NANOFABRICATION NANOIMPRINT LITHOGRAPHY

NANOFABRICATION
NANOIMPRINT LITHOGRAPHY
Dr. Nikos Kehagias
Head of Nanofabrication division
Catalan Institute of Nanotechnology (ICN)
B
Barcelona
l
Spain
Email: nikolaos.kehagias.icn@uab.es
nikolaos kehagias icn@uab es
Outline
• Nanofabrication techniques:
¾ Resolution and limits
¾ Alternative nanolithography techniques
¾Nanoimprint lithography: issues, challenges, potentials
• Nanoimprint lithography applications:
¾ Examples of passive photonic devices
¾ Functional materials
¾ 2D PhC devices for enhanced light extraction
• Nanometrology
¾ Non destructive techniques
Nanotechnology: enabling multi-billion
dollar industry
Approach towards Nanotechnology
Key Requirements of Lithography for
Manufacturing ICs*
• Critical Dimension Control
– Size of features must be controlled within wafer and wafer‐to‐wafer
Size of features must be controlled within wafer and wafer to wafer
• Overlay
– For high yield, alignment must be precisely controlled
For high yield, alignment must be precisely controlled
• Defect Control
– Other than designed pattern, no additional patterns must be imaged
• Low Cost
– Tool, resist, mask; fast step‐and‐repeat 30‐40% of total semiconductor manufacturing cost is due to lithography (Masks, resists, metrology)
– At the end of the roadmap, μP will require 39 mask levels
*ITRS 2005/6, Lithography
NANOFABRICATION
METHODS
Fabrication methods for small structures
Decrease in minimum feature size with
time (Moore’s
(Moore s law)
Nanopatterning techniques
• Nanolithography
techniques
• EUV/UV lithography
lith
h
• Electron beam lithography
• Focused ion beam lithography
• X-ray
X ray lithography
• Alternative
lithography techniques
•Template assisted self assembly techniques
• Micro-contact printing
• Nanostensil technique (nano-mask
(nano mask lithography)
• Ink-jet lithography
• Nanoimprint lithography
Nanopatterning techniques
Patterning
g time for 10% of a 4” wafer as function of obtainable line width for different
lithography techniques. The arrows and the question mark in the NIL bar indicate
that faster imprint times may be obtainable by optimizing the imprint process.
Template assisted self assembly techniques
““Self-assembly”
lf
bl ” refers
f
to the
h deposition
d
off an organized
d layer
l
onto a
substrate with a high-degree of control and/or ordering.
Colloidal self assembly
Set-up
Material: Polymethyl metacrylate with
a mean diameter of 368nm
(<5% polydispersity)
Substrate: Glass
Concentration: 4% wt in de-ionized
water
Acoustic vibration: white noise (404kHz)
Drawing speed: stepping motor at
1.3mm/hr
Colloidal self assembly
Cross section SEM images: 3D ordering
Stochastic resonance-like behaviour
L – noise level
L40 - best
Standing wave formation
at high noise level leads to
locally suppression (or
optimization) of noise
vibration
Local but uncontrollable
i
increase
i llattice
in
tti ordering.
d i
Block copolymer self assembly
Requirements for graphoepitaxy
Mesa width ~ 50 nm
(or as narrow as possible)
Wall height ~ 30 nm
Groove width
40 – 200 nm
Patterned sidewall material
- Would like to test both PS
and PMMA wetting walls
- Fab-friendly materials ideal
Base must have surface OH
groups to allow us attach
Neutral
eu a po
polymer
y e b
brush
us
Substrate
Patterned Silicon dioxide
Patterned HSQ
Designed Nanostructures via Templating
Silicon-based trenches and
aligned nanostructures
nanostructures.
Angled lamellae nanostructures
Nanostensil Lithography
The Nanostensil
Th
N
t
il ttechnique
h i
iis a patterning
tt i method
th d b
based
d on
shadow mask evaporation
A thin membrane is used as a solid mask to transfer the patterns
from the membrane to the substrate during the evaporation
Full-wafer stencils
Side view stencil
Nanostensil Lithography
Main advantages:
• No resist, development or baking
• Non contact
• Re usable
• Micro and nanostructuring in a single step
• High flexibility of materials (metals, oxides, SAMs)
Challenges:
• Clogging occurs due to the accumulation of
deposited material on top and inside the membrane
apertures.
• Blurring
• Contamination of stensil
• Stiffness of stensil
Dip-pen Lithography
Ink transfer using a coated AFM tip by capillary effect.
Dip-pen lithography of SAMs
Introduction to Nanoimprint
Proposed by S.Y. Chou (Minnesota Uni., USA) in 1995
(Appl. Phys. Lett., 67, 3114 (1995))
Idea: a nanometer-size pattern is transfered not by electron, ion or
other beams, but by a stamp via mechanical contact between the
stamp and a substrate with a polymer.
Advantages:
• Cost
C
efficient
ffi i
• High throughput
• High
Hi h resolution
l i
• Simple
• Flexible
Fl ibl
Current Fabrication methods
Electron Beam Lithography
Extreme UV Lithography
Scanning Probe Lithography
Ad t
Advantages
Ad t
Advantages
Ad t
Advantages
• Very accurate control of pattern with direct writingg
p
• No mask needed
• Highly automated
• 5nm resolution possible
• Extreme UV is 10‐14nm wavelength source
g
• Resolution approaching 30nm
• High Throughput
• Very good control of pattern and resolution
p
Approximately 10nm possible
• Highly automated
Disadvantages
Disadvantages
Disadvantages
•Very low throughput
Less than 10 wafers per hour
• Expensive Hardware cost 6‐10 Million
Hardware cost 6‐10 Million
• Mask fabrication is difficult
• Reflective optics can be expensive
CaF instead of SiO2 optics
• Cost of EUV startup ~50‐60
• Cost of EUV startup 50‐60 million
• Very slow process
• Instrument can be costly
• Time of process eliminates
industrial feasibility
Alternative method:Nanoimprint Lithography
• Nanoimprint lithography (NIL) is simple in comparison to alternatives
• High throughput capabilities
• Low cost for a next-generation technology (No need for small λ laser sources
and optics)
• High cost in master mold, but all other molds can be made from this master
Lithography Resolution (nm) Cost (M $)
Throughput
Feasible
248 nm 90 8
√
√
193 nm
45
20
√
√
157 nm
32
50
√
√
EUV
EUV 16
100
√
√
Ebeam
10
5‐10
x
√
Imprint
14
1
√
√
R&D machines can be purchased for 100k 1 master Æ10.000 sub mastersÆ100 million disks
$250.000Æ $1.000 eachÆ10c per disk for mask cost
Nanoimprint enables multiple billion dollar
industries
MEMS/NEMS
Displays
Wireless Com.
Com
NIL
Data storage
Etc.
Biotech
Semicond. IC’s
Pharmaceutical
Nanoimprint Lithography (NIL)
Stamp (Si
(Si, Quartz
Quartz, etc)
Advantages
Resist (polymer, monomer)
• Resolution (sub 10 nm)
Substrate
Imprint
(Pressure +heat or UV light)
• Fast (sec/cycle)
• Low
L
costt ($0.2M
($0 2M vs $25M)
• Simple
• Flexible (UV, heat)
Applications
Release
(
(cool
ld
down )
RIE of residual layer
High resolution
Complex patterns
• Semiconductors
• Optics
O ti
• Bio
• Organic electronics
• Sensors
Functional devices
Multimode NIL
Thermal Reversal NIL Reverse UV NIL Transparent stamp with metal protrusions
UV light, pressure, heat
Inking
Whole layer transfer
Development
Single NIL tool capable of multiple modes pattering/fabrication
Highly versatile, yet simple, nanofabrication tool
Step & Stamp/flash NIL
NPS 300 Nano imPrinting Stepper
• Thermal + UV nanoimprinting
• Up to 300 mm wafers
• Sub‐20 nm features
S b 20
f t
• 250 nm overlay accuracy
• Automatic alignment
~ 10 nm holes in polymer
T. Haatainen et al., VTT 2001
Step and Stamp nanoimprint lithography
In liquid alignment:
Pre- and post-exposure.
S.V. Sreenivasan et. al., Semiconductor Fabtech, 25th ed., 111, 2005.
Defects caused due to material
failure in small features with large
feature height.
Roll-to-Roll NIL
Bendable Ni stamp AFM images of stamp and imprint
• Printing speed from 0.3 to 20 m/min
• Line depth of 151 – 112 nm • Min feature at 5m/min is 50 nm
Min feature at 5m/min is 50 nm
Courtesy of T. Mäkelä et al., VTT, Finland
Roll to roll NIL
Se Hyun Ahn et al., ACS Nano, 3, 8, 2304, 2009
Adv. Mater. 2008, 20, 2044–2049
Polymer stamps
State of the art of NIL techniques
Smallest/
largest
features in
same print
NIL
2 nm,
N/A
SSIL
8 nm,
50 nm/5 µm
SFIL
UV-NIL
Soft
S
ft UV
UVNIL
Min
pitch
(nm)
14
Largest
wafer
printed
(mm)
200
Overlay
Accuracy
(nm)
500
t align,
t print,
t release,
t cycle
Minutes,
10s, Min,
10-15 min
Full cycle 2.5
min
i with,
ith 20 s
without full
auto
collimation.
50
200
250
10 nm
25 nm/ µm
50
300
50
20
wafers/hr
9nm/100µm
12
200
20
20s/step
3 wafers/hr
25nm/ 20µm
150
200
1-50µm
4-5
4
5 min
i ca.
12wafer/hr
NIL issues and complications
NIL
NIL metrologies critically needed:
t l i
iti ll
d d
Blazed gratings
• Critical Dimension measurements of sub‐50 nm features
• Quantify fidelity of imprint pattern transfer
• Feedback on pattern quality needed to engineer and optimize NIL
db k
li
d d
i
d
i i
NIL materials science :
• Resist material selection is done empirically
• Guidelines for imprinting functional materials?
Guidelines for imprinting functional materials?
• Imprinted nanostructures may have different properties
• Possible orientation and anisotropic properties
• Low temp and low pressure
• Minimal shrinkage
• Mechanical strength and tear resistance
• Mold fill Æ Viscosity
• Tg • T
g for thermoplatic resist (imprint usually done 70
for thermoplatic resist (imprint usually done 70‐80°C
80 C above T
above Tg)
Tearing of pillars
NIL issues and complications
Template
• Usually fabricated from Si, quartz, or nickel
• Critical dimension control
• Critical dimension control
• Defect free fabrication & Inspection
• Adhesion and use of antisticking coating on template
• Cleaning & re‐use
• designing for imprint uniformity –> Uniform residual layer
Courtesy of Dr C Gourgon (CNRS‐LTM)
Courtesy of Dr C. Gourgon (CNRS
LTM) Overlay accuracy
• NIL has no distortion due to lens (since no lens is used)
NIL has no distortion due to lens (since no lens is used)
• Smaller error budget for template pattern placement
• Mask/template distortion due to pressure and/or temperature & defects
Moiré concentric circles Aligned Misaligned Principles of NIL
T‐P vs. time diagram of NIL process Stamp
Polymer layer
Substrate
(a)
Heat
Apply pressure
(b)
Cool down
Separate
(c)
Residual layer
(d)
Etch residual
layer
(e)
Demolding Viscosity dependance on MW, P and T
MW dependance
MW dependance
⎧Μ ,
η 0 ∝ ⎨ 3.4± 0.2
,
⎩Μ
M < Mc
M > Mc
Pressure dependance
Δ ln η
− 2 Δ ln η
≈ −4 × 10
ΔP (bar )
ΔT
Temperature dependance
C1 (T − Tg )
η (T )
log aT = −
= log 0
C 2 + T − Tg
η 0 (Tg )
William Landel Ferry equation Squeeze flow theory during a typical NIL process
z
Stamp
Polymer
l
wi
z
S
x
y
S/2
h pr
vy=0
vy((z))
h(t)
Substrate
Continuity equation: Navier Stokes equation: Residual Polymer height 2 F pr
1
1
= 2 +
t
3
2
h (t ) h0
n0 Ls
N
N
N
i =1
i =1
i =1
ho ∑ (s i + wi ) = h f ∑ (si + wi ) + h pr ∑ (wi )
∇p = η 0 ∇ 2 u
Estimated imprinting time ηο s 2 ⎜⎛ 1
1
tf =
− 2
2
⎜
2 P ⎝ h f ho
H. Schift and L.J. Heyderman, Nanorheology“. Chapter 4 in, Alternative Lithography“, ed. C. Sotomayor‐Torres. Kluwer Academic (2003).
⎞
⎟
⎟
⎠
Polymers used in NIL
Material
Glass
transition
Temperature
Molecular
weight
g
Viscosity
Solvent
PMMA
105 oC
75k
10 ± 2
(mPas)
Anisole
mr-L 6000
mr-NIL 6000
40 oC
7k
2,4 ±1
(mPas)
PGMEA/
Anisole
mr-II 7000
mr
60 oC
120k
4±2
(mPas)
PGMEA
mr-I 8000
115 oC
120k
5±2
((mPas))
PGMEA
Polystyrene
(PS)
100 oC
50k
-
Toluene
Typical refractive index values for polymer are between 1.3 ‐ 1.6
Functional polymers
Polymers with embedded NC’s (CdSe, CdSe, etc.), NP (Au, TiO
( ,
), y (
)
2 etc.), Dyes (Rhodamine etc.)
2, Polymers with embedded NP (Au, TiO2, etc.)
Surface modification of polymers (nanoparticle deposition, change of the polymer surface tension, etc.)
h
f th
l
f
t i
t )
5.00
[ -6.63V -> -3.96V ] -9.02V -> -1.99V
[V]
-2.00
-3.00
-4.00
-5.00
[ µV ]
Di‐block co‐polymers (PS‐b‐PMMA)
-6.00
-7.00
-8.00
0
-9.00
0
Conductive polymers (polypyrrole, polyaniline etc.)
[ µV ]
5.00
NIL process challenge: imprint quality
control
Fundamental process challenges
Critical Dimensions
Critical dimensions (CD)
Critical dimensions (CD) Width
Height
Slope
Residual layer
1 μm
Residual layer thickness and uniformity over large areas (> 300mm)
Residual layer
100 nm
Nanoimprint lithography process
Stamp
Stamp with different size protrusions
Polymer layer
Substrate
Heat
Imprint
C l down
Cool
d
Stamp bending
Separate
Etch residual
layer
Different filling factors Æ lead to
inhomogeneous residual layer
Photonic circuit
Combination of variable scale features on the same stamp
Mathematical model
The resist movement is determined by the 2D pressure distribution P(x,y,t) calculated from the following
problem:
{
}
∇ [D( x, y ,t ) + h( x, y )] ∇P ( x, y ,t ) = 12η
3
∂D( x, y ,t )
, ( x, y ) ∈ Ω f , t ∈ (0,T ],
∂t
P ( x, y ) = 0, ( x, y ) ∈ Ω / Ω f ,
(1)
t
D( x, y ,t ) = d0 − ∫ Vst (ζ ) dζ + δ st ( x, y ,t ) + δ sb ( x, y ,t ),
0
where d0 is the initial resist thickness; h is the stamp relief height; δst and δsb are the normal displacement
of the stamp and substrate surface, respectively; Vst is the stamp velocity; T is the duration of the
imprinting process; η is the dynamic viscosity of the resist; Ω is the considered domain of the stamp; Ωf is
the part of Ω, in which all cavities are filled with the resist.
q
((1)) is derived from 3D Navier-Stokes equations
q
with the understanding
g that the resist motion is
Equations
largely directed along the substrate surface.
For the calculation of δst and δsb, the stamp and the substrate are represented as semi-infinite regions (an
elastic medium bounded by a plane). In this case, the elastic normal displacement is described by the
following expression:
1− σ 2
δ ( x, y ,t ) =
πE
∫∫
Ω
P ( x ′, y ′,t ) dx ′dy ′
( x − x ′) + ( y − y ′)
2
where
h
σ is
i Poisson's
P i
' ratio
ti and
d E is
i modulus
d l off elasticity.
l ti it
2
, ( x, y ) ∈ Ω, t ∈ (0,T ],
Experimental parameters
Polymer used: PMMA and mr-I8030E
Initial polymer thickness: 340 nm and 318 nm
Imprinting
p
g temperatures:
p
180 oC - 200 oC
Dynamic Viscosity : 2×104 Pa⋅s @ 180°C and 3×103 Pa⋅s @ 200°C.
Chirped grating structures stamp was used
Stamp relief: ~300 nm
Simulation parameters:
• stamp velocity:1 nm/s,
• duration of the imprinting process: 268 sec
• grid size:128×128 pixel
Instruments used:
• Dektak profilometer (Veeco instruments)
• Reflectometer
Stamp design
Resist PMMA 75K.
Imprinting parameters: the stamp cavities depth - 300 nm, the initial resist thickness - 340 nm,
the imprint temperature - 190°C, the resist viscosity - 104 Pa⋅s.
Experiment
Simulation
500
H, nm
400
experiment
simulation
300
Comparison
p
of measured and
simulated values of resist
thickness
200
Accuracy
100
0
0
2.6%
6% 2
2.4%
4%
2.1%
1%
1 9% 2
1.9%
1.5% 1.3% 2
0.5% 0.5% 1.5%
0%
2
4
6
zone number
8
10
0%
2 4%
2.4%
12
Resist mr-I 8000 (Micro Resist Technology GmbH).
Imprinting parameters: the stamp cavities depth - 300 nm, the initial resist thickness - 318 nm,
the imprint temperature - 180°C, the resist viscosity - 2×104 Pa⋅s.
600
500
H, nm
400
300
200
simulation
experiment
100
0
-4200
-4000
-3800
-3600
x, μm
-3400
-3200
-3000
(b)
600
600
500
500
400
400
H, nm
H, nm
(a)
300
200
200
simulation
experiment
100
0
-4200
300
-4000
-3800
-3600
x, μm
-3400
simulation
experiment
100
-3200
-3000
(c)
0
-4200
-4000
-3800
-3600
x, μm
-3400
-3200
-3000
(d)
((a)) The
Th optical
ti l microscopy
i
i
images
off the
th test
t t structure
t t
i
imprinted
i t d in
i the
th resist
i t att 180°C. Horizontal
H i
t l color
l lines
li
indicate zones of profilometer measurements of resist thickness. White isolines specify the calculated
distribution of the stamp/substrate deformation (numbers signify the elastic displacement in nanometers). (b)(d) Comparison of measured and simulated profiles of resist thickness for the test structure.
Resist mr-I 8000 (Micro Resist Technology GmbH).
Imprinting parameters: the stamp cavities depth - 300 nm, the initial resist thickness - 318 nm,
the imprint temperature - 200°C, the resist viscosity - 3×103 Pa⋅s.
600
500
H, nm
400
300
200
simulation
experiment
100
0
-4400
-4200
-4000
-3800
x, μm
-3600
-3400
-3200
(b)
600
600
500
500
400
400
H, nm
H, nm
(a)
300
200
200
simulation
experiment
100
0
-4400
300
-4200
-4000
-3800
x, μm
-3600
simulation
experiment
100
-3400
-3200
(c)
0
-4400
-4200
-4000
-3800
x, μm
-3600
-3400
-3200
(d)
((a)) The
Th optical
ti l microscopy
i
i
images
off the
th test
t t structure
t t
i
imprinted
i t d in
i the
th resist
i t att 200°C. Horizontal
H i
t l color
l lines
li
indicate zones of profilometer measurements of resist thickness. White isolines specify the calculated
distribution of the stamp/substrate deformation (numbers signify the elastic displacement in nanometers). (b)(d) Comparison of measured and simulated profiles of resist thickness for the test structure.
Viscosity estimation for resist mr-I 8000 at 180°C.
the resist dynamic viscosity = 10 4 Pa⋅s
500
500
400
400
H, nm
H, nm
the resist dynamic viscosity = 3 ×103 Pa⋅s
300
200
300
200
-4800
-4600
-4400
-4200
-4000
-3800
-3600
-3400
-3200
-3000
-2800
-4800
-4600
-4400
-4200
-4000
x, μm
-3800
-3600
-3400
-3200
-3000
-2800
-3200
-3000
-2800
x, μm
the resist dynamic viscosity = 2 ×104 Pa⋅s
H, nm
500
400
300
200
-4800
-4600
-4400
-4200
-4000
-3800
-3600
-3400
-3200
-3000
-2800
x, μm
The best fit of simulation results to the experimental data.
the resist dynamic viscosity = 10 5 Pa⋅s
500
500
400
400
H, nm
H, nm
the resist dynamic viscosity = 3 ×104 Pa⋅s
300
200
300
200
-4800
-4600
-4400
-4200
-4000
-3800
x, μm
-3600
-3400
-3200
-3000
-2800
-4800
-4600
-4400
-4200
-4000
-3800
x, μm
-3600
-3400
NIL Potentials
Intel microprocessor-Brief history
Intel microprocessor-Fabrication steps
35 nm
35 nm
Three dimensional Si stamp for NIL applications 3D nanofabrication techniques
C
Conventional methods:
ti
l
th d
Electron beam
Focused ion beam
Two photon polymerization
Non‐conventional methods:
Combination of NIL and X‐
ray Lithography
Combination of lithographic steps and wet etching
Reverse NIL
3D nanofabrication techniques
Direct patterning of three dimensional structures by NIL
Transistor Metal T‐gate with 90 nm wide foot M. Li et. al
3D‐Hot embossing of undercut structures
N. Bogdanski et. al
Triangular Profile Imprint
Z. Yu et. al
3D nanofabrication techniques
Towards three dimensional photonic crystals
Woodpile‐like structure
Determistic defect
Reverse UV NIL technique
Selective Transfer mode
3D woodpile like structures
1 Layer
1 μm
10 μm
3 layers
4 μm
2 layers