euv presentation
DESCRIPTION
Extreme ultraviolet lithographyTRANSCRIPT
Extreme Ultra-Violet Extreme Ultra-Violet LithographyLithography
• 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
Outline
Mask Maker’s Holiday:
“large” k1
Mask Maker’s Burden: “small” k1
Why EUV?
Minimum lithographic feature size =
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)
k1*λ
NA
ftp://download.intel.com/research/silicon/EUV_Press_Foils_080204.pdf
There are only so many “tricks” to increase this gap, and they are very expensive … we MUST go to a shorter wavelength!
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: 1012
• Defects:• Size that must be found and repaired: 100nm (25nm as projected on wafer)• Number of such defects allowed: 0
• Data:• Total file size needed for all 22-25 layers: 200GB
• Cost:• Cost for mask set (depreciation, labor, etc): ~$800k-1.3M
ftp://download.intel.com/technology/silicon/Chuck Gwyn Photomask Japan 0503.pdf
Current Lithographic Technology
193 nm Excimer Laser Source
Computer Console
Exposure Column(Lens)
Wafer
Reticle (Mask)
www.tnlc.ncsu.edu/information/ceremony/lithography.ppt
• 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
• Exposure field 26x32mm
• Steppers capable of >100300mm wafers per hourat >100 exposures per wafer
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
Tin
http://www.sematech.org/resources/litho/meetings/euvl/20021014/16-Spectro.pdf
• Pre-ionized plasma excited by powerful IR laser or electric arc of up to 60,000 A to cause emission
Plasma Compositions for 13.5nm
Argon Tin
Argon
• 13.5nm photons only generated by one ion stage (Xe11+)
• Even this stage emits 10 times more at 10.8nm than 13.5
• Maximum population of this stage is 45%
• On the plus side, Argon is very clean and easy to work with
Argon is horribly inefficient: to produce 100W at 13.5nm, kilowatts of other wavelengths would have to be removed
Tin
• Optimum emission when tin is a low-percentage impurity
• All ion stages from Sn8+ to Sn13+ can contribute
• Tin tends to condense on optics
Tin is great as a 13.5nm source, if we can engineer a way to use it without destroying our optics
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
http://www.zeiss.com/C1256A770030BCE0/WebViewAllE/D6279194C2955B2EC12570CF0044E537
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%
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 systemPress 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 ResistsBest Positive Resist
2.3mJ/cm2 LER=7.2nm
Best Negative Resist
3.2mJ/cm2 LER=7.6nm
39nm 3:1 (space:line)
LER – Line Edge Roughness
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 22- nm 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