large-scale nems fabrication: directed self-assembly...
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NSF Summer Institute 2006Teri W. Odom
Large-scale NEMS Fabrication: Directed Self-Assembly or
Nanolithography
Teri W. OdomNorthwestern University
7 August 2006
NSF Summer Institute 2006Teri W. Odom
Goals of Nanofabrication• Goals
– Parallel processing of components over large areas
– Fabrication of structures 10 nm– Cost effectiveness
• Function– Nanoprocessors– Sub-wavelength optics– Biological assays
• Issues– Material properties
• ultra-small grains• amorphous materials
– Multilayer structures• registration• alignment
?
x 1/100
NSF Summer Institute 2006Teri W. Odom
Making Nanostructures (< 100 nm)Pattern Electron beam, edge lithography, scanning probe
Master
Replica
Multi-level Device
Replicate
Patterntransfer
NSF Summer Institute 2006Teri W. Odom
Conventional Lithography
Directed Assembly
Scanning Probe Lithography
Nanofabrication Techniques
Contact Nanolithography
NSF Summer Institute 2006Teri W. Odom
Photolithography roadmap
W. Wakamiya (Selete)
NSF Summer Institute 2006Teri W. Odom
Planar Fabrication Processes
Etch Grow Dope Lift-off
Expose
PATTERN TRANSFER
LITHOGRAPHY
NSF Summer Institute 2006Teri W. Odom
Process Flow in Photolithography
NSF Summer Institute 2006Teri W. Odom
Evaporation and Lift-off
T. Odom et al. Langmuir, 18, 5314 (2002)
NSF Summer Institute 2006Teri W. Odom
Electron Beam Lithography
Paul Scherrer Inst
L. Sohn (Princeton)
NSF Summer Institute 2006Teri W. Odom
E-beam Patterning of PMMA
250 nm
Whitesides group (Harvard)
NSF Summer Institute 2006Teri W. Odom
Focused Ion Beam (FIB)
www.fibics.com
NSF Summer Institute 2006Teri W. Odom
Next Generation Lithography
Bell labs
NSF Summer Institute 2006Teri W. Odom
SCattering with Angular Limitation Projection Electron-Beam Lithography
100 keV
www1.bell-labs.com/project/SCALPEL/sot.html
NSF Summer Institute 2006Teri W. Odom
Extreme Ultraviolet Lithography (EUV)
• Vacuum operation• 11-14 nm light• Reflective coatings on
optics and masks
www-als.lbl.gov/als/science/ sci_archive/53euv.html
NSF Summer Institute 2006Teri W. Odom
Conventional Lithography
Directed Assembly
Scanning Probe Lithography
Nanofabrication Techniques
Contact Nanolithography
NSF Summer Institute 2006Teri W. Odom
Nano-Imprint Lithography
Nanonex
mask
patterned resist
S. Chou (Princeton)
NSF Summer Institute 2006Teri W. Odom
Laser-assisted Direct Imprinting
S. Chou (Princeton), Nature 417, 835 (2002)
NSF Summer Institute 2006Teri W. Odom
Laser-assisted Embossing
Silicon nanowells
500 nm
100-nm sphere mold
500 nm
nanosphere mold
J.E. Barton and T.W. Odom, Nano Letters 4, 1525 (2004)
NSF Summer Institute 2006Teri W. Odom
Soft Lithographic Techniques
Near field lithographyMicrotransfer molding(μTM)
Micromolding in capillaries (MIMIC)
Microcontact printing(μCP)
NSF Summer Institute 2006Teri W. Odom
Micromolding Techniques
G.M. Whitesides, Angewandte Chemie 37, 550-575 (1998)
NSF Summer Institute 2006Teri W. Odom
Replica Molding (REM)
12 nm
8 nm
NSF Summer Institute 2006Teri W. Odom
Microtransfer Molding (μTM)
G.M. Whitesides, Angewandte Chemie 37, 550-575 (1998)
NSF Summer Institute 2006Teri W. Odom
Micromolding in Capillaries (MIMIC)
G.M. Whitesides, Angewandte Chemie 37, 550-575 (1998)
NSF Summer Institute 2006Teri W. Odom
MIMIC of Systems in Solvent
G.M. Whitesides, Angewandte Chemie 37, 550-575 (1998)
NSF Summer Institute 2006Teri W. Odom
Extending Soft lithography to Sub-1000 nm
T. Odom et al. Langmuir, 18, 5314 (2002)
NSF Summer Institute 2006Teri W. Odom
Patterning using Edge Techniques
Controlled overetchingTopographically directedetching
Topographically directed photolithography
Near field photolithography
hυ hυ
NSF Summer Institute 2006Teri W. Odom
Near Field Photolithography
G. Whitesides, Appl. Phys. Lett. 70, 2658 (1997) T. Odom et al. Langmuir 18, 5314 (2002)
NSF Summer Institute 2006Teri W. Odom
Topographically Directed Photolithography
elastomericmold
photoresist
solvent
embossedpattern
photoresist
Pattern transfer
G.M. Whitesides, Appl. Phys. Lett., 73, 2893 (1998)
NSF Summer Institute 2006Teri W. Odom
Topographically Directed Etching
< 50 nm
1 µm
~50 nm
M1 M2
1 µm
M1M2
G. Whitesides, JACS 121, 8356 (1999)
NSF Summer Institute 2006Teri W. Odom
Controlled Overetching
2 μm
50 nm
T. Odom et al. JACS 124, 12112 (2002); G. Whitesides, Adv. Mat. 13, 604 (2001)
NSF Summer Institute 2006Teri W. Odom
Conventional Lithography
Directed Assembly
Scanning Probe Lithography
Nanofabrication Techniques
Contact Nanolithography
NSF Summer Institute 2006Teri W. Odom
Intro to Scanning Probe Lithography• High Resolution Patterning Using Scanning Probes
– Chemical and molecular patterning (DPN)– Mechanical patterning
• Scratching • Nanoindentation
– Local heating– Voltage bias application
• Field Enhanced Oxidation (of silicon or metals) • Electron exposure of resist materials
– Manipulation of nanostructures • Factors Important in Scanning Probe Lithography
– Resolution– Alignment accuracy– Reliability – Throughput
NSF Summer Institute 2006Teri W. Odom
AFM: General Overview
NSF Summer Institute 2006Teri W. Odom
Optical Detection of Cantilever Changes
(A+B)-(C+D)
A BC D
(A+C)-(B+D)
NSF Summer Institute 2006Teri W. Odom
Scanning Probe Lithography (AFM)Mechanical scratching
C. Lieber (Harvard), Science 257, 375 (1992); H. Dai (Stanford), APL 11, 1508 (1998) C.F. Quate (Stanford), J. of App. Phys. 70, 2725 (1991); www.nanoscience.de/group_r/mfm
50 nm
Chemical modification
Electrostatic writing Magnetic writing
Molecular writing
NSF Summer Institute 2006Teri W. Odom
Dip-Pen Nanolithography (DPN)
http://www.chem.northwestern.edu/~mkngrp/timeref.html#dpn
NSF Summer Institute 2006Teri W. Odom
AFM Lithography Scratching• Material is removed from the substrate leaving deep
trenches with the characteristic shape of the plough used • The advantages of nanoscratching for lithography
– Precision of alignment– The absence of additional processing steps, such as etching the
substrate. • Depending on the applied load, AFM can characterize
micro-wear processes silicon for magnetic head sliders, polymers for electronic packaging and liquid crystals displays.
http://www.ntmdt.ru/SPM-Techniques/Lithographies/AFM_Lithography_-_Scratching_mode51.html
NSF Summer Institute 2006Teri W. Odom
Nanoindentation and Scratching
Diamond-like Carbon (DLC)
15, 20, 25 μN
1.5 nm deep at 4.4 μN
NSF Summer Institute 2006Teri W. Odom
Millipede: Data Storage in a Polymer• Tips are brought into contact
with a thin polymer film • Bits are written by heating a
resistor built into the cantilever to a temperature of ~ 400 C. The hot tip softens the polymer and briefly sinks into it, generating an indentation.
• For reading, the resistor is operated at lower temperature, ~300 C. When the tip drops into an indentation, the resistor is cooled by the resulting better heat transport, and a measurable change in resistance occurs.
• The 1,024-tip experiment achieved an areal density of 200 Gb/in2
http://www.research.ibm.com/resources/news/20020611_millipede.shtml
NSF Summer Institute 2006Teri W. Odom
Electric Field Enhanced Oxidation
• Voltage bias between a sharp probe tip and a sample generates an intense electric field at the tip– Oxidization of silicon– Anodization of metals
• The high field desorbs the hydrogen on the silicon surface and enables exposed silicon to oxidize in air
• Oxidation depends on humidity• Can achieve sub-50 nm feature sizes
http://www.ntmdt.ru/SPM-Techniques/Lithographies/AFM_Oxidation_Lithography_mode37.html
NSF Summer Institute 2006Teri W. Odom
AFM Nanolithography
Digital Instruments
NSF Summer Institute 2006Teri W. Odom
Parallel Field Enhanced Oxidation
Oxidation of silicon with 50 probe tips. Probes are spaced by 200 μm.http://www.stanford.edu/group/quate_group/LithoFrame.html
Typical scan area of commercial AFMs.
NSF Summer Institute 2006Teri W. Odom
Electron Exposure of Organic Polymers
• Electron Exposure of Resist– When a conducting tip is biased negatively with respect to a
sample, electrons are field-emitted from the tip• Exposure Using Scanning Probes
– Polymers have low threshold voltage, high sensitivity, sub-100-nm resolution, and good dry etch resistance.
– Resist can be easily deposited on substrates– The polymer surface is soft and pliable which minimizes the
tip wear
http://www.stanford.edu/group/quate_group/LithoFrame.html
NSF Summer Institute 2006Teri W. Odom
Patterns in Resist Transferred to Si• Feature sizes of patterns written determined by the
exposure dose • Can be accurately controlled down to about 25 nm in
50-100 nm thick resist
http://www.stanford.edu/group/quate_group/LithoFrame.html
NSF Summer Institute 2006Teri W. Odom
Non Contact AFM Lithography• Silicon probe tip acts as a source of electrons• The field emission current from the tip is used as the
feedback signal to control the tip-sample spacing
http://www.stanford.edu/group/quate_group/LithoFrame.html
NSF Summer Institute 2006Teri W. Odom
AFM Manipulation of Polystyrene
Digital Instruments
Tip Direction
NSF Summer Institute 2006Teri W. Odom
STM Lithography• Application of voltage pulse between tip and sample• “Pushing” atoms• Advantages of STM Lithography
– Information storage devices– Nanometer patterning technique– Manipulations of big molecules and individual atoms
• Example of STM Lithography: local exposure of LB film
http://www.ntmdt.ru/SPM-Techniques/Lithographies/STM_Lithography_mode50.html
NSF Summer Institute 2006Teri W. Odom
• Tunneling through a rectangular barrier
• Elastic tunneling versus inelastic tunneling– Elastic tunneling: energy of tunneling electrons conserved– Inelastic tunneling: the electron loses a quantum of energy within the tunneling
barrier
One dimensional (1D) tunneling
( )202
2m V Eκ = −
Incident wave Transmitted wave
Exponential decay
ikzI Ae−Ψ =
zII Be κ−Ψ =
'ik zIII Ce−Ψ =
NSF Summer Institute 2006Teri W. Odom
STM: General Overview
CurrentAmplifier
FeedbackControl
PositionControl
Tip Atoms
~ 1nm
~30 nm
Surface AtomsBias Voltage
Tip Path
PiezoelectricTransducer
NSF Summer Institute 2006Teri W. Odom
Constant Current ModeSI
NG
LE S
CA
NSC
HEM
ATI
C V
IEW
SCAN
Z
x
• Δ Z(x,y): Constant integrated DOS• If surface atoms have identical p(E),
contour of atomic corrugation• Spatial resolution depends on
• Status of tip• Electronic properties of sample• Applied bias voltage
NSF Summer Institute 2006Teri W. Odom
Constant Height ModeSI
NG
LE S
CA
NSC
HEM
ATI
C V
IEW
SCAN
I
x
• Δ I(x,y): Variation of DOS at fixed height• High contrast and fast scanning• Improved performance
• Insensitive to low frequency mechanical vibrations and electronic noise
• Piezoelectric hysteresis reduced
NSF Summer Institute 2006Teri W. Odom
STM: Manipulation of Atoms
NSF Summer Institute 2006Teri W. Odom
STM Manipulation of Atoms
M. Crommie (UC Berkeley), Science 262, 218 (1993)
NSF Summer Institute 2006Teri W. Odom
Feedback Controlled Lithography (FCL)• FCL monitors the STM feedback signal and the tunneling
current during patterning– Terminates the patterning process when a bond is broken– Controlled doses of electrons can be written over an area to
remove hydrogen atoms and create templates of individual dangling bonds
• Examples of organic molecules patterned on Si:H (100) surfaces: norbornadiene, copper phthalocyanine and C60
Mark C. Hersam, Northwestern University
NSF Summer Institute 2006Teri W. Odom
Conventional Lithography
Directed Assembly
Scanning Probe Lithography
Nanofabrication Techniques
Contact Nanolithography
NSF Summer Institute 2006Teri W. Odom
Nanosphere Lithography
Ag Nanoparticles
Colloidal crystal mask
R. P. van Duyne (Northwestern)
NSF Summer Institute 2006Teri W. Odom
Organic Multi-layers as Molecular Rulers
P. Weiss (Penn State), Science 291, 1019 (2001)
NSF Summer Institute 2006Teri W. Odom
Size Reduction Lithography
G.A. Somorjai (UC Berkeley), J. Phys. Chem. B 107, 3340 (2003)
NSF Summer Institute 2006Teri W. Odom
Summary of Nanolithography Strategies• Photons
– UV, DUV, EUV, x-rays– Diffraction, depth of focus
• Particles– Electrons and ions– Writing is serial, writing area is small
• Physical contact– Printing, molding, embossing– Adhesion of mold and replica, pattern transfer element
• Edge-based technologies– Near field phase shifting lithography, topographic methods– Diffraction
• Deposition– Shadow evaporation– Low flexibility in fabricating masks
• Self-assembly– Surfactant systems, block copolymers– Control over order, density of defects G. Whitesides (Harvard), Chem. Rev. 99, 1823 (1999)