Fabrication of IDAs for biosensors by advances mask aligner lithograhy

153 Pages·2016·12.72 MB·English

by  Stefan Partel

Fabrication of interdigitated
electrode arrays for biosensors by
advanced mask aligner
lithography

Dipl.-Ing.(FH) Stefan Partel, MSc.

A dissertation submitted for the fulfillment
of the requirements for the
doctoral degree at the Technical Faculty,
University of Freiburg
Laboratory for Sensors

Doctoral adviser
Prof. Dr. Gerald Urban
Laboratory for Sensors, Department of Microsystems Engineering – IMTEK, University of Freiburg
Laboratory for Sensors
Department of Microsystems Engineering – IMTEK
University of Freiburg

Disputation
Freiburg im Breisgau, 13.05.2016
Dean
Prof. Dr. Georg Lausen, Freiburg im Breisgau, Germany
Doctoral committee
Chair: Prof. Dr. Jürgen Wöllenstein, University of Freiburg, Germany
Co-chair: Prof. Dr.-Ing. Ulrike Wallrabe, University of Freiburg, Germany
1st referee: Prof. Dr. Gerald Urban, University of Freiburg, Germany
2st referee: PD. Dr. rer. nat. Andreas Erdmann, Friedrich-Alexander University of Erlangen-Nürnberg, Germany
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Abstract
This research is directed towards development and fabrication of a highly sensitive electrochemical
biosensor. The amperometric sensor is based on redox cycling at interdigitated electrode arrays (IDA)
with gap distances in nano or submicron regime. The focus is on the fabrication of IDAs with
conventional mask aligner lithography. For highest sensitivity the crucial dimension is in the
nanometer or submicron range which is below the diffraction limit of the light. For economic usage,
other substrate materials other than silicon were implemented. A dissolution rate monitor (DRM)
based on interferometry was built. With the collected data from DRM measurements the photoresist
behavior at the development step was studied and simulations were investigated to optimize the
lithography process. Due to simulations a biosensor with a 1 µm electrode gap on a transparent
substrate (Gen1) was realized by adding a thin titanium layer, which prevents backside reflections
from substrate and enhances the resolution. The electrochemical characterization of the chip shows an
amplification factor of 14 (for PAP).
The second fabricated biosensor is based on a multilayer stack (Gen2) and focuses on electrode
gap reduction towards nanometers. It has been demonstrated that electrode gaps down to 140 nm are
possible. This fabrication approach has the ability to adjust the gap size in the thermal oxidation step
rather than with lithography. The gap distance can be controlled by the oxidation step. The
electrochemical measurements have proven that this fabrication method is suitable for IDA biosensors
fabrication.
A third sensor design (Gen3) was developed which meets the requirements for mass production
of nano IDAs. Furthermore, the process eliminates both the lift-off process and the thermal oxidation
process steps and allows a further simplification in tuning of the electrode gap. The requirements on
the lithography process are not as high as for the Gen2 chip and an initial structure of 1 µm is sufficient
for electrode gaps in the nanometer range. This process approach has the ability to use polymers as a
substrate due to relative low process temperatures. The gap distance can be controlled by the
deposition process rather than by lithography. The undercut which is formed during deposition
guarantees a separation of the electrodes. With the introduction of assistant features (AsFe) the yield
can be increased by forming a larger undercut profile and is reducing the linewidth variation in
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lithography. Electrochemical measurements have demonstrated the potential of this fabrication
technique. Amplification factors of 116 at a collection efficiency of 99.5 % for ferrocenemethanol are
achieved at an electrode gap distance of 160 nm (to our knowledge, this is the highest published
amplification factor for IDA biosensors so far). The fabrication process allows an economic mass
production where the initial pattern can be fabricated by hot embossing or injection molding and the
subsequent forming of the undercut by a deposition process. The design was optimized with the help
of simulation and verifies that advanced mask aligner lithography can be utilized to fabricate gap sizes
down to sub 100 nm.
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Zusammenfassung
Die Arbeit beschäftigt sich mit der Entwicklung und Herstellung eines hoch sensitiven
elektrochemischen Biosensors. Der amperometrische Sensor basiert auf Redoxreaktionen an
ineinandergreifenden Elektrodenstrukturen (IDAs) mit Elektrodenabständen im Submikrometer –
bzw. Nanometer-Bereich. Die Herstellung der Initialstrukturen erfolgte dabei durch Mask Aligner
Lithographie. Der Lithographieprozess wurde unter Zuhilfenahme von Simulationen optimiert. Dazu
wurde ein Dissolution Rate Monitor (DRM) angefertigt, der den Fotolackabtrag während des
Entwicklungsprozesses misst. Die somit erhaltenen Daten ermöglichen es ein parameterbasiertes
Fotolackmodell zu entwickeln. Mithilfe der Simulation konnte ein erster Biosensor (Gen1) mit einem
Elektrodenabstand von einem Mikrometer auf einem transparenten Substrat hergestellt werden. Dies
wurde mithilfe einer dünnen Titanschicht realisiert, die die Rückseitenreflektion am Substrat
unterdrückt. Die elektrochemische Auswertung zeigte eine Signalverstärkung von 14 (PAP).
Der zweite hergestellte Biosensor (Gen2) basiert auf einem mehrschichtigen Substrataufbau und
ermöglicht eine weitere Reduktion des Elektrodenabstandes. Elektrodenabstände bis 140 nm wurden
mit dieser Fertigungsmethode realisiert. Der Elektrodenabstand wird primär durch den thermischen
Oxidationsprozess definiert. Somit können mit nur einer Lithographiemaske die Elektrodenabstände
im Nachhinein angepasst werden. Elektrochemische Messungen haben gezeigt, dass auch diese
Herstellungsmethode für Biosensoren geeignet ist.
Der dritte hergestellte Biosensor (Gen3) verzichtet komplett auf einen lift-off Prozess und lässt
ebenfalls eine Anpassung des Elektrodenabstandes nach der Lithographie zu. Die Anforderungen an
den Lithographieprozess sind hierbei relative gering, eine Initialstruktur von 1 µm ist ausreichend, um
effektive Elektrodenabstände im Nanometerbereich zu erzielen. Dabei wird der Abstand primär durch
einen Beschichtungsprozess gesteuert und die Lithographie spielt eine untergeordnete Rolle. Durch
die Beschichtung wird ein negativer Flankenwinkel erreicht, der nötig ist um die Elektroden elektrisch
zu separieren. Mittels Hilfsstrukturen (AsFe) kann der Flankenwinkels bei kritischen Strukturen
optimiert werden, was zu einer präzisieren Linienbreite führt und somit die Prozessstabilität
verbessert. Mit dieser Herstellungsmethode konnten Verstärkungsfaktoren von 116
(ferrocenemethanol) erreicht werden. Unseres Wissens ist dies die bisher höchste dokumentierte
Verstärkung, die mittels IDAs erzielt wurde. Der Herstellungsprozess ist hervorragend für die
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Massenfertigung geeignet, die Initialstruktur kann beispielsweise mittels Spritzguss oder Heißprägen
erstellt werden. Der negative Flankenwinkel und die Elektroden werden mittels Beschichtung
hergestellt. Das Maskendesign wurde mit Hilfe von Simulation optimiert. Durch die
Prozesskombination und die Strukturoptimierung ist es möglich, mit Mask Aligner Belichtung
Strukturen unter 100 nm zu erzeugen.
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Authors bibliography
Publications associated to the thesis:
Peer reviewed Journals
S. Partel, C. Dincer, S. Kasemann, J. Kieninger, J. Edlinger, G. Urban, “Lift-off free fabrication
approach for periodic structures with tunable nano gaps for interdigitated electrode arrays”, ACS
Nano, vol. 10, no. 1, pp. 1086–1092, Jan. 2016. DOI: 10.1021/acsnano.5b06405
S. Partel, S. Kasemann, P. Choleva, C. Dincer, J. Kieninger, G. Urban, “Novel fabrication process
for sub-μm interdigitated electrode arrays for highly sensitive electrochemical detection”, Sensors
and Actuators B: Chemical, vol. 205, pp. 193-198, Aug, 2014. DOI: 10.1016/j.snb.2014.08.065

Peer reviewed conference papers
S. Partel, G.A. Urban;” Innovative method to suppress local geometry distortions for fabrication of
interdigitated electrode arrays with nano gaps” Proc. SPIE 9780, vol. 9780, pp. 978015–978015–8,
San Jose, 2016. DOI: 10.1117/12.2218527
S. Partel, G.A. Urban, K. Motzek, “Simulation model validation of two common i-line photoresists”,
Microelectronic Engineering, vol. 110, pp. 75-79, 2013. DOI:10.1016/j.mee.2013.01.054
K. Motzek, S. Partel, U. Vogler, A. Erdmann, “Numerical optimization of illumination and mask
layout for the enlargement of process windows and for the control of photoresist profiles in proximity
printing”, Proc. SPIE 8171, Physical Optics, 81710K, Marseille, 2011. DOI:10.1117/12.896755
K. Motzek, A. Erdmann, U. Hofmann, N. Ünal, M. Hennemeyer, M. Hornung, P. Hudek, S. Partel,
A. Heindl, M. Ruhland, “Mask Aligner Lithography Simulation – From Lithography Simulation to
Process Validation”, Microelectronic Engineering, vol. 98, pp. 121-124, Berlin, 2011.
DOI:10.1016/j.mee.2012.07.076
S. Partel, M. Mayer, P. Hudek, C. Dinçer, J. Kieninger, G. A. Urban, K. Motzek, L. Matay,
“Fabrication process development for a high sensitive electrochemical IDA sensor”, Microelectronic
Engineering, vol. 97, pp. 235-240, Berlin, 2011. DOI:10.1016/j.mee.2012.03.028
K. Motzek, A. Bich, A. Erdmann, M. Hornung, M. Hennemeyer, B. Meliorisz, U. Hofmann, N. Unal,
R. Voelkel, S. Partel, P. Hudek, “Optimization of illumination pupils and mask structures for
proximity printing”, Microelectronic Engineering, vol. 87, no. 5–8, pp. 1164-1167, Ghent, 2009.
DOI:10.1016/j.mee.2009.10.038
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S. Partel, S. Zoppel, P. Hudek, A. Bich, U. Vogler, M. Hornung, R. Voelkel, “Contact and Proximity
Lithography using 193nm Excimer Laser in Mask Aligner”, Microelectronic Engineering, vol. 87,
no.5–8, pp. 936-939, Ghent, 2009. DOI:10.1016/j.mee.2009.11.171
B. Meliorisz, S. Partel, T. Schnattinger, T. Fühner, A. Erdmann, and P. Hudek, “Investigation of high-
resolution contact printing”, Microelectron. Eng., vol. 85, no. 5–6, pp. 744–748, Copenhagen, 2008.
DOI: 10.1016/j.mee.2007.12.012

Conferences
S. Partel, G. Urban, “Innovative method to suppress local geometry distortions for fabrication of
interdigitated electrode array with nano gaps”. Poster at SPIE Advanced Lithography, Optical
Microlithography, San Jose, 2016.
S. Partel, S. Kasemann, P. Choleva, C. Dincer, J. Kieninger G. Urban, “Novel fabrication process for
sub-µm interdigitated electrode arrays for highly sensitive electrochemical detection” In proceedings
of the 23nd Anniversary World Congress on Biosensors - Biosensors 2014, Melbourne, Australia,
2014.
S. Partel, “Resolution enhancement for Mask-Aligner lithography by using 193 nm ArF excimer
laser”, Ultra optics status seminar, Fraunhofer IOF, Mar. 27, 2014, Jena, (Invited talk)
K. Motzek, S. Partel, “Modeling photoresist development and optimizing resist profiles for mask
aligner lithography”, Talk at “9th IISB Lithography Simulation Workshop 2011” in Hersbruck
M. Mayer, S. Partel, P. Hudek, R. Schneider, “A new flexible development Rate Monitor (DRM)”,
talk at 8th IISB Lithography Simulation Workshop 2010 in Hersbruck

Reviewed online article
S. Partel, M. Mayer, K. Motzek, “In-situ measurement and characterization of photoresists during
development”, SPIE Newsroom, May 2012. DOI: 10.1117/2.1201204.004198

Patent:
S. Partel, S. Kasemann, J. Edlinger, C. Dincer, J. Kieninger, G. Urban : STRUCTURE AND
METHOD OF MANUFACTURING AN ELECTRODE STRUCTURE. 2015, Patent submission
number 800418726, 19. Jun 2015

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Acknowledgement
First of all, I would like to thank my supervisor Prof. Dr. Gerald Urban, who gave me the
opportunity to write this thesis. Without him I would not have made this journey. I also would like to
thank him for his guidance during my research and writing of this thesis. I would like to thank
PD Dr. Andreas Erdmann for his readiness to co-examine this thesis and for his helpful remarks but
also for the productive discussions about resist calibration and simulation.
Many thanks go to the lecturer Günther Stangl, who was initiating the link to
Prof. Dr. Gerald Urban at IMTEK. Without Günther I would not have started my thesis. His advices
were also very helpful for my research. Many thanks go to Dr. Peter Hudek for all his fruitful advices
and inputs about simulation during the project.
A number of individuals have been very helpful to me. I would first like to thank
Dr. Johannes Edlinger for giving me the opportunity to work at the Research Centre for
Microtechnology and doing my thesis at the same time, and also Dr. Robert Merz who was initiating
this constellation. I also want to thank Dr. Pavlina Choleva for her support on thermal diffusion and
wet etching processes. Markus Mayer MSc. for the great software development for the dissolution rate
monitor. Dr. Lenka Gajdosova for her patience with taking over thousand SEM images for photoresist
profile analysis. Dr. Sandra Stroj for the support on deep UV experiments and meaningful discussions
about light propagation. Matthias Domke MSc. for his help on dicing the biosensors with the fs-laser.
Special thanks go to Dr. Stephan Kasemann for his help on deposition processes as well as dry etching
techniques. I would also like to thank him for numerous technical discussions about process
development.
I would also like to acknowledge Dr. Kristian Motzek for his great discussions about lithography
simulation and resist calibration. Also for the rigorous simulations he was performing to verify my
simulations. I would also thank Dr. Jochen Kieninger for his driving support at the beginning of my
thesis as well as the constructive discussions during my thesis. Special thanks go to
Dipl.-Ing. Can Dincer who helped me with the electrochemical characterization. It has always been
pleasant and enjoyable to visit Freiburg because of him.
Finally, I thank my better half Petra, for her endless faith and support.
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Table of Contents
Abstract.......................................................................................................................................... i
Zusammenfassung ...................................................................................................................... iii
Authors bibliography .................................................................................................................. v
Acknowledgement ...................................................................................................................... vii
Table of Contents ......................................................................................................................... 1
List of Abbreviations ................................................................................................................... 4
1. Introduction and scientific problem ................................................................................. 6
1.1 Motivation ........................................................................................................................ 6
1.2 Background on analytical devices .................................................................................... 7
1.3 Scientific problem ............................................................................................................ 9
1.4 Scope of work ................................................................................................................... 9
2. Fundamentals of fabrication technologies and sensor design ...................................... 11
2.1 Photolithography ............................................................................................................ 11
Lithography processing .......................................................................................... 13
Photoresist tone and different photoresists ............................................................. 15
2.2 Photolithography simulation basics ................................................................................ 17
Simulation of light propagation .............................................................................. 18
Existing photoresist models .................................................................................... 18
Data acquisition of photoresist during development .............................................. 20
2.3 Thermal oxidation and growth of silicon dioxide .......................................................... 26
2.4 Dry Etching of silicon and silicon dioxide ..................................................................... 27
2.5 Physical vapor deposition (PVD): sputtering and evaporation ...................................... 29
2.6 Electrochemical sensing techniques ............................................................................... 34
The electrochemical cell ......................................................................................... 34
1