Seminar: Lithography Feb. 7th, 2005
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FLCC
FLCC Seminar: PSM Lithography MonitorsGarth Robins and Greg McIntyre UCB
FLCC Research Results: Photomasks as precision instruments for monitoring aberrations and polarization in projection printing with Professor Andy Neureuther
Design, SEM, AFM and AIMS results for 193 nm in collaboration with Photronics and AMD
February 7th, 2005
Seminar: Lithography Feb. 7th, 2005
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A special thanks to the following organizations and individuals for all of their tremendous help and support while conducting this research:
Photronics Bryan KasprowiczMarc CangemiRamkumar Karur-ShanmugamRand CottleJustin NovakMark Smith
AMD Jongwook KyeHarry LevinsonAlden Acheta
UC Berkeley Frank GennariGarth Robins
Seminar: Lithography Feb. 7th, 2005
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Polarization
Illumination
PSM Performance
Fogging
Flare
Trans Imbalance
Aberrations
Immersion
Design / Process variation
Metrology
CMP
Resist
* Screenshots taken in Frank Gennari’s Simple Display
Multi-Student Process-EDA Test Mask
Seminar: Lithography Feb. 7th, 2005
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Feature Level Compensation and Control
PSM Polarimetry: Monitoring Polarization at 193nm High-NA and
Immersion with Phase Shifting Masks
Greg McIntyre
Seminar: Lithography Feb. 7th, 2005
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• High-NA / Polarization Effects• PSM Polarimeters: Concept• Initial Experimental Results• Improved Design• Simulated Examples• Mask Topography Effects• Proposed Reticle Design
PSM Polarimetry: Outline
Seminar: Lithography Feb. 7th, 2005
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Background: High NA Vector Effects
Z – component leads to:• Image reversal of TM component, Loss of depth of focus, Loss of image contrast
xz
y
Low NA
= ETM NAEz = ETM sin()
High NA
Z component of E-field introduced at High NA from radial pupil component
Z-component negligible
TMTE
mask
wafer
Seminar: Lithography Feb. 7th, 2005
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• Z Component is derivative of XY components
• Polarization Monitor maximizes z-component proximity effect in pattern center for one polarization component (reciprocity)
)()()()()sin()(00
xExk
jxE
k
kxE
n
NAxExE TMTM
xTM
resistTMz
PSM Polarization Analyzer: Concept
X polarization Ez PSF Y polarization Ez PSF
PSF (Airy pattern)
y
x
0
180
Cr
• Proximity effect (point spread function) derived for z-component
kx
ko
Seminar: Lithography Feb. 7th, 2005
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Increasing NA
EoyEoxMask
Wafer
xz
y
TM
TE
Similar Effect Observed by Monitoring Nulls of Periodic Alternating-Phase Grating
Linear
Radial
Seminar: Lithography Feb. 7th, 2005
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0 180
13.34 mJ/cm
0.52 % CF
14.4 mJ/cm
0.49 % CF
Signal is dose when center resist just clears
FLCC Test Mask: Experimental Verification of High-NA Signal (Jan 05)
• 4-phase PSM test mask provided by Photronics• Original concept: periodic 0-180 radial grating
MaskLayout
0 180
Proposed Design Improvement
Resist
Incr
easi
ng d
ose
Seminar: Lithography Feb. 7th, 2005
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HorizontalCutline(at center)
VerticalCutline
(center)
TE(y) linear TM(x) linear 45 linear 135 linear unpolarizedor circular
Mask pattern
0
1
2
3
4
TE(y) l
inear
TM(x
) line
ar
45 lin
ear
135
linea
r
unpo
larize
dCen
ter
Inte
nsi
ty (
CF
)Central intensity signal shows excellent response: Linear Polarization Patterns (simulation)
Signal
Simulated resist image
Dose
Seminar: Lithography Feb. 7th, 2005
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0.0
0.5
1.0
1.5
2.0
R L un-polarized
R
L
R
L
018090270
Circular Polarization Analyzers:
UnpolarizedRight Circular Left Circular
Incident light
pattern
Cen
tral
Int
ensi
ty (
%C
F)
Seminar: Lithography Feb. 7th, 2005
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Off-Axis Polarization Analyzers:
090
180270
+ =
Introduce 4-phase linear progression to monitor polarization from off-axis illumination
Mask making becomes quite challenging
M
c NAP =
MaskSEM
Seminar: Lithography Feb. 7th, 2005
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0
0.5
1
1.5
2
2.5
3
0 1 2 3 4 5 6 7
BPM TE
BPM TM
BPM 45
BPM 135
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
1 2 3 4 5
TE
TM
45
135
unpol
Proposed Technique: Polarimeter = 6 analyzers
On-Axis
135
TM
Off-Axis
TE 45 TM 135 TE
018090270
45
TE
45 135
TE 45 TM 135 TE
Response: symmetric Response: asymmetric
Seminar: Lithography Feb. 7th, 2005
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Compare intended design to a (simulated) actual measurement:• Intended (80% TE polarized, 20% unpolarized) • Actual (70% TE polarized, 30% unpolarized).
0 1 2 3 4
L
R
135
45
TM
TE
Actual
Intended
Response (center Intensity / clear field)
Signal change for on-axis test case
Ana
lyze
r -15.7%CF
+15.7%CFNo change
No change
+1.9%CF
-1.9%CF
On-Axis Off-Axis135
TM
45
TE
135
TM
45
TE
0 0.5 1 1.5
135
45
TM
TE
Actual
Intended
Response (center Intensity / clear field)
Signal change for off-axis test case
Ana
lyze
r +6.4%CF
-9.1%CF
-1.1%CF
+0.6%CF
Practical Example: Response for two polarization states
>1% CF/ % polarization >0.5% CF/ % polarization (including expected resist effects)
Seminar: Lithography Feb. 7th, 2005
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TE TM
Mask Topography Effects: Off-Axis Analyzer
1) Thin simulation Thick for only Case B
LPG only jumbles one polarization component (local TM)
2) Thin cases are not symmetric2 effects in same plane get jumbled – introduce 0 order
i.e. redirection (LPG) and diffraction (RPG)
0
0.2
0.4
0.6
0.8
1
1.2
Incident Light
Central Intensity
TE TM
ThinThickTE
TM
45
Seminar: Lithography Feb. 7th, 2005
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0
1
2
3
4
00.50.81
TE linea
r
TM lin
ear
45 lin
ear
135
linea
r
unpo
larize
d
Cen
ter
Inte
nsi
ty (
CF
)
c
TM Analyzer: Signal deterioration due to mask topography as mask dimensions decrease (i.e. c increases)
Seminar: Lithography Feb. 7th, 2005
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4-phase linear phase progression difficult to manufacture
Seminar: Lithography Feb. 7th, 2005
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PSM Polarimeters require very coherent illumination, perhaps provided by a pinhole on backside of reticle
Cluster (frontside reticle)
Pinhole (in chrome on backside reticle)
Radius ~ 100um
polarimeter
))(tan(arcsinMn
NAtr
g
Crpolarimete
t = mask thicknessng = mask index of refractionC = monopole location
Proposed Test Reticle Design
Seminar: Lithography Feb. 7th, 2005
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Summary • Monitors derived from basic principles• Initial experimental results appear to validate principles of technique• Simulated examples of new design promise to monitor polarization:
• 1 %CF / % polarization state (on-axis)• 0.5 %CF / % polarization state (on-axis)
• Discussed practical limitations• Proposed test reticle design
Seminar: Lithography Feb. 7th, 2005
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Feature Level Compensation and Control
Aberrometry: Are pattern and probe aberration monitors ready for prime time?
Garth [email protected]
Seminar: Lithography Feb. 7th, 2005
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Aberrometry: Outline• λ = 193nm AIMS
results
• Factor targets into components
• Lithography demons
• Improve performance through adjusting design dimensions
•0°•90°•180°•270°
Probe
Rings
defocus
Seminar: Lithography Feb. 7th, 2005
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~BF
1 step = 0.145 RU
•0°•90°•180°•270° defocus
• Alternating 0°/180° phase-shifted rings surrounding a 90° phase-shifted probe
• Aberration perturbs spillover electric-field
• Sensitivity > 60%CF/1RU
Response to focus
How Targets Work
AIMS imageMask layout
AIMS intensity cut
2RZ3055cr_all
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20Focal Plane
Pea
k In
tens
ity (1
00%
C
F)
0° probeT3 (90° probe)T3 0° outer ring
-1RU +1RU
T3 center probe
Isolated probe0° outer ring
Seminar: Lithography Feb. 7th, 2005
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AIMSTM
TEMPEST
Litho.SEM
SPLAT 6.0
Mask EM effects High-NApolarization effects
Mask erroreffects
Resist effects
SPLAT
• 0°/90°/180° phase region intensity imbalance
• Reduced coupling of TE mode (TM contrast ↓)
• Mitigation of high-angle effects (n)
• Mask geometry
• Pixilation
• Layer registration
Panoramic
SimulationExperiment
This poster Lithography Demons
Seminar: Lithography Feb. 7th, 2005
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• Factor target into elements and parameterize
• 0°/90°/180°/270° phase-shifted rings, probes, lines, and rings surrounding probes
• λ = 193nm, NA = 0.80
•0°•90°•180°•270°
Probe
Rings
defocus
r_cr neck
• λ = 193nm, NA = 0.80, σ = 0.3• 1 RU = 42 (λ / 2 NA2) = 2.4125 μm
Strategy of Factorization
Seminar: Lithography Feb. 7th, 2005
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• 4-phase multi-student test mask fabricated and donated by Photronics, Inc. as part of UC Berkeley’s Feature Level Compensation and Control grant
• Process: chrome open, then 90°, then 180° phase etch w/ bias
• Position, programmed bias, processing (pullback)
• Measure edge bias on isolated lines and probes
Mask Making Flow & Tolerances1) Open all cr
2) 90° etch (for 90° & 270° regions)
3) 180° etch (for 270° & 180° regions)
Potential errors
Alignment/etch depth/effective phase
Quartz
Quartz
Quartz
90°270° 0°180°
Seminar: Lithography Feb. 7th, 2005
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• SEMs indicate biases & alignment
• Observe isolated probes + full 2-ring defocus target
Mask Making Results
90°0° 270°180°
Nominal-sized iso-probes
2-Ring defocus target
90°
0°180°
cr
Layer Edge bias (nm) Alignment (nm)
Chrome
(e-beam)
+14+40 NA
90° -53 0
180° -31 36
270° See iso probe See iso probe
Seminar: Lithography Feb. 7th, 2005
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Performance of Isolated Lines
2-Ring defocus target
Iso-lines in dark field
-20
-15
-10
-5
0
5
10
15
20
25
0 100 200 300 400 500
Mask design width/2 (nm)
Ed
ge
bia
s (f
abri
cate
d -
d
esig
n)
(nm
)
0° Line90° Line180° Line270° Line
AIMSFab 193nm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 90 180 270Nominal Line Phase
Pea
k In
ten
sity
(10
0% C
F)
@ B
F 0nm50nm100nm120nm150nm200nm250nm
AIMSFab 193nm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250 300Measured Linewidth (nm)
Pea
k In
ten
sity
(10
0% C
F)
@ B
F
0° line180° line0° Ring180° RingSPLAT
0.207 λ/NA 1.04 λ/NA
NA = 0.80, σ = 0.3
0°SPLAT
180°
• Bias(size, phase) (L)
• Peak intensity (R)
• Typical linewidth = 150nm
• MEEF = 1.3
wnom = 150nm
Design Width
Seminar: Lithography Feb. 7th, 2005
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• Bias(size, phase) (L)• Peak intensity (R)• Edge effects in phase
etched holes are important
Performance of Isolated ProbesNA = 0.80, σ = 0.3
Iso-probes in dark field
-20
-15
-10
-5
0
5
10
15
0 100 200 300 400 500
Mask design radius (nm)
Ed
ge
bia
s (f
abri
cate
d -
d
esig
n)
(nm
)
0° Probe90° Probe180° Probe270° Probe
AIMSFab 193nm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 90 180 270Nominal Iso-Probe Phase (deg.)
Inte
nsi
ty (
100%
CF
)
0nm50nm100nm120nm150nm200nm250nm
AIMSFab 193nm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250 300Iso-Probe Measured Diameter (nm @ wafer)
Inte
nsity
@ B
est
Focu
s (1
00%
CF)
0.207 λ/NA
rnom = 109nm
Design Diameter
0°180°
SPLAT
1.04 λ/NA
Seminar: Lithography Feb. 7th, 2005
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• Look at 2R_035cr targets iso-rings• λ = 193nm, NA = 0.80, σ = 0.3• 1 RU = 42 (λ / 2 NA2) = 2.4125 μm• 11 focal planes, 0.7 μm steps• 1 step = 0.290 RU (programmed)
81.5% CF
98.1% CF
~1.2×
79.5% CF
42.3% CF
~1.9×
Example of Rings
0° 180° 0°
180° 0° 180°
• Single 0° & 180° rings of different sizes & thicknesses w/ no probe
• Ring intensity vs. center intensity
• MEEF
Seminar: Lithography Feb. 7th, 2005
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Iso-Rings (σ = 0.3)
0
0.2
0.4
0.6
0.8
1
1.2
120 130 140 150 160 170
Measured Width (nm)
Inte
nsi
ty (
100%
CF
)
Ring (0°)
Ring (180°)
Performance of Rings
• Peak intensity difference with phase is as-expected (L)
• Center spillover is also strongly dependant upon ring phase (R)
• Response through focus is same for thickest ring (B)
Z3 Iso-ring
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10
Focal Plane
Inte
nsi
ty (
100%
CF
)
L 180° iso_ ring_ ir1
M 0° iso_ ring_ ir2
S 180° iso_ ring_ ir3
L 0° iso_ ring_ ir4
M 180° iso_ ring_ ir5
S 0° iso_ ring_ ir6
Center spillover response to focus
Iso-Rings (σ = 0.3)
0
0.2
0.4
0.6
0.8
1
1.2
120 130 140 150 160 170
Measured Width (nm)
Inte
nsi
ty (
100%
CF
)
Center (0°)
Center (180°)
0°180° 0°180°
Ring Intensity Center Intensity
Seminar: Lithography Feb. 7th, 2005
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Performance of Probeless Targets
2RZ3055cr_all
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20Focal Plane
Pea
k In
ten
sity
(10
0% C
F)
0° probeT1 (no probe, 180° inner ring)T4 (no probe, 0° inner ring)
• Two 2-Ring defocus targets shown with no probes
• Response through focus is quite strong even without probe
• Expect symmetric shift from BF between the targets
• Bias, intensity imbalance, & phase etch error contribute to non-ideality
Center Intensity
Seminar: Lithography Feb. 7th, 2005
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Target Synthesis Via Phasor Diagram
• 90° probe & expected performance
• Non-idealities: truncation/Z0, phase etch, probe size, intensity imbalance/spillover– Probe length is smaller than intended
– Probe likely rotated due to an EM effective phase error & additional phases in hole
– Unwanted length changes are produced by bias
– Unwanted rotation is due to effective phase etch
– Extra component due to finite size and bias
Re
Im
0.0
0.5
1.0
-1.0 -0.5 0.0 0.5 1.0
Defocus (RU)
Inte
ns
ity
(1
00
%C
F)
2pE
22Rp EE
2RE
0pE
2RE
22 pE
constantEandE Rp
Re
Im
?
Ideal phasor diagram
0.0
0.5
1.0
-1.0 -0.5 0.0 0.5 1.0
Defocus (RU)
Inte
nsi
ty (
100%
CF
)
SPLAT
19%
34%
Lateral shift
Center intensity
Iso-probe intensity
Seminar: Lithography Feb. 7th, 2005
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•0°•90°•180°•270° defocus
Mask layout2RZ3055cr_all
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20Focal Plane
Pea
k In
tens
ity (1
00%
C
F)
1 step = 0.145 RU
• 2-Ring defocus target w/ 90°, 270°, & “no probe”
• “No probe” target should be symmetric about BF
• “No probe” ~ 270° probe
• 90° brighter at BF
Target Measurements Revealing Phasor Gotchas
-1RU +1RU
Isolated probe
90°
270°
No probe
Center Intensity
• Complimentary 90°/270° probe target responses should be reflected about BF, but not symmetric
Seminar: Lithography Feb. 7th, 2005
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0
1
2
3
4
5
6
7
0 2 4 6 8 10
Target
Po
siti
on
of
Min
imu
m(F
oca
l P
lan
e)
Position of minimum
Focal plane of Strehl peak
ip1T3
Peak
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10
Focal Plane
Inte
nsi
ty (
100%
CF
)
2rz3_035cr_ip1_017sig_recheckABCDEFGHI
1000 pixels
1000
pix
els
A
B
C
D
E
F
G
H
I
A B C D E F G H I
• Image one 2-ring defocus target at 9 positions in the AIMS field
• Could be a tilt in both X & Y
Measuring AIMS Field Flatness
Seminar: Lithography Feb. 7th, 2005
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FLCC
Summary• PAP designed, fabricated and tested on AIMS• Strategy of factoring insight into factors contributing to 2nd-
order effects in the phasor addition of the composite performance
• Sub-printable probe intensities weaker than expected performance nearly that of a probeless design.
• Nearly probeless… still useful w/ ~50% of the CF/RU defocus (away from best focus)
• Target components reveal ideas for monitoring mask making…
• MEEF• Overall the targets gave a much stronger and more sensitive
signal to focus that isolated probes (Strehl ratio) and with further sizing and target phase combinations both focus and EM performance can be extracted