1 Metrological Scanning Probe Microscopes – Instruments for DimensionalNanometrology 3 Hans-Ulrich Danzebrink, Frank Pohlenz, Gaoliang Dai, and Claudio Dal Savio 1.1 Introduction 3 1.2 H
Trang 1Nanoscale Calibration Standardsand Methods
Edited by
G Wilkening, L Koenders
Nanoscale Calibration Standards and Methods: Dimensional and Related Measurements in the Micro- and Nanometer Range.
Edited by Gunter Wilkening, Ludger Koenders Copyright c 2005 Wiley-VCH Verlag GmbH & Co KGaA, Weinheim
Trang 3Prof Dr Gnter Wilkening
National Metrology Institute (PTB),
Nano- und Micrometrology Department
Guenter.Wilkening@ptb.de
Dr Ludger Koenders
National Metrology Institute (PTB),
Nano- und Micrometrology Department
Ludger.Koenders@ptb.de
Cover Picture
Illustration: Hans-Ulrich Danzebrink
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Trang 41 Metrological Scanning Probe Microscopes – Instruments for Dimensional
Nanometrology 3
Hans-Ulrich Danzebrink, Frank Pohlenz, Gaoliang Dai, and
Claudio Dal Savio
1.1 Introduction 3
1.2 High-Resolution Probing Systems 4
1.2.1 Sensor Objective with Beam Deflection Detection 5
1.2.2 Sensor Objective with Piezolever Module 7
1.2.3 Sensor Objective with Tuning Fork Module 8
1.2.4 Sensor Head for Combined Scanning Probe and Interference
Microscopy 9
1.3 Metrology Systems Based on Scanning Probe Microscopes 12
1.3.1 Scanning Force Microscopes of Type Veritekt 13
1.3.2 Metrological Large Range Scanning Force Microscope 15
Acknowledgments 19
References 19
2 Nanometrology at the IMGC 22
M Bisi, E Massa, A Pasquini, G B Picotto, and M Pisani
2.3 Atomic Scale Metrology 28
2.3.1 Lattice Parameter of Silicon 29
2.3.2 Combined Optical and X-Ray Interferometry (COXI) 30
2.4 Phase-Contrast Topograpy 31
2.4.1 Detection of Small Lattice Strain 31
2.4.2 Phase-Contrast Imaging 32
Trang 53.2 Measurement of Non-linearity in Optical Interferometers 40
3.3 Combined Optical and X-ray Interferometry 41
3.4 Measurement of Small Angles 42
3.5 X-ray Interferometry and Scanning Probe Microscopy 43
3.6 Conclusions 43
References 44
Part II Instrumentation – Long-range Scanning Probe Microscope
4 Advances in Traceable Nanometrology with the Nanopositioning and
4.5 Measuring Opportunities and Performance with Focus Sensor 55
4.6 Focus Probe with SFM Cantilever 58
4.7 Conclusion 58
Acknowledgements 59
References 59
5 Coordinate Measurements in Microsystems by Using AFM-Probing:
Problems and Solutions 60
Dorothee Hser, Ralph Petersen, and Hendrik Rothe
5.1 Introduction 60
5.2 Realizing CMMs for Microsystems 61
5.3 Problems and Solutions 64
5.3.1 Dynamics of Positioning System 64
Trang 66.3.3 Measurement Result of the Mean Pitch Value 83
6.3.4 Measurement of the Local Pitch Variation 83
6.4 A Selected Measurement Result of a Microroughness Standard 85
6.4.1 Measurement Result of a Glass Flatness Standard 86
6.4.2 Measurement of a PTB Microroughness Standard 87
6.4.3 Comparison of the Roughness Measurement Results Derived from SFM
and Stylus Instruments Using Gaussian Filter 88
6.4.4 Comparison Using Morphological Filters 89
6.4.5 Evaluation Results Using PTB Reference Software 90
6.5 Outlook and Conclusion 91
References 92
Part III Instrumentation – Development of SPM and Sensors
7 Traceable Probing with an AFM 95
K Dirscherl and K R Koops
7.4 Real-Time Control Through SSE2 Assembly 103
7.4 Implementation of the Measurement Controller 104
Trang 78.2 Existing Setup – Without Drift Compensation 111
8.3 Measurement Method and Setup for Drift Compensation 112
8.4 Experiment and Results 115
8.5 Summary 118
References 118
9 DSP-Based Metrological Scanning Force Microscope
with Direct Interferometric Position Measurement and
Improved Measurement Speed 119
Gaoliang Dai, Frank Pohlenz, Hans-Ulrich Danzebrink, Klaus Hasche,and Gnter Wilkening
9.1 Introduction 119
9.2 Instrument 120
9.2.1 Principle 120
9.2.2 DSP-Based Signal Processing System 121
9.2.3 Calibration of the Tip Signal for Traceably Measuring the Bending
of the Cantilever 123
9.3 Correction of Nonlinearity of the Optical Interferometers
in the M-SFM 124
9.3.1 Review of Nonlinearity Correction Methods 124
9.3.2 Adapted Heydemann Correction in a Fast Servo Control Loop 125
9.3.3 Performance of the Interferometers in the M-SFM Veritekt C 126
9.4 Improving the Measurement Speed 128
9.5 A Measurement Example of Step-Height Standard 129
10.2 Instrumentation and Experimental Details 133
10.3 Results and Discussion 136
10.3.1 Imaging in the Confocal and SPM Mode 136
10.3.2 One-Dimensional Optical and SPM Measurements 138
10.4 Summary and Conclusions 141
Acknowledgments 142
References 142
11 Combined Shear Force–Tunneling Microscope with Interferometric Tip
Oscillation Detection for Local Surface Investigation and Oxidation 144
Andrzej Sikora, Teodor Gotszalk, and Roman Szeloch
11.1 Introduction 144
11.2 Instrumentation 145
11.3 Local Surface Electrical Properties Investigation 152
VIII Contents
Trang 812.3.2 Spectroscopic Noise Analysis and Determination of the Hooge
Constant 163
12.3.3 Force Calibration and Electrical Calibration 165
12.4 Application: Force Calibration of a Stylus Instrument 167
12.5 Conclusions 169
References 170
Part IV Calibration – Overview
13 Towards a Guideline for SPM Calibration 173
T Dziomba, L Koenders, and G Wilkening
13.3.2 Flatness Measurements and Signal Noise 179
13.3.3 Repeatability and Noise 181
13.3.4 Tip Shape 182
13.4 Calibration of the Scanner Axes 183
13.4.1 Lateral Calibration 183
13.4.2 Calibration of the Vertical Axis 186
Using Laser Interferometers 187
Using Transfer Standards 188
Evaluation of Step Height 188
13.5 Uncertainty of Measurements 190
Acknowledgments 191
References 191
Trang 914 True Three-Dimensional Calibration of Closed Loop Scanning Probe
Microscopes 193
J Garnaes, A Khle, L Nielsen, and F Borsetto
14.1 Introduction 193
14.2 Model of the Measurement System 194
14.3 The Correction Matrix 195
14.4 Theory for Estimating the Vertical Skew 196
14.5 Experimental Results and Discussion 200
14.6 Conclusion 202
Acknowledgements 202
Appendix 203
References 204
15 Height and Pitch at Nanoscale – How Traceable is Nanometrology? 205
L Koenders and F Meli
15.1 Introduction 205
15.2 Comparison on One-Dimensional Pitch Standards (NANO 4) 206
15.2.1 Standards and Measurand 206
15.2.2 Participants and Measurement Methods 207
16 The Behavior of Piezoelectric Actuators and the Effect on Step-Height
Measurement with Scanning Force Microscopes 220
A Grant, L McDonnell, and E M Gil Romero
16.1 Introduction 220
16.2 Experimental 222
16.2.1 Scanning Force Microscopes 222
16.2.2 Z Calibration with Step-Height Standards 223
16.2.3 Z Calibration with Fiber-Optic Displacement Sensor 223
16.3 Results 224
16.3.1 Effect of Voltage Sweep 224
16.3.2 Effect of Z Actuator Offset 225
16.3.3 Implications of Actuator Offset for Sample Tilt 227
16.3.4 Implications of Actuator Offset for Scanner Curvature 227
Trang 1017.3.1 Micromilling 235
17.3.2 Sputtering 237
17.4 Conclusions 240
References 241
Part V Calibration – Standards for Nanometrology
18 Standards for the Calibration of Instruments
for Dimensional Nanometrology 245
L Koenders, T Dziomba, P Thomsen-Schmidt, and G Wilkening
19 “Atomic Flat” Silicon Surface for the Calibration of Stylus Instruments 259
S Grger and M Dietzsch
19.1 Calibration of Stylus Instruments 259
19.2 “Atomic Flat” Silicon as Calibration Standard 263
19.3 Selection of the Measurement Instrument for the Assessment of
Flatness 264
19.4 Calibration of the Stylus Instrument ME 10 265
19.5 Characteristics of the Measurement Instrument After Modification 267
19.6 Conclusions and Outlook 268
References 268
Trang 1120 Investigations of Nanoroughness Standards by Scanning Force Microscopes
and Interference Microscope 269
R Krger-Sehm, T Dziomba, and G Dai
20.1 Introduction 269
20.2 Standardization Aspects 270
20.3 Manufacturing of Calibration Specimens 271
20.3.1 Conditions for Smaller Roughness 271
20.4.3 Measurements with Interference Microscope 275
20.4.4 Scanning Force Microscope Measurements 276
20.4.5 Long Range SFM Measurements 278
20.4.6 Relation to Proven Roughness Standards 279
20.5 Conclusions and Outlook 279
Acknowledgments 281
References 281
21 Testing the Lateral Resolution in the Nanometre Range
with a New Type of Certified Reference Material 282
M Senoner, Th Wirth, W Unger, W sterle, I Kaiander, R L Sellin,and D Bimberg
21.1 Introduction 282
21.2 Description of the Reference Material 283
21.3 Modeling of Lateral Resolution 284
21.3.1 Analysis of a Narrow Strip 288
21.3.2 Analysis of a Straight Edge 289
21.3.3 Analysis of Gratings 291
21.4 Conclusions 294
Acknowledgments 294
References 294
Part VI Calibration – Tip shape
22 Reconstruction and Geometric Assessment of AFM Tips 297
Torsten Machleidt, Ralf Kstner, and Karl-Heinz Franke
22.1 Introduction 298
22.2 Reconstruction of the Tactile Tip 299
22.2.1 Imaging the Tip Using Scanning Electron Microscopy 299
22.2.2 Reconstruction by Known Sample Structure 300
22.2.3 Blind Tip Estimation 301
22.2.4 Motivation 301
22.2.5 Tip Assessment 302
XII Contents
Trang 1223 Comparison of Different Methods of SFM Tip Shape Determination for
Various Characterisation Structures and Types of Tip 311
S Czerkas, T Dziomba, and H Bosse
Part VII Calibration – Optical Methods
24 Double Tilt Imaging Method for Measuring Aperture Correction Factor 323
Yen-Liang Chen, Chao-Jung Chen, and Gwo-Sheng Peng
24.1 Introduction 323
24.2 Traceability of Step Height 324
24.3 Working Principle of DIT method 325
Trang 1325.2.1 Two Waves Interferometry 332
25.2.2 Multiple Waves Interferometry 337
25.3 Statistical Errors on Processing Elementary Fringe Patterns 337
25.4 Wavelengths and Displacements Measurement 340
25.5 Absolute Distance Measurement 341
26.4 The Uncertainty of the Complete Calibration Facility 349
26.4.1 The Measurement Uncertainty of the Comparator 349
26.4.2 The Measurement Uncertainty of the Standard Laser Interferometer
Taking Into Account the Refractive Index of Air and the ThermalExpansion 352
26.4.3 The Expanded Measurement Uncertainty of the Entire Calibration
Facility 355
Signs and Symbols of the Model Equations and the UncertaintyBudgets: 356
References 357
Part VIII Application – Lateral Structures
27 Lateral and Vertical Diameter Measurements on Polymer Particles with a
Metrology AFM 361
F Meli
27.1 Introduction 361
27.2 Experimental Setup 363
27.3 Measurement Results and Discussion 365
27.3.1 Height Measurements on Gold Colloids 365
27.3.2 Possible Systematic Deviations with Height Measurements on Gold
Trang 1429.2.2 Definition of Top CD Operator 390
29.2.3 SEM Model Input Parameter Variations 390
29.2.4 Experimental Parameter Variations 392
29.2.5 Measurement Results 393
29.3 Modified Exponential Fit Operator for High Sidewall Angles 394
29.4 Gauss Fit Operator 396
29.5 Signal Decay Operator 398
Part IX Application – Surface
31 Experimental Characterization of Micromilled Surfaces by Large-Range
AFM 413
P Bariani, G Bissacco, H N Hansen, and L De Chiffre
31.1 Introduction 413
31.2 Micromilling of Hardened Tool Steel 414
31.3 Surface Topography Measurement 415
31.4 Large-Range Atomic Force Microscopy 416
31.5 Techniques Used for Comparison 416
31.6 Evaluation of Sampling Conditions for the Different Techniques 417
31.7 Results 418
31.8 Discussion and Conclusions 422
Trang 1532.2 Requirements for Surface Roughness of Mass Standards 425
32.3 Surface Roughness Measurement Methods Applied to Mass
Stan-dards 426
32.3.1 Mechanical Profiler (NAWC-US) 427
32.3.2 Near Field Microscope (LPUB, FR) 427
32.3.3 Angle-Resolved Light Scattering (BNM-INM, FR) 428
32.3.4 Angle-Resolved Light Scattering (Lasercheck, US) 428
32.3.5 Total Integrated Light Scattering (SP, SE) 429
32.4 Results and Instruments Comparison 429
35 Atomic Force Microscope Tip Influence on the Fractal and Multi-Fractal
Analyses of the Properties of Randomly Rough Surfaces 452
P Klapetek, I Ohldal, and J Blek
35.1 Introduction 452
35.2 Data Simulation and Processing 453
35.3 Fractal Properties Analysis 454
35.4 Multi-Fractal Properties Analysis 457
35.5 Results and Discussion 460
Trang 1636.2.5 Projected Area 470
36.2.6 Projected Area 473
36.2.7 Surface Area 473
36.2.8 Elastic Reconstruction 474
36.2.9 Building the Area Functions 475
36.2.10 Indenter Angle and Radius 476
37.3.2 Crack Opening Displacement Analysis 489
37.4 Adaptation to Finite Element Analysis 491
37.4.1 Adaptation Concept 491
37.4.2 Mesh Transfer from FEA to Experiment 493
37.4.3 Verification Platform 494
Derotation and Displacement Matching 494
Determination of Material Properties 495
37.5 Application of DIC to Micromachined Gas Sensor 496
37.6 Conclusions 498
Acknowledgments 498
References 498
Trang 1738 PTB’s Precision Interferometer for High Accuracy Characterization of Thermal
Expansion Properties of Low Expansion Materials 500
R Schdel and A Abou-Zeid38.1 Introduction 500
Trang 18H.-U Danzebrink, F Pohlenz, G Dai,
and C Dal Savio
National Metrology Institute (PTB),
Braunschweig, Germany
Hans-Ulrich.Danzebrink@ptb.de
Chapter 2
M Bisi, E Massa, A Pasquini,
G B Picotto, and M Pisani
E Manske, R Mastylo, T Hausotte,
N Hofmann, and G Jger
Technical University Ilmenau,
Institute of Process- and Sensor
Engineering, Ilmenau, Germany
eberhard.manske@tu-ilmenau.de
Chapter 5
D Hser, R Petersen, and H Rothe
Measurement and Information
Technology, University of the Federal
Armed Forces, Hamburg, Germany
doro@unibw-hamburg.de
G Dai, F Pohlenz, H.-U Danzebrink,
M Xu, K Hasche, and G WilkeningPhysikalisch-Technische Bundesanstalt(PTB), Braunschweig, Germanygaoliang.dai@ptb.de
kai.dirscherl@ptb.deChapter 8
A Sikora, D V Sokolov, and
H U DanzebrinkNational Metrology Institute (PTB),Braunschweig, Germany
Hans-ulrich.danzebrink@ptb.deChapter 9
G Dai, F Pohlenz, H.-U Danzebrink,
K Hasche, and G WilkeningNational Metrology Institute (PTB),Braunschweig, Germany
gaoliang.dai@ptb.de
Trang 19A Sikora, T Gotszalk, and R Szeloch
Faculty of Microsystems Electronics
and Photonics, Wroclaw University
Institute for Semiconductor
Technology, Technical University of
Danish Institute of Fundamental
Metrology, Lyngby, Denmark
jg@dfm.dtu.dk
Chapter 15
L Koenders1and F Meli2
1National Metrology Institute (PTB),Braunschweig und Berlin, Germany2
Swiss Federal Office of Metrology andAccreditation (METAS),
Bern, SwitzerlandThorsten.Dziomba@ptb.deChapter 16
A Grant, L McDonnell, and
E M Gil RomeroCentre for Surface & Interface Analysis,Department of Applied Physics &Instrumentation, Cork Institute ofTechnology, Ireland
lmcdonnell@cit.ieChapter 17
J Schbel and E WestkmperInstitute of Industrial Manufacturingand Management, University ofStuttgart, Germany
ins@ipa.fraunhofer.deChapter 18
L Koenders, T Dziomba, P Schmidt, and G Wilkening
Thomsen-National Metrology Institute (PTB),Berlin/Braunschweig, GermanyLudger.koenders@ptb.deChapter 19
S Grger and M DietzschInstitute of Production MeasuringTechnology and Quality Assurance,Chemnitz, Germany
sophie.groeger@mb.tu-chemnitz.de
Trang 202Institut fr Festkrperphysik,
Tech-nische Universitt Berlin, Germany
mathias.senoner@bam.de
Chapter 22
T Machleidt, R Kstner, and
K.-H Franke
Computer Graphics Program, Technical
University of Ilmenau, Germany
Torsten.machleidt@tu-ilmenau.de
Chapter 23
S Czerkas, T Dziomba, and H Bosse
National Metrology Institute (PTB),
Braunschweig, Germany
slawomir.czerkas@ptb.de
Chapter 24
Y.-L Chen, C.-J Chen, and G.-S Peng
Center for Measurement Standards/
ITRI, Taiwan, Republic of China
Gwo-sheng.peng@cms.tw
Chapter 25
V Nascov
National Institute for Laser, Plasma
and Radiation Physics,
Carl g.frase@ptb.deChapter 29
C G Frase, W Hßler-Grohne, E Buhr,
K Hahm, and H BosseNational Metrology Institute (PTB),Braunschweig, Germany
Carl G.Frase@ptb.deChapter 30
J FlggeNational Metrology Institute (PTB),Braunschweig, Germany
Jens.Fluegge@ptb.deChapter 31
P Bariani, G Bissacco, H N Hansen,and L De Chiffre
Department of Manufacturing, neering and Management, TechnicalUniversity, Lyngby, Denmarkpbl@ipl.dtu.dk
Trang 21Engi-XXII List of Contributors
Swedish National Testing and
Research Institute, Boras, Sweden
3
Naval Air Warfare Center,
China Lake, USA
4
Equipe Optique de Champ Proche
LPUB, Dijon, France
Zerrouki@cnam.fr
Chapter 33
U Jacobsson1and P Sjvall2
1Measurement Technology,
2Chemistry and Materials Technology,
SP Swedish National Testing and
Research Institute, Boras, Sweden
ulf.jacobsson@sp.se
Chapter 34
SSt Lnyi
Slovak Academy of Science, Institute
of Physics, Bratislava, Slovakia
lanyi@savba.sk
Chapter 35
P Klapetek1, I Ohldal2and J Blek1,2
1Czech Metrology Institute, Brno,Czech Republic
2Department of Physical Electronics,Faculty of Science, Masaryk University,Brno, Czech Republic
pklapetek@cmi.czChapter 36
D ShumanNanoMc Company, New York, USAdavid.shuman@nanomc.comChapter 37
J Keller, D Vogel, and B MichelFraunhofer Institute for Reliability andMicrointegration (IZM), Dept
Mechanical Reliability and MicroMaterials, Berlin, GermanyMichel@izm.fhg.deChapter 38
R Schdel and A Abou-ZeidNational Metrology Institute (PTB),Braunschweig, Germany
rene.schoedel@ptb.de
Trang 22Nanoscale Calibration Standards and Methods: Dimensional and Related Measurements in the Micro- and Nanometer Range.
Edited by Gunter Wilkening, Ludger Koenders Copyright c 2005 Wiley-VCH Verlag GmbH & Co KGaA, Weinheim
Trang 23Metrological Scanning Probe Microscopes –
Instruments for Dimensional Nanometrology
Hans-Ulrich Danzebrink, Frank Pohlenz, Gaoliang Dai, and Claudio Dal Savio
Abstract
An overview of PTB’s activities in the field of dimensional nanometrology usingscanning probe microscopes (SPMs) is presented The chapter is divided into twoparts: the development of (1) high-resolution probing systems and (2) completeSPM metrology systems The subject of SPM-probing system design comprises,among other things, the concept of the “sensor objective” to combine conven-tional microscopy with scanning probe techniques In the field of complete me-trological SPM systems, the measuring properties of one of the existing SPMmetrology systems have been significantly improved by including laser inter-ferometers directly into the position control loop and by a clear reduction ofthe nonlinearity of the interference signals In addition, the application spectrum
of metrological SPM has been considerably extended by the establishment of anSPM system with a measuring volume of 25 mmq 25 mm q 5 mm
1.1
Introduction
In many fields of material sciences, biology, and medicine, conventional scanningprobe microscopes (SPMs) serve to visualize small structures with dimensionsdown to atoms and molecules as well as to characterize object-specific properties(magnetism, friction, thermal conductivity, and the like) For a large part of theinvestigations, the image information obtained with the SPM is completely suffi-cient for the qualitative investigation of the sample Because of their high spatialresolution, use of these microscopes is also of great interest for metrological ap-plications This is why the PTB has begun using SPMs in dimensional metrology
as one of the first national metrology institutes [1, 2]
A fundamental requirement for precise length measurements is, however, theaddition of a length measuring system to the microscope scanning system Forthis purpose, the piezo actuators that serve for positioning and scanning of sam-
3 1.1 Introduction
Nanoscale Calibration Standards and Methods: Dimensional and Related Measurements in the Micro- and Nanometer Range.
Edited by Gunter Wilkening, Ludger Koenders Copyright c 2005 Wiley-VCH Verlag GmbH & Co KGaA, Weinheim
Trang 24ments have in the past few years proceeded to equip the individual axes of thepositioning system with laser interferometers This allows the positioning values
to be continuously traced back to the wavelength of the laser light and thus to the
SI unit “meter” The fundamental idea is to treat the SPM like a miniaturizedthree-coordinate measuring machine and to correct its metrological propertieswith the device’s control software
As in the case of coordinate measuring machines, the SPM measuring systemscan be divided into probing system and positioning unit The structure of thepresent chapter reflects this aspect The first part describes the PTB activities
in the development of high-resolution probing systems based on scanningprobe microscope techniques The second part deals with precise positioningunits and with the complete SPM measuring and calibration devices that areavailable at PTB
1.2
High-Resolution Probing Systems
PTB’s development of probing systems based on SPMs is aimed at constructingand optimizing these measuring heads for use in dimensional nanometrology.Needless to say that the sensor systems described cannot only be used for metro-logical applications, but are of general interest for scanning probe microscopy andcoordinate measuring techniques
The scanning force microscopes (SFMs) are those of the family of SPMs thatare of special importance for dimensional metrology This is mainly due to thefact that their use is not limited to conductive surfaces as it is, for example, thecase for scanning tunnel microscopes The design principle of an SFM isshown in Figure 1.1 In this case, the deflection detection system of the cantilevermoving relative to the surface is based on an optical beam deflection principle,thus keeping the cantilever with the integrated measuring tip in a constant dis-tance to the surface The sample is then investigated line by line, and the profilesare subsequently composed in a computer to form an image
Trang 25In addition to the properties important from the viewpoint of metrology such asstability, sensitivity, and noise behavior, different other aspects have been incorpo-rated into PTB’s device development:
x Combination of the SPM measuring heads with optical
micro-scopes: here, the optical function extends from visualization to
quantitative dimensional or analytical methods
x The use of different detection principles: the movement and
position of the measuring tip is measured by an external optical
procedure or via an intrinsic electrical measuring principle
x The use of different measuring tip materials: in recent
develop-ments, special diamond tips are used in addition to silicon and
silicon nitride tips
1.2.1
Sensor Objective with Beam Deflection Detection
As the name already suggests, the concept of the so-called sensor objectivedirectly takes up the combination of microscope objective and sensor, the sensor
in this case working as a scanning probe microscope The special feature of thissensor head development is that existing optical standard microscopes are used as
a basis: because of the compact geometry and the special design, the sensor jective (composed of SPM module and imaging optics) can be directly screwedinto the turret of an optical microscope [12] This allows two microscopy worlds
ob-to be ideally combined
In measuring operation, the advantages of the combined system become vious Firstly, the well-proven conventional light microscopy is used for fast andextensive surface investigation The spectrum of tasks extends from the orienta-tion on the measurement object to quantitative optical measurements (see Sec-tion 1.2.4) Then local measurement is performed with the slower serial scanningprobe procedure in the measurement area defined for calibration or, generally, atthose points of the sample which require a high resolution
ob-5 1.2 High-Resolution Probing Systems
Fig 1.1 Sketch of a scanning
force microscope (SFM) with
cantilever probe and beam
deflection detection.
Trang 26strate wafer (step height: approx 0.28 nm) have been resolved with this ing setup despite the relatively large measuring circle (sample, microscope body,granite stand, positioning stages – cf Figure 1.2) [13] These measurements wereperformed in a dynamic SFM mode using conventional silicon cantilever probes.Traditional beam deflection technique was applied to detect the bending of thecantilever All optoelectronic elements of the beam deflection system have beenarranged outside the measuring head, since a spatial integration was not intendedwhen this version of the measuring head was constructed This arrangement can
measur-be optimized, in particular, with respect to its mechanical stability The furtherobjective of the PTB development went, however, beyond the integration of thebeam deflection system into the measuring head This is why measuring headsbased on probes with monolithically integrated deflection detection have beendeveloped (see Sections 1.2.2 and 1.2.3)
Fig 1.2 Conventional standard microscope with screwed-in sensor objective – the version shown here allows the device to be operated as optical near-field microscope in addition to scanning force and optical microscopy The enlarged image section in addition shows a dia- grammatic representation of the beam path inside the objective.
Trang 27Sensor Objective with Piezolever Module
One possibility of integrating the deflection detection system into the sensorprobe (i e., as near as possible to the measuring tip) consists in utilizing thepiezoresistive effect of the cantilever material (here silicon) [14] Comparable tothe strain gauge principle, the movement of the cantilever can thus be directlyconverted into a measurable electrical signal This means that an adjustment of
a light beam on the cantilever is not necessary This improves user-friendliness
of the system and avoids possible errors as a result of inexact adjustment height measurements have, for example, shown that scattered light or reflectionsfrom the surface can lead to disturbing interference patterns or that the rough-ness of the rear side of the cantilever affects the measurement when optical meth-ods are used for deflection detection These error sources are avoided by mono-lithically integrated deflection sensors
Step-For realization of the piezoresistive cantilevers (briefly referred to as vers”), the piezoresistive elements were arranged in the form of a completeWheatstone bridge and incorporated into the silicon cantilevers by ion implanta-tion This work was performed in cooperation with NanoWorld Services GmbH,Forschungszentrum Jlich and Surface Imaging Systems (SIS) GmbH [15] As aspecial option, one of the Wheatstone resistors is realized as an electrically con-trollable resistor that allows the measuring bridge to be nulled
“piezole-During the design of our very compact SFM measuring head, which is based onthese piezolevers, special attention was directed toward the requirement fordetachable contacts of the cantilever chips [16] In the piezolever SFMs so far rea-lized, the cantilever chips were glued on small ceramic boards and the contactswere bonded To avoid these complex additional process steps, the cantileverchips should be directly clamped and, at the same time, electrically contacted
To achieve this spring contacts were used that are made of gold-plated platinumberyllium (see Figure 1.3(b)) These “fingers” are arranged on a steel spring that
is pressed-on or flapped-back with the aid of a very small cam to allow the probes
to be exchanged The complete holder must be exactly preadjusted and work freefrom mechanical play in order to contact the electrodes on the rear side of thechip reproducibly with the fingers, to exert enough force on the chip and toachieve good contacting As can be seen in Figure 1.3(b), the contacts are only
50mm apart from each other The latter emphasizes the desired mechanical cision of the contacting mechanism
pre-The dimensions of the whole SFM module that comprises both a piezo elementfor the dynamic excitation of the cantilever and the electrical connections for thesensor signals were reduced to 4 mm q 3.5 mm q 35 mm only (see Figure1.3(c)) This compact design allows the combination with different measuringheads and measuring microscope objectives Topographic measurement resultsobtained with this piezolever module are described and shown in Section 1.2.4(Figure 1.6) together with interference-optical measurements
7 1.2 High-Resolution Probing Systems
Trang 28A great advantage of the mirror optics used in the sensor objective versiondescribed above (Section 1.2.1) was the fact that the dimensions and the opticalparameters could be calculated by optical computational programs and manufac-tured with diamond turning machines This finally allowed the whole sensor ob-jective to be designed and constructed at our own options and the space requiredfor the SFM module and the positioning mechanics to be taken into account Asdescribed, the compact piezolever module does not require so much space This iswhy these aspects are no longer important and the combination with a commer-cial microscope objective as shown in Figure 1.3(a) furnishes a solution that ismore universal This combination – microscope objective and SPM module –has been realized for all measuring head versions so far developed (cf also Figure1.4(a)).
1.2.3
Sensor Objective with Tuning Fork Module
Another possibility of integrating the deflection detection system into the ing probe consists in using a cantilever arm made of quartz [17] In operation, thisquartz is – just like the tuning fork in a quartz clock – excited to swing after anelectrical voltage has been applied The measurement of the distance between theprobe and the surface and thus imaging the surface is performed by recording the
measur-Fig 1.3 Piezolever module combined with a standard mi- croscope objective Part (b) shows the finger contacts for fastening and electrical con- tacting.
Trang 29current flowing through the quartz This signal is proportional to the lever armvibration and reacts very sensitive to changes of the damping when the distancebetween the tip and the surface varies.
Diamond tips designed at PTB are fastened on these tuning forks to allow highlateral resolution of the measurement (tip radii I 100 nm) [18] Figure 1.4(b)shows a quartz probe with tip The selection of diamond as tip material isbased on both the mechanical properties (stability and resistance to abrasion)and the optical properties that are important for the future use of the probes inoptical near-field microscopy
To test the efficiency of the tuning fork measuring head, topographic ments were performed on structures with dimensions in the nanometer range.The samples used here are made of self-organized InAs quantum dots on aGaAs substrate These quantum dots have pyramidal geometries (width approx.20–30 nm, height approx 4–6 nm) The mechanical stability of the whole micro-scope is sufficiently high to image such nanostructures Investigations of thenoise resulted in values of less than 0.6 nm (root mean square value) on a profile
measure-2mm in length
Because of their extremely slim construction and their adjustment-free tion detection, the tuning fork sensors can be tilted relative to the surface withoutany problem This also allows measurements to be performed on object areasdifficult to access such as structure edges or inclined areas These propertiesallow these as well as the piezolever sensors to be used as sensitive probes in acoordinate measuring machine Relevant developments have already beeninitiated at PTB
deflec-1.2.4
Sensor Head for Combined Scanning Probe and Interference Microscopy
Up to now, imaging optics in SFMs only served as visualization tools to determinethe area of interest for the measurement and to aid during probe alignment Inthe sensor head realization described in this chapter, the functionality has been
9 1.2 High-Resolution Probing Systems
Fig 1.4 “Tuning fork” module with positioning mechanics and adapter ring for the microscope objective as well as a micrograph of the tuning fork lever arm with the diamond tip (b).
Trang 30with the aid of an adapter (cf Sections 1.2.2 and 1.2.3) or (2) new internal opment of the whole interferential sensor head with additional SFM module Asolution according to (1) can directly be achieved by adapting the adapter ringmentioned in Section 1.2.2 and shown in Figure 1.3(a) In view of the plannedimprovement of the optical properties of the objective, which will be explained
devel-Fig 1.5 View of the bined SFM and interference microscope composed of sensor head and commercial basic instrument.
Trang 31com-in the followcom-ing, preference has, however, been given to the com-internal development
of the measuring head
Core piece of the newly developed sensor head is a Michelson interferometer inwhich the illumination is not performed via the internal, filtered microscopewhite light lamp, but via external laser sources coupled to optical fibers Thisway, an essential heat source is removed from the measuring setup and themechanical stability is improved Even more important is the fact that due tothe small illumination aperture of the optical fiber aperture correction becomesnegligible in the interference-microscopic evaluation This clearly reduces themeasurement uncertainty
At present, a HeNe laser (l¼ 632.80 nm) or a frequency-doubled Nd-YAG laser(l¼ 532.26 nm) can optionally be used as external laser sources in the measuringsetup If desired, this allows operation in the multiwavelength interferometrymode by which, compared to operation with only one wavelength, the range ofunambiguous measurements of the interference microscope is extended
For combination with a scanning probe microscope, the compact SFM modulewith piezolevers already described in Section 1.2.2 was mounted on the sensorhead below the beam splitting cube The cantilever can be seen in the image sec-tion of the optical microscope (both in the “live image” and in the interference-microscopic image; see Figure 1.6: on the left above) so that measurement areaselection is very user-friendly The interference-optical measurement (e g., inphase-shifting mode) is performed simultaneously over the whole image section;
in the current configuration, the optical measuring range amounts to approx
900mmq 900 mm It can, however, also be varied by using different optical tems In the case of a higher optical magnification it has, however, to be takeninto account that the depth of focus is reduced and the advantage of an opticalsurvey image is no longer valid In a second step, the object area to be investigatedwith a high lateral resolution is moved below the SFM measuring tip with the aid
sys-11 1.2 High-Resolution Probing Systems
Fig 1.6 Topography image of an 80-nm step-height standard (H80) (a) image recorded in the interference-optical mode (range 900 mm q 900 mm) – the SFM cantilever can be seen in the circle marked at the upper-left corner; (b) Section measured with the integrated SFM module (range 40 mm q 20 mm).
Trang 32less than 1 nm [20] Figure 1.6 shows a comparison of the results of ments performed on an 80 nm standard in the interference-microscope modeand in the SFM mode.
measure-Another advantage of this combined device becomes obvious in the case ofheterogeneous objects As soon as the optical constants of substrate and measure-ment structure differ, the optical wave in the interference microscope experiencesdifferent phase jumps on reflection This leads to a measurement error as long asthe relevant optical constants are not taken into account in the interference-micro-scopic evaluation Determination of these constants for thin layers in the nan-ometer range is, however, quite time-consuming and often imprecise, so this cor-rection is only conditionally possible This is different in the case of the device onhand: Here, the measured value of the interference microscope is corrected by theSFM module that had been calibrated before It is worthwhile pointing out thatthe SFM calibration was, as already described, performed with the same interfer-ence microscope, although on a sample with homogeneous surface This exampleshows the complementary properties of the two independent measuring princi-ples combined in one measuring instrument [20]
1.3
Metrology Systems Based on Scanning Probe Microscopes
In addition to other development activities in the field of SPM metrology, twocommercial SFMs have been extended by miniaturized homodyne laser interfe-rometers and their data acquisition system has been improved in the past 2years The positioning system of a third device developed into a large rangeSFM at PTB has already been equipped with laser interferometers by the manu-facturer These laser interferometers were developed in cooperation with the Tech-nical University IImenau and SIOS Messtechnik GmbH In the case of all de-vices, special attention was already paid during the construction of the interfe-rometer extension and the instrument design to the fact that principles as mini-mization of Abbe errors and tilting were complied with At PTB, the SFMs
Trang 33described serve for the calibration of standards and the general characterization ofmicrostructures In the following, the SFMs equipped with laser interferometerswill be referred to as metrological SFMs.
1.3.1
Scanning Force Microscopes of Type Veritekt
Since 1995, two metrological SFMs with integrated laser interferometers havebeen constructed on the basis of the commercial SFM Veritekt-3 of Carl Zeiss,Jena These devices allow measurement objects to be characterized in “contact”SFM mode with a measuring range of 70q 15 q 15 mm3
(x, y, z) Compared
to other instruments, the advantage of these SFMs is that a precise flexurehinge stage is used as the basis for the positioning system and that position-con-trolled piezo actuators (with integrated capacitive sensors) are used for each axis
of motion A skilful geometry of the flexure hinges allows factors such as talk of the axes and nonorthogonality of the directions of motion to be minimized.The operating principle of the integrated laser interferometers and the proce-dure of how they are used to calibrate the capacitive sensors in the piezo actuators
cross-is described in detail in [21, 22] Figure 1.7 shows the diagrammatic sketch of thetwo Veritekt SFMs Veritekt B that has been completed in 1996 and optimized inthe following years with respect to a minimization of the Abbe error, is used forcalibrations at PTB The results of international and internal comparisons [23, 24]have confirmed suitability of this SFM for calibration tasks
On the basis of the experience gained with Veritekt B, another metrologicalSFM, Veritekt C (see Figure 1.8), has been developed in the years until 2002.Essential subassemblies of the commercial basic instrument were adopted andsupplemented by modern measuring and evaluation electronics The arrange-
13 1.3 Metrology Systems Based on Scanning Probe Microscopes
Fig 1.7 Sketch of the metrological scanning force microscope Veritekt with integrated laser interferometers (source: TK Ilmenau).
Trang 34ment of the laser interferometers was revised in such a way that it is now alsopossible to adapt measuring heads working in different SFM modes.
Contrary to the measuring strategy used for Veritekt B, in which the laser ferometers are used for calibration of the capacitive sensors at discrete measure-ment points (l/2 zero points of the interferometer signals) and calculation of cor-rection values, Veritekt C directly includes the interferometer values in the SFM’scontrol loop To allow the interferometers to be used as measuring and controlsystems, the data acquisition electronics were completely changed and signal pro-cessing realized on the basis of a fast signal processor [5] Integration of thesedata acquisition electronics into Veritekt C allows the resolution of the interferom-eter values to be increased to 0.04 nm and the interferometers to be operated at adata rate of 20 kHz
inter-As nonlinearity of the interferometer signals (which amounts to approx 3 nm
in the uncorrected form) is a limiting factor when measurement uncertainties inthe range of a few nanometers are concerned, diverse correction procedures forthe nonlinearity were investigated when the measuring electronics was modified.Finally, a procedure that follows the principle developed by Heydemann [25] wasembedded into the control loop of the interferometers This procedure correctsthe deviations of the interferometers’ electrical signals ud and ud in amplitude,offset, and phase by an ellipse fitting method:
udw u1+ p udw1
r(u2cosa – u1sina) + q:
In view of the calculation effort involved, this algorithm is usually not ted as online method The investigations performed on Veritekt C have, however,shown that the ellipse parameters p, q, r, anda can be assumed to be constantover a sufficiently long period of time and need not, therefore, be permanentlydetermined during correction This allows the procedure to be integrated into
implemen-Fig 1.8 View of the SFM Veritekt C.
Trang 35the interferometer’s measuring circle without restriction of the data rate The rection described allowed remaining nonlinearities of the interferometer signals
to simultaneously determine the measurement data of both the positioning tem and the SFM sensor acting as null indicator This makes deceleration ofthe movement during acquisition of the measurement point data unnecessary;this “scan-on-the-fly” measuring principle allows the measurement velocity inthe x-direction (fast scan axis) to be increased to up to 25 mm/s as a function
sys-of the topography to be investigated Because sys-of the fast data acquisition, the fluence of thermal drift and other environmental factors can be reduced
in-Modernization of the data acquisition software, an automated sample ing system, and the efforts taken to realize automatic measuring processes (batchprocesses) have further improved the handling of the device Because of the use
position-of laser interferometers as displacement measuring sensors, calibration position-of themeasuring system so far required can be dispensed This leads to a reduction
of the whole measuring time
1.3.2
Metrological Large Range Scanning Force Microscope
For an increasing number of practical applications of scanning probe microscopy– also in the field of SPM metrology – the measuring range of piezo scanningstages (x, yI 100–200 mm) is too small These applications comprise, for exam-ple, the determination of roughness in accordance with written standards and in-vestigations on lateral standards whose evaluation requires measurements in themillimeter range For the reasons mentioned, different concepts have been devel-oped to extend the measuring range of SFMs with the aim of increasing the dis-placement range of piezo actuators [26] or using alternative positioning systems[27]
The PTB decided to develop and manufacture a positioning system on the basis
of the so-called nano measuring machine [27] that meets the specific metrologicalrequirements of industrial metrology This device was combined with a measur-ing head based on a focus sensor known from the Veritekt SFM A measuringinstrument is thus available that combines a positioning range of 25 q 25 q
5 mm3with the detection principles of scanning force microscopy – the so-calledmetrological large range scanning force microscope (LR-SFM) Its operating prin-ciple is shown in Figure 1.9
The object stage is moved via three linear driving systems that are positioncontrolled by laser interferometers Two angle-measuring systems have beenincluded in the control unit to correct for guidance errors of the motion stage
15 1.3 Metrology Systems Based on Scanning Probe Microscopes
Trang 36Similar to the Veritekt SFMs, the reference system is formed by plane mirrors; inthe case of the LR-SFM, the mirrors have been combined to form a cube corner.The resolution of the measuring system amounts to 0.08 nm or 0.001, respec-tively The construction of the device is aimed at achieving coincidence of measur-ing and reference plane to minimize Abbe errors.
To increase the dynamics of the positioning system, a compact vertically ing piezo stage was arranged on the sample stage of the NMM This one allowsfast scanning with a range of up to 2mm Its compact and stiff design results in ahigh mechanical resonance frequency frof 20 kHz The movement of this stage ismeasured and its position controlled via a capacitive sensor arranged in the mid-dle of three symmetrically arranged piezo actuators During scanning of the sam-ple, the lateral movement is performed exclusively with the NMM, whereas theheight adjustment results from a combined movement of the vertically adjustable
mov-z piemov-zo stage and the NMM The whole device is controlled via two signal sor systems One is responsible for the NMM, the other realizes height adjust-ment and data acquisition More detailed information about the measuring tech-niques used and the control systems implemented can be found in [28, 29] Thephoto in Figure 1.10 shows the metrological LR-SFM
proces-After finishing the design of the measuring software for the complete device,extensive investigations into the metrological properties of the LR-SFM werecarried out As an example, the first results of measurements performed on aflatness standard and on a sinusoidal lattice standard are shown
The topographic image of the flatness standard (Figure 1.11) can be used to timate the quality of the motion (influenced by the guidance mechanism) and toevaluate the instrument’s noise behavior The image shows that the structuremeasured is very flat and that artifacts as they may, for example, be caused bythe ball bearings, are not detectable The residual instrument noise (3 nm p-v)
es-Fig 1.9 Diagrammatic sketch of the metrological large range SFM (LR-SFM)
(components such as drives and rails are not shown for reasons of clarity),
(source: TK Ilmenau).
Trang 37is mainly due to external influences such as building vibrations and acoustic citations, and it should be reduced by optimizing the environmental conditions.Suitability of the LR-SFM for measurements on lateral standards and determi-nation of the structure period is illustrated by the example of a sinusoidal lattice.Figure 1.12 shows the scan image of a one-dimensional lattice that has beenscanned in the x-direction with a measuring range of 1.35 mm (this corresponds
ex-to 20 times the scanning range of the Veritekt SFMs!) As calculation of the ture period is based on a statistical procedure, a larger number of structuresallows us to improve the measurement uncertainty of the measuring procedure,provided the sample structure is homogeneous Repeated measurements on thissinusoidal lattice showed an identical periodic value of 416.67 nm This resultagrees with the reference value from diffractrometric optical measurements with-
struc-in two decimal places
17 1.3 Metrology Systems Based on Scanning Probe Microscopes
Fig 1.10 View of the
metrological large range
SFM (LR-SFM).
Fig 1.11 Investigations into the guiding
properties and noise behavior of the LR-SFM
Topography image of a flatness standard.
Trang 38high spatial resolution of the measuring instrument and agreement of the sured values with reference values from international comparisons.
mea-The investigations initiated to optimize the LR-SFM and extend it by alternativedetection principles are permanently continued and are to demonstrate that themeasuring system is also suitable for the measurement of structures with a topo-graphy up to the millimeter range Measurement tasks such as calibration of tipgeometries on indenters for hardness measurement, investigation of structures
on photo masks from semiconductor industry, determination of dimensionalparameters on parts in the field of microsystem technology and the like arealready demanded by industry and represent potential fields of application forthe metrological LR-SFM
1.4
Summary
Special emphasis in the field of dimensional nanometrology at PTB is placed onthe development and optimization of measuring instruments for SPM metrology.The development of sensor heads comprises, among other things, the concept ofthe “sensor objective” to combine conventional microscopy with scanning probetechniques It is characterized by its extraordinary versatility that is due to the use
of different measuring heads and detection principles In the field of completemetrological SFM systems, the measuring properties of one of the existing Veri-tekt systems have been significantly improved by including laser interferometersdirectly into the position control loop and by a clear reduction of the nonlinearity
of the interference signals In addition, the application spectrum of metrologicalscanning probe microscopy has been considerably extended by the establishment
of an SFM system with a measuring volume of 25 mmq 25 mm q 5 mm.The experience gained in the past few years has shown that it is precisely theperformance of development work in the field of SPM instrumentation at PTBthat is of decisive importance for the quality and understanding required for sub-sequent use of these devices and their calibration No study of operating instruc-
Trang 39tions or training courses can replace the know-how gained in this work Many velopment projects have produced innovative solutions to reply to metrologicalquestions In accordance with our philosophy, these activities are carried outalmost exclusively together with partners from industry and are, if possible,based on commercially available components Several examples of successfultechnology transfer (among others Physik Instrumente (PI) GmbH, SIOS Mess-technik GmbH, Surface Imaging Systems (SIS) GmbH) can be shown; they havebeen implemented in many industrial products in the whole world.
de-Because of the continuing miniaturization in many high-technology fields andthe increasing number of metrological applications of SPMs, scanning probemicroscopy will be of outstanding importance for the future work in the field
of dimensional nanometrology at PTB
Acknowledgments
We wish to thank all colleagues of the “Micro- and Nanometrology” Departmentand the Working Group “Quantitative Scanning Probe Microscopy” for the goodcooperation Especially Dr L Koenders, Dr R Krger-Sehm, Dr J W.G Tyrrell,Dipl.-Phys Th Dziomba, H Wolff, M Kempe, Dr M Xu, Dr D V Sokolov,
Dr D V Kazantsev and Dipl.-Ing.(FH) D Schulz have contributed to the workbeing a success Furthermore, we thank Professor Dr K Hasche and Dr G.Wilkening for their support Thanks are also due to our partners from industry:Surface Imaging Systems (SIS) GmbH (among others Dr H.-A Fuß), NanoWorldServices GmbH/Nanosensors GmbH (among others Dipl.-Phys Th Sulzbach),Ilmenau Technical University and SIOS Messtechnik GmbH (among othersProf G Jger and Dr T Hausotte) and Physik Instrumente (PI) GmbH(among others Dr H Marth und K Pollak)
19 References
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