molecular design of moisture insensitive hybrid adhesive films a dissertation submitted to the ...

143 Pages·2015·6.5 MB·English

MOLECULAR DESIGN OF MOISTURE INSENSITIVE HYBRID ADHESIVE FILMS

A DISSERTATION
SUBMITTED TO THE DEPARTMENT OF
MATERIALS SCIENCE AND ENGINEERING
AND THE COMMITTEE ON GRADUATE STUDIES
OF STANFORD UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

MARTA GIACHINO
JUNE 2015
© 2015 by Marta Giachino. All Rights Reserved.

Re-distributed by Stanford University under license with the author.

This work is licensed under a Creative Commons Attribution-

Noncommercial 3.0 United States License.
http://creativecommons.org/licenses/by-nc/3.0/us/

This dissertation is online at: http://purl.stanford.edu/wq639pr8079

ii
I certify that I have read this dissertation and that, in my opinion, it is fully adequate
in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Reinhold Dauskardt, Primary Adviser
I certify that I have read this dissertation and that, in my opinion, it is fully adequate
in scope and quality as a dissertation for the degree of Doctor of Philosophy.
William Nix
I certify that I have read this dissertation and that, in my opinion, it is fully adequate
in scope and quality as a dissertation for the degree of Doctor of Philosophy.
Geraud Dubois
Approved for the Stanford University Committee on Graduate Studies.
Patricia J. Gumport, Vice Provost for Graduate Education
This signature page was generated electronically upon submission of this dissertation in
electronic format. An original signed hard copy of the signature page is on file in
University Archives.
iii
A
BSTRACT

Effective bonding of organic/inorganic interfaces is paramount to the structural
reliability of modern multilayer device technologies such as flexible electronics,
photovoltaics, and nanoelectronic devices, in which organic/inorganic interfaces are
ubiquitous. For example, strong adhesion of an underfill epoxy to a silicon substrate is
critical to extending the lifetime of advanced integrated circuits and three-dimensional
stacking technologies. Often, the synergistic effects of mechanical loads due to thermal
expansion mismatch, temperature cycling, and moisture can weaken the adhesion of these
polymer-silicon interfaces. As a result, the underfill epoxy adhesion can fail with
significantly lower fracture energy compared to the cohesive fracture energy of the
underfill epoxy.
Many existing approaches to strengthen these polymer-Si interfaces are based
on incremental changes in the underfill epoxy to increase the adhesion to the silicon
substrate. We demonstrate a technique to both quantify and model the mechanical and
kinetic debonding behavior of an epoxy resin that either: 1) is molecularly toughened
with a flexibilizer molecule, or 2) contains silica filler particles. By introducing filler
particles into the bisphenol-F-based resin, the critical fracture energy at the epoxy/Si
interface can significantly exceed that of the unfilled epoxy/Si interface; however, despite
this increase in fracture energy in ambient conditions, the underfill epoxies exhibit an
absence of a debond threshold in the presence of moisture, resulting in continued growth
of interfacial defects even at low loads.
Rather, hybrid molecular materials containing both organic and inorganic
components that are resistant to moisture are uniquely capable of simultaneously
achieving high critical fracture energy and moisture insensitivity. By combining chemical
synthesis processes together with optimized solution deposition conditions, we can
achieve nanometer length-scale mixing of organic/inorganic components to synthesize
hybrid molecular structures with targeted functionalities, such as the ability to form a
high-performance moisture-insensitive bond between an organic layer and an inorganic
substrate. We synthesized hybrid organic/inorganic films via a sol-gel synthesis approach
iv
using two precursors: an epoxy-functionalized silane and a zirconium alkoxide. By
unraveling the underlying hydrolysis and condensation reactions of the precursors that
occur in solution and utilizing optimized dip and spray coating techniques, we can
manipulate the hybrid molecular structure formation and the composition throughout the
film, resulting in organic/inorganic interfaces with a 10-fold increase in adhesion energy
and a 3-fold improvement in moisture-insensitivity.
v
A
CKNOWLEDGEMENTS

I would first like to thank my research adviser, Professor Reinhold Dauskardt.
Reiner was always very supportive of new research directions and ideas, and his positive
reinforcement made my experience at Stanford truly exceptional. I am very grateful for
Reiner’s willingness to discuss any subject, whether technical or personal, which made
for an open and collaborative work environment within the group. He also worked
tirelessly to ensure that funding for our programs was never an issue, and I really
appreciate his efforts in always securing it. It has been an absolute pleasure to learn from
Reiner through the years, and I will be forever grateful for his encouragement towards
my pursuit of a Ph.D. during my first year of graduate school.
Next, I would like to thank Professor Geraud Dubois. Geraud has acted as my co-
adviser throughout most of my graduate studies and I am extremely grateful for all of the
time, effort and support that he put forth in my research project and towards mentoring
me. Geraud has a true passion for mentoring and his dedication to my program was
invaluable throughout our collaboration. He spent countless hours coaching me on how to
use my time wisely in the lab and tried to teach me how to think like a chemist! I am also
thankful for his and Reiner’s support towards obtaining the IBM Ph.D. Fellowship to
support me for 2013-2015 and the IBM Fran Allen Mentoring Award.
I would also like to thank Professor William Nix for serving on my reading
committee and for teaching the “Thin Film Mechanics” course one more time. It was by
far one of the most useful courses I’ve taken at Stanford and it strongly contributed to my
research. I would also like to thank Professors Nick Melosh and Stacey Bent for serving
on my defense committee. Thank you all for your guidance, support and feedback on my
research.
The work in this dissertation required significant financial support and I would
like to thank the Intel Corporation, the Semiconductor Research Corporation, the Air
Force Office of Scientific Research (AFOSR) and the Department of Energy (DOE) for
their support. I would also like to thank the Intel/Semiconductor Research Corporation
Education Alliance for supporting me as a scholar during the academic years of 2010-
vi
2012. Through these programs, I was able to work with outstanding industry
collaborators who had valuable input to my research: Shawna Liff (Intel), Nisha
Ananthakrishnan (Intel), and Kay Blohowiak (The Boeing Company).
During my years working in the Materials Science and Engineering Department, I
would not have been very efficient if it hadn’t been for the outstanding administrative
staff. I would like to thank Billie Kader, Jane Edwards, Doris Chan and Sylvia Paris for
all of their help. I would especially like to thank Fi Verplanke and Carol Scott for being
my go-to’s for any academic or funding-related problem and always having an answer or
solution right away.
Throughout my time at Stanford, I was very fortunate to work with an exceptional
group of brilliant, dynamic and fun students in the Dauskardt research group and within
the Materials Science Department. I would like to thank previous group members, who
strongly contributed to my growth and training: Taek-Soo Kim, Mark Oliver, Ryan
Birringer, Yusuke Matsuda, Alex Hsing, Chris Bruner and Linying Cui. I would also like
to thank the mechanics expert, Fernando Novoa, who could always answer my questions
about modeling or subcritical curves. To the current group members, especially Brian
Watson, Warren Cai, Scott Isaacson, Ryan Brock, Siming Dong and Daisy Yuen, thank
you for all the laughs (especially Warren’s great jokes) and all the invaluable tips you
provided me in the lab.
I made some of the best friends I could ask for here at Stanford, most of which I
met in this research group: Jeffrey Yang, Stephanie Dupont, Krysta Biniek and Florencia
Paredes. I’m so thankful for all of the help and knowledge that Jeff passed down to me
about hybrid materials, and more importantly, he was the best roommate and friend I
could have ever asked for. I’m going to miss our take-out nights! I’m so glad that Krysta
and I could go through every process of our Ph.D. together (from classes, to quals, and
eventually to the defense). My Ph.D. would have been much more difficult without her
support and empathy. Stephanie’s countless jokes and match-making interests made the
office chats the highlight of my day. I’m so happy to have gotten to know her so well in
the past years. Florencia was the glue that brought us together and I will be forever
grateful for that! Finally, I would like to thank Gage Hills, who has been so supportive
and loving throughout the past years. I could always count on him to keep me grounded
vii
especially during the difficulties that a Ph.D. can bring. I’m so happy to have him in my
life and I’m excited to see what happens in our next adventures together.
Last but not least, I wouldn’t be here without my family. My grandparents, Renata
and Carlo Galbiati, were my number one fans throughout all of my studies and I am so
grateful to have had so much support from them. My aunt, Chiara Galbiati, was the one
who originally suggested that I study materials science and I am always thankful for that.
Finally, I want to sincerely thank my parents, Monica and Piero Giachino, who have
made many sacrifices so that my brother and I could succeed and be happy. Both my
parents and my brother, Carlo Giachino, have shown me so much unconditional love and
support in all of my decisions and they are the backbone that I can always count on.
viii
T C
ABLE OF ONTENTS

Abstract.............................................................................................................................. iv
Acknowledgements............................................................................................................ vi
Table of Contents............................................................................................................... ix
List of Tables................................................................................................................... xiii
List of Figures.................................................................................................................. xiv

Chapter 1: Introduction .................................................................................................. 1
1.1. Research Overview................................................................................................ 1
1.2. Organic/Inorganic Interfaces in Semiconductor Packaging.................................. 2
1.3. Hybrid Organic-Inorganic Materials via Sol-Gel Chemistry................................ 4
1.4. Synopsis of Dissertation........................................................................................ 7
1.5 References............................................................................................................... 9

Chapter 2: Fracture Mechanics Experimental Methods............................................ 13
2.1 Fracture Mechanics............................................................................................... 13
2.1.1 Strain Energy Release Rate, G..................................................................... 13
2.1.2 Stress Intensity Factor, K............................................................................. 14
2.1.3 Fracture Toughness as a Material Property................................................. 14
2.2 Thin Film Fracture Testing................................................................................... 15
2.2.1 Double Cantilever Beam Test Geometry..................................................... 15
2.2.2 Critical Fracture Energy Measurements...................................................... 16
2.3 Subcritical Crack Growth Measurement .............................................................. 18
2.4 References ............................................................................................................ 22

Chapter 3: Sol-Gel Synthesis and Hybrid Film Characterization............................. 24
3.1. Sol-Gel Chemistry............................................................................................... 24
3.1.1. Metal Alkoxide Precursors......................................................................... 24
3.1.2. Organosilane Precursors............................................................................. 26
ix
3.1.3. Organosilane and Metal Alkoxide Reactions............................................. 27
3.2. Hybrid Film Synthesis and Deposition................................................................ 28
3.2.1. Hybrid Film Synthesis................................................................................ 28
3.2.2. Dip Coating Hybrid Films.......................................................................... 29
3.2.3. Spray Coating Hybrid Films....................................................................... 30
3.3. Materials Characterization Techniques............................................................... 32
3.3.1. X-ray Photoelectron Spectroscopy............................................................. 32
3.3.2. Fourier Transform Infrared Spectroscopy.................................................. 34
3.3.3. Nuclear Magnetic Resonance Spectroscopy............................................... 35
3.3.4. Scanning Electron Microscope Imaging..................................................... 37
3.4 References ............................................................................................................ 39

Chapter 4: Adhesion of Underfill Epoxy/Silicon Interfaces ...................................... 41
4.1. Introduction ......................................................................................................... 41
4.2. Experimental Procedure....................................................................................... 42
4.2.1. Sample Preparation..................................................................................... 42
4.2.2. Adhesion Testing........................................................................................ 43
4.2.3. Subcritical Debond Testing........................................................................ 44
4.2.4. Fracture Surface Characterization.............................................................. 45
4.3. Results and Discussion........................................................................................ 45
4.3.1. Adhesion and Cohesion in Inert Environments.......................................... 45
4.3.2. Subcritical Debonding of Underfill Epoxies ............................................. 47
4.3.3. Subcritical Debonding of Underfill Epoxies with Hybrid Films .............. 55
4.4. Conclusion.......................................................................................................... 57
4.5. References........................................................................................................... 59

Chapter 5: Heterogeneous Solution Deposition of High-Performance Adhesive
Hybrid Films .................................................................................................................. 62
5.1. Introduction ......................................................................................................... 62
5.2. Experimental Procedure....................................................................................... 63
5.2.1 Dip Coating Hybrid Films .......................................................................... 63
x