Glancing Angle Deposition

77 Pages·2007·11.44 MB·English

Growth of Nanostructures by
Glancing Angle Deposition
Project written by
Jeppe Mørch Nørgaard, Nina Brodam Lorentzen,
René Petersen, and Morten Vesterager Madsen

2007

Institute of Physics and Nanotechnology
Aalborg University - Nanotechnology
Theme:
Nanofabrication
Title:
Growth of Nanostructures by Glancing Angle Deposition
Project Periode:
P6, 1/2-07 - 26/5-07
Project Group:
Nano, Gr. N642
Groupmembers:
Jeppe Mørch Nørgaard
Nina Brodam Lorentzen
Ren´e Petersen
Morten Vesterager Madsen
Supervisor:
Kjeld Pedersen
Number of Copies: 6
Number of Pages: 73
Number of Appendices: 2
Total Number of Pages: 77

Abstract
Thisprojectisbasedonthecentralquestion: Howcannanorodsbegrowninanorderedarray
andwithspecificdirectionandshape? Howcantheybeutilizedandcharacterized? Ithasbeen
shown that by utilizing a glancing angle deposition technique, surfaces with unique properties
can be obtained. This includes antireflective coatings, waveguides etc. In this report the self
shadowingeffectofglancingangledepositionisexaminedboththeoreticallyandexperimentally
to explore the potential of the technique. In general, three different aspects of the production
method are examined; the effect of the angle of incidence, the addition of seed particles to the
sample, and the impact of the rotation of the sample. To determine the correct conditions
under which the experiments should be performed, Monte Carlo simulations of the deposition
are carried out. Waveguides are theoretically considered and a model for light scattering of
columnar structures is developed. A glancing angle deposition setup is built to experimentally
demonstrate the self shadowing mechanism. Columnar structures are grown both with and
withouttheuseofseedparticles, however, structuresgrownfromseedparticlesexhibitamore
porousstructure. Itisconcludedthatbyutilizingglancingangledeposition,periodicstructures
exhibiting two dimensional photonic bandgabs can be grown.
Keywords: GLAD, PBG, and SIMBAD.

Preface
This bachelor project is a part of the 6th semester 2007 Nanotechnology at Aalborg Univer-
sity. The report is written by group N642, consisting of four nanotechnology students with
nanofabrication as overall topic.
The report has a hierarchical structure, so the theory described in the first section forms the
basis of later sections. As a consequence the report has to be read chronologically to get the
best understanding of the content. The report is therefore not suitable as a thesaurus.
References are devised according to the Harvard method, listing author and publication year
in square brackets. The alphabetic reference list can be found in the back of the report.
References placed in the end of a section refer to the whole section, if placed inside a sentence
they only refer to that specific sentence.
Vectors are written as~a, averages as a¯, and the inverse trigonometric functions as sin−1.
We would like to thank the following people who, besides our supervisor, have contributed to
the project:
• Laboratory technician Kim Houtved Jensen and Hans Nilsson - for technical assistance
in the workshop.
• Jens Rafaelsen - for assistance with SEM imaging.
• Associate professor Thomas Garm Pedersen for assistance in the theoretical part of the
report.
3
Contents
1 Introduction 6
1.1 Glancing Angle Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.1 Antireflective Coatings Made by GLAD . . . . . . . . . . . . . . . . . . 6
1.1.2 Photonic Crystals and their Applications . . . . . . . . . . . . . . . . . 7
1.2 Problem Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Glancing Angle Deposition 9
2.1 Oblique Angle Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Ballistic Deposition Model. . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Simulation of Ballistic Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.1 The Principle of the Simulation . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.2 Periodic Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Deposition Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.1 Calculation of Deposition Rate . . . . . . . . . . . . . . . . . . . . . . . 24
3 Optical Phenomena in Nanostructures 27
3.1 Photonic Band Gap Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.1 Simple Square Columnar Structure . . . . . . . . . . . . . . . . . . . . . 28
3.1.2 Cylindrical Columnar Structure . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Photonic Bandstructure Calculations . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 Light Scattering from Cylindrical Structures . . . . . . . . . . . . . . . . . . . . 34
3.4 Light Scattering Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4 Methods and Materials 42
4.1 The Creation of a GLAD Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.1.1 The Setup in the Vacuum Chamber . . . . . . . . . . . . . . . . . . . . 42
4.2 Light Scattering Measuring Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.3 Experiment Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.3.1 Preparation of Wafer for Spincoating of Polystyrene Spheres . . . . . . 49
4.3.2 Silver as Deposition Material and Silicon Wafers . . . . . . . . . . . . . 49
5 Experimental Results and Discussion 51
4
CONTENTS
5.1 Deposition of Seed Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.1.1 Lithography Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.1.2 Spincoating of Seed Particles . . . . . . . . . . . . . . . . . . . . . . . . 52
5.2 GLAD Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.1 Angle of Incidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.2.2 Effect of Seedparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.2.3 Rotation of the Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.3 Scattering Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6 Discussion 64
6.1 Scattering of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.2 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7 Conclusions and Perspectives 67
7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
7.2 Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
A Appendix A - Calculations 69
B Appendix B - Technical Drawings 70
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1
Chapter
Introduction
Fabricationofnewmaterialsbasedonstructuresonthenanoscalehasanenormousimpactona
wide variety of technological areas. Materials consisting of a closely packed array of nanorods
are examples of a very porous structures with interesting properties. The changes in basic
physical properties arise because the ratio between volume and diameter is much different
from macroscopic materials. The small sizes can result in quantum effects or nano optical
effects when the structures are smaller than the wavelength of electrons and light respectively.
Nanorods are believed to be one of the most important building blocks for the assembly of
integrated nano-electrical, nano-optical and nano-mechanical systems [Ye et al., 2004]. They
are also of great interest as individual nanodevices including nanoelectronics, field emitters,
nano-optics, and photonic crystals [Ye et al., 2004].
1.1 Glancing Angle Deposition
A technique capable of fabricating ordered arrays of nanostructures is Glancing angle depo-
sition, GLAD. It was first reported in 1959 by [Smith, 1959] and [Knorr and Hoffman, 1959].
The technique utilizes a flow of atoms or molecules from gas phase impinging on a substrate
from an oblique angle in a vacuum which results in a deposited film showing a columnar
morphology. The angle of incidence controls the tilt of the columns and affects the degree
of shadowing and thus the porosity of the film. If the substrate is rotated around the sub-
strate normal, the morphology of the film is dramatically changed. A porous film consisting
of isolated evenly spaced columns is demonstrated by [Liu, 1999] using this technique. The
morphologyofthecolumnscanbecontrolledbychangingthesubstrateangularfrequencyand
substratepositionrelativetotheevaporationsource. Thinfilmscontainingcomplexstructures
canbegrownbyrotatingthesubstrateinpredefinedcycleswithanumberofdifferentfrequen-
cies. By utilizing GLAD it is furthermore possible to grow multi-component nanostructures
by changing the source material during deposition. These structures are expected to enhance
the complex functionality achieved by conventional single-component layers. Structures with
accurate predetermined properties can thus be designed and grown utilizing GLAD.
1.1.1 Antireflective Coatings Made by GLAD
Nanorod structures created by GLAD can be used as anti-reflective coatings as demonstrated
by[Cartwright, 2007],whocreatedthinopticalfilmswitharefractiveindexclosetothatofair.
The optical film consists of an array of oblique nanorods, which collectively have a refractive
index as low as 1.05. The author also claims that several graded layers of film can produce
an optical coating that virtually eliminates reflection at all wavelengths. The antireflective
coating is achieved by utilizing the fact that if a material encompassed by air is to minimize
theamountoflightitreflects,itssurfacemusthavearefractiveindexclosetothatofair,which
is almost one. Solids in general do, however, not have refractive indices between 1 and 1.4,
therefore GLAD is used to grow silica nanorods at an oblique angle on an aluminium nitride
surface. These nanorods are separated enough to allow air to reside between them, so the
effective refractive index is that of the nanorods and air combined. Therefore, by increasing
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