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Electrochemical nanopatterning of Si
surfaces through insulating layers
by Atomic Force Microscope scratching


Der Technischen Fakultät der
Universität Erlangen-Nürnberg
zur Erlangung des Grades



DOKTOR-INGENIEUR


vorgelegt von

Zhang, Yan


Erlangen 2007















Als Dissertation genehmigt von
der Technischen Fakultät der
Universität Erlangen-Nürnberg



Tag der Einreichung: 14.12.2007
Tag der Promotion: 14.04.2008
Dekan: Professor Dr. –Ing. Habil. J. Huber
Berichterstatter: Professor Dr. Sc. Tech. P. Schmuki
Professor Dr. Rer. Nat. A. Winnacker


Elektrochemische Nanostrukturierung von
Si-Oberflächen durch selektives Ritzen von
isolierenden Dünnfilmen mit dem
Rasterkraftmikroskop


Der Technischen Fakultät der
Universität Erlangen-Nürnberg
zur Erlangung des Grades



DOKTOR-INGENIEUR

vorgelegt von

Zhang, Yan


Erlangen 2007

Acknowledgements

A journey is easier when you travel together. Interdependence is certainly more valuable than
independence. During the time of my PhD, I have been accompanied and supported by many
people. It is a pleasant aspect that I have now the opportunity to express my gratitude for all of
them.
The first person I would like to thank is my supervisor Patrik Schmuki. I have been in his lab
since 2002 when I started my PhD. During these years, His enthusiasm and integral view on
research and his mission for providing 'high-quality papers', has made a deep impression on me.
Besides of being an excellent supervisor, Patrik is also a good friend to give me some advises for
life.
I would like to thank my best friends Eugeniu Balaur and Andrei Ghicov who always help me. I
would like to thank lovely Helga Hildebrand who not only performed the surface analysis but
also helped me for general stuffs and Julia Kunze and Sebastian Kleber (Poldi) who helped me
for the German translation.
I cannot forget the guide of Stefan Fenchel, Lionel Santinacci and Thierry Djenizian. I thank
them all for having shared many experiences and thoughts with me. I would also like to thank all
my colleagues of LKO who gave me the feeling of being at home at work.
I would like to thank Prof Göken and Greil, Dr. Karsten Durst and Peter Cromme to offer me the
chance to use their AFM.
I would also like to thank the others who took effort in providing me with valuable comments on
this thesis: Prof. Sannakaisa Virtanen, Yosuke Kawamura, James Ellis, Kai Kessler, Kunyuan
Gao, Yin Xiaowei, Zhou Hongben, Zhou Yizhou, Andres Munoz and Dong Wensheng.
I am very grateful for my parents for their love and patience during the PhD period.



Contents

Abstract...........................................................................................................................................1
Introduction ....................................................................................................................................5
Chapter 1......................................................................................................................11
Overview................11
1.1 Micro- and nano-structuring.................................................................................................11
1.2 Techniques based on scanning probe microscopy ...............................................................13
1.3 Metal Electrochemical Deposition.......................................................................................14
Chapter 2.................19
Theoretical Aspects and Literature Overview...........................................................................19
2.1 Atomic force microscopy.....................................................................................................19
2.1.1 Introduction ..................................................................................................................19
2.1.2 AFM Principle..............................................................................................................20
2.1.3 AFM Operation Modes22
2.2 Nanomechanics ....................................................................................................................26
2.2.1 Force vs. Distance Curves............................................................................................26
2.2.2 Load vs. penetration depth curve .................................................................................29
2.2.3 Phase transformation32
2.3 Semiconductor electrochemistry..........................................................................................35
2.3.1 N- and P-type Semiconductors: Doping.......................................................................35
2.3.2 the semiconductor-electrolyte interface .......................................................................36
2.3.3 Mechanism for deposition of metals onto an n-type semiconductor ...........................38
2.3.4 Breakdown of the Space Charge Layer........................................................................40
2.3.5 Schottky Barriers (Metal-Semiconductor Junctions) ...................................................41
2.4 Metal electrochemical deposition.........................................................................................43
2.4.1 Kinetics and Mechanism of Electrodeposition.............................................................43
2.4.2 Deposition of a metal on a foreign substrate................................................................45
2.4.3 Nucleation and Growth ................................................................................................46
2.4.4 Typical morphology of electrodeposited films ............................................................50
2.5 Self-assembled Monolayer...................................................................................................53
2.5.1 Definition of Self-assembled Monolayer (SAM).........................................................53
2.5.2 Advantages of Self-assembled Monolayers .................................................................55
2.5.3 SAMs Formation..........................................................................................................56
Chapter 3.......................................................................................................................................59
Experimental.................................................................................................................................59
3.1 Sample preparation...............................................................................................................59
3.1.1 H-terminated Si..59
3.1.2 organic layer coated Si .................................................................................................59
3.2 Scratching.............................................................................................................................60
3.2.1 Atomic force microscopes............................................................................................60
3.2.2 AFM-tips.....61
3.2.3 Atomic force microscopes operating............................................................................63
3.2.4 Nanoscratching.............................................................................................................65






3.2.5 Micro-scratching ..........................................................................................................67
3.3 Electrochemical experiments ...............................................................................................67
3.3.1 Electrolytes...................................................................................................................67
3.3.2 Electrochemical cell .....................................................................................................68
3.3.3 Electrochemical techniques..........................................................................................68
3.4 Characterization techniques .................................................................................................69
3.4.1 Scanning electron microscopy (SEM)..........................................................................69
3.4.2 Auger electron spectroscopy (AES).............................................................................70
3.4.3 X-ray photoelectron spectroscopy (XPS or ESCA) .....................................................70
Chapter 4.......................................................................................................................................73
Results and Discussion........73
4.1 Copper electrodeposited on scratched oxide covered Si......................................................73
4.1.1a AFM-scratching of Si surfaces...................................................................................73
4.1.1b Scratching induced selective electrochemical metal deposition ................................75
4.1.2 Electrochemical characterization of the substrate (intact and scratched surfaces) ......76
4.1.3 Morphology of the deposits (SEM characterization) .................................................100
4.1.4 Conclusions ................................................................................................................129
4.2 Copper deposited on scratched SAM coated Si .................................................................132
4.2.1 Self-assembled monolayers (SAM) ...........................................................................132
4.2.2 Immersion copper plating on SAM coated Si ............................................................139
4.2.3 Electrochemical deposition of copper on SAM coated Si..........................................148
4.2.4 Conclusions..153
Conclusions .................................................................................................................................155
References ...................................................................................................................................162
List of symbols ............................................................................................................................169
List of publications.....................................................................................................................172
Curriculum Vitae .......................................................................................................................173




Inhaltsverzeichnis

Kurzfassung ....................................................................................................................................1
Einleitung ........................................................................................................................................5
Kapitel 1 ........................................................................................................................................11
Überblick.................11
1.1 Micro- and nano-structuring (Mikro- und Nanostrukturierung) ..........................................11
1.2 Techniques based on scanning probe microscopy (Rastersondenmikroskopische Techniken)
....................................................................................................................................................13
1.3 Metal Electrochemical Deposition (Elektrochemische Metallabscheidung) .......................14
Kapitel 2 ........................................................................................................................................19
Theoretische Aspekte und Literaturüberblick..........................................................................19
2.1 Rasterkraftmikroskopie ........................................................................................................19
2.1.1 Einleitung .....................................................................................................................19
2.1.2 AFM Prinzip.................................................................................................................20
2.1.3 AFM Operationsmodi ..................................................................................................22
2.2 Nanomechanic.......26
2.2.1 Kraft-Abstands-Kurven................................................................................................26
2.2.2 Belastung-Eindringtiefe-Kurve ....................................................................................29
2.2.3 Phasenübergänge..........................................................................................................32
2.3 Halbleiterelektrochemie .......................................................................................................35
2.3.1 n- und p- Halbleiter.35
2.3.2 Halbleiter-Elektrolyt Grenzfläche ................................................................................36
2.3.3 Mechanismus der Metallabscheidung auf n-Halbleiter................................................38
2.3.4 Zusammenbruch der Raumladungsrandschicht ...........................................................40
2.3.5 Metall-Halbleiter Übergänge – Schottky Übergang.....................................................41
2.4 Elektrochemische Metallabscheidung..................................................................................43
2.4.1 Kinetik und Mechanismus der elektrochemischen Abscheidung ................................43
2.4.2 Abscheidung eines Metalls auf einem fremden Substrat .............................................45
2.4.3 Keimbildung und Wachstum........................................................................................46
2.4.4 Typische Morphologie elektrochemisch abgeschiedener Filme ..................................50
2.5 Selbstorganisierte Monolagen..............................................................................................53
2.5.1 Definition selbstorganisierter Monolagen....................................................................53
2.5.2 Vorteile selbstorganisierter Monolagen .......................................................................55
2.5.3 Bildung selbstorganisierter Monolagen56
Kapitel 3 ........................................................................................................................................59
Experimentelles ............................................................................................................................59
3.1 Probenvorbereitung ..............................................................................................................59
3.1.1 H-terminiertes Si ..........................................................................................................59
3.1.2 organisch beschichtetes Si............................................................................................59
3.2 Kratzen .................................................................................................................................60
3.2.1 Rasterkraftmikroskopie (AFM)....................................................................................60
3.2.2 AFM Spitzen ................................................................................................................61
3.2.3 AFM Bedienung...........................................................................................................63






3.2.4 Nanokratzen .................................................................................................................65
3.2.5 Mikro-Kratzen..............................................................................................................67
3.3 Elektrochemische Experimente............................................................................................67
3.3.1 Elektrolytlösungen .......................................................................................................67
3.3.2 Elektrochemische Zelle................................................................................................68
3.3.3 Elektrochemische Methoden........................................................................................68
3.4 Analysemethoden.....69
3.4.1 Rasterelektronenmikroskopie (SEM)...........................................................................69
3.4.2 Augerelektronenspektroskopie (AES)..........................................................................70
3.4.3 Röntgeninduzierte Photoelektronenspektroskopie.......................................................70
Chapter 4 ......................................................................................................................................73
Ergebnisse und Diskussion ..........................................................................................................73
4.1 Kupferabscheidung auf angekratztem oxidbedecktem Si ....................................................73
4.1.1a AFM Kratzen auf Si Oberflächen...............................................................................73
4.1.1b Selektive Metallabscheidung in Kratzer ....................................................................75
4.1.2 Elektrochemische Charakterisierung des Substrates (intakte und zerkratzte
Oberflächen)..........................................................................................................................76
4.1.3 Morphologie der Abscheidungen (SEM Charakterisierung) .....................................100
4.1.4 Schlussfolgerungen ....................................................................................................129
4.2 Kupferabscheidung auf gekratztem, SAM bedeckten Si ...................................................132
4.2.1 Selbstorganisierte Monolagen....................................................................................132
4.2.2 Stromlose Kupferabscheidung auf SAM bedecktem Si.............................................139
4.2.3 Elektrochemische Kupferabscheidung auf SAM bedecktem Si ................................148
4.2.4 Schlussfolgerung ........................................................................................................153
Schlussfolgerung.........................................................................................................................155
Referenzen...................................................................................................................................162
Abkürzungsliste..........................................................................................................................169
Publikationsliste .........................................................................................................................172
Lebenslauf..............173



Abstract

The ability to develop well-defined structures on material surfaces offers the opportunity
of many new applications and has become an important field of research, not only for physics and
chemistry but also for biologists and engineers. A major challenge is to miniaturise these surface
structures as can be achieved by new processes such as; self- assembly, soft lithography, dip-pen-
lithography, scanning probe lithography or laser-induced patterning. In this thesis a mikro-
indenter and scanning force microscope are utilized as a form of scanning probe lithography to
mechanically modify coated Si-surfaces with a diamond probe.
The coating was either an electrically insulating layer (eg. a ca. 10 nm thermal or native
oxide layer) grown on an n- or p-type Si (100) or organic substances (undecylenic acid, 1-decene,
1-octadecene), which were covalently attached to a hydrogen-terminated n- or p-type Si (111)
surface.
By selectively removing the insulating coating by mechanically scratching the surface,
masks for the electrochemical deposition of copper were produced. Copper was then deposited
into these defects and onto the Si-surface under controlled conditions (e.g. electrolyte
concentration and over-potential)
Copper electrodeposition into these template scratches on oxide covered Si was
investigated with an emphasis on nucleation and growth of these deposits. The electrolyte
concentration, voltage and type of silicon wafers had a considerable effect on the nucleation,
growth and morphology of the copper deposits. Copper preferentially deposited on the scratch
edges rather than in the scratch bottom at certain electrolyte concentrations. At relatively high
over-potentials, the deposition rate increase leads to a dendritic morphology of the copper
deposits. The nucleation, growth and morphology of copper deposited at a very high voltage
pulse (-100 V vs. Ag/AgCl) on both oxide covered and oxide free Si surfaces was also
investigated.
As well as electrochemical plating, immersion plating in copper containing electrolyte
solutions of scratched wafers was studied. The influences of semiconductor substrate type (1-
octadecene coated n-type Si and p-type Si) and plating parameters, such as immersion time, on
the copper deposit’s morphology are presented. The morphology of copper deposits on different
surfaces was investigated using Scanning Electron Microscopy (SEM). Auger electron
spectroscopy (AES) scans were performed to obtain the information of the selectivity of the
copper deposition.
The results indicated that both oxide and the organic layers acted as good masks for the
selective deposition of copper. Under optimised conditions, homogeneous and well-connected
copper wires in 100 nm range were obtained selectively in the scratch.

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