a study of attenuated psm structure for euvl to minimize...
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2008 International Workshop on EUV LithographyJune 10-12, 2008, Maui, Hawaii, USA
A Study of Attenuated PSM Structure for E
UVL to Minimize Mask Shadowing Effect
Sangsul Lee1, Chang Young Jeong1, Tae Geun Kim1, Hyun-Duck Shin1, Eun Jin Kim2, Hye-Keun Oh2,
Jinho Ahn1
1Division of Advanced Materials Science and Engineering, Hanyang University2Department of Applied Physics, Hanyang University
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
Contents
Introduction-
Requirem
e
nts for EUVL Mask- How to reduce absorber stack thickness?
Attenuated PSM structure for minimizing shadowing effect-
The Sche
matic of attenuated PS
M - The reflectivity & phase shift change with absorber stack-
The characteristics of proposed attenuated PS
M
The Imaging performance of Binary mask & attenuated PSM- The pattern shift with the absorber stack thickness- H-V bias & pattern shift between binary m
ask and attenuated PS
M
Conclusions
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The structure of EUVL Mask
Absorber
Multilayer
Substrate
Capping
Buffer
ARC
• To improve DUV contrast for inspection
• Low DUV & EUV reflection• Low sheet resistance for e-beam writing
• To protect ML from absorber-etch damage
• High etch selectivity to absorber• Low stress
• To protect ML from unexpected oxidation
• Prevention of O2 & H2
• To reflect EUV wavelength
•To support mask structure with minimum distortion
• To absorb EUV for image formation
• Patterning characteristics
• High contrast >100:1• Low stress: <100 MPa
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
Requirements for EUVL Mask
Requirements for high lithographic
performance
-
High image contrast (<1% reflectance on absorber
pattern)
-
Minimized shadowing effect
: Due to reflective mask and oblique illumination (6º?
8º?)
: Correction for shadowing effect should be
considered
-
High flatness control
-
High surface roughness control (Flare)
-
High durability against EUV exposure
-
Low thermal expansion substrate
Requirements for mask manufacturing
-
Easy for mask processing
: writing, etching, cleaning…
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The Sche
m
atic of attenuated PSM
Febry-Perot structure
• Phase difference ( φ1 - φ2 )
: 180 ±
6°
• EUV reflectivity R1 : 5~12%
• DUV reflectivity : <5%
• Conventional etch process
• Minimum shadow effect
R1
, φ1
R2
,
φ2
Multilayer
Substrate
■TaN attenuator■Al2 O3 spacer■Mo phase shifter
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
How to reduce absorber stack thickness m
aintaining high image contrast?
•
Oscillating reflectivity (7 nm period (~1/2 wavelength))
-
>70nm
absorber thickness is needed to achieve high
image
contrast
•
TaN material is a good EUV attenuator
Simulated EUV Reflectivity
1.4%reflectivity
Measured EUV Reflectivity
How about using phase shift concept?
-
to improve image contrast
-
to reduce absorber stack thickness
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The DUV reflectivity contour with TaN attenuator and Al2O3 spacer thickness variation
16 18 20 22 24
2
4
6
8
10
Thickness of Al2O3(nm)
Thi
ckne
ss T
aN (n
m)
16 18 20 22 24
2
4
6
8
10
Thickness of Al2O3(nm)
For 257nm wavelengthFor 199nm wavelength
0.5000
5.000
9.500
14.00
18.50
23.00
24.50
• The thickness variation of Al2 O3 is less sensitive than TaN
• The DUV reflectivity (< 5%) could be achieved with the thinnest absorber stack (TaN (3nm) / Al2 O3 (18nm))
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The Measured DUV reflectivity with Mo thickness variation
10 15 20 25 300
10
20
30
40
50
Thickness of Mo (nm)
@ 257nm @ 199nm
Effect of Mo thickness variation in TaN(3nm)/Al2
O3
(18nm)/Mo/Ru/ML
Reflectivity does not change
with Mo thickness
4.5% reflectivity
21% reflectivity
•
The Mo thickness variation does not affect the D
UV reflectivity
•
The structure of TaN(3nm)/Al2
O3
(18nm)/Mo/Ru/ML showes a good inspection contrast at 257nm wavelength
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The EUV reflectivity and phase shift simulation of TaN(3nm)/Al2
O3
(18nm)/Mo/Ru/ML structure
Conditions: Phase tolerance: ±6
°EUV reflectivity: >5%
20 22 24 26 28 30 32 34 36 38 40-230-220-210-200-190
-180-170-160
-150-140-130
036912
151821
242730
EUV
Ref
lect
ance
(%)
Phas
e shi
ft (d
eg)
Thickness(nm) of Mo
7nm
Effect of Mo thickness variation in TaN(3nm)/Al2 O3 (21nm)/Mo/Ru/ML
• Optimized stack condition of attenuated PSM
- 180±6°
phase shift tolerance and 5~12% of EUV reflectivity
- Large Mo thickness latitude (7nm)
- Thin absorber stack (52nm~58nm)
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The m
easured DUV Inspection contrast
200 250 300 350 4000
20
40
60
80
100
Ref
lect
ance
(%)
Wavelength (nm)
Ru capped ML Att-PSM
10nm
Attenuated PSM
structure:
TaN/Al2
O3
/Mo/Ru/ML
ML
Ru(2nm)
Mo(28nm)
Al2
O3
(21nm)
TaN(3nm)
R1 DUV (%)
R2 DUV (%)
Contrast(%)
@257nm 46.38% 1.72% 92.84%
DUV (at 257 nm) reflectivity measurement with favorable condition
of att-PSM structure( TaN 3nm/Al2
O3
21nm/Mo 28nm/ Ru 2 nm/ML )
TEM imageMeasured 257nm DUV Reflectivity
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The condition of aerial image simulation
Simulation condition
List of mask structure
Type Structure Thickness of absorber stack (nm)
BIM Al2O3(20nm)/TaN(27nm)/Ru(2nm)/ML40 47nm
BIM Al2O3(24nm)/TaN(28nm)/Ru(2nm)/ML40 52nm
BIM Al2O3(22nm)/TaN(35nm)/Ru(2nm)/ML40 57nm
BIM Al2O3(29nm)/TaN(36nm)/Ru(2nm)/ML40 65nm
BIM Al2O3(34nm)/TaN(341nm)/Ru(2nm)/ML40 75nm
Type Structure Thickness of absorber stack (nm)
BIM Al2O3(20nm)/TaN(27nm)/Ru(2nm)/ML40 47nm
BIM Al2O3(24nm)/TaN(28nm)/Ru(2nm)/ML40 52nm
BIM Al2O3(22nm)/TaN(35nm)/Ru(2nm)/ML40 57nm
BIM Al2O3(29nm)/TaN(36nm)/Ru(2nm)/ML40 65nm
BIM Al2O3(34nm)/TaN(341nm)/Ru(2nm)/ML40 75nm
Parameter Value
Median wavelengthTemporal bandwidthNAMagnification factorSpatial coherence factor, sigmaIncident anglePattern size
13.5nm2% FWHM0.2540.5
6°22nm Iso, 22/32nm L/S
Parameter Value
Median wavelengthTemporal bandwidthNAMagnification factorSpatial coherence factor, sigmaIncident anglePattern size
13.5nm2% FWHM0.2540.5
6°22nm Iso, 22/32nm L/S
TaN
substratesubstrate
Mo/SiMo/Si
Al2O3
TaN
substratesubstrate
Mo/SiMo/Si
Al2O3
Mo: 2.7nmSi: 4.15nm
This stack was proposed in SPIE 2006 by Seung Yoon Lee (Hanyang University)
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The pattern shift with absorber stack thickness at 22n
m isolated line
Pattern shiftAerial image
•
As the absorber stack thickness increased, the
pattern shift increased
•
Using 52nm absorber stack reduced pattern
shift(~1nm) compared to 75nm absorber stack
52nm absorber thickness
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The pattern shift with absorber stack thickness at 22/32nm L/S
• As the absorber stack thickness increased, the pattern shift increased
• Using 52nm absorber stack reduced pattern shift(~1nm) compared to 75nm absorber stack
Pattern shiftAerial image
52nm absorber thickness
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The condition of aerial image simulation
Simulation condition
List of mask structure
TaN
substratesubstrate
Mo/SiMo/Si
Al2O3
Mo
R1
, φ1 R
2
,
φ2
Attenuated PSM
TaN
substratesubstrate
Mo/SiMo/Si
Binary mask
Parameter Value
Median wavelengthTemporal bandwidthNAMagnification factorSpatial coherence factor, sigmaIncident anglePattern size
13.5nm2% FWHM0.2540.5
6°32nm L/S, 45nm L/S
Parameter Value
Median wavelengthTemporal bandwidthNAMagnification factorSpatial coherence factor, sigmaIncident anglePattern size
13.5nm2% FWHM0.2540.5
6°32nm L/S, 45nm L/S
Type Structure Absorber thickness (nm) REUV(abs) (%)
Att-PSM
TaN(3nm)/Al2O3 (21nm)/Mo(28nm)/Ru(2nm)/ML 52nm 9.5 %
BIM TaN(52nm)/Ru(2nm)/ML 52nm 0.2%
Type Structure Absorber thickness (nm) REUV(abs) (%)
Att-PSM
TaN(3nm)/Al2O3 (21nm)/Mo(28nm)/Ru(2nm)/ML 52nm 9.5 %
BIM TaN(52nm)/Ru(2nm)/ML 52nm 0.2%
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The aerial image of horizontal &
vertical pattern between binary and attenuated PSM
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.080.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Position
BIM_Vertical BIM_Horizontal PSM_Vertical PSM_Horizontal
• The Attenuated PSM shows steeper edge profile and higher image contrast compared to the binary mask
• The Horizontal pattern shows higher image contrast and negligible pattern shift compared to vertical pattern
45nm L/S pattern32nm L/S pattern
-0.06 -0.04 -0.02 0.00 0.02 0.04 0.060.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Inte
nsi
ty
Position
BIM_Vertical BIM_Horizontal PSM_Vertical PSM_Horizontal
Positi
on
Positi
on
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
The H-V CD bias and pattern shift with defocus
• The H-V CD bias increased and pattern shifted with defocus
• The attenuated PSM shows less H-V CD bias compared to the binary mask
-> Larger process window than binary mask
• 32nm pattern shows larger H-V CD bias compared to 45nm pattern
• The Pattern shift is less sensitive than the H-V CD bias to the optical property of absorber
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15123456789
1011
BIM_32nm_L/S BIM_45nm_L/S PSM_32nm_L/S PSM_45nm_L/S
H-V
bia
s
Defocus
DoF: 0.20um
-0.15 -0.10 -0.05 0.05 0.10 0.15
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Pa
ttern
Sh
ift
Defocus
BIM_32nm L/S BIM_45nm L/S PSM_32nm L/S PSM_45nm L/S
0
DoF: 0.20um
Defoc
us
Defoc
us
H-V
bia
s
June 10-12, 2008, Maui, Hawaii, USA 2008 International Workshop on EUV Lithography Hanyang University
Conclusions
Proposed optimized attenuated PSM structure
-
TaN(3nm)/Al2
O3
(21nm)/Mo(28nm)/Ru/ML: TaN (attenuator), Al2
O3
(spacer), Mo (phase shifter) - Total thickness: 52 nm
: Minimized shadowing effect
- High DUV contrast for m
a
sk inspection : > 90% @ 257nm
- Large Mo thickness latitude
The Imaging performance of BIM & attenuated
PSM
-
The attenuated P
S
M show
s steeper edge profile and higher image contrast co
mpared to the binary m
ask -
The attenuated P
S
M show
s less H
-
V C
D bias co
m
pared to the binary mask-
The pattern shift is less sensitive than the H
-V CD bias with the optical property of absorber
- Larger process window than binary m
ask
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