Lithography - The University of Hong Kong
Lithography - The University of Hong Kong
Lithography - The University of Hong Kong
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ELEC 7364 Lecture Notes <br />
Summer 2008<br />
<strong>Lithography</strong><br />
by STELLA W. PANG<br />
from <strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan, Ann Arbor, MI, USA<br />
Visiting Pr<strong>of</strong>essor at<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> <strong>Hong</strong> <strong>Kong</strong><br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 1 S. W. Pang<br />
<strong>Lithography</strong> Requirements<br />
Resolution down to 24 nm<br />
Depth <strong>of</strong> Focus better than 0.5 µm<br />
Linewidth Control better than 4 nm<br />
Low Defect Density <strong>of</strong> 30/m 2 and Large Chip Size <strong>of</strong> 1600 mm 2 <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 2 S. W. Pang
<strong>Lithography</strong> Projection<br />
<br />
<br />
<br />
<br />
Photons with Short Wavelength<br />
EUV - Similar to X-Ray with High Energy Photons<br />
Masks are Difficult to Make Even with 4:1 or 10:1 Reduction<br />
Alternative <strong>Lithography</strong> Difficult to be Accepted<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 3 S. W. Pang<br />
<strong>Lithography</strong> - Mask to Patterns<br />
Mask Design and Layout with CAD Tools<br />
Mask Making by Direct Write: 1:1 up to 10:1<br />
Full Wafer Printing or Projection Printing <strong>of</strong> 1 Die at a Time<br />
High Throughput Needed (>50 Wafers/hr)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 4 S. W. Pang
Optical <strong>Lithography</strong><br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 5 S. W. Pang<br />
Optical <strong>Lithography</strong> Process<br />
<br />
<br />
<br />
<br />
Mask Design - CAD<br />
Files<br />
Optical Mask (Ni<br />
/Quartz)<br />
Photoresist Coating<br />
Exposure and<br />
Development<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 6 S. W. Pang
Photoresist<br />
Mostly organic polymer<br />
- properties change after exposure to radiation<br />
(photons, electrons, ions)<br />
- selective removal <strong>of</strong> exposed (positive) or<br />
unexposed (negative) area by development <br />
Photoresist Requirements<br />
- Resolution (L min ) <br />
- Sensitivity (Throughput)<br />
- Etch Resistance (Pattern Transfer)<br />
- Spectral response, contrast, adhesion, pin hole<br />
density, thickness variation, stability (Pattern<br />
Quality)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 7 S. W. Pang<br />
Resist Preparation<br />
<br />
<br />
<br />
Cleaning – remove surface contamination; Organic<br />
solvents, Oxide Etch <br />
Dehydration – remove moisture on surface; Bake at<br />
HMDS on Si<br />
<br />
<br />
<br />
Si Surface is Terminated with Si-O-Si(CH 3 ) 3 instead <strong>of</strong> Si-OH<br />
Polymer Layer has better Adhesion to –CH 3 group<br />
More Uniform Coating and Better Adhesion <strong>of</strong> Photoresist<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 9 S. W. Pang<br />
Spin Coating <strong>of</strong> Resist<br />
<br />
<br />
Liquid applied, changed to uniform coating after<br />
spinning and baking<br />
Balance between Centrifugal Force, Viscosity<br />
Resistance, and Solvent Evaporation<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 10 S. W. Pang
Photoresist Thickness after Spinning<br />
T = KS α ( ηβ<br />
ω γ R 2 )1/ 3<br />
T - Photoresist Thickness<br />
S - % Solid in photoresist (affects η)<br />
η - Viscosity<br />
ω - Spin speed in angular velocity (2000-6000 rotation per min – rpm)<br />
R – € Radius <strong>of</strong> wafer<br />
S and η could vary as solvent is evaporated<br />
Spin time ~30 to 60 s<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 11 S. W. Pang<br />
Photoresist Spin Curve<br />
T~ω -n where 0.4
Pre-Bake or S<strong>of</strong>t-Bake<br />
Remove solvents (80-90 % removal)<br />
Release stress<br />
Improve adhesion<br />
Excessive: Reduce resist sensitivity<br />
Insufficient: Reduce Developer Contrast<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 13 S. W. Pang<br />
Exposure<br />
Control Exposure Does – e.g. 10-100 mJ/cm 2;<br />
depends on photoresist sensitivity and affects<br />
pr<strong>of</strong>ile and feature size<br />
Optical Radiation: g-line: 436 nm; i-line: 365<br />
nm; Excimer Laser: KrF – 248 nm; ArF – 193<br />
nm; <br />
F 2 – 157 nm; Immersion Lens with n>1<br />
Exposure modes: Contact printing; Proximity<br />
printing; Projection printing (step and scan<br />
with reduction); Direct Write<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 14 S. W. Pang
Projection vs. Contact/Proximity Printing<br />
<br />
<br />
Research Labs - Contact and Proximity Printing Since<br />
Systems are Cheaper, Smaller, and Easier to Use<br />
Industry - Projection Printing with High Throughput<br />
for High Reproducibility, Low Defects, and More<br />
Automation<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 15 S. W. Pang<br />
Contact and Proximity Printing<br />
<br />
<br />
<br />
1X Mask - High Resolution Features more Difficult to<br />
Make<br />
Contac Printing Could Generate Defects on Masks and<br />
Substrates<br />
Resolution is Reduced by Gap<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 16 S. W. Pang
Projection Printing<br />
4-10X Mask -<br />
Easier to Make<br />
Optimized for<br />
Resolution,<br />
Depth <strong>of</strong> Focus,<br />
Throughput<br />
Resolution<br />
improves by<br />
shorter<br />
Wavelength (λ)<br />
and Higher<br />
Numerical<br />
Aperture (NA)<br />
while Depth <strong>of</strong><br />
Focus becomes<br />
Worse<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 17 S. W. Pang<br />
Optics for Optical Projection<br />
Simple Ray Optics, assume light travels in straight rays<br />
Numerical Aperture (NA) <br />
€<br />
(n=1 in air)<br />
NA = D 2 f = n sinα<br />
NA determines how much light is transmitted or collected<br />
at the image plane, influence exposure time and<br />
resolution<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 18 S. W. Pang
Resolution<br />
Resolution and Depth <strong>of</strong> Focus<br />
l min = k λ <br />
NA<br />
k: 0.5 to 0.7; experimental<br />
parameter<br />
€<br />
Depth <strong>of</strong> Focus <br />
λ<br />
DOF = k '<br />
NA 2 k'~0.5<br />
€<br />
For λ=365 nm; NA=0.45; k=0.7; k'=0.5<br />
l min =0.57 µm; DOF=0.9 µm<br />
Trade<strong>of</strong>f between l min and DOF, with better resolution, DOF<br />
is less<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 19 S. W. Pang<br />
Fraunh<strong>of</strong>er<br />
Diffraction Pattern<br />
Through Circular<br />
Aperture<br />
Light Intensity on Wafer<br />
Modulation Transfer<br />
Function - High on<br />
Mask, Lower on Wafer<br />
Due to Optics<br />
Diffraction<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 20 S. W. Pang
Resist Development<br />
Typical Condition: 1 min, 20 °C in developer<br />
Selective resist removal based on<br />
- Chemical Transformation (e.g. carboxylic acid<br />
formation during positive resist exposure)<br />
- Change in MW (faster development for low MW<br />
polymer)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 21 S. W. Pang<br />
<br />
<br />
<br />
Hard Bake or Post Bake<br />
Typical Condition: 10 min, 120 °C on Hot Plate<br />
Improves Etch Resistance and Adhesion, Prevents<br />
Swelling<br />
Resist Flows and Pr<strong>of</strong>ile becomes Tapered<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 22 S. W. Pang
2 Component Positive Resist<br />
Binder + Sensitizer; acid formed due to radiation<br />
which can be dissolved in base developer<br />
Resin/Binder (Novolac Co-polymer), >80 %<br />
- MW 500-20000, doesn't interact with radiation<br />
- Phenolic group, acidic, can be dissolved in base<br />
solution (~15 nm/s)<br />
- Structure and composition <strong>of</strong> polymer determine<br />
viscosity and developer solubility<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 23 S. W. Pang<br />
<br />
<br />
<br />
Sensitizer in 2 Component Positive Resist<br />
Sensitizer/Inhibitor (200 nm/s)<br />
Changes in Sensitizer due to exposure (chemical<br />
transformation)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 24 S. W. Pang
Chemical Transformation <strong>of</strong> Positive Resist<br />
<br />
<br />
<br />
Sensitizer Activated by Photons - Chemical<br />
Transformation<br />
Release <strong>of</strong> N 2 <br />
Carboxylic Acid Form in Presence <strong>of</strong> H 2 O<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 25 S. W. Pang<br />
One Component Positive Resist<br />
PolyMethylMethacrylate (PMMA)<br />
MW 200-1000K, high resolution, low sensitivity<br />
Bond breaking (chain scission) due to exposure to radiation<br />
MW reduced and low MW polymer is removed during<br />
development<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 26 S. W. Pang
2 Component Negative Resist<br />
Cross linking to generate longer polymer chain with<br />
higher MW<br />
Non-planer solvent (e.g. Tolune, Xylene) removes low<br />
MW polymer (~100 nm/s); leaves behind high MW<br />
polymer (~1 nm/s)<br />
Rubber Matrix (~Resin)<br />
- Soluble in non-planar solution (e.g. Tolune,<br />
Xylene, ~100 nm/s)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 27 S. W. Pang<br />
Sensitizer in 2 Component Negative Resist<br />
Sensitizer (R-N 3 )<br />
<br />
Free radicals generated when exposed to radiation,<br />
causing cross-linking <strong>of</strong> polymer. MW increased and<br />
low MW polymer is removed during development,<br />
leaving behind high MW polymer (exposed area)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 28 S. W. Pang
Cross Linking <strong>of</strong> Negative Resist<br />
<br />
<br />
<br />
Reactive Radicals are generated by Radiation<br />
Release <strong>of</strong> N 2 <br />
Radicals Link up with Other Polymer Chains and Form<br />
new Compounds with Higher Molecular Weight<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 29 S. W. Pang<br />
One Component Negative Resist<br />
PolyMethylMethacrylate (PMMA)<br />
Cross linking occurs when dosage is<br />
high enough due to free radical<br />
accumulation that starts up chain<br />
reaction for cross linking<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 30 S. W. Pang
Improvements in Resist Technology<br />
Chemical Amplification (CA) Resist<br />
- High Sensitivity, High Contrast<br />
- Process harder to control, sensitive to<br />
contaminants in air, less etch resistance<br />
- Photon absorption causes decomposition <strong>of</strong><br />
Photoacid Generator (PAG), forming Acid,<br />
during post bake, inducing cascade <strong>of</strong> Chemical<br />
Transformations in Resist<br />
Multilayer Resist (Bilayer, Trilayer)<br />
- High Resolution, Better Etch Resistance with<br />
Thicker Resist, Planarization<br />
- More Complicated process with additional dry<br />
etching <strong>of</strong> bottom layer resist<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 31 S. W. Pang<br />
<br />
Silylated Resist<br />
Silylated Resist (Introduce Si in Polymer)<br />
- Use to increase etch resistance during O 2 plasma<br />
etching <strong>of</strong> bottom layer resist<br />
- Only a small amount <strong>of</strong> Si needed (
Resist Contrast and Sensitivity<br />
Resist Contrast depends on photoresist and UV property, affects<br />
resist pr<strong>of</strong>ile<br />
Development Curve (Contrast) For Positive Photoresist<br />
γ p<br />
=<br />
1<br />
log( D o<br />
D 1<br />
)<br />
e.g.<br />
<br />
<br />
Positive resist (AZ 1450J), 0.5 µm thick <br />
€<br />
D o =33 mJ/cm 2 ; D 1 =21 mJ/cm 2 ; γ=5.1 <br />
Large γ - more vertical resist pr<strong>of</strong>ile <br />
3 regions on development curve: <br />
A. Low Exposure - small but finite development rate (e.g. 1 nm/s) <br />
B. Medium Exposure - solubility increases with exposure dose <br />
C. High Exposure - resist fully removed when D≥ D o (e.g. 100 nm/s)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 33 S. W. Pang<br />
<br />
<br />
Negative Resist Contrast<br />
Resist Contrast depends on photoresist and UV property, affects<br />
resist pr<strong>of</strong>ile<br />
Development Curve (Contrast) For Negative Photoresist<br />
γ n<br />
=<br />
1<br />
log( D 1<br />
D 0<br />
)<br />
Similar to Positive Photoresist development curve, but Reversed: <br />
A. Low Exposure - Fast development € rate <br />
B. Medium Exposure - solubility decreases with exposure dose <br />
C. High Exposure - resist will not be removed<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 34 S. W. Pang
Light Absorption and Sensitivity<br />
<br />
<br />
I = I o e -αz where α is absorption coefficient<br />
Less dose near bottom <strong>of</strong> resist, Could affect resist<br />
pr<strong>of</strong>ile<br />
Resist Sensitivity - minimum dose required to define<br />
patterns in resist <br />
- positive resist: S=D o , minimum dose needed to remove<br />
exposed resist<br />
- negative resist: S=D 2 , minimum dose needed to keep<br />
exposed resist at 50% thickness<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 35 S. W. Pang<br />
<br />
<br />
Resist Pr<strong>of</strong>ile<br />
Depends on resist contrast and exposure pr<strong>of</strong>ile<br />
Ideal pr<strong>of</strong>ile - Vertical<br />
dT<br />
dx = ∞<br />
€<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 36 S. W. Pang
€<br />
<br />
<br />
Calculate Resist Pr<strong>of</strong>ile<br />
From Development Curve<br />
T(D,x) = γT o<br />
log<br />
€<br />
Let Exposure Dose D(T ,x) = I(x)te −α (T o −T )<br />
Where I(x) = Light Intensity; t = Exposure Time<br />
Slope <strong>of</strong> Resist (Pr<strong>of</strong>ile) =<br />
€<br />
D o<br />
D(T, x)<br />
T(D,x)<br />
T o<br />
= γ log<br />
T(D,x) € = γT o<br />
[log<br />
I(x)te ]<br />
−α (T o −T )<br />
D o<br />
D(T ,x)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 37 S. W. Pang<br />
dT<br />
dx<br />
D o<br />
€<br />
To Get Vertical Pr<strong>of</strong>ile<br />
Large contrast (γ)<br />
Small absorption (α) - get more light down to<br />
bottom <strong>of</strong> resist<br />
Little light scattering (large dI(x)/dx)<br />
High D o so that some <strong>of</strong> the scattered light will<br />
not expose resist<br />
Short exposure time to reduce scattering<br />
Thinner resist for less light scattering<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 38 S. W. Pang
Modulation Transfer Function (MTF)<br />
Ratio <strong>of</strong> modulation <strong>of</strong> an optical image to that<br />
<strong>of</strong> an object - represent image quality<br />
Depends on optical system and resist -<br />
wavelength, numerical aperture, contrast,<br />
light coherence, spatial frequency<br />
MTF (λ, NA, γ, S, f)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 39 S. W. Pang<br />
Light Distribution and MTF<br />
<br />
Mask Modulation<br />
M mask<br />
= I m −max − I m −min<br />
I m −max<br />
+ I m −min<br />
<br />
Wafer Modulation<br />
If I min = 0, then M = 1; If I min ≠ 0, then M
MTF and Linewidth<br />
<br />
<br />
If γ = ∞ (vertical pr<strong>of</strong>ile), MTF affects linewidth<br />
Exposure Time Affects Dose - Linewidth for Positive<br />
Photoresist is Reduced for Longer Exposure Time<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 41 S. W. Pang<br />
Light Coherence and Resolution<br />
<br />
<br />
<br />
<br />
<br />
Resolution also depends on Light Coherence (S)<br />
Coherent Light (S = 0) – Light passes slit in 1 angle<br />
(point source)<br />
Incoherent Light (S = 1) – Light with different angles<br />
and phases<br />
f = spatial frequency; line and space, or period <strong>of</strong><br />
gratings = 1/2L<br />
f c = cut<strong>of</strong>f frequency, minimum feature size that can be<br />
defined<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 42 S. W. Pang
MTF - Pattern Transfer Quality<br />
<br />
<br />
<br />
<br />
<br />
MTF = 1: Sharp Transition from Light to Dark<br />
MTF = 0: No difference between I max and I min , can't<br />
form any patterns<br />
f<br />
Poor image quality at low MTF c<br />
= 2NA<br />
λ<br />
For Coherent light S=0: Lower resolution, better image<br />
quality (High MTF); MTF=1 for f≤0.5 f c <br />
For Partial Coherent or Incoherent light S>0: Higher<br />
€<br />
resolution, worse image quality; MTF>0 for f≤f c ;<br />
MTF=0 for f=f c <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 43 S. W. Pang<br />
MTF Needed For Given Feature Size<br />
Smallest features that can be patterned with <br />
λ=200 nm, NA=0.5:<br />
Can't work with MTF=0<br />
If resist requires MTF=0.6 MTF = 0.6 =<br />
or 2L=0.33 µm; f=3 lines/µm; or l min = 0.165 µm<br />
Below this resolution, image quality is so poor<br />
€<br />
that it is not useful (e.g. can't do 5 lines/µm at<br />
f c ; or l min = 0.1 µm)<br />
1<br />
2L ( f )<br />
2NA<br />
λ ( f c )<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 44 S. W. Pang
Phase Shifting Mask (PSM)<br />
Traditional<br />
Mask<br />
Phase Shifted<br />
Mask<br />
<br />
<br />
Make adjacent phases to be 180° out <strong>of</strong> phase with one another.<br />
This provides destructive interference and reduce diffraction,<br />
therefore reducing I min and increasing MTF with better contrast<br />
and resolution<br />
Resolution can be increased by 2 times or more depending on S<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 45 S. W. Pang<br />
Contrast Function<br />
I max<br />
− I min<br />
Contrast Function = I max<br />
+ I min<br />
at phase shifted image<br />
Improve Resolution using Same Optical System<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 46 S. W. Pang<br />
€
Phase Shifted Mask Formation<br />
d(n −1) = λ 2 ;n = c v<br />
d =<br />
λ<br />
2(n −1)<br />
<br />
<br />
<br />
Add a transparent layer (e.g. quartz/polymer) such that the<br />
adjacent apertures are 180° out <strong>of</strong> phase - Optical thickness<br />
shifted by λ /2 €<br />
Need to take into account all adjacent features<br />
For phase shifted mask<br />
- Higher light intensity in exposed area, less residue left<br />
behind after development<br />
- Lower light intensity in unexposed area, larger process<br />
window for over-exposure, better resist pr<strong>of</strong>ile, and less<br />
undercutting<br />
- Intense computation needed for mask design to account for<br />
all adjacent apertures.<br />
- Significant improvement in resolution<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 47 S. W. Pang<br />
Next Generation <strong>Lithography</strong><br />
Non-Optical <strong>Lithography</strong><br />
Resolution limit - 100 nm and below<br />
Extreme UV (EUV) Reflective Projection<br />
Xray <strong>Lithography</strong> (XRL)<br />
Electron Beam <strong>Lithography</strong> (EBL)<br />
Nanoimprint <strong>Lithography</strong> (NIL)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 48 S. W. Pang
Extreme UV (EUV) Reflective Projection<br />
<br />
<br />
<br />
<br />
S<strong>of</strong>t Xray - λ=10-15 nm; photon energy ~100 eV<br />
All Vacuum, all reflective optics<br />
EUV Source - High power laser (Nd-YAG) to heat up<br />
supersonic Xe jet to produce EUV<br />
Reflective Optics - >50 multiple layers <strong>of</strong> thin films <strong>of</strong><br />
dissimilar n and α to form optical interference and<br />
high reflectivity (e.g. Mo/Si). Layer thickness=λ/4<br />
- e.g. Mo/Si with Layer thickness = λ/4 <br />
- Need better than 0.01 nm thickness control and<br />
0.3 nm smoothness<br />
- improved reflectivity (from ~50% to >70%)<br />
- no damage for long exposure time<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 49 S. W. Pang<br />
EUV SYSTEM AND MASK<br />
<br />
<br />
All Reflective Optics with Multiple Mirrors for<br />
Reduction<br />
Mirrors and Mask with Alternating Layers <strong>of</strong> High and<br />
Low Mass Materials for Constructive Interference<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 50 S. W. Pang
EUV System<br />
Projection system with 4-10X reduction<br />
Scanning mask and wafer<br />
Small NA (e.g. 0.25) with large DOF<br />
Could have large process window such that<br />
Phase Shifting Mask (PSM) or Optical<br />
Proximity Correction (OPC) is not needed<br />
Closer to Optical <strong>Lithography</strong><br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 51 S. W. Pang<br />
EUV vs. Optical <strong>Lithography</strong><br />
193 nm DUV is Used - Pushed As Far As<br />
Possible<br />
- Phase-Shifted Masks <br />
- Double Exposure<br />
- High Index Lens Immersion<br />
- Below 32 nm<br />
EUV Concerns<br />
- Control <strong>of</strong> Mo/Si Layer Thickness (
Xray <strong>Lithography</strong> (XRL)<br />
Short wavelength Xray - λ=1 nm; photon energy <br />
~10 KeV<br />
All Vacuum, membrane mask based on xray<br />
absorption<br />
Xray Sources - Laser or Plasma Generated Xray<br />
source<br />
- Heat up target (e.g. Fe-Ni) by high intensity laser<br />
or heat up gases by electromagnetic wave to<br />
generate high temperature plasma that emits<br />
xray. Pulsed laser or EM power is <strong>of</strong>ten used<br />
- ~10% efficient. Need to increase source<br />
brightness<br />
- Need to reduce debris from plasma using<br />
shielding or <strong>of</strong>f center excitation<br />
- Xray pulses with very high power for short time<br />
can damage mask/sample. Better to have lower<br />
power but high repetition rate<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 53 S. W. Pang<br />
Compact Synchrotron or Electron Storage Ring<br />
Particle accelerator with magnetic<br />
confinement and electrons are accelerated in<br />
a ring close to speed <strong>of</strong> light (~1 GeV)<br />
Xray emits from tangent <strong>of</strong> curved trajectory.<br />
Can get multiple exposure stations (~25) from<br />
1 ring<br />
Emitted Xray: Broad Spectrum emission, need<br />
filtering for exposure<br />
Bright source with high throughput and high<br />
resolution<br />
Expensive (>25 M) and needs backup system<br />
Large floor space, concern about downtime<br />
and reliability<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 54 S. W. Pang
Xray Mask<br />
<br />
<br />
<br />
Materials for absorber and membrane depend on α<br />
Concerns about Xray Mask and Exposure<br />
- Thick absorber with high α and thin membrane with low α<br />
for high mask contrast. Difficult to pattern thick absorber,<br />
thin membrane is less stable<br />
- Membrane need to be transparent in visible light for<br />
alignment<br />
- Need resist with high sensitivity for high throughput and<br />
low α to expose thick layer<br />
Advantages <strong>of</strong> XRL<br />
- High resolution due to short λ<br />
- High throughput compared to direct writing<br />
- No proximity correction needed<br />
- Immune to low MW particles with low α (e.g. dust)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 55 S. W. Pang<br />
High Resolution Xray Mask<br />
<br />
<br />
Angle Evaporation on Sidewalls and Top Surface with Alternative<br />
Layers <strong>of</strong> High/Low MW<br />
Linewidth Controlled by Layer Thickness<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 56 S. W. Pang
Electron Beam <strong>Lithography</strong> (EBL)<br />
Very short wavelength λ=0.01 to 0.05 nm,<br />
depending on electron energy<br />
λ(nm) =<br />
0.039<br />
V(keV )<br />
Electron energy~10-50 KeV<br />
<br />
€<br />
All Vacuum, either direct write or projection<br />
electron beam through membrane mask<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 57 S. W. Pang<br />
Direct Write EBL<br />
<br />
<br />
<br />
Input computer designs and generate patterns by<br />
scanning electron beam<br />
Need electron source with high brightness (e.g. field<br />
emission source rather than thermionic emission<br />
source) for high throughput<br />
Need good lens system to focus down to small beam<br />
size<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 58 S. W. Pang
Distortions in EBL<br />
Astigmation - misalignment <strong>of</strong> lenses that causes<br />
beam shape to change; Can be corrected by<br />
magnetic lenses<br />
<br />
Spherical Aberration - electrons land at different spots<br />
(focus points) due to their entry through lens from<br />
different point <strong>of</strong>f central axis. Increase minimum<br />
spot size<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 59 S. W. Pang<br />
<br />
Distortions in EBL<br />
Astigmation - misalignment <strong>of</strong> lenses that causes<br />
beam shape to change; Can be corrected by<br />
magnetic lenses<br />
<br />
Spherical Aberration - electrons land at different spots<br />
(focus points) due to their entry through lens from<br />
different point <strong>of</strong>f central axis. Increase minimum<br />
spot size<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 60 S. W. Pang
Additional Distortions in EBL<br />
Chromatic Aberration - due to energy spread <strong>of</strong><br />
electrons. Slower electrons are brought to focus<br />
closer to lens than faster electrons; Increase<br />
minimum spot size<br />
<br />
Spot size also depends on Mutual Columbic Repulsion<br />
<strong>of</strong> electrons and Diffraction limit <strong>of</strong> electrons<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 61 S. W. Pang<br />
<br />
<br />
Feature Size by EBL<br />
Once a beam gets minimum spot size through lenses,<br />
feature size limitation depends on electron scattering<br />
in resist and substrate<br />
Electrons scatter around until energy is lost or exit<br />
through resist surface by backscattering - Resolution<br />
depends on resist thickness due to scattering<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 62 S. W. Pang
Electron Penetration Range<br />
Monte Carlo simulation is used to track<br />
electron paths - Most electron energy is<br />
absorbed in substrate<br />
Maximum electron penetration range<br />
R(cm) = 4.6x10−6<br />
ρ<br />
V(keV ) 1.75<br />
e.g. ρ=1 g/cm 3 ; V=25 KeV; R g =12.9 µm<br />
€<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 63 S. W. Pang<br />
Proximity Effect<br />
<br />
Amount <strong>of</strong> Dose depends on position and shape <strong>of</strong><br />
features and their neighbors - Proximity correction by<br />
exposure dose adjustment using computer s<strong>of</strong>tware<br />
to calculate dosage from all adjacent features<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 64 S. W. Pang
Early Imprint <strong>Lithography</strong><br />
• ~1040 Movable Clay, Ceramic, and Wooden type Invented in<br />
China<br />
• ~1440 Gutenberg in Germany Commenced work on his<br />
Printing press with Metal moving type<br />
Woodblock<br />
Edition <strong>of</strong><br />
Chinese Play<br />
Gutenberg<br />
Press<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 65 S. W. Pang<br />
Types <strong>of</strong> Imprint <strong>Lithography</strong><br />
Hot Embossing – <strong>The</strong>rmoplastic<br />
– Polymer Flows above Glass Transition<br />
Temperature under Pressure<br />
Step and Flash Imprint <strong>Lithography</strong> (SFIL) – UV<br />
Assisted<br />
– UV Curable Polymer Flows and Solidifies after<br />
UV Exposure<br />
Reversal Nanoimprint <strong>Lithography</strong> – with and without<br />
UV, Mold Coating, and Transfer to Substrate<br />
– Multiple Imprints to Generate 3D Nanostructures<br />
– Low Temperature and Low Pressure<br />
– Flexible: no Residual Layer, no Liquid Fill<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 66 S. W. Pang
Applications <strong>of</strong> Imprint <strong>Lithography</strong><br />
Semiconductor Integrated Circuits<br />
– Mix and Match with Optical <strong>Lithography</strong><br />
Hard Disk Drives<br />
– High Resolution, High Density, Double-Sided,<br />
and Low Cost<br />
Light Emitting Diodes and Flat Panel Displays<br />
– High Resolution, High Density, Large Area, and<br />
Low Cost<br />
Biomedical Systems<br />
– High Resolution, High Density, Large Area, 3D<br />
Fluidic System, and Low Cost<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 67 S. W. Pang<br />
Full Wafer Imprint<br />
Imprint Throughput<br />
– Imprint Large Area (8 inch diameter) with High<br />
Throughput<br />
– Need Uniform Pressure between Mold and<br />
Substrate such as Air Cushion Pressure<br />
Step and Repeat Imprint<br />
– Similar to Optical <strong>Lithography</strong>, Easier to Control<br />
– Easier to make Imprint Mold with Smaller Area<br />
– Lower Throughput<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 68 S. W. Pang
Concerns <strong>of</strong> Imprint <strong>Lithography</strong> - I<br />
Patterning<br />
– High Resolution Tools Needed<br />
– Line Width Roughness Induced by <strong>Lithography</strong><br />
and Etching<br />
– Uniform Residual Layer<br />
1X Mold<br />
– CD Control<br />
– High Cost for Master – Multiple Molds can be<br />
Duplicated by Imprinting<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 69 S. W. Pang<br />
Concerns <strong>of</strong> Imprint <strong>Lithography</strong> - II<br />
Overlay<br />
– 3 Sigma <strong>of</strong> 10 nm Needed<br />
– Easier with Step and Scan than Full Wafer<br />
Imprint<br />
Defects<br />
– Contact between Mold and Substrate<br />
– Mold Cleaning and Defect Removal<br />
– Avoid Trapped Air by Using Vacuum, Flat Molds<br />
/Substrates, Spin-Coating rather than<br />
Dispensing<br />
– Lower Pressure to Avoid Mold Damage<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 70 S. W. Pang
MODES OF REVERSAL IMPRINTING<br />
<br />
<br />
<br />
<br />
NIL <br />
T>>T g <br />
CONVENTIONAL<br />
IMPRINT<br />
Embossing Inking<br />
Whole-Layer Transfer<br />
T>>T g <br />
T~T<br />
T~T g , non-planar g , planarized<br />
COATING ON MOLD<br />
3 IMPRINT MODES<br />
DEPENDS ON TEMPERATURE, PRESSURE,<br />
AND PLANARIZATION<br />
X. D. Huang, L.-R. Bao, X. Cheng, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20,<br />
2872-2876 (2002). <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 71 S. W. Pang<br />
HARD INERT SiC MOLDS FOR NANOIMPRINTING<br />
C 2 F 2 /O 2 30/10 sccm, 150 W rf POWER, -350 V, 6 Pa<br />
ETCH RATES: SiC 30 nm/min; Cr/Ni 0.8 nm/min; RESIST 200 nm/min<br />
ARRAYS OF DOTS IN SiC<br />
DEPTH = 320 nm 600 nm<br />
DEPTH = 800 nm<br />
GAP = 50 nm<br />
WIDTH = 100 nm<br />
High Aspect Ratio 8:1<br />
S. W. PANG, T. TAMAMURA, M. NAKAO, A. OZAWA, AND H. MASUDA, J. VAC. SCI.<br />
TECHNOL. B 16, 1145 (1998).<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 72 S. W. Pang
IMPRINTING ON METAL AND CERAMIC<br />
Nanoimprint Directly into Al<br />
Combine <strong>Lithography</strong> and Pattern<br />
Transfer <br />
SiC Mold with 40 nm Nanostructures<br />
4 µm Wide, 25 µm Deep CERAMIC Imprinted<br />
at 20 MPa, 30 s Using Polyimide MOLD<br />
Ceria-Zircronia Ceramic For Ultrasonic<br />
Imaging With High Resolution<br />
1 µm<br />
40 nm DOTS<br />
75 µm<br />
SINTERED at 1500 °C, 60 min<br />
DEPTH = 25 µm<br />
J. A. Bride, S. Baskaran, N. Taylor, J. W. Halloran, W. H. Juan, S. W. Pang, AND M. O'Donnell, Appl.<br />
Phys. Lett. 63, 3379-3381 (1993).<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 73 S. W. Pang<br />
MULTIPLE STEPS IN Al BY SINGLE<br />
NANOIMPRINTING<br />
THREE DEPTHS OF 100, 200, AND 300 nm<br />
500 µm<br />
x 20 µm/div; z 500 nm/div<br />
x 5 µm/div; z 500 nm/div<br />
S. W. Pang, T. Tamamura, M. Nakao, A. Ozawa, and H. Masuda, J. Vac. Sci. Technol. <br />
B 16, 1145-1149 (1998).<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 74 S. W. Pang
IMPRINTING ON FLEXIBLE SUBSTRATE<br />
50 µm THICK FLEXIBLE KAPTON FILM<br />
IMPRINT AT 175 °C<br />
<br />
<br />
<br />
ESPECIALLY SUITABLE FOR SUBSTRATES THAT<br />
CANNOT BE EASILY SPIN-COATED<br />
FLEXIBLE POLYMER FILMS<br />
PLASTIC ELECTRONICS<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 75 S. W. Pang<br />
THREE MODES OF REVERSAL IMPRINTING<br />
<br />
200<br />
Imprinting Temp. ( o C)<br />
180<br />
<br />
160<br />
140<br />
120<br />
<br />
Embossing<br />
Transition<br />
Whole-layer<br />
Inking<br />
Whole-Layer<br />
Transition<br />
Embossing<br />
Inking<br />
Tg<br />
100<br />
80<br />
60<br />
0 50 100 150 200 250 300 350<br />
R max<br />
(nm)<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 76 S. W. Pang
PATTERNING OVER TOPOGRAPHY<br />
SUSPENDED OR SUPPORTED NANOSTRUCTURES<br />
<br />
DEPENDING ON POLYMER PROPERTIES, IMPRINT<br />
CONDITIONS, AND PATTERN DIMENSIONS<br />
5-10 µm Gaps 2-5 µm Gaps<br />
<br />
<br />
POLYCARBONATE<br />
PMMA<br />
TOUGHER POLYMER MORE BRITTLE POLYMER<br />
L.-R. Bao, X. Cheng, X. D. Huang, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20,<br />
2881-2886 (2002). <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 77 S. W. Pang<br />
THREE-DIMENSIONAL NANOSTRUCTURES<br />
<br />
<br />
MULTIPLE IMPRINTS OF POLYMERS PATTERNS<br />
CAN TO USED TO FORM STACKED POLYMER LAYERS<br />
WITH SIMILAR OR DIFFERENT PROPERTIES<br />
<br />
<br />
<br />
<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 78 S. W. Pang
MULTIPLE LAYER 3D NANOSTRUCTURES<br />
3D PATTERNING BY REPEATED IMPRINTING<br />
<br />
<br />
L.-R. Bao, X. Cheng, X. D. Huang, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20,<br />
2881-2886 (2002). <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 79 S. W. Pang<br />
SELECTIVE SU-8 POSTS TRANSFER BY<br />
REVERSAL UV IMPRINT<br />
2 s Exposure; Bake: 65 °C 1 min, 95 °C 5 min; 1 min Development<br />
Reversal UV Imprint: 80 °C, 5 MPa, 1 min; 1 s UV Exposure; 80 °C, 5 MPa, 1 min<br />
1.3 µm Diameter Posts Selectively Transferred to 5 µm Wide, 300 nm Deep SU-8 Gratings<br />
1 µm 1 µm<br />
Polymer Posts Transferred Selectively only to Top <strong>of</strong> Gratings<br />
Allows Complex Structures Formation on Selected Areas<br />
C. Peng and S. W. Pang, J. Vac. Sci. Technol. B 24, 2968-2972 (2006).<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 80 S. W. Pang
LOW TEMPERATURE AND LOW PRESSURE REVERSAL UV<br />
NANOIMPRINT TO FORM SEALED CHANNELS<br />
Quartz<br />
SU-8<br />
UV<br />
Si<br />
Si<br />
a. Coating SU-8 on Quartz b. Imprint with UV<br />
Quartz<br />
Cured SU-8<br />
Si<br />
c. Coating Thin SU-8 Adhesion<br />
Layer on Si Substrate<br />
u<br />
Quartz<br />
Cured SU-8<br />
SU-8<br />
<br />
<br />
<br />
UV<br />
Quartz<br />
Cured SU-8<br />
Cured SU-8<br />
Si<br />
u<br />
Si<br />
d. Imprint with UV e. Formation <strong>of</strong> Channels<br />
in SU-8<br />
Sealed Channels Formation by Reversal Imprint with UV Exposure<br />
Low Temperature (55 °C) and Low Pressure (2 MPa) Used for Reversal<br />
Imprint<br />
Top SU-8 Layer UV-Cured before Reversal Imprint, Resulting in Good<br />
Channel Pr<strong>of</strong>ile Control Because No SU-8 Flow<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 81 S. W. Pang<br />
4 LAYER OF STACKED NANOCHANNELS<br />
1. Pattern SU-8 Coated Glass by UV Imprint: 55 °C, 1 MPa, 2 s UV<br />
2. Transfer Patterned SU-8 to Si Substrate with Thin SU-8 Adhesion Layer by<br />
Reversal UV Imprint: 55 °C, 2 MPa, 2 s UV<br />
3. Repeat Above Processes to Fabricate 3D Multiple Level Nanochannels<br />
400 nm Channels 200 nm Channels<br />
400 nm Channels 200 nm Channels<br />
Good Channel Pr<strong>of</strong>ile with 4 Repeated Reversal Imprints<br />
Uniform Array and Multiple Levels <strong>of</strong> 3D Nanochannels Formed by<br />
Repeating Reversal UV Nanoimprint<br />
B. Yang and S. W. Pang, J. Vac. Sci. Technol. B 24, 2984-2987 (2006).<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 82 S. W. Pang
REVERSAL IMPRINT TO TRANSFER METAL<br />
PATTERNING OVER NANOSTRUCTURES<br />
- COAT SU-8, METAL,<br />
AND PO LYMER<br />
ON GLASS MOLD<br />
(a )<br />
Glas s<br />
SU-8<br />
Metal<br />
Polym er<br />
Glass<br />
SU-8<br />
Metal<br />
Polymer<br />
- PATTERN POLYMER AND<br />
METAL BY LITHOGRAPHY<br />
AND ETCHING<br />
(b)<br />
A: IMPRINT TO Si<br />
B: IMPRINT TO SU-8<br />
Glass<br />
SU-8<br />
Metal<br />
Polymer<br />
Si<br />
Glass<br />
SU-8<br />
Metal<br />
SU-8<br />
Si<br />
- REVERSAL IMPRINT<br />
(c1)<br />
- REV ERSAL IMPRINT<br />
(c2)<br />
Metal<br />
Polym er<br />
Si<br />
Metal<br />
SU-8<br />
Si<br />
- SE PARATE MOLD<br />
(d1)<br />
- SEP ARATE MOLD<br />
(d2)<br />
<br />
<br />
Glass Mold with Cured SU-8 Layer and Etched Metal Patterns<br />
Metal Patterns Directly Transferred to Substrate Structures<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 83 S. W. Pang<br />
PATTERNED 3D METAL STRUCTURES FORMING<br />
CHANNELS WITH SUBSTRATE<br />
Glass Mold: SU-8 Gratings with 5 µm Period, 270 nm Deep, 2.5 µm Thick and<br />
0.5 µm Al Patterned by <strong>Lithography</strong> and Etching<br />
Reversal UV Imprint: 80 °C, 5 MPa, 1 min; 1 s UV Exposure; 80 °C, 5 MPa, 1 min <br />
SU-8 Gratings on Si Substrate: 5 µm Period, 340 nm Deep, 3.5 µm Thick<br />
Al Gratings<br />
<br />
SU-8 Gratings<br />
1 µm<br />
3D Channels with Interconnects Fabricated Using Structures in Mold,<br />
Patterning and Etching <strong>of</strong> Metal, and Structures on Substrate<br />
C. Peng and S. W. Pang, IEEE Inter. Conf. Nanotechnology, Cincinnati, Ohio, July 2006.<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 84 S. W. Pang
IMPRINTED 3-D GRATING WITH SEALED CAVITIES<br />
Duo Mold Imprinting<br />
Polymer Coating on Low Surface Energy Mold<br />
Surface Area also Determines Surface Adhesion<br />
Grating<br />
Grating<br />
Closed<br />
Cavities<br />
Si<br />
Closed Si<br />
1 µm<br />
Cavities<br />
1 µm<br />
FDTS Treated<br />
(Low Surface<br />
Energy)<br />
FDTS Treated<br />
(Low Surface<br />
Energy)<br />
Material: PMMA (Mw ∼15k)<br />
Both Molds (700 nm Period<br />
Mold and Square Mold)<br />
Treated With FDTS<br />
Imprinted at 5 MPa and <br />
150 °C<br />
Transferred to Substrate at 2<br />
MPa and 80 °C<br />
Y. P. <strong>Kong</strong>, H. Y. Low, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 22, 3251-3256 (2004). <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 85 S. W. Pang<br />
SURFACE ENERGY MODIFIED BY SEQUENTIAL SILANE<br />
TREATMENTS<br />
Polymer Adheres to Mold With Higher Surface Energy<br />
PEDS- FDTS<br />
Treated Mold<br />
(Medium Surface Energy)<br />
Surface Treatment<br />
FDTS b <br />
PEDS c -FDTS<br />
PEDS<br />
Surface Energy a <br />
(MJ/m 2 )<br />
11.8 ± 0.3<br />
18.3 ± 0.4<br />
37.6 ± 0.9 <br />
a By contact angles and the geometric-mean method<br />
b Perfluorodecyltrichlorosilane<br />
FDTS<br />
Treated Mold<br />
(Low Surface Energy)<br />
c Phenethylmethyldichlorosilane<br />
Adhesion - Higher Surface Energy<br />
Release - Lower Surface Energy<br />
Surface energy difference<br />
~6.5 mJ/m 2<br />
Y. P. <strong>Kong</strong>, H. Y. Low, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 22, 3251-3256 (2004). <br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 86 S. W. Pang
SURFACE PROPERTIES OF Si TREATED WITH SILANES<br />
Sample<br />
Lower Surface Energy for FDTS Treated Surface<br />
than PETS or MOPTS Treatment<br />
Contact angle<br />
for H 2<br />
O<br />
Contact angle<br />
for CH 2<br />
I 2<br />
Surface energy (mJ/m 2 )<br />
γ s<br />
O 2<br />
Plasma 26.9 47.7 65.2<br />
PETS 108.1 69.9 23.4<br />
MOPTS 73.6 58.7 34.6<br />
FDTS 103.0 99.8 11.7<br />
PETS (PhenEthyl TrichloroSilane)<br />
MOPTS (Methacryl Oxypropylene TrichloroSilane)<br />
FDTS (1H,1H,2H,2H-perFluoroDecyl TrichloroSilane)<br />
Si C 2 H 4<br />
Cl<br />
CF 3<br />
(CF 2 ) 7 C 2 H 4 Si<br />
Cl<br />
O<br />
CH 2 C C O C 3 H 6<br />
CH 3<br />
Cl<br />
Surface Energy Can be Controlled by Various Surface Treatments<br />
Silanes Can be Mixed in Various Ratio for Desired Surface Energy<br />
L.-R. Bao, L. Tan, X. D. Huang, Y. P. <strong>Kong</strong>, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 21, 2749 (2003).<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 87 S. W. Pang<br />
Cl<br />
Cl<br />
Cl<br />
Si<br />
Cl<br />
Cl<br />
Cl<br />
Example <strong>of</strong> <br />
Step and Flash Imprint <strong>Lithography</strong> (SFIL) <br />
at Molecular Imprints <br />
Courtesy <strong>of</strong> Dr. D. Resnick <br />
Applications in Memory and Hard Disk Drives<br />
Imprint Technology Issues<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 88 S. W. Pang
Large and Diverse Market Opportunities<br />
from Molecular Imprints<br />
Semiconductor ICs<br />
Hard Disk Drives<br />
Light Emitting Diodes<br />
Future Applications<br />
CMOS Image Sensors<br />
(CIS)<br />
Flat Panel Displays<br />
Bio-Medical<br />
89<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 89 S. W. Pang<br />
Step & Flash Imprint <strong>Lithography</strong> (S-FIL) <br />
from Molecular Imprints <br />
High resolution fused silica<br />
template, coated with release layer<br />
Template<br />
Step 1: Dispense<br />
drops<br />
Planarization layer<br />
Substrate<br />
Imprint fluid<br />
dispenser<br />
Low viscosity fluid (Si<br />
-containing for S-FIL,<br />
Organic for S-FIL/R)<br />
Step 2: Lower<br />
template and fill<br />
pattern<br />
Step 3: Polymerize<br />
imprint fluid with UV<br />
exposure<br />
Template<br />
Planarization layer<br />
Substrate<br />
Planarization layer<br />
Substrate<br />
very low imprint pressure < 1/20<br />
atmosphere at room temp<br />
Same Process Used for<br />
Step & Repeat and<br />
Whole Substrate<br />
Patterning<br />
Step 4: Separate<br />
template from<br />
substrate<br />
Template<br />
Planarization layer<br />
Substrate<br />
Step & Repeat<br />
<strong>The</strong> <strong>University</strong> <strong>of</strong> Michigan – Visiting Pr<strong>of</strong>. HKU p. 90 S. W. Pang
Stepper Technology for Non-Volatile Memory<br />
from Molecular Imprints<br />
Tool is being used for process development, device<br />
prototyping, and for integrating the imprint process into<br />
the CMOS process flow<br />
- Toshiba using tool for device prototyping (MNE, 2007)<br />
– 18nm lithography with