Transcript EUV Presentation - Penn State University

Extreme Ultra-Violet
Lithography
Matt Smith
Penn State University
EE 518, Spring 2006
Instructor: Dr. J. Ruzyllo
Outline
• Why do we need EUV lithography?
• Brief overview of current technology
• What exactly is EUV?
• System diagram
• Challenges associated with EUV
• 13.5nm source
• Optics
• Masks
• Resists
Why EUV?
Minimum lithographic feature size =
k1*λ
NA
k1: “Process complexity factor” – includes “tricks” like phase-shift masks
λ: Exposure wavelength
NA: Numerical aperture of the lens – maximum of 1 in air, a little higher in
immersion lithography (Higher NA means smaller depth of focus, though)
Mask Maker’s
Holiday:
“large” k1
Mask Maker’s
Burden: “small” k1
There are only so
many “tricks” to
increase this gap, and
they are very
expensive … we
MUST go to a shorter
wavelength!
ftp://download.intel.com/research/silicon/EUV_Press_Foils_080204.pdf
Why EUV? Why not the next excimer line?
• Hg (G line) @ 436nm  Hg (H line) @ 405nm  Hg (I line) @ 365nm 
KrF Excimer @ 248nm  ArF Excimer @ 193nm  ???
• 157nm lithography based on the fluorine excimer laser has been largely
shelved, which leaves 193nm with extensions for production
• Below that, no laser line has the required output power
• Excimer-based steppers expose 109 steps per 300mm wafer, and
produce >100 wafers per hour – exposure times ~ 10-20ns
• Additionally, fused silica and atmospheric oxygen become absorptive by
157nm – so even incremental decreases in wavelength start to require a
major system overhaul
Mask Maker’s
Holiday:
“large” k1
Mask Maker’s
Burden: “small” k1
ftp://download.intel.com/research/silicon/EUV_Press_Foils_080204.pdf
Why EUV? It’s all about the money.
By decreasing λ by a factor of 14, we take pressure off k1 – this makes the
masks less complicated and expensive because we can skip the “tricks”
For example: a 90nm node mask set:
• Pixels:
• Number of pixels on 1 mask:
• Defects:
• Size that must be found and repaired:
• Number of such defects allowed:
• Data:
• Total file size needed for all 22-25 layers:
• Cost:
• Cost for mask set (depreciation, labor, etc):
1012
100nm (25nm as projected on wafer)
0
200GB
~$800k-1.3M
ftp://download.intel.com/technology/silicon/Chuck Gwyn Photomask Japan 0503.pdf
Current Lithographic Technology
• Lenses are very effective and perfectly transparent for
193nm and above, so many are used
• A single “lens” may be up to 60 fused silica surfaces
• System maintained at atmospheric pressure
• Lens NA ~0.5-0.85
• Up to 1.1 for immersion
Reticle
(Mask)
• Exposure field 26x32mm
• Steppers capable of >100
300mm wafers per hour
at >100 exposures per
wafer
Wafer
193 nm Excimer
Laser Source
Computer
Console
Exposure
Column
(Lens)
www.tnlc.ncsu.edu/information/ceremony/lithography.ppt
Basic Technology for EUV
All solids, liquids, and gasses
absorb 13.5nm – so system is
under vacuum
Mask must be reflective and
exceptionally defect-free
13.5nm photons generated by
plasma source
All-reflective optics
(all lens materials are opaque)
ftp://download.intel.com/technology/silicon/EUV_Press_Foils_080204.pdf (both images)
13.5nm Plasma Radiation Source
• The only viable source for 13.5nm photons is a plasma
• Powerful plasma required – temperature of up to 200,000oC,
atoms ionized up to +20 state
• Plasma must be pulsed – pulse length in pico- to nanosecond
range
Argon
• Pre-ionized plasma excited by
powerful IR laser or electric arc
of up to 60,000 A to cause
emission
Tin
http://www.sematech.org/resources/litho/meetings/euvl/20021014/16-Spectro.pdf
Plasma Compositions for 13.5nm
Argon
Argon
Tin
Tin
• 13.5nm photons only generated
by one ion stage (Xe11+)
• Optimum emission when tin is a
low-percentage impurity
• Even this stage emits 10 times
more at 10.8nm than 13.5
• All ion stages from Sn8+ to Sn13+
can contribute
• Maximum population of this stage
is 45%
• Tin tends to condense on optics
• On the plus side, Argon is very
clean and easy to work with
 Tin is great as a 13.5nm source,
if we can engineer a way to use it
without destroying our optics
 Argon is horribly inefficient: to
produce 100W at 13.5nm, kilowatts
of other wavelengths would have to
be removed
http://www.sematech.org/resources/litho/meetings/euvl/20021014/16-Spectro.pdf
Where Plasma and Optics Meet
- Ions in the source plasma have enough energy to sputter material off the
lenses of the collector optics
- If the source uses tin, that will deposit on the lenses as well
At the power levels required for real exposures,
collector optics have a lifetime of about a month
This is VERY bad for Cost of Ownership (CoO)
ftp://download.intel.com/technology/silicon/EUV_Press_Foils_080204.pdf
All-Reflective Optics
All solids, liquids, and gasses absorb 13.5nm photons
- So fused silica lenses are OUT …
- Indeed, all refracting lenses are OUT
Making EUV mirrors is no cakewalk, either …
• 50 or more alternating Mo/Si layers give the mirror its
reflectivity
• Each layer is 6.7nm thick and requires atomic
precision
• Since the angle of incidence changes across the
mirror, so do the required Mo/Si layer thicknesses
• Acceptable surface roughness: 0.2nm RMS
• Aspheric
• Net reflectance: ~70%
http://www.zeiss.com/C1256A770030BCE0/WebViewAllE/D6279194C2955B2EC12570CF0044E537
Optics System - Exposure Field
Full field: ~109
exposures per
300mm wafer
Development-size field:
> 500,000 exposures per
300mm wafer
-In July 2005, Carl Zeiss shipped the first 0.25NA full-field optics
system to ASML for integration in an EUV system
Press release: http://www.zeiss.com/C1256A770030BCE0/WebViewAllE/D6279194C2955B2EC12570CF0044E537
ftp://download.intel.com/research/library/IR-TR-2003-39-ChuckGwynPhotomaskJapan0503.pdf
EUV Masks
ftp://download.intel.com/research/library/IR-TR-2003-39-ChuckGwynPhotomaskJapan0503.pdf
EUV Masks
NO defects are ever allowed in a completed mask
• Extremely flat and defect-free substrate, perfected by smoothing layer
• All defects in multilayer reflecting stack must be completely repaired
• No defects allowed in absorber layer
• All defects in final absorber pattern must be completely repaired
(No wonder mask sets are so expensive!)
ftp://download.intel.com/research/library/IR-TR-2003-39-ChuckGwynPhotomaskJapan0503.pdf
EUV Resists
Best Positive Resist
2.3mJ/cm2 LER=7.2nm
Best Negative Resist
3.2mJ/cm2 LER=7.6nm
LER – Line Edge Roughness
39nm 3:1
(space:line)
ftp://download.intel.com/research/library/IR-TR-2003-39-ChuckGwynPhotomaskJapan0503.pdf
Conclusion
Will 193nm ever die?
• As recently as 2003, EUV was “the only viable solution” for the 45nm node
• Now Intel wants EUV for the 32nm node, but it may be pushed back more:
“In a nutshell, many believe that EUV will NOT be ready for the 32-nm
node in 2009. Some say the technology will get pushed out at the 22nm node in 2011. Some even speculate that EUV will never work.”
- EE Times, Jan 19, 2006
My opinion: never say “never” about this industry…
• A lot of work remains: increase output power of 13.5nm source, increase NA of
reflective lenses, increase lifetime of collector optics (decrease cost of ownership)
• But the potential payoff is sufficient that we will make it work