INTERFACE FORMATION AND THIN FILM DEPOSITION FOR

299 Pages·2005·4.75 MB·English

by  Aravind S Killampalli

INTERFACE FORMATION AND THIN FILM DEPOSITION FOR
MOLECULAR AND ORGANIC ELECTRONICS

A Dissertation
Presented to the Faculty of the Graduate School
of Cornell University
In Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy

by
Aravind Srinivasa Killampalli
January 2006
© 2006 Aravind Srinivasa Killampalli
INTERFACE FORMATION AND THIN FILM DEPOSITION FOR
MOLECULAR AND ORGANIC ELECTRONICS

Aravind Srinivasa Killampalli, Ph. D.

Cornell University 2006

Organic materials are playing an increasing role in modern
microelectronic devices-beyond their traditional role as photoresists. Emerging
applications such as low-κ dielectrics, semiconductors and components in
molecular electronics demand excellent control of the interface between organic
and inorganic materials. To date, almost all work concerning the formation of
inorganic-on-organic structures on pre-existing organic layers has involved
elemental evaporation of metal thin films. An alternative approach has been
examined via the reaction of an organo-transition metal complex,
tetrakis(dimethylamido)titanium, Ti[N(CH ) ] , with self-assembled
3 2 4
monolayers (SAMs) terminated by -OH, -NH and -CH groups, using x-ray
2 3
photoelectron spectroscopy (XPS). This is the first detailed study which clearly
correlates the reactivity of Ti[N(CH ) ] with the functionality and density of
3 2 4
molecules in a self-assembled monolayer. Extent of reaction, stoichiometry at
the interface, ligand loss and decomposition have also been investigated in this
study.
A second area of research has involved the formation of organic-on-
inorganic structures. Supersonic molecular beams have been employed as
sources for deposition of thin films of pentacene, an organic semiconductor, on
bare SiO and SiO modified with hexamethyldisilazane (HMDS). Organic
2 2
materials are often bound by rather weak dispersion (van der Waals) forces and
crystallize in different phases, separated in total energy by a few k T.
B
Consequently, considerable promise exists in the use of these energy tunable
molecular beams for the deposition of organic thin films. Experiments have
provided significant insight into fundamental phenomena involved in nucleation
in the monolayer regime, and both the kinetics of thin film deposition and the
microstructure in the multilayer regime, evidenced by results from ellipsometry
and atomic force microscopy (AFM). Promising performance characteristics
have been obtained for organic thin film transistors (OTFTs) fabricated from
these pentacene films which can be correlated to film microstructure. Finally,
modification of the dielectric surface with hexamethyldisilazane (HMDS) has
been found to strongly influence nucleation and greatly enhance OTFT
performance, possibly due to reduced charge trapping at the semiconductor-
dielectric interface.
BIOGRAPHICAL SKETCH

Aravind Srinivasa Killampalli was born in Madras, India on February
13, 1979 and attended St. Michael’s Academy where he graduated at the top of
his high school class in 1996. He was always fascinated by computers as a kid
and wondered how they were made. He moved to the Birla Institute of
Technology and Science (BITS), Pilani, India to pursue a Bachelors degree in
Chemical Engineering. Four years later he graduated from BITS, Pilani with
distinction and again at the top of his class. During his tenure at BITS, Pilani
he participated in two internship programs at the Central Leather Research
Institute (CLRI) and the Southern Petrochemical Industries Corporation (SPIC),
both in Madras, India. During these internships, he developed computer
algorithms to model industrial reactors and researched materials for electrodes
in polymer electrolyte membrane fuel cells (PEMFCs). During his final year at
BITS, Pilani he undertook a study oriented project on reactors for chemical
vapor deposition and followed his interests in this area to join the Ph. D
program at Cornell University. At Cornell, primary support for his research
came from the Cornell Center for Materials Research (CCMR). He received
the Edna O. and William C. Hooey Award for Excellence in Graduate Research
in December 2004 and was a finalist for the Nottingham Prize at the Physical
Electronics Conference in Madison, WI in June 2005. Aravind was awarded
the Ph.D in Chemical Engineering in January 2006 and he moved on to work
with Intel Corp. in Portland, OR in their division primarily responsible for
research and development of CVD processes.
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To my parents, brother, paternal aunts and grandmother
for their perennial affection, understanding and support

Gnanam Paramam Balam

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ACKNOWLEDGMENTS

I am indebted to Prof. James R. Engstrom for being an excellent advisor
throughout my stay at Cornell University. He is a very through and careful
surface scientist in pursuit of the truth behind any experimental result and has
helped me inculcate these values. I am grateful to my committee members,
Prof. Paulette Clancy and Prof. Joel Brock and to Prof. George G. Malliaras for
fruitful discussions concerning organic electronics. I would also like to express
my gratitude to Brian Ford and Glenn Swan for prompt help on numerous
occasions with ongoing efforts in the laboratories or when new parts needed to
be fabricated.
I had the opportunity to work with two senior graduate students, Dr. Paul
F. Ma who taught me the ropes with vacuum technology and Dr. Todd W.
Schroeder who allowed me to participate in the design and construction of our
new supersonic molecular beam system for use at Cornell High Energy
Synchrotron Source (CHESS) and I am grateful to both of them. I would also
like to thank fellow ERG member Abhishek Dube who has been my comrade in
arms in the lab and a good friend outside and younger members Manish Sharma
and Jared Mack for their assistance. Malliaras group members Alexios
Papadimitratos and Yuanjia Zhang have been excellent collaborators and it has
been a pleasure working with them.
My stay in Ithaca has been made enjoyable by several friends, Venkat,
Vishal, Dhananjay and Sourav and I am thankful to them for their company.
Special thanks to my friends from childhood: Kalyan, Sudhanva and Manthram.
We have had the best of times together going back to high school.
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Last but not the least, I am eternally thankful to my dad and mom, both
professors, for inculcating the importance of science and mathematics at a
young age and for always being there for me. Also, my aunts and grandmother
for all the love and affection they have showered on me. My little brother has
always looked up to me for inspiration and guidance and I hope that I have
done well so far and look to do better in the future.
This work was supported by the Cornell Center for Materials Research
(CCMR), a Materials Research Science and Engineering Center of the National
Science Foundation (DMR-0079992). Additional support was also provided by
a Nanoscale Interdisciplinary Research Team on Inorganic-Organic Interfaces
(NSF-ECS-0210693) and the Semiconductor Research Corporation via the
Center for Advanced Interconnect Systems Technologies (SRC task 995.011).

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TABLE OF CONTENTS

1. Introduction…………………………………………………………….1
1.1 Transistors and Integrated Circuits: Current technology………...1
1.2 Future Directions and Emerging Technologies…………………..6
1.2.1 Molecular Electronics……………………………………..7
1.2.1.1 Self-assembled monolayers……………………....8
1.2.1.2 Conjugated oligomeric systems………………...10
1.2.1.3 Polyphenylene and polyphenylene
based molecules…………..……………………...11
1.2.2 Barrier layers……………………………………………..11
1.2.3 Organic electronics……………………………………….13
1.3 Thin film deposition…………………………………………….17
1.3.1 Physical deposition processes……………………………17
1.3.2 Chemical deposition processes…………………………...19
1.3.3 Nucleation and morphology of thin films………………..24
1.3.4 Atomistic nucleation model……………………………...28
1.4 Molecular beam techniques……………………………………..30
1.4.1 Characterization of molecular beams…………………….31
1.4.1.1 Effusive beams………………………………….32
1.4.1.2 Supersonic molecular beams……………………34
1.4.2 Supersonic molecular beam scattering…………………...41
1.4.2.1 Non-reactive molecular beam scattering………..42
1.4.2.1.1 Elastic scattering……………………....42
1.4.2.1.2 Inelastic scattering……………………..42
1.4.2.1.3 Trapping and desorption………………43
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1.4.2.1.4 Molecular chemisorption……………...46
1.4.2.2 Reactive scattering……………………………...46
1.4.2.2.1 Direct collisional activation.…………..47
1.4.2.2.2 Precursor-mediated dissociation………48
1.4.2.2.3 Collision induced dissociation………...49
1.4.3 Thin film deposition using supersonic molecular
beams……………………………………………………………50
1.5 References………………………………………………….52
2. Experimental Procedures…………………………………………….56
2.1 Formation of inorganic-organic interfaces……………………...56
2.1.1 Description of molecular beam system…………………..56
2.1.2 Description and characterization of vapor
delivery source……………………………………………61
2.1.3 Sample preparation……………………………………….64
2.1.3.1 Materials………………………………………...64
2.1.3.2 Substrate preparation……………………………64
2.1.3.3 Formation of self-assembled
monolayers (SAMs)……………………………65
2.1.3.4 Formation of terminal groups…………………...66
2.1.3.5 Characterization of self-assembled
monolayers……………………………………...67
2.1.3.5.1 Contact angle measurements…………..67
2.1.3.5.2 Ellipsometry…………………………...67
2.1.3.5.3 Atomic force microscopy (AFM)……..68
2.1.3.5.4 X-ray photoelectron spectroscopy
(XPS)………………………………….68
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