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Nanoimprint Lithography
Wei WuQuantum Science ResearchAdvanced StudiesHP Labs, Hewlett-Packard
Email: wei.wu@hp.com
April. 1, 2005 2
Outline
• Background• Nanoimprint lithography− Thermal based−UV-based
• Applications based on nanofabrication−Molecular memory and logic−Single electron memory− Patterned magnetic media
• Future work• Summary
April. 1, 2005 3
ITRS Lithography Requirements
2000 2002 2004 2006 2008 2010 2012 2014 2016 2018
20
40
60
80
100
120
140
DR
AM 1
/2 P
itch
(nm
)
Year
Source: ITRS 2002 update
April. 1, 2005 4
Nano is Great but…
• New frontier of scienceo Fundamental knowledgeo Convergence of physics, chemistry and biology.
•Potential commercial impactDNA Carbon nanotubes
Molecular electronics
• Technological challenge – Lithography!
April. 1, 2005 5
Microprocessor
A microprocessor (intel P4)
April. 1, 2005 6
Photolithography
..ANkW λ
=
Source: Britney Spears guide to Semiconductor physics
April. 1, 2005 7
Next generation lithography (NGL) tools:
Extreme UV lithography (EUV)–Extremely expensive
(complex optical system, expensive and fragile mask)
X-ray lithography–Expensive light source (synchrotron preferred)–Mask material
E-beam direct write lithography (EBL)–Extremely slow (serial process)
E-beam projection lithography (EPL)–Mask material–Distortion due to heat
April. 1, 2005 8
Extreme Ultraviolet (EUV) Lithography
Source: Lawrence Livermore National Lab
Expensive
•Reflective mask and optics require < 2.5Å accuracy.
•Low efficiency (a few percent) of the light source.
• Small resist absorption length.
April. 1, 2005 9
Time for Using EBL to Write Gratings on 4 inch Wafer
EBL I used in graduate school
Resist: 950K PMMA
Dose: 600µC/cm2
Current: 4.5 pA
Area: 4inch wafer with 50% duty cycle. ~40cm2
SpA
cmcmCCurrent
AreaDoseTime 922
1055.4
40/600×≈
×=
×=
µ
158 years!
April. 1, 2005 10
Nanoimprint Lithography (NIL)
1. Imprint mold
resist
substrate
•Press Mold
•Remove Mold
2. Pattern Transfer•RIE
Chou, Krauss, and Renstrom, APL, Vol. 67, 3114 (1995); Science, Vol. 272, 85 (1996)
April. 1, 2005 11
Nanoimprint Lithography (NIL)
10 nm
•High resolution-not limited by wavelength
•High throughput -parallel process
•Low cost
Chou, Krauss, and Renstrom, APL, Vol. 67, 3114 (1995); Science, Vol. 272, 85 (1996)
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Step & Flash Imprint
•UV curable process
•Room temperature
•Low pressure
•UV polymer is applied by droping
M. Colburn, A. Grot, G. Wilson’s et al SPIE 2000
April. 1, 2005 13
UV-curable NIL with Double-layer Spin-on Resist
1. Prepare substrate, spin under layer and liquid resist on
4. Mold and substrate separation
5. Residue layer and under layer etching
2. Alignment
UV
6. Metal evaporation and lift-off
3. Press and exposure
W. Wu, H. Ge, S.Y. Chou et al., EIPBN 2004
April. 1, 2005 14
NIL is on ITRS (international technology roadmap for semiconductors)
* ITRS 2003 update
April. 1, 2005 15
Major Players
Princeton University ---- Nanonex, NanoOpto
University of Taxes at Austin ---- Molecular Imprints
University of Michigan
Hewlett-Packard
Motorola
Micro resist…
Europe:
Aachen University. Lund University…
Obducat, EVG, SUSS…
Japan:
Hitachi…
April. 1, 2005 16
Nano-circuit Crossbar Architecture
Electrodes
Molecule
Y. Chen, G.Y. Jung et al., Nanotech. 14, 462 (2003)
April. 1, 2005 17
1A-H
100
80
60
40
R (1
09oh
m)
20
10
0.8
0.6
0.4
0.2
0
2A-H 3A-H 4A-H 5A-H 6A-H 7A-H 8A-H
H P i n v e n t
Y. Chen, G.Y. Jung et al., Nanotech. 14, 462 (2003)
64 bits Cross-bar Memory at 60 nm Half-pitch by Thermal Nanoimprint Lithography
•First working circuit fabricated using NIL
•First working Molecular memory circuit
April. 1, 2005 18
Schematic of Single Electron Memory
Injection Store
e2/C dot
Coulombblockade
Channel
GateFloating gate
Buried OxideSubstrate
Poly Si Control Gate
Source
Drain
Floating Dot
dotCeE
2
=∆ kTE >>∆
• Higher operation temperature requires larger energy gap, implying smaller dot size.
• Sub-10 nm dot size is required for room temperature operation.
W. Wu, J. Gu, H. X. Ge, et al., Applied Physics Letters 83, 2268 (2003).
April. 1, 2005 19
Room Temperature Si Single Electron Memory Fabricated by NIL
30nm
-0.2 -0.1 0.0 0.1 0.21E-12
1E-11
1E-10
1E-9
∆Vth
=22 mV
tox
=13.6 nm thermal +
33.1 nm PECVD
Vds
=50 mV
Original 7 V, 1 µs
9 V, 1 µs
I ds (A
)
Vg (V)
Id vs. VgImprinted channelBefore oxidation
W. Wu, J. Gu, H. X. Ge, et al., Applied Physics Letters 83, 2268 (2003).
April. 1, 2005 20
0 2 4 6 8 10
-0.05
-0.04
-0.03
-0.02
-0.01
0.00
0.01
*same result for 1 ms pulsePulse duration 1 µs
V t (V)
Control Gate Voltage (V)
Single Electron Memory at Room Temperature Threshold vs. Pulse Voltage
W. Wu, J. Gu, H. X. Ge, et al., Applied Physics Letters 83, 2268 (2003).
April. 1, 2005 21
Threshold Shift Independent of Charging Time
10-8 10-7 10-6 10-5 10-4 10-3 10-20
10
20
30
40
Vctrl
= 7 V
Thre
shol
d sh
ift (V
)
Pulse width (Sec)
W. Wu, J. Gu, H. X. Ge, et al., Applied Physics Letters 83, 2268 (2003).
April. 1, 2005 22
Density Limit of Continuous Thin Film Magnetic Media
1. Each grain has to be large enough to be thermally stable (superparamagnetism).
2. Transition noise of each bit
Patterned magnetic media
Answer:
April. 1, 2005
Quantized Magnetic Disk
Magnetic
Nonmagnetic
Substrate
N
N
N
N
N
S
S
S
S
S
•Several orders higher density limit than continuous thin film.
–Each bit is a single domain.
–Week coupling between each bit.
•Nano-lithography needed.
Chou, Wei, Krauss and Fischer, JAP, 76(10), 6673 (1994)
April. 1, 2005
18 Gbits/in2 Large Area Quantized Magnetic Disk
W. Wu, B. Cui, X. Sun, W. Zhang, L. Zhuang, L. Kong, and S. Chou, JVSTB, Vol 16, Iss 6, 3825 (1998)
April. 1, 2005
MFM Image of 18 Gbits/in2 Large Area Quantized Magnetic Disk (After Polishing)
Every bit is a single domain.
W. Wu, B. Cui, X. Sun, W. Zhang, L. Zhuang, L. Kong, and S. Chou, JVSTB, Vol 16, Iss 6, 3825 (1998)
April. 1, 2005
30 Gbits/in2 Co Longitudinal Quantized Magnetic Disk
25 nm
MFMSEMW. Wu, B. Cui, X. Sun, W. Zhang, L. Zhuang, L. Kong, and S. Chou, JVSTB, Vol 16, Iss 6, 3825 (1998)
April. 1, 2005 27
Future Work:
Challenges of NIL:
•Yield
−It is easier to have defects, because it is a contact lithography
•Alignment accuracy is currently 10x worse than resolution
−Alignment must be achieved without high cost
April. 1, 2005 28
Summary
• Nanoimprint lithography is:• High throughput
• High resolution
• Low cost
• Capable of making real applications
• More need to be done.
April. 1, 2005 29