211
c) Sputtering by an Isotropic Neutron Flux . . . . . . . 212
d) Comparison with Computer Simulation and
Experimental Results . . . . . . . . . . . . . . . 213
5.3.3 Emission of Radioactive Primary Knockon Atoms .... 216
a) Directed Neutron Flux . . . . . . . . . . . . . . 217
b) Isotropic Neutron Flux . . . . . . . . . . . . . . 218
c) Primary Knockon Emission and Sputtering Yield . . 219
5.3.4 Mechanisms for Emitting Microparticles . . . . . . . . 220
5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . 223
References . . . . . . . . . . . . . . . . . . . . . . . . . . 225
6. Heavy noI Sputtering Induced Surface Topography Development
By G. Carter, B. Navin~ek, and J.L. Whitton (With 20 Figures) . 231
6.1 Historical Review . . . . . . . . . . . . . . . . . . . . . 231
6.2 Experimental Conditions . . . . . . . . . . . . . . . . . 234
6.2.1 Target Preparation . . . . . . . . . . . . . . . . . . 234
6.2.2 Target Environment . . . . . . . . . . . . . . . . . 235
6.2.3 Ion Beam Characteristics . . . . . . . . . . . . . . . 236
6.3 Defect Production and the Stages of Development of Surface
Topography . . . . . . . . . . . . . . . . . . . . . . . 237
6.4 Atomic Scale Topography ( ~> 100 A,) . . . . . . . . . . . . 240
6.5 Microscopic Scale Topography (100-10,000 )~A . . . . . . . . 241
6.5.1 Feature Classification . . . . . . . . . . . . . . . . 243
6.5.2 Intergranular Effects . . . . . . . . . . . . . . . . . 245
stnetnoC XI
6.5.3 Intragranular Effects . . . . . . . . . . . . . . . . . 245
a) Depressed Structures (Etch Pits) . . . . . . . . . . 246
b) Protuberant Structures (Pyramids) . . . . . . . . . 249
c) Repetitive Structures (Ripples and Facetting) ..... 253
6.6 Macroscopic Scale Topography (> 10,000 )~A and Theoretical
Considerations . . . . . . . . . . . . . . . . . . . . . . 257
6.6.1 First-Order Erosion Theory . . . . . . . . . . . . . . 257
6.6.2 Comparison of Theory with Experimental Studies .... 261
6.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 265
References . . . . . . . . . . . . . . . . . . . . . . . . . . 266
7. Development of Surface Topography Due to Gas Ion Implantation
By B.M.U. Scherzer (With 37 Figures) . . . . . . . . . . . . . 271
7.1 General Outline . . . . . . . . . . . . . . . . . . . . . 271
7.2 Historical Overview . . . . . . . . . . . . . . . . . . . . 277
7.3 Implantation of Gaseous Ions in Solids . . . . . . . . . . . 279
7.3.1 Ranges of Light Ions in Solids . . . . . . . . . . . . 279
7.3.2 Solubility and Diffusivity . . . . . . . . . . . . . . . 281
7.3.3 Gas-Solid Systems Formed by Implantation . . . . . . . 283
7.4 The Trapping of Gas at Very Low Fluences (< 1017 ionsm -2) 285
7.5 Trapping and Structural Modifications at Intermediate Fluences
(1018-1021 ions m -2) . . . . . . . . . . . . . . . . . . . 290
7.5.1 Experimental Observation of Bubble Formation ..... 291
7.5.2 Swelling and Stress . . . . . . . . . . . . . . . . . 295
7.5.3 Gas Pressure in Bubbles - Mechanisms of Bubble Growth 297
a) High Temperature (Thermal Equilibrium) Model . 297
b) Low Temperature (Overpressurized Bubble) Model 298
c) Percolation Model . . . . . . . . . . . . . . . . 299
d) Equation of State for Gas in Bubbles . . . . . . . . 299
7.6 High Fluences (1021-1023 ions m-2); Blistering and Flaking 103
7.6.1 Conditions for Blistering . . . . . . . . . . . . . . . 312
7.6.2 Parameters Influencing Surface Structure . . . . . . . . 312
a) Temperature . . . . . . . . . . . . . . . . . . . 313
b) Flux Density . . . . . . . . . . . . . . . . . . . 3 t6
c) Particle Energy ("Deckeldicke", Blister Diameter) . . 318
d) Target Orientation . . . . . . . . . . . . . . . . 320
e) Bulk Structure, Pretreatment, and Surface Roughness . 123
f) Prestressing . . . . . . . . . . . . . . . . . . . 323
g) Angle of Incidence . . . . . . . . . . . . . . . . 323
7.6.3 Gas Emission During and After Blistering and Flaking . 324
7.6.4 Depth Profiles of implanted Gas After Blistering .... 326
7.7 Models for Blistering and Flaking . . . . . . . . . . . . . . 327
7.7.1 Initial Stage Models . . . . . . . . . . . . . . . . . 328
a) Critical Swelling Model . . . . . . . . . . . . . . 328
b) Interbubble Fracture and Loop Punching Model . . . 329