Surface analytical characterization of horizontal and vertical nanotopographies at the silicon, silicon oxide, electrolyte phase boundaries [Elektronische Ressource] / vorgelegt von Michael Lublow

Michael Lublow

Informations

• Publié par: brandenburgische_technische_universitat_cottbus
• Publié le: 01 janvier 2009
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 14 Mo

Extrait

Surface Analytical Characterization of Horizontal and Vertical
Nanotopographies at the Silicon/Silicon Oxide/Electrolyte
Phase Boundaries







Von der Fakultät für Mathematik, Naturwissenschaften und Informatik
der Brandenburgischen Technischen Universität Cottbus

zur Erlangung des akademischen Grades

Doktor der Naturwissenschaften
(Dr. rer. nat.)

genehmigte Dissertation

vorgelegt von

Diplom-Physiker

Michael Lublow

geboren am 03.09.1963 in Neumünster









Gutachter: Prof. Dr. Hans-Joachim Lewerenz
rof. Dr. Jürgen Reif

Gutachter: Prof. Dr. Dieter M. Kolb

Tag der mündlichen Prüfung: 10. Dezember 2009


















































2Abstract


Nanotopography development induced by photoelectrochemical in situ conditioning of silicon is
followed using a combination of surface sensitive analysis techniques. In an etching study, vertical
nanostructure analysis reveals a buried stressed layer within silicon, identified by Brewster-angle
analysis (BAA). In conjunction with in system synchrotron radiation photoelectron spectroscopy
(SRPES), a superior quality hydrogen terminated Si(111) surface could be prepared by obliteration of
the intermediate stressed layer. Using a novel photoelectrochemical structure formation method, a
variety of vertical nanotopographies has been generated and analyzed by in situ Brewster-angle
reflectometry (BAR) and scanning probe microscopy (SPM). Shaping of the nanostructures became
possible by real-time monitoring using BAR. Appearances range from aligned single nanoislands with
improved aspect ratio to connected Si nano-networks. A model was developed to describe the
nanostructure formation based on stress-induced selective oxidation. Increased local photo-oxidation
is found to result in the formation of extended horizontal micro- and nanostructures with fractal
properties. Within a defined light intensity range, the structures reveal the azimuthal symmetry of the
investigated crystal planes (111), (100), (110) and (113). The observed features could be reproduced
using a model that is based on the interplay of stress in silicon, oxidation by light generated excess
holes and locally increased etching in fluoride containing solution.


Die durch photoelektrochemische in situ Verfahren induzierte Nanostrukturbildung auf Silicium wird
durch eine Kombination oberflächenempfindlicher Methoden untersucht. Durch schrittweise
Abtragung eines Oberflächenoxids und durch die Analyse vertikaler Nanostrukturen wird eine
verborgene Streßschicht mit Hilfe der Brewster-Winkel Analyse ermittelt. In Verbindung mit
Synchrotron-Photoelektronenspektroskopie kann eine optimierte H-Terminierung von Si(111)-
Oberflächen nach Entfernen des gestreßten Bereiches erzielt werden. Durch Anwendung einer
neuartigen photoelektrochemischen Methode wurde eine Vielzahl vertikaler Nanostrukturen erzeugt,
deren Morphologie Aspekt-optimierte nanoskopische Inseln sowie Nanostruktur-Netzwerke umfaßt.
In Modellbetrachtungen wird eine streß-induzierte selektive Oxidation als Bildungsmechanismus
vorgeschlagen. Verstärkte lokale Photooxidation wiederum führt zur Bildung ausgebreiteter Mikro-
und Nanostrukturen, die in einem mittleren Bereich der Lichtintensität die azimutale Symmetrie der
jeweiligen (111), (100), (110) und (113) Kristallorientierungen widerspiegeln. Modellhafte
Simulationen basieren auf der Wechselwirkung von Streß im Siliciumkristall, lichtgenerierter
Oxidation und erhöhter lokaler Materialabtragung in konzentrierter Ammoniumfluoridlösung.


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4Contents

Introduction .............................................................................................................................. 7
1. Fundamental aspects..........................................................................................................11
1.1 Chemical, structural and electronic properties of the SiO /Si interface ________ 11 2
1.1.1 Silicon and silicon dioxide bulk properties.......................................................................... 11
1.1.2 Properties of the SiO -Si interface....................................................................................... 13 2
1.1.3 Stress and strain at the interface... 15
1.2 Competing electronic and (photo-)electrochemical processes at the reactive
semiconductor-electrolyte interface_________________________________________ 17
1.2.1 The Marcus theory of single electron transfer..................................................................... 17
1.2.2 Energy levels in semiconductors and redox systems........................................................... 21
1.2.3 Semiconductor (photo-)corrosion........................................................................................ 25
1.3 Self-organization phenomena at the silicon/electrolyte interface ______________ 28
1.3.1 Dynamical systems .............................................................................................................. 28
1.3.2 Self-organization phenomena at silicon electrodes ............................................................. 29
2. Experimental methods and procedures............................................................................ 32
2.1 Brewster-angle analysis _______________________________________________ 32
2.1.1 The dielectric function......................................................................................................... 32
2.1.2 Brewster-angle analysis of multi-layer systems .................................................................. 37
2.2 In situ Brewster-angle reflectometry of (electro-)chemical conditioned silicon
surfaces________________________________________________________________ 44
2.2.1 Experimental arrangement................................................................................................... 44
2.2.2 The linear approximation of the reflectance ........................................................................ 45
2.3 Photoelectron spectroscopy using synchrotron radiation ____________________ 46
2.3.2 Principles of photoelectron excitation ................................................................................. 46
2.3.2 The application of synchrotron radiation............................................................................. 52
2.4 Photoelectron emission microscopy______________________________________ 56
2.4.1 Experimental arrangement.. 56
2.4.2 Contrast in photoelectron emission microscopy.................................................................. 57
2.5 Atomic force microscopy ______________________________________________ 58
2.6 Scanning electron microscopy __________________________________________ 61
2.6.1 Experimental arrangement................................................................................................... 61
2.6.2 Depth of field, chemical and spatial resolution ................................................................... 65
3. Results and discussion........................................................................................................ 69
53.1 Identification of a sub-surface stressed silicon layer ________________________ 69
3.1.1 Introductory remarks ........................................................................................................... 69
3.1.2 Ex situ Brewster-angle analysis: in loco etching results...................................................... 70
3.1.3 In situ le reflectometry: real-time monitoring results..................................... 82
3.1.4 Morphological and chemical optimization of Si(111)-1x1:H.............................................. 95
3.1.5 Synopsis: chemical and structural properties of the stressed interfacial region ................ 103
3.2 Horizontal nanostructure formation by photoelectrochemical conditioning ___ 104
3.2.1 Alignment effects and shaping of nanostructures in the divalent dissolution region ........ 105
3.2.2 Model considerations for the self-organized and engineered nanostructure formation..... 119
3.2.3 Structural changes at the Si(111) interface during anodic oscillations.............................. 125
3.2.4 Summary: in situ controlled self-organized nanostructure formation ............................... 135
3.3 Self-organized propagation of fractal silicon microstructures in concentrated
NH F _________________________________________________________________ 137 4
3.3.1 Background on fractals and macropores.............................................................