Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18,...
Transcript of Challenges for Lithography in TFH Manufacturing for Lithography in TFH Manufacturing September 18,...
Challenges for Lithography in TFH Manufacturing
September 18, 2008Peter ten Berge, ASML
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
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
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
ITRS & TFH litho roadmaps seem to be converging
Source: ITRS 2007, HGST @ IDEMA conf Dec 2006
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
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
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
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
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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
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
Pareto for CDU – Focus - system
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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
Pareto for CDU – Focus - lens
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0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e IP
D [%
]
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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
Pareto for CDU – Dose control
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100
0 50 100 150 200
Critical Dimension (L&S)
Rel
ativ
e do
se re
prod
ucib
ility
[%]
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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)
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
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
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)
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
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
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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
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
Typical temperature accommodation takes much longer for AlTiC than for Si
Thermal fluctuations lead to large AlTiC wafer magnification effects
0.00
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0 30 60 90 120 150Time [s]
Waf
er E
xpan
sion
[ppm
]
AlTiCSi
Exposure time of a wafer falls in this range
-0.10
-0.05
0.00
0.05
0.10
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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
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-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
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
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1 2 3 4 5 6 7 8 9
rowbar #
3 si
gma
Col
inea
rity
[nm
]
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
Acknowledgements
Presentation contains the highly appreciated input of Oleg Voznyi, Andre Derksen and Pascale Maury of ASML system and applications
engineering departments