Extreme Ultraviolet Light Sources Mark Hrdy 12052017 Outline BackgroundMotivation Resolution Limit UV Light Generation EUV Introduction Technical Challenges Optics MasksPellicles Light Production ID: 762179
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Extreme Ultraviolet Light Sources Mark Hrdy 12/05/2017
Outline Background/Motivation Resolution Limit UV Light GenerationEUV IntroductionTechnical Challenges:OpticsMasks/PelliclesLight ProductionContaminationPower RequirementsResistsCurrent Outlook:RequirementsCurrent StatusOngoing ConcernsThe Future of EUVClose:ReferencesQuestions University of Texas - EUV Sources - M. Hrdy 2
Background/Motivation University of Texas - EUV Sources - M. Hrdy 3
Impact of Semiconductor Industry Semiconductor industry is massive and important A major factor in this growth has been the ability to define smaller and smaller feature sizes leading to more powerful and portable devices University of Texas - EUV Sources - M. Hrdy 4 [6, 19]
Feature Size Photolithography: Technique for transferring a given pattern to the substrate by projecting light through a patterned mask that alters the chemistry of a reactive substance (photoresist) on the substrate Diffraction:Light interferes with itself upon passing through some boundaryDiffraction pattern: Resolution: Smallest resolvable feature Resolution limit: Today we will be discussing efforts to reducing feature size by reducing the wavelength ( ), specifically to Extreme Ultraviolet (EUV) regime Mask Photoresist Fraunhofer Diffraction Resolving Diffracted Signals Resolvable Unresolvable University of Texas - EUV Sources - M. Hrdy 5 [4]
Early Sources Mercury-vapor lamps are a good source of light at 365nm and 254nm Early lithography used 365nm light because of this existing source University of Texas - EUV Sources - M. Hrdy 6
Current Sources The invention of excimer lasers allowed for shorter wavelengths KrF excimer lasers provide a good source of 248nm Industry standard today is 193nm produced by ArF excimer lasers That was easy - So let’s go even shorter! University of Texas - EUV Sources - M. Hrdy 7
[9,11,12,15,22] Enter Extreme Ultraviolet Engineers and scientists knew directionally where to go, but there was no light source. One would need to be invented. “Those technologies are called extreme ultra-violet (EUV) lithography and 450-millimeter wafers and they will let Intel make smaller chips that drink less power. In other words, Intel is spending $4.1 billion to continue with Moore's Law.” – Business Insider, 2012 “In 2012, ASML also obtained a combined total of $1.9 billion in R&D funds from Intel, Samsung and TSMC.” – Semiconductor Engineering, 2014 …30+ years later … with the whole world working on it … And billions and billions of dollars We’re still using 193nm lasers… What gives?! “ASML buys 24.9% of ZEISS subsidiary Carl Zeiss SMT for EUR 1 billion in cash. Start of development of entirely new High NA optical system for the future generation of EUV.” – ASML, 2016 “… forecasts $1.482 billion will be spent on EUV this year, up from $1.036 billion last year and rising to $3 billion in 2019.” – VLSI Research, 2017 University of Texas - EUV Sources - M. Hrdy 8
Technical Challenges University of Texas - EUV Sources - M. Hrdy 9
EUV Challenges or “Why are we still waiting?!” University of Texas - EUV Sources - M. Hrdy 10
Optics - Refraction Lenses: Light refracts through transparent materials of differing indexes (n) Bragg’s Law: Problems: All useful optical materials are strongly absorbing Refractive index is a function of wavelength For X-rays, n ~ 1 for everything (no refraction) Need new optics system! Need to run in vacuum! Heat management problems! University of Texas - EUV Sources - M. Hrdy 11 [4]
Optics - Reflection At EUV wavelengths, the small but measurable differences in refractive index can add up Multilayer Reflectors: By alternating layers of high-Z/high-n and low-Z/low-n materials, multiple reflections add up The periodicity of the bilayers needs to satisfy Bragg Condition so reflected waves will constructively interfereBragg Condition: , m = 1, 2, 3,... Design Considerations: Materials cannot absorb the EUV rays Mirrors need to be manufacturable University of Texas - EUV Sources - M. Hrdy 12 Note: any defect in the layers causes a dark spot! [8]
Optics - EUV Mirrors Final Mirror: Bilayers made of Mo/Si Periodicity of bilayers is 6.9nmUp to 100 alternating layers (50 bilayers)Maximum reflectivity ~70-72% at ~13.5nm This is how λ was chosen! Mo/Si experimental vs theoretical reflection. Process has since been optimized to ~70-72% or within a few percent of optimal value. University of Texas - EUV Sources - M. Hrdy 13 [3,6]
Optics - System Mirrors are important! Problems: Relatively low NA (.33)Reflectance goes as a function of ~.72N where N is the number of mirrors Design with 11 mirrors University of Texas - EUV Sources - M. Hrdy 14 [19]
Masks/Pellicles Masks: Multilayer mirror with absorbing materials to generate contrast Problems: Defectivity of mirrors is an ongoing problem Needs pellicle or pristine tool Pellicles: Fragile polysilicon film with relatively low absorption (~15%) Problems: Absorbed X-rays become heat! Low confidence in this film with higher power source (more x-rays, more heat) .85 2 reflectance, 28% more power loss University of Texas - EUV Sources - M. Hrdy 15 [6]
Plasmas Plasma Light Production: Heat material until electrons have more thermal energy than bonding energy Atoms shed their higher orbital electronsIons are created where certain electron transitions dominate (for example Xe+10)These electron transitions emit characteristic wavelength (E = c/λ) Need a method to heat the material Need the right emitting ions University of Texas - EUV Sources - M. Hrdy 16 [2]
Plasmas University of Texas - EUV Sources - M. Hrdy 17 Efficiency too low Does not scale
Plasmas - Sn Efficiency: Sn 8+ to Sn12+ states contribute to emissionPotential for much higher efficiencies than other sources Availability: Solid metal contamination seriously problematicReflectance drops off drastically with thin Sn layer on opticsRegular cleaning and potentially part replacement necessary Despite Sn being horrible for contamination, the efficiency is better than Xe, so Sn is plasma of choice. University of Texas - EUV Sources - M. Hrdy 18
Plasmas – LPP LPP Technique: Powerful laser provides high energy photons High energy photons transfer energy and heat target Multilayer collector reflects produced light out Efficiency: LPP still needs large amounts of power Needs dual-pulse system to be effective Availability : Sn contaminates multilayer collector which ruins the efficiency of the system LPP Sn was avoided for a long time due to this issue University of Texas - EUV Sources - M. Hrdy 19 LPP with Sn droplets = Best known method! [18]
Plasmas – Dual-pulse System Dual-pulse First pulse optimizes droplet shape/density Second pulse converts newly formed droplet into emitting plasmaVery important development for efficiency; does nothing to prevent Sn debris Various Ways to Optimize:Laser frequencyPulse duration Laser powerDroplet shape/densityDroplet sizeDroplet stabilityDroplet opacityDroplet velocity University of Texas - EUV Sources - M. Hrdy 20 [6]
Debris - Ions Ion Containment: Sn is ionized when it becomes a plasma H-field contains ionized Sn Sn is guided down into ion collector Problems: This does nothing to contain non-ionized Sn Only really effective if Sn is 100% plasma University of Texas - EUV Sources - M. Hrdy 21 Magnetic field guides ions into collector Ion collector H-field [18]
Debris - Neutrals Hydrogen Backfill: Backfill with hydrogen H 2 pressure pushes Sn away from multilayer collector H 2 ionizes and etches Sn contamination Sn (s) + 4H (g) -> SnH 4 (g) ( stannane gas) SnH 4 gets pumped out of system Problems: SnH 4 breaks apart upon collisions and redeposits Sn O 2 contamination leads to tin oxides which will not etch A number of other variables limit process window (carbon contamination, chamber temp, etc ) University of Texas - EUV Sources - M. Hrdy 22 H 2 flow away from multilayer collector H etches remaining Sn SnH 4 is pumped out Sn SnH 4 H [18]
Debris - Degradation Debris mitigation effectiveness: Collector degradation has improved immensely Problems:Tool still requires a lot of maintenance10% reflectance loss is still significant power loss University of Texas - EUV Sources - M. Hrdy 23 [21]
Power Requirements Multistage kW CO 2 laserBeam profile can be optimized for droplet (both pulses)Needs to deliver massive amounts of power (next slide)Maintenance on this is also a large source of downtimeUniversity of Texas - EUV Sources - M. Hrdy 24 EUV Source [10]
Power Requirements Efficiency Estimates: η laser = .08Pout = 20kWPin = 250kW University of Texas - EUV Sources - M. Hrdy 25 P out = η laser x P in ArF run at 50kW 5x increase in power [10]
Power Requirements Efficiency Estimates: P IF = 210W (best ASML reported)ηmirror = .72 (N = 10)η pellicle = .85Pout ~ 6Wηfinal = 6W/250kW = .000024 University of Texas - EUV Sources - M. Hrdy 26 P out = ( η mirror ) N x ( η pellicle ) 2 x PIF 193nm ArF provide 40WWatts ≠ PhotonsEUV photons << 193nm [18]
Resists This is all about dose! Need to get more photons to resist for reaction. Current systems are still too slow, may be room for better resists. Variations in # of photons (shot noise) are also a problem University of Texas - EUV Sources - M. Hrdy 27
Current Outlook University of Texas - EUV Sources - M. Hrdy 28
Requirements Source power has been major limiter and requirement has grown significantly Requirements below from November 2007 Requirement at intermediate focus is now 250W for 125 wafers per hourUniversity of Texas - EUV Sources - M. Hrdy 29 [3]
Current Status - Power Figure right shows all roadmaps 2010+ that have been delayed due to EUV power ASML reported power shows consistent failure early on, but large recent gains University of Texas - EUV Sources - M. Hrdy 30 2016 [17]
Current Status - Power Recent Gains ASML reports that the introduction and optimization of the dual pulse technology is leading to massive increases in efficiency University of Texas - EUV Sources - M. Hrdy31 [6]
Current Status – Tool Sales ASML’s TWINSCAN NXE:3400B is the current state of the art Reportedly at >125 wafers per hour with 13nm resolution Intended to support 7nm and 5nm nodes Order backlog of 27 systems valued at 2.8b euros ($3.3b) University of Texas - EUV Sources - M. Hrdy 32 [1]
Ongoing Concerns Optics: Relatively low NA (.33) Next generation will likely have more mirrors and more lossProduction of mirrors is very slowMasks/Pellicles:Need greater availability of defect-free masksNeeds to be able to withstand more power and more heatDebris:Tools need to be working, not down for maintenanceUptime is still significantly lower than 193nm (70% compared to 95%)Concerns about lifetime of various components University of Texas - EUV Sources - M. Hrdy 33 Power Requirements: Tools need to be working, not down for maintenance Need to demonstrate source power in the field More power will be needed for next generations Resists: Need to be able to either get by with fewer photons or produce more
The Future of EUV Concerns mentioned previously are still problematic Power and availability are ongoing issues Also hard to forget about all the missed goals of yesteryearHowever --Generally, the attitude seems optimisticEUV orders are increasingSource power increases reported by ASML are encouragingUniversity of Texas - EUV Sources - M. Hrdy 34
Close University of Texas - EUV Sources - M. Hrdy 35
References ASML. ( n.d. ). TWINSCAN NXE:3350B. Retrieved December 04, 2017, from https://www.asml.com/products/systems/twinscan-nxe/twinscan-nxe3350b/en/s46772?dfp_product_id=9546 Attwood, D. (1999). Soft X-Rays and Extreme Ultraviolet Radiation: Principles and Applications . New York, NY: Cambridge University Press.Bakshi , V. (Ed.). (2009). EUV Lithography . Hoboken, NJ: John Wiley & Sons. Duree , G. (2011). Optics for dummies . Hoboken, NJ: Wiley Elg , D. et al, "Magnetic mitigation of debris for EUV sources," Proc. SPIE 8679, Extreme Ultraviolet (EUV) Lithography IV, 86792M (1 April 2013) Fomenkov , I., (2017, June 15). 2017 International Workshop on EUV Lithography. In EUV Lithography: Progress in LPP Source Power Scaling and Availability . Retrieved from https://www.euvlitho.com/2017/P5.pdf Global semiconductor industry market size 2019 | Statistic. Retrieved December 04, 2017, from https://www.statista.com/statistics/266973/global-semiconductor-sales-since-1988/ H. J. Levinson, Principles of Lithography, Second Edition, SPIE Press, Bellingham, WA (2005) Lapedus, M. (2014, April 17). Billions And Billions Invested. Retrieved December 04, 2017, from https://semiengineering.com/billions-and-billions-invested/ Lapedus, M. (2016, November 17). Why EUV Is So Difficult. Retrieved December 04, 2017, from https://semiengineering.com/why-euv-is-so-difficult/ Lapedus, M. (2017, September 25). Looming Issues And Tradeoffs For EUV. Retrieved December 04, 2017, from https://semiengineering.com/issues-and-tradeoffs-for-euv/ University of Texas - EUV Sources - M. Hrdy 36 Merritt, R. (2017, October 10). Intel May Sit Out Race to EUV | EE Times. Retrieved December 04, 2017, from https://www.eetimes.com/document.asp?doc_id=1332420&page_number=1 Mizoguchiet , H., et al, "Performance of 250W high-power HVM LPP-EUV source," Proc. SPIE 10143, Extreme Ultraviolet (EUV) Lithography VIII, 101431J (27 March 2017) Renk K.F. (2017) Gas Lasers. In: Basics of Laser Physics. Graduate Texts in Physics. Springer, Cham Russell, K. (2013, October 30). Intel Is Investing Billions Of Dollars Into This Unproven Technology. Retrieved December 04, 2017, from http://www.businessinsider.com/intel-is-investing-billions-in-this-tech-2013-10 Sporre , J. R., et al, "Collector optic in-situ Sn removal using hydrogen plasma," Proc. SPIE 8679, Extreme Ultraviolet (EUV) Lithography IV, 86792H (8 April 2013); doi : 10.1117/12.2012584 Tomie , T, "Tin laser-produced plasma as the light source for extreme ultraviolet lithography high-volume manufacturing: history, ideal plasma, present status, and prospects," J. Micro/ Nanolith . 11(2) 021109 (21 May 2012) Turkot , B., et al, "EUV progress toward HVM readiness," Proc. SPIE 9776, Extreme Ultraviolet (EUV) Lithography VII, 977602 (18 March 2016) Wagner, C., & Harned , N. (2010). EUV lithography: Lithography gets extreme. Nature Photonics, 4 (1), 24-26. doi:10.1038/nphoton.2009.251 Waldrop, M. M. (2016). The chips are down for Moore’s law. Nature News, 530 (7589). Retrieved December 4, 2017, from http://www.nature.com/news/the-chips-are-down-for-moore-s-law-1.19338#/ref-link-5 Yabu , T., et al, "Key components development progress updates of the 250W high power LPP-EUV light source," Proc. SPIE 10450, International Conference on Extreme Ultraviolet Lithography 2017, 104501C (16 October 2017) Yen, A, "EUV Lithography: From the Very Beginning to the Eve of Manufacturing," Proc. SPIE 9776, Extreme Ultraviolet (EUV) Lithography VII, 977632 (16 June 2016)
Questions University of Texas - EUV Sources - M. Hrdy 37
Supplemental University of Texas - EUV Sources - M. Hrdy 38
Wavelength Sources Photoelectric Effect: Excitation energy provides means for electrons to jump to higher energy orbitals When the electrons drop down to a lower energy state, they release a photon inversely proportional the drop in energyPhoton Energy: E* E i E t λ ~ 1/( Δ E ) E* E t E i Excitation energy Photoemission Basics University of Texas - EUV Sources - M. Hrdy 39
Extreme Ultraviolet Naming Early EUV System from Lawrence Livermore National Lab University of Texas - EUV Sources - M. Hrdy 40 “Soft X-ray Projection Lithography” was what we originally named it until DARPA asked us to get the “x-ray” out of the name in 1993. So it was renamed “Extreme Ultraviolet Lithography.” I suggested the name because I knew Berkeley had an “Extreme Ultraviolet Astronomy” group. At the time, nobody in our group even knew what the wavelengths of EUV were – but we needed a new name… quick. -Natale Ceglio , Lawrence Livermore National Laboratory
Plasmas - Xe Efficiency: Relatively lowOnly one ionic state contributing to 13.5nm light (Xe10+)Availability:Little/no contamination from noble gasSome issues Xe ice fragments, largely resolvedUltimately, not used because efficiency is so low and it is very difficult to manage heat in vacuum University of Texas - EUV Sources - M. Hrdy 41
Plasmas - DPP DPP Technique: Changes in current induce magnetic field Magnetic field “pinches” plasmaCurrent flowing through plasma faces increased resistanceHigher resistance induces more heatEfficiency:Power scaling is limited by thermal managementDoes not scale up to necessary powers Availability:Electrodes erode Erosion produces contamination Two schematics of pinching Z-pinch Θ-pinch DPP with Sn-plated disc University of Texas - EUV Sources - M. Hrdy 42