Template controlled integration and characterization of bottom-up grown ferroelectric nanoislands [Elektronische Ressource] / vorgelegt von Sven Clemens

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2009
• Nombre de lectures: 21
• Langue: Deutsch
• Poids de l'ouvrage: 21 Mo

Extrait

Template-Controlled Integration and Characterization
of Bottom-Up Grown Ferroelectric Nanoislands
Von der Fakultat¨ fur¨ Elektrotechnik und Informationstechnik
der Rheinisch-Westfalischen¨ Technischen Hochschule Aachen
zur Erlangung des akademischen Grades eines Doktors
der Ingenieurwissenschaften genehmigte Dissertation
vorgelegt von
Diplom-Ingenieur
Sven Clemens
aus Haan
Berichter: Universitatsprofessor¨ Dr.-Ing. Rainer Waser
Universit¨ Dr. rer. nat. Claus Michael Schneider
Tag der mundlichen¨ Prufung:¨ 30.01.2009
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfugbar¨ .IIIII
Contents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Ferroelectrics 5
2.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Piezoelectricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2 Ferroelectricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.3 Lead Titanate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.4 Ferroelectric Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Size Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Correlation Volume and Surface Effects . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Electrical and Mechanical Boundary Conditions . . . . . . . . . . . . . . . . . 13
3 Ferroelectric Nanostructure Processing 17
3.1 Lithography Based Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 Self-Assembly Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3 Hybrid Routes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.1 Stencil Based Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.2 Nucleation Site Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4 Experimental Methods - Sample Preparation 23
4.1 Chemical Solution Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1.1 Preparation of Lead Titanate Nanoislands . . . . . . . . . . . . . . . . . . . . . 24
4.1.2 of Aluminum Oxide Thin Films . . . . . . . . . . . . . . . . . . . . 26
4.1.3 Spin-On Glass Dielectrics - Silsesquioxanes . . . . . . . . . . . . . . . . . . . . 28
4.1.4 Spin-On Glass - Processing . . . . . . . . . . . . . . . . . . . . . . 30
4.2 Chemical Mechanical Polishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.1 Oxide Polishing Principle and Slurry . . . . . . . . . . . . . . . . . . . . . . . 32
4.2.2 Polisher Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3 Electron Beam Lithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.1 Nucleation Site Patterning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37IV
5 Experimental Methods - Sample Characterization 43
5.1 Scanning Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.1.1 Atomic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.1.2 Piezoresponse Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2 Electrical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.1 Large Signal I-V Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.2 Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.3 X-Ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.4 Scanning Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
6 Results and Discussion 53
6.1 Self-assembled Ferroelectric Nanoislands . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.1.1 Impact of Precursor Concentration . . . . . . . . . . . . . . . . . . . . . . . . . 54
6.1.2 Multiple Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.1.3 Crystallographic Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.1.4 Crystallization Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.1.5 Island Heights in Terms of Integration . . . . . . . . . . . . . . . . . . . . . . . 61
6.2 Registered Deposition of Ferroelectric Nanoislands . . . . . . . . . . . . . . . . . . . . 62
6.2.1 Precursor Concentration and Nucleation Site Geometry . . . . . . . . . . . . . . 63
6.2.2 Impact of Seed Layer Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.2.3 Piezoelectric and Ferroelectric Properties . . . . . . . . . . . . . . . . . . . . . 69
6.2.4 Topography and Integration Density . . . . . . . . . . . . . . . . . . . . . . . . 72
6.3 Integration I - Flowable Oxides as Insulating Matrix . . . . . . . . . . . . . . . . . . . 73
6.3.1 Embedding in Flowable Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.3.2 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.3.3 Impact of Embedding Matrix on Ferroelectric Properties . . . . . . . . . . . . . 78
6.4 Integration II - Chemical Mechanical Polishing . . . . . . . . . . . . . . . . . . . . . . 79
6.4.1 Polishing Homogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6.4.2 Material Removal Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.4.3 Sample Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.4.4 Optimized Process Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.4.5 Polishing of Ferroelectric Nanoislands . . . . . . . . . . . . . . . . . . . . . . . 86V
6.4.6 Integrated Ferroelectric Nanostructure Arrays . . . . . . . . . . . . . . . . . . . 91
6.5 Direct Electrical Characterization of Ferroelectric Nanoislands . . . . . . . . . . . . . . 94
6.5.1 Electric Measurements on Embedded Ferroelectric Grains . . . . . . . . . . . . 95
6.5.2 Equivalent Circuit Diagram and Simulation . . . . . . . . . . . . . . . . . . . . 96
6.5.3 Ferroelectric Properties of Embedded Ferroelectric Grains . . . . . . . . . . . . 99
6.5.4 Influence of the Polishing Grade . . . . . . . . . . . . . . . . . . . . . . . . . . 103
6.5.5 Increased Grain Content - Approaching a Ferroelectric Thin Film . . . . . . . . 107
6.5.6 Parasitic Current Compensation and Hysteresis Plots . . . . . . . . . . . . . . . 109
7 Conclusions 113
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
7.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
References 117
Acknowledgements 131Abbreviations
Al O aluminum oxide2 3
AFM Atomic Force Microscopy
EGMBE 2-butoxyethanol
CMP Chemical Mechanical Polishing
CSD Chemical Solution Deposition
EBL Electron Beam Lithography
FIB Focused Ion Beam
HSQ hydrogen silsesquioxane
ILD inter-layer dielectric
IPA isopropyl alcohol
MFS minimum feature size
MOCVD Metalorganic Chemical Vapor Deposition
MIBK methyl isobutyl ketone
MSQ methyl silsesquioxane
PbO lead oxide
PFM Piezoresponse Force Microscopy
PMMA poly(methyl methacrylate)
PTO lead titanate PbTiO3
PZT lead zirconate titanate Pb(Zr Ti )Ox 1-x 3
RTP Rapid Thermal Processing
SEM Scanning Electron Microscopy
SFM Scanning Force Microscopy
SOG spin-on glass
TiO titanium dioxide2
XRD X-Ray Diffraction1 Introduction
1.1 Motivation
A ferroelectric is a polar material exhibiting a spontaneous polarizationP that can be toggledS
between two stable states upon application of an external electric field. Ferroelectricity was
initially discovered in 1921 by Valasek on the basis of Rochelle Salt (sodium potassium tartrate
tetrahydrate) [1]. Anyway, it took until the the early 1940s with the discovery of the perovskite
BaTiO as a high dielectric constant material that considerable attention was paid to the phe-3
nomenon [2]. The perovskite crystal class paved the way towards a deeper understanding of
ferroelectricity on the microscopic scale and ever since ferroelectric oxides found their way
into a large variety of applications utilizing their outstanding dielectric (capacitors), piezoelec-
tric (actuators and pressure sensors), pyroelectric (temperature sensors) and non-linear optical
(holographic data storage, optical transistors) properties [3].
Today, the tremendous progress in thin-film processing and advanced ceramic fabrication opened
up an exciting new field of applications for ferroelectric materials in information technology [4].
Novel implementations comprise devices that utilize either the dielectric (tuneable capacitors;
dynamic random access memories (DRAM)) or piezoelectric (micro-electro-mechanical systems
(MEMS); surface acoustic wave (SAW)) properties of ferroelectric films [5]. The progressive
reduction of film thicknesses and operating voltages in particular enabled the development of
Ferroelectric Random Access Memories (FeRAM) in integrated circuits, non-volatile