![Page 1: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/1.jpg)
Challenges for Lithography in TFH Manufacturing
September 18, 2008Peter ten Berge, ASML
![Page 2: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/2.jpg)
Outline• Introduction
• HDD Areal density roadmap• ITRS and TFH litho roadmaps• IC & TFH: many differences
• Imaging• Optical lithography strategies • Pareto for CD control budget• Further product CD control
• Overlay• Overlay trend • AlTiC & Si properties• Effect of thermal fluctuations • Colinearity
![Page 3: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/3.jpg)
HDD Areal density roadmap
0
200
400
600
800
1000
2007 2008 2009 2010 2011 2012
year
area
l den
sity
[Gbp
si]
2007-2008 demo’s based on DTR and conventional media have
already shown >600 Gbpsicapabilities
This density compares with 1TB 2.5” HDD
(w/2-Platters)
Latest product announcements
Source: various industry publications
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0
50
100
150
200
250
0 200 400 600 800 1000
areal density [Gbpsi]
track
pitc
h, b
itlen
gth
[nm
]Trackpitch reduction is the road to areal density increase
Bitlength reduction is at a hard stop due to minimum
sensor thickness
Source: various industry publications
Trackpitch
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ITRS & TFH litho roadmaps seem to be converging
Source: ITRS 2007, HGST @ IDEMA conf Dec 2006
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High end IC & TFH litho: many differences
IC TFH Comment
Wafer material Si AlTiC 2x heavier / m2
Wafer diameter 300mm 150-200mm risk of obsolete equipmentWafer thickness 775µm 1200-2000µm not a SEMI standard
Dies / wafer ~1,000 40,000-70,000 fewer wafers requiredField wafer layout n.a. rowbar layout absolute grid
Dielectric thickness < 0.3µm > 3µm tight OPOResist thickness < 0.2µm 0.2-1.0µm wavelength / resist choice
Feature type dense L&S iso line & trench litho extendibility Wavelength ArFi ArF / KrF NA / λ vs. dose / focus Throughput scanner limited track limited "idle" time scanner
• Nevertheless the TFH industry is (necessarily) using litho tools that have their roots in the IC industry
![Page 7: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/7.jpg)
Outline• Introduction
• HDD Areal density roadmap• ITRS and TFH litho roadmaps• IC & TFH: many differences
• Imaging• Optical lithography strategies • Pareto for CD control budget• Further product CD control
• Overlay• Overlay trend • AlTiC & Si properties• Effect of thermal fluctuations • Colinearity
![Page 8: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/8.jpg)
Optical lithography strategies
CDdense L&S = k1 * λ / NA DOFdense L&S = k2 * λ / NA2
• IC dense lines & spaces shrink follows Raleigh equation:• Reduce λ (436nm → 365nm → 248nm → 193nm → 13.5nm)
Resist formulations, light sources,...• Increase NA (Larger lenses, introduction of immersion)
New processes, polarization effects,..• Reduce k1 (RET)
OPC, PSM, off axis illumination,…
• TFH iso features not (linearly) proportional to λ / NA• Shrink driven by improved contrast / focus / dose performance• Full toolbox of optical tricks (k1) is applied
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Contrast simulations suggest KrF and ArFextendibility can be achieved using reticleenhancement techniques
0
1
2
3
4
0 30 60 90 120 150nominal ISO line CD [nm]
Nor
mal
ized
Inte
nsity
Log
Slo
pe [a
.u.]
ArFKrFArFKrF
0
30
60
90
120
150
0 30 60 90 120 150nominal ISO line CD [nm]
ISO
line
CD
@ T
F [n
m] ArF
KrFArFKrF
Binary maskBinary mask
Alt PSM maskAlt PSM mask
1:20 ISO lines, NA 0.8, sigma 0.4 conv., no AF
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Pareto for ISO line CDU budget
• Four main contributors to CD uniformity error are identified • These contributors are affected by several parameters
: litho system / lens related
PARETO ISO line CDU budget @TF1
2
3
4 Wafer flatness
5, ….
Focus
Reticle NCE
Dose
Various smaller contributors
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Pareto for CDU – Focus - system
0
20
40
60
80
100
0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e fo
cus
capa
bilit
y [%
]
ArF (i)KrFArF (i)KrF
• Focus capability is hardly related to wavelength or technologynode, but much more to innovations on system platform; main driver is the 200mm – 300mm transition
Note: focus cap. data may not be accurate due to differences in measurement
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Pareto for CDU – Focus - lens
0
20
40
60
80
100
0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e IP
D [%
]
0
20
40
60
80
100
0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e ab
erra
tions
leve
l [%
]
• Lens-related focus components of KrF are relative good, while focal sensitivities are similar for ArF / KrF
ArF (i)KrFArF (i)KrF
ArF (i)KrFArF (i)KrF
248nm 193nm
Alt-PSM, ISO line CD = 60nm
NA/σ 0.8/0.92/0.72
Note: aberr. data may not be accurate due to differences in measurement
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Pareto for CDU – Dose control
0
20
40
60
80
100
0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e do
se re
prod
ucib
ility
[%]
0
20
40
60
80
100
0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e do
se a
ccur
acy
[%]
Alt-PSM, ISO CD = 50nm
λ = 248nm, NA/σ 0.8/0.3
• Dose control improvements are implemented mostly on platform level and support KrF iso line extendibility (further than for dense L&S)
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Pareto for CDU – Wafer flatness / Reticle NCE
• Wafer site flatness of < 50nm for large exposure fields is required for sub-60nm iso features*; the smaller fields used TFH manufacturing make the requirement slightly “easier”
• Mask Error Enhancement Factors > 1 can be expected in the sub-50nm iso feature region**
Source: * ITRS 2007, ** C. Mack, Field guide to optical lithography 2006
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Further improvements by Imaging CD control
• Lithography is the only technique in a (TFH) process flow that can control CD uniformity on a local level; this can be used to deal with non-uniformity caused by external sources like etch, mask, track, CMP and deposition
• Full Wafer CD uniformity corrections can be performed based on:
-2%
0%
2%
-13 0 13Slit position [mm]
Inte
nsity
cha
nge
-2%0%2%4%
-4%-14 -7 0 7 14
Dos
e C
hang
e
Requested dose
Dose on Wafer
Scan position [mm]
Field-by-field Intrafield in scan direction Intrafield scan direction
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Conclusion Imaging CD control
• Wavelength and NA do not play a dominant role for ultimate iso line imaging; extendibility of KrF & (dry) ArF litho tools depends on performance improvements of focus and dose control
• These performance improvements have become available in line with KrF and (dry) ArF litho tool roadmap
• Product wafer flatness / CMP capability and reticle quality will need to be improved
• Actual litho roadmap for individual TFH manufacturers also depends on resist process availability (wavelength and TFH specific etch-resistance, selectivity and thickness)
![Page 17: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/17.jpg)
Outline• Introduction
• HDD Areal density roadmap• ITRS and TFH litho roadmaps• IC & TFH: many differences
• Imaging• Optical lithography strategies • Pareto for CD control budget• Further product CD control
• Overlay• Overlay trend • AlTiC & Si properties• Effect of thermal fluctuations • Colinearity
![Page 18: Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18, 2008 Peter ten Berge, ASML Outline • Introduction • HDD Areal density roadmap](https://reader031.vdocuments.net/reader031/viewer/2022021811/5cb68db188c993ed638b9e45/html5/thumbnails/18.jpg)
Steep overlay trend in IC is beneficial for TFH • Overlay trend is hardly related to wavelength but more to
innovations on system platform; main driver is the 200mm –300mm transition
0
20
40
60
80
100
0 20 40 60 80 100 120 140 160
Critical Dimension (L&S)
Rel
ativ
e ov
erla
y [%
]
In TFH every nm of overlay improvement is welcome, with
current on-product performance approaching 10nm, and single-machine
overlay < 6nm
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AlTiC vs Si substrate material properties
AlTiC (64% Al2O3 - 36%Ti - C) Si
Phase Amorphous Crystalline
Thermal expansion (ppm/C) 7.5, isotropic 2.5, anisotropic
Thermal conductivity (W/m.K) 25 150Heat capacity (J/KgK) 750 700
• Wafer temperature (drift) control is important for high end IC for SMO < 10nm
• AlTiC wafers are much more sensitive to thermal fluctuations than Si wafers, due to 3x larger CTE and 6x lower thermal conductivity
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Typical temperature accommodation takes much longer for AlTiC than for Si
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Thermal fluctuations lead to large AlTiC wafer magnification effects
0.00
0.20
0.40
0.60
0.80
0 30 60 90 120 150Time [s]
Waf
er E
xpan
sion
[ppm
]
AlTiCSi
Exposure time of a wafer falls in this range
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-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0 30 60 90 120 150Time [s]
Drif
t Rat
e [0
.1pp
m/s
]
AlTiCSi
Additional measures (compared with Si) have been required to achieve sub-10nm SMO on AlTiC
0
100
200
300
400
500
600
-5 -4 -3 -2 -1 0 1 2 3 4 5overlay [nm]
# of
sam
ples
X (mean + 3s)Y (mean + 3s)
Lot of 3 AlTiC wafers
Exposure time of a wafer falls in this range
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Colinearity in rowbars – back-end requirement
Lot of 3 AlTiC wafers
• Back-end process of rowbars adds requirement to minimize short wavelength position variations across the rowbar
• Work done in high end IC on absolute grids (for matching purposes and/or dual stage tools) may help for future improvements
Measurement mark
Row bar length
dY
Least mean square fit
Measurement mark
Row bar length
dY
Least mean square fit
0
2
4
6
8
10
1 2 3 4 5 6 7 8 9
rowbar #
3 si
gma
Col
inea
rity
[nm
]
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Conclusion• Continued tool overlay improvements support the steep TFH
overlay requirements roadmap
• Additional measures must be taken for TFH manufacturing on AlTiC in order to control thermal fluctuations and drifts effects
• Both for (KrF and ArF) imaging and overlay requirements litho tools are available to support the areal density roadmap
• Actual litho roadmap for individual TFH manufacturers also depends on developments in resist process, reticle quality and wafer flatness capability
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Acknowledgements
Presentation contains the highly appreciated input of Oleg Voznyi, Andre Derksen and Pascale Maury of ASML system and applications
engineering departments