Extreme UltraViolet Lithography Outline Why do we need

Extreme Ultra-Violet Lithography

Outline • Why do we need EUV lithography? • Brief overview of current technology • What exactly is EUV? • System diagram • Challenges associated with EUV • 13. 5 nm source • Optics • Masks • Resists

Why EUV? Minimum lithographic feature size = k 1*λ NA k 1: “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” k 1 Mask Maker’s Burden: “small” k 1 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) @ 436 nm Hg (H line) @ 405 nm Hg (I line) @ 365 nm Kr. F Excimer @ 248 nm Ar. F Excimer @ 193 nm ? ? ? • 157 nm lithography based on the fluorine excimer laser has been largely shelved, which leaves 193 nm with extensions for production • Below that, no laser line has the required output power • Excimer-based steppers expose 109 steps per 300 mm wafer, and produce >100 wafers per hour – exposure times ~ 10 -20 ns • Additionally, fused silica and atmospheric oxygen become absorptive by 157 nm – so even incremental decreases in wavelength start to require a major system overhaul Mask Maker’s Holiday: “large” k 1 Mask Maker’s Burden: “small” k 1 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 k 1 – this makes the masks less complicated and expensive because we can skip the “tricks” For example: a 90 nm 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 for mask set (depreciation, labor, etc): 1012 100 nm (25 nm as projected on wafer) 0 200 GB ~$800 k-1. 3 M ftp: //download. intel. com/technology/silicon/Chuck Gwyn Photomask Japan 0503. pdf

Current Lithographic Technology • Lenses are very effective and perfectly transparent for 193 nm 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 26 x 32 mm • Steppers capable of >100 300 mm 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. 5 nm – so system is under vacuum Mask must be reflective and exceptionally defect-free 13. 5 nm 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. 5 nm Plasma Radiation Source • The only viable source for 13. 5 nm photons is a plasma • Powerful plasma required – temperature of up to 200, 000 o. C, 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. 5 nm Argon Tin • 13. 5 nm photons only generated by one ion stage (Xe 11+) • Optimum emission when tin is a low-percentage impurity • Even this stage emits 10 times more at 10. 8 nm than 13. 5 • All ion stages from Sn 8+ to Sn 13+ 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 Argon is horribly inefficient: to produce 100 W at 13. 5 nm, kilowatts of other wavelengths would have to be removed Tin is great as a 13. 5 nm 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 (Co. O) ftp: //download. intel. com/technology/silicon/EUV_Press_Foils_080204. pdf

All-Reflective Optics All solids, liquids, and gasses absorb 13. 5 nm 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. 7 nm 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. 2 nm RMS • Aspheric • Net reflectance: ~70% http: //www. zeiss. com/C 1256 A 770030 BCE 0/Web. View. All. E/D 6279194 C 2955 B 2 EC 12570 CF 0044 E 537

Optics System - Exposure Field Full field: ~109 exposures per 300 mm wafer Development-size field: > 500, 000 exposures per 300 mm wafer -In July 2005, Carl Zeiss shipped the first 0. 25 NA full-field optics system to ASML for integration in an EUV system Press release: http: //www. zeiss. com/C 1256 A 770030 BCE 0/Web. View. All. E/D 6279194 C 2955 B 2 EC 12570 CF 0044 E 537 ftp: //download. intel. com/research/library/IR-TR-2003 -39 -Chuck. Gwyn. Photomask. Japan 0503. pdf

EUV Masks ftp: //download. intel. com/research/library/IR-TR-2003 -39 -Chuck. Gwyn. Photomask. Japan 0503. 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 -Chuck. Gwyn. Photomask. Japan 0503. pdf

EUV Resists Best Positive Resist 2. 3 m. J/cm 2 LER=7. 2 nm Best Negative Resist 3. 2 m. J/cm 2 LER=7. 6 nm LER – Line Edge Roughness 39 nm 3: 1 (space: line) ftp: //download. intel. com/research/library/IR-TR-2003 -39 -Chuck. Gwyn. Photomask. Japan 0503. pdf

Conclusion Will 193 nm ever die? • As recently as 2003, EUV was “the only viable solution” for the 45 nm node • Now Intel wants EUV for the 32 nm 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. 5 nm 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